GB2630800A

GB2630800A - Methods and compounds

Info

Publication number: GB2630800A
Application number: GB2308576.4A
Authority: GB
Inventors: D Bull Steven; D Tibbetts Joshua; Cunningham William
Original assignee: University of Leicester
Current assignee: University of Leicester
Priority date: 2023-06-08
Filing date: 2023-06-08
Publication date: 2024-12-11
Also published as: WO2024252135A1; GB202308576D0

Abstract

Stereoselective methods of producing a stereoisomer of p-menthane-3,8-diol (PMD) are disclosed. The first stereoselective method comprises hydrating the alkene group of isopulegol. This method may involve direct alkene hydration or epoxidizing the alkene to form an epoxide, preferably using H2O2 or a peroxycarboxylic acid e.g., mCPBA, and then reducing said epoxide. A further step involving an alcohol inversion step of the stereoisomer of PMD, preferably comprising an oxidation step of the secondary alcohol, preferably using PCC/dichloromethane or TCICA followed by a selective reduction step, preferably using H2, NaBH4, LiAlH4, DIBAL-H or L-Selectride. The second stereoselective method comprises the steps of a) performing a ring opening reaction on verbenol in the presence of an aldehyde or ketone and a compound containing a source of halogen; b) dehalogenation, preferably using a reducing agent such as LiAlH4; and c) hydrogenating, preferably using PtO2/H2 and deprotecting the resulting diol. A further step involving an alcohol inversion step of the stereoisomer of PMD may occur. Also disclosed are compositions comprising 95mol% or greater of a stereoisomer of p-menthane-3,8-diol and insect repellents, flavourings or fragrances comprising such compositions. Also disclosed are methods of reducing resistance of a target insect or tick species to a PMD repellent.

Description

METHODS AND COMPOUNDS

FIELD OF THE INVENTION

The present invention relates to stereoselective methods of producing stereoisomers of pmenthane-3,8-diol, to compositions comprising one or more stereoisomers of pmenthane-3,8-diol, to insect repellents, fragrances or flavourings comprising such compositions, to methods of reducing resistance of a target insect or tick species to a pmenthane-diol repellent and to certain stereoisomers of p-menthane-3,8-diol.

BACKGROUND

Para-menthane-3,8-diol (PMD) is a naturally occurring monoterpene obtained as an isomeric mixture (4 stereoisomers) in varying proportions from distillation of the essential oil of the Australian lemon-scented gum tree Corymbia citriodora and other plants. The C. citriodora mixture has been demonstrated to be an effective repellent of disease-carrying biting insect vectors, including mosquitos that are known to spread malaria and the Zika virus.

There have been attempts with varying success to separate or synthesise some of the stereoisomers of PMD. The structures of the eight isomers of PMD are shown in Scheme 1, below.

Vanek T et al.; "Biotransfonnation of citronellal by Soloman aviculare suspension cultures: preparation of p-menthane-3,8-diols and determination of their absolute configurations-, J Nat Prod. 2003; 66(9); pp. 1239-41. doi: 10.1021/np0301588. PMID: 14510606 discloses the transformation of citronellal by Solanzun aviculare suspension cultures to menthane-3,8-diols. cis-Menthane-3,8-diol dominated over the trans-isomer (39% and 15%, respectively). Y. Yuasa et al; Org. Proc. Res. Dev. 2000, 4, 3, 159-161 discloses production from citronellal of diastereomeric repellents ofp-menthane-3,8-diol by treatment with 0.25% sulfuric acid. J. Drapeau et al.; "Green synthesis of paraMenthane-3,8-diol from Eucalyptus citriodora: Application for repellent products", Comptes Rendus Chimie, Volume 14, Issues 7-8, 2011, Pages 629-635, hit -)s://doi onV10.101 -i 2011 02.008 discloses a method for the synthesis ofpara-menthane-3,8-diol (PMD), as a repellent active against mosquitoes, from Eucalyptus citriodora essential oil by a treatment of citric acid in a biphasic medium (H20/essential oil). S. S. Lemaire et al; Journal of Agricultural and Food Chemistry 2021 69 (37), 1109511109 (doi: 10.1021/acsjafc.1c03897) discloses the synthesis of four stereoisomers of PMDs as mixtures that are then separated by chromatography and the repellent activity of the isomers against A. albopicnis mosquitoes studied. Barasa et al.; "Repellent Activities of Stereoisomers ofp-Menthane-3,8-diols Against Anopheles gambiae (Diptera: Culicidae)", Journal of Medical Entomology, Volume 39, Issue 5, 1 September 2002, Pages 736-741, Ints* anti 10 6011/0,-2585-39 '3 R6 discloses the synthesis of four stereoisomers of p-menthane-3,8-diol, which make up the natural product obtained from Eucalyptus citriodora, by cyclising citronellal using sulfuric acid in a non-selective fashion and separating out PMD isomers using column chromatography. Repellency assays were said to show that all the four were equally active against Anopheles gambiae s.s. Racemic blends and the stereoisomeric mixture of all the four isomers were also reported as equally repellent.

Natural OH ''OH OH PMD-1 PMD-2 PMD-3 PMD-4 (1-cis-3-trans-4) (1-trams-3-cis-4) Non-natural OH OH OH 10H ------'"OH! OH --TON OH PMD#5 PMD-6 PMD-7 PMD43 (1-cis-3-cis-4) (1-trans-3 r ns-4) Scheme 1. Stereoisomers of PMD Further examples of references discussing the synthesis and/or testing of PMD or related compounds include; Agric. Biol. Chem., 1982, 46, 319-320, bisects, 2018, 9, 60, J Am. Ifosq. Control Assoc., 1996, 12, 243-246, J. Am. Mosq. Control Assoc., 2006, 22, 507514, Hely. Chim. Ada, 2002, 85, 3400-3413, and, J. Gore, Synthesis (Stuttg)., 1988, 972975.

GB-A-2282534 discloses an insect repellent c mposition containing one or both isomers 01'p_mentbane-3,8-diol which has been extracted. from a nafttral oil or synthesised chemically, and. a carrier. CN-A-103193598 discloses a synthesis of p-In enth an 0-3. 8-di ol US-A-2010/0278755 discloses a simple method of producingpara-menthane-3,8-diol in relatively high yield.

The effect of each individual stereoisomer as arthropod (e.g. tick or insect, especially, mosquito) repellents is unclear, because not all the stereoisomers are available and those that are available in mixtures are difficult and expensive to separate or resolve into enantiomerically pure compounds. Individual stereoisomers in relatively pure form may also find uses as fragrances, flavourings and in other uses.

Thus, there is a need for quantities of the individual isomers of PMD and so there is a need for improved stereoselective methods that are able to provide such stereoisomers in relatively pure form.

It is an aim of the present invention to address this need.

SUMMARY

In a first aspect, there is accordingly provided a stereoselective method of producing a stereoisomer of p-menthane-3,8-diol, the method comprising the steps of a. providing a stereoisomer of a compound of formula (I):

OH

b. hydration of the alkene group of the compound of formula (I) to produce the stereoisomer of p-menthane-diol of formula (II):

OH

OH (II) The step of hydrating the alkene of formula (I) according to the first aspect of the invention may comprise performing direct alkene hydration. Alternatively, the step of hydrating the alkene of formula (I) according to the first aspect of the invention may comprise epoxidizing the alkene to form an epoxide and then reducing the epoxide.

The stereoisomer may be a compound of formula (I) that is selected from a compound of formula (la; 53); a compound of formula (Ib; 56); a compound of formula (lc; 63); or a compound of formula (Id; 66): OH "1/0 H (Ia; 53) (II); 56) (Ic; 63) (Id; 66).

The stereoisomer of a compound of formula (I) may be selected from a compound of formula (Ia; 53); a compound of formula (Ib; 56); a compound of formula (Ic; 63); or a compound of formula (Id; 66) and wherein the method thereby produces the stereoisomer of p-menthane-diol of formula (11a, PMD 1); the stereoisomer of p-menthane-diol of formula (11b; PMD 2); the stereoisomer of p-menthane-diol of formula (Ilc; PMD 3) or the stereoisomer of p-menthane-diol of formula (IId; PMD 4) respectively:

OH

(IIa, PMD 1) (1b, PMD 2) (Ilc; PMD 3) (11d, PMD 4) #11 /O H The method may further comprise a step of alcohol inversion of the stereoisomer of pmenthane-diol of formula (II).

The step of alcohol inversion may comprise a step of oxidation of the secondary alcohol followed by a step of reduction.

The step of oxidation of the secondary alcohol may comprise generally any suitable method of alcohol oxidation, for example a Swern oxidation (for example wherein an alcohol is oxidized to an aldehyde or ketone using oxalyl chloride, dimethyl sulfoxide (DMSO) and an organic base, such as triethylamine), a Parikh-Doering oxidation (e.g. wherein dimethyl sulfoxide (DMSO) may be used as the oxidant and the solvent, activated by the sulfur trioxide pyridine complex (SO3*CSH5N) in the presence of triethylamine or diisopropylethylamine as base) or other methods. The step of oxidation may involve treating the stereoisomer of p-menthane-diol of formula (II) with an oxidant selected from pyridinium chlorochromate (in CHC13); or trichloroisocyanuric acid (TCICA).

The step of selective reduction may be performed using any suitable method. For example, the step of selective reduction may be performed by treating the product of the step of oxidation of the secondary alcohol with a reductant selected from hydrogen gas, (e.g. catalytically using hydrogen gas, for example with Pd/C), NaBH4, LiA1H4, diisobutylaluminium hydride (DIBAL-H); or L-Selectride (lithium tri-secbutyl(hydrido)borate(1-)).

The compound of formula (lc; 63) or the compound of formula (Id; 66) may be provided by a method comprising a step of alcohol inversion of the compound of formula (Ia; 53) or the compound of formula (Ib; 56) respectively.

The step of alcohol inversion may be any suitable method that converts the alcohol to a good leaving group (e.g. sulfonate) and then uses a reagent (e.g. carboxylate) to carry out an SN2 reaction at that centre.

In some cases, the step of alcohol inversion of the compound of formula (Ia; 53) or the compound of formula (lb, 56) may be an oxidation/reduction alcohol inversion or a Mitsunobu-type inversion.

Epoxidizing the alkene group of the compound of formula (I) may comprise any suitable method. For example, epoxidizing the alkene group of the compound of formula (I) may comprise treatment of the compound of formula (I) with hydrogen peroxide or a peroxycarboxylic acid, optionally meta-chloroperoxybenzoic acid (mCPBA) In other methods, epoxidizing the alkene group of the compound of formula (I) may comprise the use of a metal-based catalysts, for example, tungsten-based catalysts (e.g. PW4024[PTC]3).

Reducing the epoxide may comprise treating the epoxide with a reducing agent selected from hydrogen gas (e.g. using the catalyst Pd/C), NaBH4, LiAIH4, diisobutylaluminium hydride (DIBAL-H); or L-Selectride (lithium tri-sec-butyl(hydrido)borate(1-)).

The compound of formula (I) may be produced by a ring closing reaction in which a compound of formula (XXI): (XXI) is treated with a Lewis acid (e.g. zinc bromide), to produce a compound of formula (I):

OH

In a second aspect, there is accordingly provided, a stereoselective method of producing a stereoisomer of p-menthane-3,8-diol, the method comprising the steps of: a. providing a stereoisomer of a compound of formula (III):

OH

b. performing a ring opening reaction on the compound of formula (III) in the presence of a carbonyl compound of formula RiC(0)R2 and a compound containing a source of halogen (X), to form (a stereoisomer of) compound of formula (IV): R1 (IV) wherein Xis halo and RI and R2 are independently H, or a linear or branched CI C9 alkyl chain which may be optionally substituted, c. dehalogenating the compound of formula (IV) to form a compound of formula (VI):, (VI) d. hydrogenating and deprotecting the diol of the compound of formula (VI), thereby producing the stereoisomer of p-menthane-diol of formula (II):

OH

RI and R2 may each be CH3 The compound containing the source of halogen may comprise N-halosuccinimide.

Dehalogenating the compound of formula (IV) to form the compound of formula (VI) may comprise treating the compound (IV) with a reducing agent, optionally LiAlift.

Hydrogenating the compound of formula (VI) may comprise treating it with H2 in the presence of Pt02.

The stereoisomer of a compound of formula (HI) may be selected from a compound of formula (Ina, 68); or a compound of formula (Illb, 85): OH or OH (Illb, 85).

Preferably the compound of formula (III) is selected from a compound of formula (Mc; 68) or (Illd; 85): (Mc; 68); (IIId; 85).

The stereoisomer of a compound of formula (III) may be selected from a compound of formula (II la); a compound of formula (Illb; 85); a compound of formula (Illc; 68); or a compound of formula (III& 85) and wherein the method thereby produces the stereoisomer of p-menthane-diol of formula (He, PMD 5); or the stereoisomer of pmenthane-diol of formula (Ilf; PMD 6) respectively: or 1/40 H (He, PMD 5)

OH

(Hf; PMD 6).

N-halosuccinimide may comprise AT-bromosuccinimide.

The method may further comprise a step of alcohol inversion of the stereoisomer of pmenthane-diol of formula (H) The step of alcohol inversion may comprise a step of oxidation of the secondary alcohol followed by a step of reduction.

The step of oxidation of the secondary alcohol may comprise treating the stereoisomer of p-menthane-diol of formula (II) with an oxidant selected from pyridinium chlorochromate (in CHC13); or trichloroisocyanuric acid (TCICA).

The step of selective reduction may be performed by treating the product of the step of oxidation of the secondary alcohol with a reductant comprising an alkali metal (e.g. lithium metal), ammonia and a proton source (which may be an alcohol, e.g. ethanol).

The alcohol inversion of the stereoisomer of p-menthane-diol of formula (He; PMD 5) or of formula (1If; PMD 6): :11:11.4POH OH PMD 6) (He, PMD 5) or may produce the stereoisomer of p-menthane-diol of formula (11g, PMD 7); or the stereoisomer of p-menthane-diol of formula (IIb; PMD 8) respectively: OH '1'110H

OH or

(1Ig, PMD 7) (11h, PMD 8).

Methods according to the first or second aspects result in high purity stereoisomers of PMD. This enables all of the stereoisomers of PMD to be produced as separated isomers.

Thus, in a third aspect, there is accordingly provided a composition comprising 95mol% or greater of a stereoisomer of p-menthane-3,8-diol selected from the stereoisomer of pmenthane-diol of formula (Ha, PMD 1); of formula (Hb, PMD 2); of formula (Hc, PMD

II

3) of formula (IId; PMD 4); of formula (IIe; PMD 5), of formula (IIf; PMD 6), of formula (Ilg, PMD 7) or of formula (Ilh, PMD 8): °LOH 0 H

H OH

(Ha, PMD 1) PMD 2) (1k; PMD 3) PMD 4)

QO H OH

H 0 H

(lie; PMD 5) (Ilf; PMD 6) 11/40H.#110H (IIh; PMD 8).

(IIg; PMD 7) ; or The composition may comprise 96mol% or greater of the stereoisomer of p-menthane3,8-diol, optionally 97mo1% or greater of the stereoisomer of p-menthane-3,8-diol, optionally 98mol% or greater of the stereoisomer of p-menthane-3,8-diol, optionally 99m o1% or greater of the stereoisomer of p-menthane-3,8-diol.

Surprisingly, and contrary to the conventional view, the inventors have discovered that different isomers have different repellency profiles to different species of mosquito. It is also likely that different isomers would also affect other species differently.

In a fourth aspect, there is accordingly provided an insect repellent comprising at least one composition as discussed above.

In a fifth aspect, there is accordingly provided a fragrance comprising at least one composition as discussed above.

In a sixth aspect, there is accordingly provided a flavouring comprising at least one composition as discussed above.

Because the different isomers have different repellency profiles to different species of mosquito, this may enable compositions containing one or more of the isomers of PMD to be used to reduce the development of resistance. This may involve identifying a measure of the degree of resistance of the target species to a composition comprising a first stereoisomer of p-menthane-diol; determining a second stereoisomer of p-menthane-diol with a lower degree of resistance of the target species than the first stereoisomer.

Thus, in a seventh aspect, there is accordingly provided a method of reducing resistance of a target insect or tick species to a p-menthane-diol repellent, the method comprising: identifying a measure of the degree of resistance of the target species to a composition comprising a first stereoisomer of p-menthane-diol; determining a second stereoisomer of p-menthane-diol with a lower degree of resistance of the target species than the first stereoisomer.

In an eight aspect, there is provided a compound of formula: (11e, PMD 5) (I lf, PMD 6) a_ OH (IIg, PMD 7).

Different combinations of isomers may be used to give different flavour/odour/repellency profiles. Thus, the invention provides for compositions that may find use in a number of products, for example as, or in, repellent sprays, creams, candles, perfumes, nebulisers, toothpastes, lip balms, sun creams, aftershaves, chewing gums, mouth washes, sprays, candles, vaping products and perfume products.

As regards insect repellents, currently approved mixtures of PMD stereoisomers may be replaced with single isomer products to mitigate potential insect resistance and human toxicity issues.

The PMD isomers may find use as active mosquito/insect repellents. It would be advantageous to change the use of particular PMD isomers as resistance develops.

The availability of non-resistant pleasant smelling PMD isomers for long term use would be advantageous as an effective way of reducing malaria/Zika transmission (or other vector-borne or insect-borne diseases) in rural communities.

Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the various aspects of the invention or of the dependent claims may be combined with features of the other aspects or independent claims as appropriate, and in combinations other than those explicitly set out in the discussion of the various aspects or claims, as supported by the description.

DEFINITIONS

"Substituted," when used in connection with a chemical substituent or moiety (e.g., an alkyl group), means that one or more hydrogen atoms of the substituent or moiety have been replaced with one or more non-hydrogen atoms or groups, provided that valence requirements are met and that a chemically stable compound results from the substitution.

"Optionally substituted" refers to a parent group which may be un-substituted or which may be substituted with one or more substituents. Suitably, unless otherwise specified, when optional substituents are present the optional substituted parent group comprises from one to three optional substituents thus the group may be substituted with 0, 1, 2 or 3 of the optional substituents. Suitably, the group is substituted with 1, 2 or 3 of the optional substituents.

Optional substituents may be selected from Ci-s alkyl, C1-6 alkyl, C2-7 alkenyl, C2-7 alkynyl, C1-12 alkoxy, C5-20 aryl, C3-10 cycloalkyl, C3-10 cycloalkenyl, C3-10 cycloalkynyl, C3-20 heterocyclyl, C3-2o heteroaryl, acetal, acyl, acylamido, acyloxy, amidino, amido, amino, aminocarbonyloxy, azido, carboxy, cyano, ether, formyl, guanidino, halo, hemiacetal, hemiketal, hydroxamic acid, hydroxyl, imidic acid, imino, ketal, nitro, nitroso, oxo, oxycarbonyl, oxycarboyloxy, sulfamino, sulfamyl, sulfate, sulfhydryl, sulfinamino, sulfinate, sulfino, sulfinyl, sulfinyloxy, sulfo, sulfonamido, sulfonamino, sulfonate, sulfonyl, sulfonyloxy, uredio groups. In some aspects, the optional substituents are 1, 2 or 3 optional substituents independently selected from OH, Chs alkyl, C1-6 alkyl, OCI-12 alkyl, and halogen. More suitably, the optional substituents are selected from OH, Ci-s alkyl and OCI-12 alkyl; more suitably, the optional substituents are selected from Ci-s alkyl and OC1-12 alkyl.

"Independently" or "Independently selected" is used in the context of statement that, for example, "each R16, R17 is independently H, Ci-s alkyl..." and means that each instance of the functional group, e.g., R16, is selected from the listed options independently of any other instance of R16 or R17 in the compound. Hence, for example, H may be selected for the first instance dills in the compound; methyl may be selected for the next instance of R16 in the compound; and ethyl may be selected for the first instance of R17 in the compound.

Ct-s alkyl: refers to straight chain and branched saturated hydrocarbon groups, having from 1 to 8 carbon atoms, and C1-6 alkyl to straight chain and branched saturated hydrocarbon groups, having from 1 to 6 carbon atoms. Suitably a C1-7 alkyl; suitably a C 1-6 alkyl; suitably a C1-5 alkyl; more suitably a C1-4 alkyl; more suitably a C1-3 alkyl. Examples of alkyl groups include methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl, butyl, t-butyl, pent-l-yl, pent-2-yl, pent-3-yl, 3-methylbut-l-yl, 3-methylbut-2-yl, 2-methylbut-2-yl, 2,2,2-trimethyleth-l-yl, n-hexyl, n-heptyl, n-octyl and the like.

"Alkylene" refers to a divalent radical derived from an alkane which may be a straight chain or branched, as exemplified by -CH2CH2CH2CH2-. The alkylene may have the number of carbons as discussed above for alkyl groups.

"Aryl" refers to fully unsaturated monocyclic, bicyclic and polycyclic aromatic hydrocarbons having at least one aromatic ring. Aryl groups as used herein preferably are preferably "C5-20 Aryl" a fully unsaturated monocyclic, bicyclic and polycyclic aromatic hydrocarbons having at least one aromatic ring and having a specified number of carbon atoms that comprise their ring members (e.g., C5-20 aryl refers to an aryl group having from 5 to 20 carbon atoms as ring members). The aryl group may be attached to a parent group or to a substrate at any ring atom and may include one or more non-hydrogen substituents unless such attachment or substitution would violate valence requirements. Suitably, a is selected from a C6-12 aryl, more suitably, a C6-10 aryl. Examples of aryl groups include phenyl.

"Halogen-or "halo": refers to a group selected from F, Cl, Br, and I. Preferably, the halogen or halo is F or Cl. In some aspects, preferably the halogen is F. In other aspects, suitably the halogen is Cl.

As used herein the term "comprising" means "including at least in part" and is inclusive or open ended. When interpreting each statement in this specification that includes the term "comprising," features, elements and/or steps other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner. It should be understood that while various aspects in the specification are presented as "comprising," this includes aspects that "consist essentially of or "consist of that aspect.

The term "consisting essentially of limits the scope of a claim to the specified materials or steps "and those that do not materially affect the basic and novel characteristic(s)" of the claimed invention. When the phrase "consisting essentially of appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause.

The term "consisting of excludes any element, step, or ingredient not specified in the claim; "consisting of defined as "closing the claim to the inclusion of materials other than those recited except for impurities ordinarily associated therewith. When the phrase "consists of appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which: Figure 1 shows a photograph of samples of the eight PMD stereoisomers.

Figure 2 shows protective efficacy of the eight PMD stereoisomers tested against An. gambicte mosquitoes in an arm-in-cage dose response test. The figure shows protective efficacy of each stereoisomer at different concentrations. Data points represent mean protective efficacy and error bars represent standard error.

Figure 3 shows protective efficacy of the eight PMD stereoisomers that were tested against Ae. Aegypti mosquitoes in an arm-in-cage dose response test. The figure shows protective efficacy of each stereoisomer at different concentrations. Data points represent mean protective efficacy and error bars represent standard error.

Figure 4 shows protective efficacy of the eight PMD stereoisomers that were tested against Pyrethroid resistant An. gambiae mosquitoes in an arm-in-cage dose response test. The figure shows protective efficacy of each stereoisomer at different concentrations. Data points represent mean protective efficacy and error bars represent standard error.

Figure 5 shows protective efficacy of the eight PMD stereoisomers that were tested against DEET-insensitive Ac. aegypti mosquitoes in an arm-in-cage dose response test. The figure shows protective efficacy of each stereoisomer at different concentrations. Data points represent mean protective efficacy and error bars represent standard error.

Embodiments of the present invention will now be described further, with reference to the Examples, below.

General Chemistry Methods All reagents and solvents were purchased from the commercial suppliers Acros Organic, Alfa Aesar, Fisher Scientific, Fluka, Fluorochem, Sigma-Aldrich, TCI and VWR. Inert reactions were carried out using oven dried glassware under a nitrogen atmosphere with dry solvents obtained from an Innovative Technology Inc. PS-400-7 solvent purification system. Reactions were monitored using pre-coated aluminium backed commercial TLC plates with visualisation by 254 nm UV light or staining with phosphomolybdic acid in ethanol. Column chromatography was carried out using silica with 60 A mean pore size.

Nuclear magnetic resonance spectra were recorded using either a Bruker Avance 300, 400 or 500 MHz spectrometer, or an Agilent Technologies 500 MHz spectrometer. All '3C spectra were run proton decoupled and all spectra were run in deuterated solvents CDC13 or DMSO-d6 unless otherwise stated. Chemical shifts (6) are reported in parts per million (ppm) and are referenced to the residual solvent peaks. Coupling constants (J) are quoted to the nearest 0.1 Hz. Abbreviations used in reporting peaks were s, d, t, q, quin, m, and br s to denote singlet, doublet, triplet, quartet, quintet, multiplet and broad singlet respectively.

Mass spectra were recorded using an Ag lent QTOF or Broker (ESI-TOF) spectrometer in either methanol or acetonitrile with either the (M+H)' or the (M+Na) m/z value reported to 4 decimal places.

Infrared spectra (4000 cm-1 to 650 cm-1) were recorded on a Perkin Elmer Spectrum 100 FT-IR spectrometer using a Universal ATR accessory for sampling. The machine has internal calibration and only selected peaks are quoted in v (wavenumbers, All capillary melting point determinations were carried out using Btichi 535 melting point apparatus and reported to the nearest degree Celsius (°C).

Examples

The invention is further illustrated by the following Examples.

2 steps 6 steps 85% 16% ?OH 9401-1 3 steps 49% 6 steps 19% 4 steps 8 steps OH 72% 10% steps OH 8 steps OH 12% 43% Scheme 2. Summary of syntheses of the eight, possible stereoisomers of p-menthane-3,8-diol (PMD 1 to 8) in this study.

The syntheses discussed below afford access to all eight stereoisomers of PMD in multigram quantities, with an alternative two-step catalytic synthesis of two of the repellent PMD isomers having been developed. Access to these individual stereoisomers could potentially overcome the issue of resistance which occurs with the currently most widely used insect repellent, achiral N,N-diethyl-m-toluamide (DEET) that only exists in a single chemical form. Commercial PMD is currently approved by the FDA as a mixture of four stereoisomers with no reports of mosquitos developing resistance to date however large-scale usage of an insect repellent may lead to the development of resistance over time. Access to each of the individual PMD stereoisomers means that there are eight chemically distinct mosquito repellents available for use, which will enable any resistance problems that emerge to be addressed by switching between PMD stereoisomers. Therefore, development of resistance to a single PMD repellent stereoisomer used as a mosquito repellent in the field can be countered by its replacement with one of the other seven non-resistant 7 PMD stereoisomers as required. Ongoing switching of the eight PMD stereoisomers as resistance to individual stereoisomers appears will therefore ensure that PMD retains its effectiveness as an insect repellent in mosquito and tick populations. Furthermore, some of the isomers have distinct odours (e.g. strong menthol vs citrus), whilst other isomers are barely perceptible to the human nose, thus providing opportunities for their selective use in the flavour and fragrances industries. For example, PMD formulations containing different isomers with significantly different smells could be marketed to enable consumers to choose their favourite PMD fragrance, which would encourage its correct application and long term use. The PMD stereoisomers with less strong odours could potentially be added to perfumes to afford protection against insect bites without the desired smell of the perfume being compromised. Finally, monoterpenes are the second most widely used class of flavourings (e.g. menthol) used in e-cigarettes, thus affording great opportunities for the PMD isomers to be used as novel flavours/odourants with insect repellent properties for use in e-cigarettes and incense burners.

Scheme 3, below, illustrates steps in the methods used to synthesise the 1-cis-3-trans-4PMD 2 and 1-trans-3-cis-4-PMD 4 isomers. Scheme 4 illustrates steps in the methods used to synthesise the 1-cis-3-cis-4-PMD 5 and 1-trans-3-trans-4-PMD 7 isomers.

mCPBA CH2Cl2 2 h, 0°C to rt, 92°/

OH 57a/b Et2O

2 h. 0°C to rt, 87%

OH PMD 2

ZnBr2 (20%) 0 'C to rt, 2 h, toluene. 60% PPh3 (1.5 equiv.) p-NO2-C8H4-COOH(1.5 equiv.) EtO2CN=NCO2Et (1.5 equiv.) toluene, 0 °C to rt, 5 h. N2, 90% K2CO3 (5 equiv.) Me0H, rt, 3 h 88% (i) mCPBA (1.5 equiv.) CH2Cl2, 2 h, 0 'C to rt OH (H) LiAIH4, Et2O, 2 h 0 "C to rt, 86% over 2 steps

O O NO2

Scheme 3. Synthesis of 1-cis-3-trans-4-PMD 2 and 1-trans-3-cis-4-PMD 4 isomers.

tBuO0H (7 equiv.) Cr03 (0.05 equiv.) Pyridine (0.10 equiv.) CH2Cl2, rt, 24 h, 45% (-)-a-pinene Bu2AIH (1.2 equiv) CH2Cl2, -78 °C 3 h, N2,83% LiAIH.

Et2O, N2 0 °C to rt 54% over 2 steps 83a H2 (1 atm.) PtO2 (5%) hexane, rt, 4 h Li (20 equiv.) NH3/Et20/EtOH (20:10:1) -78 °C, 3 h, 76% PMD 7 Br Acetone 24 h, dark, rt

DH PMD 5

Pyridinium tosylate (10%) Et0H, rt, 16 h 80% over 2 steps TCICA (0.5 equiv.) pyridine (1.6 equiv.), MeCN rt, 2h, 94% Scheme 4. Synthesis of the 1-cis-3-cis-4-PMD 5 and 1-trans-3-trans-4-PMD 7 isomers.

In the Examples, novel stereoselective syntheses are described of all eight, possible stereoisorners of p-menthane-3,8-diol (PMD). Naturally occurring PMD stereoisomers are known to have mosquito/insect repellent properties. Using enantiomers of the biorenewable and inexpensive monoterpenoids alpha-pinene (derived from cheap crude sulfate turpentine, a waste by-product of paper industry) and citronellal (derived from beta-pinene from CST), stereoselective chemical transformations have been carried out to produce all eight, possible isomers of PMD in their pure forms. These eight isomers exhibit a variety of different pleasant scents of differing strengths.

PROCEDURES FOR THE SYNTHESIS OF PMD ISOMERS

Synthetic Procedures (-)-Isopulegol epoxide (54a/b) To a stirred solution of (-)-isopulegol (7.70 g, 50 mmol) in dichloromethane (125 mL) at 0 °C was added a solution of rneia-chloroperbenzoic acid (18.43 g of 70 wt%, 75 mmol) in dichloromethane (125 mL) dropwi se over 20 minutes. The resulting solution was stirred at 0 °C for 30 minutes and then room temperature for 3 hours, at which point a white precipitate formed. 1M NaOH (150 mL) was added and the biphasic reaction stirred for an additional 5 minutes before being separated. The organic layer was washed with 1M NaOH (2 x 150 mL), water (100 mL) and brine (100 mL), before being dried over MgSO4. The solvent was removed in vacuo to give the title compound as a colourless oil (7.89 g, 46 mmol) in 93% yield (ratio of diastereomers 55:45) which was used without further purification.

11-1NMR (300 MHz, Chloroform-d) 5 3.71 (td, J= 10.5, 4.4 Hz, 1H, Ma), 3.35 (d, J= 2.0 Hz, 1H, 54b), 3.28 (td, J= 10.5, 4.6 Hz, 1H, 54b), 2.92 (d, J= 4.1 Hz, 1H, Mb), 2.81 (d, J = 2.4 Hz, 1 H, 54a), 2.66 (d, J= 4.1 Hz, 1H, 54b), 2.59 (d, J= 4.6 Hz, 1 H, Ma), 2.53 (dq, .I= 4.6, 0.7 Hz, 1H, 54a), 2.08 -1.98 (m, 11-1, 54a), 1.97 -1.81 (m, 2H, Mb), 1.75 -1.61 (m, 3H, 2 x 54a and 1 x 54b), 1.54 -1.38 (m, 3H, 1 x Ma and 2 x 54b), 1.36 (d, J= 0.7 Hz, 311, 54b), 1.31 (d, J= 0.7 Hz, 3H, 54a), 1.26 -1.05 (m, 2H, 1 x 54a and 1 x 54b) 1.03 -0.80 (in, 11 H, 6 x 54a and 5 x 54b) 13C NMR (126 MHz, Chloroform-d) 71.4, 70.6, 60.5, 59 3, 53.0, 52.3, 51.3 49.0, 43.6, 42.9, 34.0, 34.0, 31.3, 31.0, 27.8, 22.2, 21.1, 17.0.

I.R (thin film) v. (cm-1): 3421 (0-H), 2921, 2867 (C-H), 1450 FIRMS (ESI): tri:z calculated for CI oH1802 requires 193.1199 for [M+Na] ; found 193.1202 (IR, 3R, 4R)-p-Menthane-3,8-diol (P1VID 1) Method 1 To a stirred solution of LiA1114 (71 mL 1 0 M in TITO at 0 °C under N2 was added (-)-isopulegol epoxide (6.01 g, 35 mmol) in dry diethyl ether (100 mL) dropwise over 20 minutes. The resulting solution was stirred at 0 °C for 30 minutes and then at room temperature for 2 hours. The reaction was then cooled to 0 °C and quenched by dropwise addition of water (3 mL), followed by 2M NaOH (6 mL) and water (6 mL) After warming to room temperature and stirring for 15 minutes, the reaction was dried over MgSO4 and filtered before evaporating the solvent under reduced pressure to give the title compound as a white solid (5.48 g, 32 mmol) in 91% yield.

Method 2 To a stirred solution of (-)-isopulegol (0.770 g, 5.00 mmol) in toluene (1.05 mL, 10.00 mmol) was added PW4024[PTC]3 (0.113 g, 2259 gmo1-1, 0.05 mmol, 1 mol%) and the resulting mixture was heated to 35 °C and stirred for 15 minutes. Na2SO4 (0.211 g, 1.50 mmol) was dissolved in a solution of 50 wt% aqueous 11202 (0.290 mL, 5 05 mmol) before adjusting the pH to 7 with 2 M NaOH. The aqueous solution was then added dropwise over 5 minutes to the stirred organic solution and the resulting biphasic mixture stirred rapidly (500 rpm) for 5 hours. The organic layer was then removed and dissolved in methanol (25 mL) before adding NaOH (0.040 g, 1.00 mmol) and 10% Pd/C (0.530 g, 0.50 mmol of Pd). Nitrogen was bubbled through the resulting suspension for 5 minutes before bubbling hydrogen through it for 15 minutes. The reaction was sealed under an atmosphere of hydrogen and stirred for 24 hours. Nitrogen was bubbled through the reaction for 5 minutes before filtering through celite and removing the solvent in vacua. The crude product was purified by silica gel flash column chromatography (petroleum ether: ethyl acetate (7:3), R-= 0.3) to afford the title compound as a white solid (0.62 g, 3.61 mmol) in 72% yield.

PTC = mixture of MeW(C81-117)3 and MeNE(CioH203 m.p. 72 -74 °C 11-1 NMR (500 MHz, Chloroform-a) S 3.72 (1H, app. td, = 10.4, 3,/,,x-°y = 4.3 Hz, C3H), 3.22 (21-1, br s, 2 x OH), 2.00 -1.89 (1H, m, C2Ha), 1.75 -1.60 (2H, m, C5Ha and Cala), 1.51 -1.31 (2H, m, Cl H and C4H), 1.23 (61-1, s, C9H3 and Cl OH3), 110 -0.98 (1H, m, C2Hb), 0.96 -0.86 (5H, m, C5Hh and C6Hh and C7H3).

13C NMR (126 MHz, Chloroform-d) 75.1 (C8), 72.9 (C3), 53.5 (C4), 44.7 (C2), 34.7 (C6), 31.4 (C9/C10), 30.2 (C9/C10), 27.2 (C5), 23.8, 22.0 (C7) I.R (thin film) v. (cm-1): 3257 (0-H), 2975, 2952, 2920, 2843 FIRMS (ESL): m,z calculated for CioH2002 requires 195.1356 for [M+Na]'; found 195.1356 [a]M: -11 (c = 1.0, CHC13) Method 3 (-)-Isopulegol (3.08 g, 20 mmol), acetic acid (4 5 mL) and water (16 mL) were heated at 110 °C for 24 hours with vigorous stirring. The reaction was cooled and diluted with water (20 mL) and dichloromethane (20 mL) The organic layer was separated, dried over MgSO4 and the solvent removed in vacuo to give a crude product containing 55% PMD 1, 40% unreacted (-)-isopulegol and 5% of other impurities. The product was purified by column chromatography (20% EtOAc in petrol) to give PMD-1 as a white solid in 51% yield (1.76 g).

(2S,5R)-2-(2-hydroxypropan-2-y1)-5-methylcyclohexan-l-one (58)

H

To a stirred solution of (1 R, 3R, 4R)-p-Menthane-3,8-diol (0.172 g, 1.00 mmol) and pyridine (0.13 mL, 1.60 mmol) in acetonitrile (5 mL) at 0 °C was added trichloroisocyanuric acid (0.116 g, 0.50 mmol) in acetonitrile (5 mL) dropwise over 5 minutes. The reaction was stirred at room temperature for 5 hours, at which point a light yellow precipitate had formed. The reaction was then filtered and concentrated under reduced pressure, before being dissolved in ethyl acetate (10 mL) The organic solution was then washed with water (10 mL) and brine (10 mL), before being dried over MgSO4 and filtered. The solvent was evaporated under reduced pressure to give the title compound as a pale yellow oil (0.150 g, 0.88 mmol) in 88% yield. This was used without further purification.

11-1NMR (400 MHz, Chloroform-d) 6 3.95 (br s, 1H, OH), 2.39 -2.28 (in, 2H), 2.17 -2.07 (m, 3H), 2.00 (td, = 12.8, 1.4 Hz, 111), 1.94 -1.75 (m, 2H), 1.52 (qd, = 12.8, 3.0 Hz, 1H), 1.42 -1.32 (m, 1H), 0.97 -0.90 (m, 1H), 1.21 (s, 3H, C(OH)CH3CH3), 1.20 (s, 3H, C(OH)CH3CH3), 1.01 (d, J= 6.2 Hz, 3H, CHCHs).

13C NMR (101 MHz, Chloroform-d) 215.2, 71.3, 58.8, 51.5, 35.5, 34.0, 28.7, 28.6, 25.6, 22.3.

I R (thin film) yin. (cm-1) 3518 (0-H), 2944, 2928, 2871, 2757, 1693 (C=0) FIRMS (ESI): niiz calculated for C10E12002 requires 194 1199 for [M+Na]'; found 194.1199 (+)-Isopulegol (56)

OH

Zinc bromide (2.26 g, 10 mmol) was suspended in toluene (15 mL) and cooled to 0 °C, before (-)-citronellal (9.00 mL, 50 mmol) was added dropwise over 10 minutes. The solution was stirred at 0 °C for 30 minutes before being warmed to room temperature and stirred for 3 hours. Saturated ammonium chloride (100 mL) was added and the resulting mixture was extracted with diethyl ether (3 x 100 mL) The combined organic phases were then washed with saturated ammonium chloride (100 mL), before being dried over MgSO4. The solvent was removed in vacuo and the crude oil was purified by flash column chromatography (Petroleum ether: ethyl acetate (95: 5), 1,r-= 0.15) to give the title compound as a colourless oil (4.63 g, 30 mmol) in 60% yield.

NMR (500 MHz, Chloroform-a) 6 4.90 (d, J= 2.0 Hz, 1H), 4.85 (d, J = 2.0 Hz, 1H), 3.46 (td, J= 10.6, 4.2 Hz, 1 H), 2.04 (ddt, J= 10.6, 4.2, 2.1 Hz, 1H), 1.92 -1.74 (m, 2H), 1.73 -1.64 (m, 5H), 1.50 (m, 1 H), 1.32 (qd, J= 13.3, 3.8 Hz, 1 H), 0.95 (n, 5H).

13C NMR 026 MHz, Chloroform-a) 6 146.8, 113.0, 70.5, 54.3, 42.8, 34.5, 31.6, 29.8, 22.4, 19.4.

I.R. (thin film) vmax (cm 1): 3404 (0-H), 2949 (C-H), 2920 (C-H), 2869 (C-H), 1646 (C=C). HRMS (EST): nrz calculated for CioH180: requires 155. 1436 for [M+H] ; found 155.1440 [c]f) . +13 (c = 1.0, CHC13) (+)-Isopulegol epoxide (57a/b)

OH 57a1b

55: 45 To a stirred solution of (+)-isopulegol (3.08 g, 20 mmol) in dichloromethane (50 mL) at 0 °C was added a solution of meta-chloroperbenzoic acid (7.37 g of 70 wt%, 30 mmol) in dichloromethane (50 mL) dropwise over 20 minutes. The resulting solution was stirred at 0 °C for 30 minutes and then room temperature for 3 hours, at which point a white precipitate formed. 1M NaOH (60 mL) was added and the biphasic reaction stirred for an additional 5 minutes before being separated. The organic layer was washed with 1M NaOH (2 x 60 mL), water (40 mL) and brine (40 mL), before being dried over MgSO4. The solvent was removed in menu to give the title compound as a colourless oil (3.14 g, 18.5 mmol) in 92% yield (ratio of di astereomers 55:45) which was used without further purification.

1H NMR (500 MHz, Chloroform-d) 8 3.71 (td, J= 10.5, 4.4 Hz, 1H, 57a), 3.35 -3.22 (m, 2H, 2 x 57b), 2.92 (d, .1= 4.1 Hz, 1H, 57b), 2.81 (s, 111, 57a), 2.66 (d, ./= 4.1 Hz, 1H, 57b), 2.59 (d, J -4.6 Hz, 1H, 57a), 2.53 (dq, J -4.6, 0.7 Hz, 1H, 57a), 2.08 -1.98 (m, 1H, 57a), 1.97 -1.81 (m, 2H, 57b), L75 -L61 (m, 3H, 2 x 57a and 1 x 57b), 1.54 -1.38 (m, 3H, 1 x 57a and 2 x 57b), 1.36 (s, 3H, 57b), 1.31 (s, 3H, 57a), 1.26 -1.05 (m, 2H, 1 x 57a and 1 x 57b) 1.03 -0.80 (m, 11H, 6 x 57a and 5 x 57b) 13C NMR (126 MHz, Chloroform-d) 71.4, 70.6, 60.4, 59.3, 53.0, 52.3, 51.3, 49.1, 43.7, 43.0, 34.0, 34.0, 31.3, 31.0, 27.8, 22.2, 21.0, 17.0.

1.R. (thin film) vi,ia (cm -1): 3439 (0-H), 2921, 2868 (C-H), 1450 HRMS (ESL): m calculated for CloHt802 requires 193.1199 for [M+Na]' ; found 193.1200 (15, 35, 45)-p-Menthane-3,8-diol (PM D 2) To a stirred solution of LiA1H4 (35 mL, 1.0 M in THE) at 0 °C under N2 was added (+)-isopulegol epoxide (3.00 g, 17.6 mmol) in dry diethyl ether (75 mL) dropwise over 20 minutes. The resulting solution was stirred at 0 °C for 30 minutes and then at room temperature for 2 hours. The reaction was then cooled to 0 °C and quenched by dropwise addition of water (1.5 mL), followed by 2M NaOH (3 mL) and water (3 mL). After warming to room temperature and stirring for 15 minutes, the reaction was dried over MgSO4 and filtered before evaporating the solvent under reduced pressure to give the title compound as a white solid (2.62 g, 15.2 mmol) in 87% yield.

m.p. 72 -74 °C H NMR (400 MHz, Chloroform-0 6 3.72 (11-1, app. td, = 10.4, 3.1ax-oq = 4.3 Hz, C3H), 3.10 (2H, br s, 2 x OH), 2.00 -1.89 (1H, m, C21-14, 1.75 -1.60 (2H, m, C51-la and Cala), 1.51 -1.31 (2H, m, C1H and C4H), 1.23 (6H, s, C9H3 and C101-13), 1.10 -0.98 (11-1, m, lb), 0.96 -0.86 (5H, m, C5Hb and C61-lb and C7113).

13C NMR (101 MHz, Chloroform-d) 75.1 (C8), 72.9 (C3), 53.5 (C4), 44.7 (C2), 34.7 (C6), 31.4 (C9/C10), 30.2 (C9/C10), 27.2 (CS), 23.8, 22.0 (C7) R (thin film) \Amu, (cm-'): 3257 (0-H), 2952, 2920, 2843 HRMS (ESI): in calculated for CioH2o02 requires 195.1356 for [M+Na] ; found 195.1357 [a]a° +11 (c = 1.0, CHC13) (1S,2S,511)-5-Methyl-2-(prop-1-en-2-yl)eyclohexyl 4-nitrobenzoate (62) To a stirred solution of (-)-isopulegol (4.62 g, 30 mmol) in toluene (300 mL) was added triphenylphosphine (11.80 g, 45 mmol) followed by 4-nitrobenzoic acid (7.52 g, 45 mmol). The resulting solution was cooled to 0 °C and diethyl azodicarboxylate (7 05 mL, 45 mmol) was added dropwise over 10 minutes. The reaction was then stirred at room temperature for 5 hours before being filtered and the solvent evaporated under reduced pressure. The resulting crude solid was suspended in hot diethyl ether, before being cooled and filtered. The solvent was then evaporated under reduced pressure and the resulting yellow oil was purified by flash column chromatography (Petroleum ether: diethyl ether (98: 2), fti = 0.30) to give the title compound as a yellow solid (8.03 g, 26 mmol) in 88% yield.

m.p. 94 -96 °C H NMR (500 MHz, Chloroform-d) 6 8.28 (d, J= 7.3 Hz, 2H), 8.17 (d, J= 7.3 Hz, 2H), 5.55 (s, 1H), 4.76 (s, 1H), 4.71 (s, 1H), 2.11 (t, J= 11.9 Hz, 2H), 1.96 -1.85 (m, 2H), 1.84 NO2 -1.67 (m, 5H), 1.32 (t, J = 13.3 Hz, 1H), 1.10 (q, J = 12.7 Hz, Ill), 0.93 (d, J =6.4 Hz, 3H).

13C NMR (126 MHz, Chloroform-d) S 164.0, 150.6, 146.0, 136.5, 130.7, 123.7, 111.2, 72.5, 47.1, 39.3, 34.6, 27.2, 25.5, 22.6, 22.2.

I.R. (thin film) v.. (cm-1) 3114, 2941, 2963, 2867, 2844, 1719 (C=0), 1519 (N-0), 1274 (N-0).

HRMS (ESI): m-calculated for C17H21N04 requires 304.1543 for [M+H] 1; found 304 1545 [a],f) +54 (c = 1.0, CHC13) (+)-Neoisopulegol (63) To a stirred solution of 62 (6.06 g, 20 mmol) in methanol (200 mL) was added potassium carbonate (13.82 g, 100 mmol) and the resulting suspension stirred for 5 hours. The resulting solid was filtered off and the solvent evaporated under reduced pressure. The crude product was dissolved in dichloromethane (150 mL) and 2M NaOH (150 mL) and stirred for 10 minutes. The phases were separated and the organic phase washed with 2M NaOH (2 x 150 mL) and brine (150 mL) The solvent was then evaporated under reduced pressure to give the title compound as a colourless oil (2.88 g, 19 mmol) in 94% yield.

1H NMR (500 MHz, Chloroform-d) S 4.95 (s, tH, C=CHH), 4.78 (s, 1H, C=CHH), 3.99 (s, 1H, CHOH), 1.97 (m, 2H), 1.82 -1.67 (m, 6H), 1.49 -1.44 (m, 2H), 1.19 -1.07 (m, 1H), 0.98 -0.91 (m, tH), 0.89 (d, J= 6.5 Hz, 3H, CHCH3) 13C NMR (126 MHz, Chloroform-d) S 147.5, 111.4, 66.5, 48.6, 41.1, 34.9, 26.0, 24.1, 22.9, 22.4.

1.R. (thin film) vmns (cm) 3676, 3454, 2921, 1733, 1643, 1532.

HRMS (PSI): m z calculated for CioHisO: requires 155.1430 for [M+1-1] '; found 155.1456 [a]a° +30 (c = 1.0, CHC13) (+)-Neoisopulegol epoxide (64a/b) H 'OH H 'OH 64a1b 76: 24 To a stirred solution of (+)-neoisopulegol (2.70 g, 17.5 mmol) in dichloromethane (45 mL) at 0°C was added a solution of meta-chloroperbenzoic acid (6.46 g of 70 wt%, 26.3 mmol) in dichloromethane (45 mL) dropwise over 20 minutes. The resulting solution was stirred at 0 °C for 30 minutes and then room temperature for 3 hours, at which point a white precipitate formed. 1M NaOH (55 mL) was added and the biphasic reaction stirred for an additional 5 minutes before being separated. The organic layer was washed with 1M NaOH (2 x 55 mL), water (40 mL) and brine (40 mL), before being dried over MgSO4. The solvent was removed in vacuo to give the title compound as a white solid (2.78 g, 16.4 mmol) in 93% yield (ratio of diastereomers 76:24) which was used without further purification.

m.p. 47 -50 °C 1H NMR (500 MHz, Chloroform-a) 6 4.32 (s, 1H, 64a), 4.05 (s, 1H, 64b), 3.06 (d, J = 4.0 Hz, 1 H, 64b), 2.80 (d, J= 4.6 Hz, 1 H, 64a), 2.64 -2.54 (in, 3H, 1 x 64a and 2 x 64b), 2.49, (d, J= 4.6 Hz, 1H, 64a), 1.90 -1.41 (m, 1211), 1.39 (s, 6H, CCH3 of 64a and 64b), 1.07 0.98 (m, 2H, 1 x 64a and 1 x 64b), 0.94 -0.88 (m, 2H, 1 x 64a and 1 x 64b), 0.86 (d, J= 6.7 Hz, 6H, CHCH3 of 64a and 64b) 13C NMR (126 MHz, Chloroform-a) 6 68.0, 67.5, 60.4, 60.2, 52.4, 51.5, 44.3, 43.8, 42.1, 41.9, 34.9, 34.7, 25.7, 25.6, 22.4, 22.3, 22.3, 22.0, 21.5, 21.3.

I.R. (thin film) vit. (cm-1): 3477 (0-H), 2947, 2923, 2864, 2845, 1717, 1523 FIRMS (EST): m'z calculated for C1oH1802 requires 193.1199 for [M+HI; found 193.1201 (1R, 3S, 4R)-p-Menthane-3,8-diol (PMD 3)

OH 9tOH

Method 1 To a stirred solution of Li AlH4 (29 mL, 1.0 M in THF) at 0 °C under N2 was added (+)-neoisopulegol epoxide (2.43 g, 14.3 mmol) in dry diethyl ether (70 mL) dropwise over 20 minutes. The resulting solution was stirred at 0 °C for 30 minutes and then at room temperature for 2 hours. The reaction was then cooled to 0 °C and quenched by dropwise addition of water (1.2 mL), followed by 2M NaOH (2.4 mL) and water (2.4 mL) After warming to room temperature and stirring for 15 minutes, the reaction was dried over MgSO4 and filtered before evaporating the solvent under reduced pressure to give the title compound as a white solid (2.31 g, 13.4 mmol) in 87% yield.

Method 2 To a solution of 58 (1.90g, 11.20mmol) in dry diethyl ether (55m L) at -78 "C under an inert atmosphere was added lithium tri-sec-butylborohydride (16.80 mL, 1 0 M in TI-IF) dropwise over a 10-minute period. The reaction was left to stir for 90 minutes at -78 °C, then for a further 3 hours at room temperature. The reaction was cooled to 0 "C and quenched by slow addition of 2M NaOH (11.20mL), followed by 30% hydrogen peroxide (6.1mL) The solution was left to stir for a further hour at room temperature. The hydrogen peroxide was then quenched using saturated aqueous sodium bisulfite (50 mL), before acidification with IM HCl to pH 5. The organic layer was separated and the aqueous layer was extracted with diethyl ether (2 x 50mL) and washed with water (50mL) and brine (50mL) The combined organic layers were dried over magnesium sulfate, filtered and the solvent was removed under reduced pressure. The crude product was further purified using silica gel column chromatography (petroleum ether:ethyl acetate (9:1), Kt.= 0.10) to give the title compound as a white solid (1.40 g, 8.14 mmol) in 73% yield.

m.p. 67 -69 °C 1H NMR (400 MHz, Chloroform-d) 8 4.41 (app. q, 3,Lx_eq and --ecfreci = 2.9 Hz, 1H, C3H), 2.46 (br s, 21-1, 2 x 01/), 1.87 -1.74 (m, 3H, C1H and C2FL and C61-10, 1.74 -L64 (2H, m, C5H2), 1.36 (s, 3H, C9H3), 1.23 (s, 3H, C10H3), 1.20 -1.14 (m, 1H, C4H), 0.97 -0.90 (m, 1H, C6Hh), 0.88 (d, J= 6.2 Hz, 3H, C7H3).

13C NMR (101 MHz, Chloroform-d) 73.5 (C8), 68.3 (C3), 48.5 (C4), 42.7 (C2), 35.0 (C6), 29.1 (C10), 29.0 (C9), 25.8 (C1), 22.3 (C7), 20.4 (C5) I.R (thin film) v. (cm-1): 3248 (0-H), 2944, 2906, 2866 FIRMS (ESI): m/z calculated for CloH2002 requires 195.1356 for [M+Na] . found 195.1355 +16 (c = 1.0, CHC13) (1 R,2R,5S)-5-Methyl-2-(prop-l-en-2-yOryclohexyl 4-nitrobenzoate (65) NO2 To a stirred solution of (+)-isopulegol (4.55 g, 30 mmol) in toluene (300 mL) was added triphenylphosphine (11.62 8, 45 mmol) followed by 4-nitrobenzoic acid (7.40 8, 45 mmol). The resulting solution was cooled to 0 °C and diethyl azodicarboxylate (6.95 mL, 45 mmol) was added dropwise over 10 minutes. The reaction was then stirred at room temperature for 5 hours before being filtered and the solvent evaporated under reduced pressure. The resulting crude solid was suspended in hot diethyl ether, before being cooled and filtered. The solvent was then evaporated under reduced pressure and the resulting yellow oil was purified by flash column chromatography (Petroleum ether: diethyl ether (98: 2), IV= 0.30) to give the title compound as a yellow solid (8.00 g, 26 mmol) in 90% yield.

m.p. 94 -96 °C H NMR (500 MHz, Chloroform-d) 6 8.28 (d, J = 7.3 Hz, 2H), 8.17 (d, J = 7.3 Hz, 2H), 5.55 (s, 1H), 4.76 (s, 1H), 4.71 (s, 1H), 2.11 (t, J= 11.9 Hz, 2H), 1.96 -1.85 (m, 2H), 1.84 -1.67 (m, 5H), 1.32 (t, J= 13.3 Hz, 1H), 1.10 (q, J= 12.7 Hz, 1H), 0.93 (d, J =6.4 Hz, 3H).

13C NMR (126 MHz, Chloroform-d) 6 164.0 150.6, 146.0, 136.5, 130.7, 123.7, 111.2, 72.5, 47.1, 39.3, 34.6, 27.1, 25.5, 22.6, 22.2.

I.R. (thin film) (cm-1): 3114, 2941, 2928, 2867, 2843, 1719 (C=0), 1519 (N-0), 1275 (N-0).

FIRMS (ESI): trti calculated for Ci7F121N04 requires 304.1543 for [M+H] ; found 304.1545 [a],f) -54 (c = 1 0, CHCI3) (-)-Neoisopulegol (66)

OH

To a stirred solution of 65 (6.06 g, 20 mmol) in methanol (200 mL) was added potassium carbonate (13.82 g, 100 mmol) and the resulting suspension stirred for 5 hours. The resulting solid was filtered off and the solvent evaporated under reduced pressure. The crude product was dissolved in dichloromethane (150 mL) and 2M NaOH (150 mL) and stirred for 10 minutes. The phases were separated and the organic phase washed with 2M NaOH (2 x 150 mL) and brine (150 mL) The solvent was then evaporated under reduced pressure to give the title compound as a colourless oil (2.72 g, 19 mmol) in 88% yield.

H NMR (500 MHz, Chloroform-d) 6 4.95 (s, tH, C=CHH), 4.78 (s, 1H, C=CHH), 3.99 (s, 1H, CHOH), 1.97 (m, 2H), 1.82 -1.67 (m, 611), 1.49 -1.44 (m, 2H), 1.19 -1.07 (m, 1H), 0.98 -0.91 (m, 1 F), 0.89 (d, J= 6.5 Hz, 311, CHM) 3C NMR (126 MHz, Chloroform-d) 6 147.5, 111.4, 66.5, 48.6 41.1 34.9, 26.0, 24.1, 22.9, 22.4.

I.R. (thin film) v., (cm): 3675, 3473, 2910, 1643.

FIRMS (ESI): 111/Z calculated for Ciollis0: requires 155.1430 for [M+H] ; found 155.1471 [a]f: -30 (c = 1.0, CHCI3) (-)-Neoisopulegol epoxide (67a/b) To a stirred solution of (-)-neoisopulegol (2.63 g, 17.1 mmol) in dichloromethane (45 mL) at 0°C was added a solution of meta-chloroperbenzoic acid (6.29 g of 70 wt%, 25.6 mmol) in dichloromethane (45 mL) dropwise over 20 minutes. The resulting solution was stirred at 0 °C for 30 minutes and then room temperature for 3 hours, at which point a white precipitate formed. 1M NaOH (55 mL) was added and the biphasic reaction stirred for an additional 5 minutes before being separated. The organic layer was washed with 1M NaOH (2 x 55 mL), water (40 mL) and brine (40 mL), before being dried over MgSO4. The solvent was removed in vacua to give the title compound as a white solid (2.63 g, 15.5 mmol) in 91% yield (ratio of diastereomers 76:24) which was used without further purification.

m.p. 47 -50 °C 11-1NMR (500 MHz, Chloroform-d) 6 4.32 (s, 1H, 67a), 4.05 (s, 1H, 67b), 3.06 (d, J= 4.0 Hz, 1H, 67b), 2.80 (d, J= 4.6 Hz, 1H, 67a), 2.64 -2.54 (m, 3H, 1 x 6Th and 2 x 67b), 2.49, (d, J= 4.6 Hz, 1H, 67a), 1.90 -1.41 (m, 12E), 1.39 (s, 6H, CCH3 of 67a and 67b), 1.07 0.98 (m, 2H, 1 x 67a and 1 x 67b), 0.94 -0.88 (m, 2H, 1 x 67a and 1 x 67b), 0.86 (d, J= 6.7 Hz, 611, CHCH3 of 67a and 67b) 13C NMR (126 MHz, Chloroform-d) 6 68.0, 67.5, 60.4, 60.2, 52.4, 51.5, 44.3, 43.8, 421, 41.9, 34.9, 34.7, 25.7, 25.6, 22.4, 22.4, 22.3, 22.0, 21.6, 21.3.

I.R. (thin film) vim, (cm): 3472 (0-H), 2946, 2922, 2863, 2844, 1733, 1446 HRMS (ESL): 111/Z calculated for C1d-11802 requires 193.1199 for [M+H] ; found 193.1200

H

OH 67a/b

75: 25 (15, 3R, 4S)-p-Menthane-3,8-diol (PMD 4) To a stirred solution of LiA1H4 (30 mL, 1 0 M in Tan at 0 °C under N2 was added (-)-neoisopulegol epoxide (2.55 g, 15.0 mmol) in dry diethyl ether (70 mL) dropwise over 20 minutes. The resulting solution was stirred at 0 °C for 30 minutes and then at room temperature for 2 hours. The reaction was then cooled to 0 °C and quenched by dropwise addition of water (1.2 mL), followed by 2M NaOH (2.4 mL) and water (2.4 mL). After warming to room temperature and stirring for 15 minutes, the reaction was dried over MgSO4 and filtered before evaporating the solvent under reduced pressure to give the title compound as a white solid (2.39 g, 13.9 mmol) in 94% yield.

m.p. 67 -69 °C H NMR (400 MHz, Chloroform-d) 6 4.41 (app. q, 3./ax-eq and/ 3. eq-eq = 2.9 Hz, 111, C3H), 2.14 (br s, 2H, 2 x OH), 1.87 -1.74 (m, 311, CHI and CaL and Cala), 1.74 -1.64 (211, m, C5H2), 1.36 (s, 3H, C9H3), 1.23 (s, 3H, CIOH3), 1.20 -1.14 (m, 1H, C41-I), 0.97 -0.90 (m, 111, C6Hb), 0.88 (d, .1= 6.2 Hz, 3H, C7H3).

13C NMR (101 MHz, Chloroform-a5 73.5 (C8), 68.3 (C3), 48.5 (C4), 42.7 (C2), 35.0 (C6), 29.1 (C10), 29.0 (C9), 25.8 (C1), 22.3 (C7), 20.4 (C5) I.R. (thin film) vmas (cm"): 3248 (0-1-1), 2944, 2906, 2866 FIRMS (ESI): calculated for Cm112002 requires 195.1356 for [M+Na] ; found 195.1358 [Ge]a' * -16 (c = 1.0, CHC13) (1R,2R,SR)-2-(2-hydroxypropan-2-y1)-5-methyleyclohexyl 4-methylbenzenesulfonate To a stirred solution of (1R, 3R, 4R)-p-Menthane-3,8-diol (1.28 g, 7.44 mmol) in pyridine (3.00 mL, 74.4 mmol) at 0 °C was added para-toluenesulfonyl chloride (2.84 g, 14.88 mmol) over 5 minutes. The reaction was warmed to room temperature and stirred for 16 hours, before cooling to 0 °C and quenching with 3 M HCl (20 mL). The resulting solution was extracted with dichloromethane (3 x 20 mL) and the combined organic layers were then washed with 1 M HC1 (50 mL), water (50 mL) and brine (50 mL) The organic layers were dried over magnesium sulfate, filtered, and the solvent removed in mow to give the title compound as a white solid (2.24 g, 6.87 mmol) in 92% yield which was used without further purification.

m.p. 50 -52 °C ITINMR (400 MHz, Chloroform-0 6 7.81 (d, J= 8.3 Hz, 21-1, Arom. C-H), 7.33 (d, J= 8.3 Hz, 2H, Arom. C-H), 4.84 (td, 7 = 10.9, 4.3 Hz, 11-1, CHO-S-), 2.44 (s, 3H, Ar-CHs), 2.24 -2.14 (m, 1H), 1.96 -1.87 (m, 1H), 1.72 -1.62 (m, 2H), 1.54 -1.42 (m, 1H), 1.27 -1.14 (m, 8H), 1.11 -1.00 (m, 1 H), 0.93 -0.83 (m, 41-1).

13C NIVIR (101 MHz, Chloroform-d) 145.1, 134.8, 130.0, 127.6, 84.7, 72.7, 52.3, 42.3, 34.0, 31.7, 28.9, 27.4, 25.7, 21.8, 21.8.

1.R. (thin film) vim, (cm"): 3230 (0-H), 2958, 2919, 2840, 1597, 1452, 1352 (S=0).

HRMS (ESI): it calculated for C17H2604S requires 349.1444 for [M+Naf; found 349.1450.

(-)-Verbenone (70) Method 1 To a stirred suspension of chromium (VI) trioxide (0.038 g, 3.75 mmol) in dichloromethane (600 mL) at room temperature was added pyridine (0.60 mL, 7.50 mmol) followed by tenbutylhydroperoxide (72 mL of 70% aqueous solution, 525 mmol). After stirring for 5 minutes, (-)-a-pinene (10.20 g, 75 mmol) was added over 5 minutes while maintaining the temperature of the reaction constant. The reaction was stirred for 24 hours at room temperature before being poured into 1M aqueous sodium thiosulfate (550 mL) After stirring for 1 hour, the organic layer was separated and concentrated in vacua. The crude product was then purified by silica gel column chromatography (petroleum ether:ethyl acetate (9:1), Rt = 0.30) to give the title compound as a pale yellow oil (5.06 g, 34 mmol) in 45% yield.

Method 2 To a stirred solution of (-)-a-pinene (6.80 g, 50 mmol) in acetone (225 mL) and water (25 mL) at room temperature was added N-hydroxyphthalimide (8.97 g, 55 mmol) and pyridinium chlorochromate (10.78 g, 50 mmol). The reaction was stirred at room temperature for 5 hours before adding a further portion of pyridinium chlorochromate (10.78 g, 50 mmol) and being left to stir for 19 hours. Magnesium sulfate was added and the resulting slurry was filtered through a pad of celite before concentrating the resulting solution under reduced pressure. The resulting brown slurry was dissolved in dichloromethane (300 mL) and aqueous NaHCO3 (300 mL). The layers were separated and the aqueous layer extracted with a further portion of dichloromethane (300 mL) The combined organic phases were washed with aqueous NaHCO3 (2 x 300 mL), water (300 mL) and brine (300 mL), before being dried over magnesium sulfate, filtered and concentrated in vacuo. The crude product was then purified by silica gel column chromatography (petroleum ether:ethyl acetate (9:1), IV= 0.30) to give the title compound as a pale yellow oil (2.18 g, 14.5 mmol) in 29% yield.

Method 3 To a solution of (-)-a-pinene (13.60 g, 100 mmol) in toluene (20 mL) was added dibromobis(4-methylpyridine)cobalt and the resulting solution was heated to 70 °C before bubbling oxygen through for 8 hours. The reaction was left to cool overnight and then heated to 70 °C before bubbling oxygen through for a further 8 hours. The solvent was removed in vacuo and the resulting oil was dissolved in dichloromethane (200 mL) To the resulting stirred solution at 0 °C was added trichloroisocyanuric acid (3.71 g, 16 mmol) and TEMPO (0.025 g, 0.16 mmol) before being warmed to room temperature and stirred for 1 hour. The reaction was filtered through celite and washed with aq. Na2CO3 (100 mL), 1 M HC1 (100 mL), water (100 mL) and brine (100 mL) The organic layer was dried over magnesium sulfate, filtered, and the solvent removed in vacua. The crude product was then purified by silica gel column chromatography (petroleum ether:ethyl acetate (9:1), Rf = 0.30) to give the title compound as a pale yellow oil (2.98 g, 20 mmol) in 20% overall yield.

11-1 NMR (300 MHz, Chloroform-d) 5 5.72 (q, = 1.6 Hz, 111, C=CH), 2.80 (dt, .1= 9.1, 5.5 Hz, 1H, CH2), 2.64 (td, J = 5.9, 1.6 Hz, 1H), 2.41 (ddd, J = 6.6, 5.5, 1.6 Hz, 1H), 2.08 (d, J = 9.1 Hz, 1H, CH2), 2.01 (d, J = 1.6 Hz, 3H, HC=CCH3), 1.49 (s, 3H, CH3), 1.01 (s, 3H, CH3).

3C NMR (75 MHz, Chloroform-d) 204.2, 170.3, 121.3, 57.7, 54.2, 49.8, 41.0, 26.7, 23.7, 22.2.

(-)-cis-Verbenol (68)

OH

To a stirred solution of (-)-verbenone (6.00 g, 40 mmol) in dry dichloromethane (500 mL) at -78 °C was added diisobutylaluminium hydride (40 mL of 1.2 M solution in toluene, 48 mmol) dropwise over 45 minutes. After stirring for 4 hours at -78 °C, the reaction was warmed to 0°C and quenched by slow addition of water (2 mL), followed by 4 M NaOH (2 mL) and water (5 mL) The reaction was stirred for 20 minutes at room temperature before adding magnesium sulfate and stirring for a further 10 minutes. The solids were filtered off and the solvent removed in vacuo to give the title compound as a white solid (5.40 g, 36 mmol) in 83% yield.

m.p. 63 -65 °C NMR (500 MHz, Chloroform-d) 5 5.36 (dd, J = 3.1, 1.6 Hz, 1H, C=CH), 4.51 -4.39 (m, 1H, CHOH), 2.44 (dt, J = 9.0, 5.8 Hz, 1H, CH2), 2.29 (m, 1H), 1.97 (t, J = 5.6, 1H), 1.73 (s, 3H, C=CCH3), 1.60 (d, J = 7.5 Hz, 1H), 1.35 (s, 3H, CH3), 1.31 (d, J = 9.1 Hz, 1H), 1.08 (s, 3H, CH3).

13C NMR (126 MHz, Chloroform-d) 147.5, 119.5, 73.7, 48.4, 47.9, 39.1, 35.7, 27.0, 22.8, 22.7.

(4aR,8R,8aR)-8-Bromo-2,2,4,4,7-pentamethy1-4a,5,8,8a-tetrahydro-4Hbenzo [d][1,3[dioxine (69) To a stirred solution of N-bromosuccinimide (6.18 g, 35 mmol) in acetone (90 mL) at room temperature in the dark was added (-)-cis-verbenol (5.28 g, 35 mmol) in acetone (90 mL) dropwise over 30 minutes. The reaction was stirred at room temperature for 24 hours at which point it had turned pale yellow. The solvent was removed in VaC110 to give a pale yellow slurry. To this was added hexane (100 mL) and the white precipitate was removed via filtration. The filtrate was concentrated in vacno to give the crude product as a pale yellow oil (9.35 g). This was generally used without further purification due to its propensity to degrade when handled for extended periods of time at room temperature. A small amount (50 mg) was quickly purified by silica gel column chromatography (petroleum ether: diethyl ether (19:1), Rs= 0.40 to give spectroscopically pure product as a white solid (43 mg).

m.p. 54 -57 °C 1H NMR (400 MHz, Chloroform-c/) 6 5.65 (m, 11-1, C=CH), 4.59 (t, J = 2.1Hz, 1H, CHOH), 4.40 (t, J = 2.1 Hz, 1H, CHBr), 2.46 -2.33 (m, 1H), 2.09 (m, tH), 1.89 -1.80 (m, 4H), 1.50 (s, 3H, CH3), 1.45 (s, 3H), 1.35 (s, 3H), 1.16 (s, 3H).

13C NMR (126 MHz, Chloroform-c/) 130.5, 127.1, 99.7, 74.0, 69.0, 53.5, 32.9, 31.8, 28.7, 27.6, 24.9, 22.9, 21.8.

(4aR,8aS)-2,2,4,4,7-pentamethy1-4a,5,6,8a-tetrahydro-4H-benzo[d][1,3] dioxine (80) To a stirred solution of lithium aluminium hydride (58 mL of 1.0 M in THE) at 0 °C was added 69 (9.08 g, 32 mmol) in dry diethyl ether (100 mL) dropwise over 30 minutes. The reaction was stirred at 0 °C for 30 minutes, and then at room temperature for 4 hours. The reaction was cooled to 0 °C and quenched via slow addition of water (2.6 mL), 2 M NaOH (5.2 mL) and water (5.2 mL). The reaction was warmed to room temperature and stirred for 30 minutes, at which point a white precipitate had formed Magnesium sulfate was added and the reaction stirred for 10 minutes before being filtered and concentrated in vacua The crude product was purified using silica gel column chromatography (petroleum ether: diethyl ether (19:1), RI = 0.40) to give the title compound as a colourless oil (3.86 g, 18.4 mmol) in 54% overall yield over two steps from (-)-cis-verbenol.

1H NMR (500 MHz, Chloroform-d) 6 5.55 (d, J= 3.9 Hz, 1H, C=CH), 4.42 (s, 1H, CHOH), 2.12 -2.02 (m, 1H), 2.00 -1.91 (n, 1H), 1.81 (n, 1H), 1.73 (s, 3H, CH3), 1.63 (m, 1H), 1.49 (s, 3H, CH3), 1.40 (s, 6H, 2 x CH3), 1.23 (dt, J= 13 1, 3.2 Hz, 1H), 1.20 (s, 3H, CH3).

13C NMR (126 MHz, Chloroform-d) 6 141.6, 120.9, 98.6, 73.2, 62.0, 40.7, 32.1, 31.2, 30.0, 29.3, 25.0, 23.7, 18.8.

I.R. (thin film) vi,ia (cm): 2989, 2971, 2882, 1447, 1371 HRMS (ESL): m/z calculated for Ci3H2202 requires 211.1693 for [M+H] found 211.1695 (15, 3S, 4R)-p-Menthane-3,8-diol (PMD 5) _ 'OH 9/71-0 H io To a stirred solution of 80 (1.050 g, 5.00 mmol) in hexane (40 mL) at room temperature was added platinum (IV) oxide (0.057 g, 0.25 mmol). The reaction was purged with nitrogen gas before having hydrogen bubbled through for 15 minutes and then being left to stir under a hydrogen atmosphere for 4 hours. Nitrogen was then bubbled through the reaction for 5 minutes, before filtering through celite and removing the solvent in vacua To the residue was added ethanol (100 mL) and pyridiniumpara-toluenesulfonate (0.126 g, 0.50 mmol) and the reaction stirred for 16 hours. The solvent was then removed in vacuo before adding hexane (100 mL) and filtering off the resulting white precipitate. Removal of the solvent in vacuo gave the title compound as a white solid (0.688 g, 4.00 mmol) in 80% yield. The product was found to be spectroscopically pure but could be further recrystallised from hexane.

m.p. 80 -83 °C 111 NMR (500 MHz, Chloroform-d) 6 4.41 (app. q, 3./ax-eq and/ 3._ eq-eq = 3.2 Hz, 111, C3H), 2.54, (br s, 211, 011) 1.95 -1.82 (m, 2H, C1H and C5fL), 1.74 -1.61 (m, 3H, C2H2 and C61-18), 1.61 -1.47 (m, 2H, C5Hb and C6Hb), 1.34 (s, 3H, C9H3), L24 (s, 3H, ClOH3), 1.26 -1.19 (m, 1H, C4H), 1.18 (d, ./= 7.4 Hz, 3H, C7H3).

13C NMR (126 MHz, Chloroform-0 S 73.5 (C8), 69.2 (C3), 48.9 (C4), 39.4 (C2), 31.9 (C6), 28.9 (C9), 28.9 (C10), 26.4 (C1), 21.1 (C7), 15.6 (C5) I.R. (thin film) vma, (cm-1) 3275 (0-H), 2969, 2911, 2850, 1686.

FIRMS (ESI): mt., calculated for C10E12002 requires 195.1356 for [M+Na] ; found 195.1339 [a]g): +22 (c = 1.0, CHC13) (+)-Verbenone (84) Method 1 To a stirred suspension of chromium (VI) trioxide (0.038 g, 3.75 mmol) in dichloromethane (600 mL) at room temperature was added pyridine (0.60 mL, 7.50 mmol) followed by tertbutylhydroperoxide (72 mL of 70% aqueous solution, 525 mmol). After stirring for 5 minutes, (±)-a-pinene (10.20 g, 75 mmol) was added over 5 minutes while maintaining the temperature of the reaction constant. The reaction was stirred for 24 hours at room temperature before being poured into 1M aqueous sodium thiosulfate (550 mL). After stirring for 1 hour, the organic layer was separated and concentrated in vacua. The crude product was then purified by silica gel column chromatography (petroleum ether:ethyl acetate (9:1), R./= 0.30) to give the title compound as a pale yellow oil (5.51 g, 37 mmol) in 49% yield.

Method 2 To a stirred solution of (+)-a-pinene (6.80 g, 50 mmol) in acetone (225 mL) and water (25 mL) at room temperature was added N-hydroxyphthalimide (8.97 g, 55 mmol) and pyridinium chlorochromate (10.78 g, 50 mmol). The reaction was stirred at room temperature for 5 hours before adding a further portion of pyridinium chlorochromate (10.78 g, 50 mmol) and being left to stir for 19 hours. Magnesium sulfate was added and the resulting slurry was filtered through a pad of celite before concentrating the resulting solution under reduced pressure. The resulting brown slurry was dissolved in dichloromethane (300 mL) and aqueous NaHCO3 (300 mL). The layers were separated and the aqueous layer extracted with a further portion of dichloromethane (300 mL) The combined organic phases were washed with aqueous NaHCO3 (2 x 300 mL), water (300 mL) and brine (300 mL), before being dried over magnesium sulfate, filtered and concentrated in vaczto. The crude product was then purified by silica gel column chromatography (petroleum ether:ethyl acetate (9:1), Kr= 0.30) to give the title compound as a pale yellow oil (3.07 g, 21 mmol) in 41% yield.

1-1-1 NMR (500 MHz, Chloroform-d) 8 5.72 (q, J= 1.6 Hz, 1H, C=CH), 2.80 (dt, J= 9.1, 5.5 Hz, 1H, CH2), 2.64 (td, J = 5.9, 1.6 Hz, 1H), 2.41 (ddd, J = 6.6, 5.5, 1.6 Hz, 1H), 2.08 (d, J = 9.1 Hz, 1H, CH2), 2.01 (d, I = 1.6 Hz, 311, HC=CCH3), 1.49 (s, 3H, CH3), 1.01 (s, 3H, CH2).

13C NMR (126 MHz, Chloroform-d) 204.2 170.3, 121.3, 57.7, 54.2, 49.8, 41.0, 26.7, 23.7, 22.2.

(+)-cis-Verbenol (85)

OH

To a stirred solution of (+)-verbenone (6.00 g, 40 mmol) in dry dichloromethane (500 mL) at -78 °C was added diisobutylaluminium hydride (40 mL of 1.2 M solution in toluene, 48 mmol) dropwise over 45 minutes. After stirring for 4 hours at -78 °C, the reaction was warmed to 0°C and quenched by slow addition of water (2 mL), followed by 4 M NaOH (2 mL) and water (5 mL). The reaction was stirred for 20 minutes at room temperature before adding magnesium sulfate and stirring for a further 10 minutes. The solids were filtered off and the solvent removed in vacuo to give the title compound as a white solid (4.74 g, 31 mmol) in 78% yield.

ni.p. 63 -65 °C Ill NMR (400 MHz, Chloroform-a) 5 5.36 (dd, J = 3.1 1.6 Hz, 1H, C=CH), 4.51 -4.39 (m, 1H, CHOH), 2.44 (dt, J = 9.0, 5.8 Hz, 1H, CH2), 2.29 (in, 1H), 1.97 (t, J = 5.6, 1H), 1.73 (s, 3H, C=CCH3), 1.59 (s, 111), 1.35 (s, 311, CH3), 1.31 (d, J = 9.1 Hz, 1H), 1.08 (s, 3H, CH3).

13C NMR (101 MHz, Chloroform-d) 147.6, 119.5, 73.7, 48.4, 47.9, 391, 35.8, 27.0, 22.8, 22.8.

(4aS,8S,8aS)-8-bromo-2,2,4,4,7-pentamethy1-4a,5,8,8a-tetrahydro-4Hbenzo [d][1,3]dioxine (86) To a stirred solution of N-bromosuccinimide (6.18 g, 35 mmol) in acetone (90 mL) at room temperature in the dark was added (-)-cis-verbenol (5.28 g, 35 mmol) in acetone (90 mL) dropwise over 30 minutes. The reaction was stirred at room temperature for 24 hours at which point it had turned pale yellow. The solvent was removed in vacuo to give a pale yellow slurry. To this was added hexane (100 mL) and the white precipitate was removed via filtration. The filtrate was concentrated in vacuo to give the crude product as a pale yellow oil (9.41 g). This was used without further purification due to its propensity to degrade when handled for extended periods of time at room temperature.

NMR spectra matched those of its enantiomer.

(4aS,8aR)-2,2,4,4,7-pentamethy1-4a,5,6,8a-tetrahydro-411-benzo[d][1, 31dioxine (87) To a stirred solution of lithium aluminium hydride (58 mL of 1.0 M in THF) at 0 °C was added 86 (9.41 g, 33 mmol) in dry diethyl ether (100 mL) dropwise over 30 minutes. The reaction was stirred at 0 °C for 30 minutes, and then at room temperature for 4 hours. The reaction was cooled to 0 °C and quenched via slow addition of water (2 6 mL), 2 M NaOH (5.2 mL) and water (5.2 mL). The reaction was warmed to room temperature and stirred for 30 minutes, at which point a white precipitate had formed. Magnesium sulfate was added and the reaction stirred for 10 minutes before being filtered and concentrated in vacno The crude product was purified using silica gel column chromatography (petroleum ether. diethyl ether (19:1), R/= 0.40) to give the title compound as a colourless oil (3.75 g, 18 mmol) in 51% overall yield over two steps from (+)-cis-verbenol.

1-1NMR (500 MHz, Chloroform-d) 6 5.55 (d, J= 3.9 Hz, 1H, C=CH), 4.42 (s, 1H, CHOH), 2.12 -2.02 (m, 111), 2.00 -1.91 (m, 1H), 1.81 (m, 1H), 1.73 (s, 3H, CH3), 1.63 (m, 1H), 1.49 (s, 31-1, CH3), 1.40 (s, 6H, 2 x CH3), 1.27 -1.21 (m, 11-1), 1.20 (s, 3H, CH3).

13C NMR (126 MHz, Chloroform-06 141.6, 120.9, 98.6, 73.2, 62.0, 40.7, 32.1, 31.2, 30.0, 29.3, 25.0, 23.7, 18.8.

I.R. (thin film) v.. (cm-1): 2979, 2908, 2852, 1438, 1375 FIRMS (ESI): nrz calculated for C13H2202 requires 211.1693 for [M+Hr; found 211.1693 (1R, 3R, 4S)-p-Menthane-3,8-diol (PMD 6) To a stirred solution of 87 (1.050 g, 5.00 mmol) in hexane (40 mL) at room temperature was added platinum (IV) oxide (0.057 g, 0.25 mmol). The reaction was purged with nitrogen gas before having hydrogen bubbled through for 15 minutes and then being left to stir under a hydrogen atmosphere for 4 hours. Nitrogen was then bubbled through the reaction for 5 minutes, before filtering through celite and removing the solvent in vacuo. To the residue was added ethanol (100 mL) and pyridinium para-toluenesulfonate (0.126 g, 0.50 mmol) and the reaction stirred for 16 hours. The solvent was then removed in vacuo before adding hexane (100 mL) and filtering off the resulting white precipitate. Removal of the solvent in vacuo gave the title compound as a white solid (0.731 g, 4.25 mmol) in 85% yield. The product was found to be spectroscopically pure but could be further recrystallised from hexane.

m.p. 80 -83 °C 1-11 NMR (500 MHz, Chloroform-d) S 4.41 (app. q, 3,Lix-eq and 3/eq-cq = 3.2 Hz, 1H, C3H), 2.52, (br s, 2H, OH) 1.95 -1.82 (m, 2H, C1H and C51-1.), 1.74 -1.61 (m, 31-1, C2H2 and CoHa), 1.61 -1.47 (m, 2H, CSHh and C6Hb), 1.34 (s, 3H, C9113), 1.24 (s, 3H, C1 0A3), 1.26 -1.19 (m, 1H, C4H), 1.18 (d, ./= 7.4 Hz, 3H, C7H3).

13C NMR (126 MHz, Chloroform-d) S 73.5 (C8), 69.2 (C3), 48.9 (C4), 39.4 (C2), 31.9 (C6), 28.9 (C9), 28.9 (C10), 26.4 (C1), 21.1 (C7), 15.6 (CS).

I R (thin film) v. (cm-1) 3233 (0-H), 2948, 2907, 2851.

FIRMS (ESL): m ± calculated for CioH2002 requires 195.1356 for [M+Na]'; found 195.1358 [a]o: -22 (c = 1.0, CHC13) (251,5S)-2-(2-hydroxypropan-2-y1)-5-methylcyclohexan-l-one (98) 0H 0 To a stirred solution of (15, 35, 4R)-p-Menthane-3,8-diol (1.90 g, 11.0 mmol) in acetonitrile (60 mL) at room temperature was pyridine (1.34 mL, 16.6 mmol) dropwise. To the resulting solution was added trichloroisocyanuric acid (1.28 g, 5.5 mmol) in acetonitrile (60 mL) dropwise over 15 minutes while maintaining the reaction at room temperature. After stirring for 1 hour, the reaction was filtered to remove the resulting pale yellow precipitate and the concentrated in metro. To the resulting residue was added ethyl acetate (75 mL) and water (75 mL). The layers were separated and the organic layer washed with brine (75 mL), before being dried over magnesium sulfate, filtered, and the solvent removed in vacno to give the title compound as a spectroscopically pure clear oil (1.75 g, 10.3 mmol) in 94% yield.

NMR (300 MHz, Chloroform-d) 6 3.96 (s, 1H, OH), 2.56 -2.45 (m, 111), 2.45 -2.29 (m, 2H), 2.14 (m, 1H), 2.03 -1.71 (m, 3H), 1.71 -1.60 (m, 1H), 1.21 (s, 6H, C(OH)(CH3)2), 0.93 (d, J = 7.1 Hz, 3H, CHCH3).

13C NMR (75 MHz, Chloroform-d) 6 216.3, 71.6, 59.2, 49.7, 31.7, 30.8, 28.6, 25.6, 24.5, 18.8.

I.R. (thin film) v. (cm-1): 3478 (0-H), 2956, 1692 (C=0).

FIRMS (ESI): m,± calculated for CioHis02 requires 171.1380 for [M+H]+; found 171.1383. [ag° : -12 (c = 1.0, CHCI3).

(1,9, 3R, 4R)-p-Menthane-3,8-diol (PMD 7) A stirred solution of 98 (1.70 g, 10.0 mmol) in dry diethyl ether (90 mL) and ethanol (10 mL) was cooled to -78 °C. Ammonia (200 mL) was condensed into the reaction flask followed by portion wise addition of lithium (1.40 g, 200 mmol). A dark blue colour was observed and the reaction was stirred at -78 °C for 4 hours before gradually warming to room temperature over 16 hours to evaporate ammonia. Water (50 mL) was added and the reaction was then acidified to pH 2 using 6 M HC1. The layers were separated and the aqueous layer was extracted with dichloromethane (3 x 100 mL). The combined organic

OH

layers were washed with brine (200 mL), dried over magnesium sulfate, filtered and concentrated in vacua. The resulting crude product was recrystallised from hexane to give the title compound as a white solid (1.30 g, 7.6 mmol) in 76% yield m.p. 98 -101 °C NMR (300 MHz, Chloroform-d) 6 3.95 (app. td, = 10.7, 3..7-ax-eq = 4.4 Hz, 111, C3H), 2.68 (br s, 2H, 2 x OH), 2.17 -2.04 (m, 1H, C1H), 1.85 -1.74 (m, 1H, CaL), 1.57 -1.45 (m, 4H, C2Hh and C5EL and C6H2), 1.41 (m, 1H, C4H), 1.25 (s, 3H, C9H3), 1.23 (s, 3H, CIOH3), 1.21 -1.07 (m, 1H, CSHh), 0.98 (d, J = 7.3 Hz, 3H, C7H3).

3C NMR (75 MHz, Chloroform-d) 6 75.3 (C8), 68.9 (C3), 54.8 (C4), 41.7 (C2), 31.4 (C6), 30.2 (C10), 28.3 (C1), 24.0 (C9), 22.3 (C5), 18.4 (C7).

I R (thin film) v. (cm-I) 3253 (0-H), 2968, 2930, 2874 HRMS (ESL): m calculated for CioH2002 requires 195.1356 for [M+Na]'; found 195.1357.

[a]g: -4 (c = 1.0, CHC13).

(2R,5R)-2-(2-hydroxypropan-2-yI)-5-methylcyclohexan-l-one (59) To a stirred solution of (1R, 3R, 43)-p-Menthane-3,8-diol (2.20 g, 13.0 mmol) in acetonitrile (70 mL) at room temperature was pyridine (1.55 mL 19 2 mmol) dropwise. To the resulting solution was added trichloroisocyanuric acid (1.49 g, 6.4 mmol) in acetonitrile (70 mL) dropwise over 15 minutes while maintaining the reaction at room temperature. After stirring for 1 hour, the reaction was filtered to remove the resulting pale yellow precipitate and the concentrated in vacua. To the resulting residue was added ethyl acetate (75 mL) and water (75 mL) The layers were separated and the organic layer washed with brine (75 mL), before being dried over magnesium sulfate, filtered, and the solvent removed in vacua to give the title compound as a spectroscopically pure clear oil (2.16 g, 12.7 mmol) in 98% yield.

111 NMR (400 MHz, Chloroform-d) 5 3.92 (s, 1H, OH), 2.52 (dd, J= 13.5, 5.8 Hz, 1H), 2.45 -2.33 (m, 2H), 2.15 (dd, J= 13.5, 3.5 Hz, 1 H), 2.03 -1.86 (m, 2H), L80 (td,J= 12.4, 3.9 Hz, 1H), 1.71 -1.60 (m, 1H), 1.22 (s, 6H, C(OH)(CH3)2), 0.95 (d, J = 7.1 Hz, 311, CHCH3).

13C NMR (101 MHz, Chloroform-d) 6 216.2, 71.6, 59.2, 49.7, 31.7, 30.8, 28.7, 25.6, 24.5, 18.8.

I.R (thin film) vinax (cm-1): 2954, 2948, 1693 (CO)= HRMS (ESI): m/z calculated for C1411802 requires 193.1199 for [M+Na] ; found 193.1202.

[a]1)°: +12 (c = 1.0, CHC13).

(IR, 3S, 4S)-p-Menthane-3,8-diol (PMD 8) A stirred solution of 59 (2.16 g, 12.7 mmol) in dry diethyl ether (115 mL) and ethanol (13 mL) was cooled to -78 °C. Ammonia (200 mL) was condensed into the reaction flask followed by portion wise addition of lithium (1.79 g, 256 mmol). A dark blue colour was observed and the reaction was stirred at -78 °C for 4 hours before gradually warming to room temperature over 16 hours to evaporate ammonia. Water (75 mL) was added and the reaction was then acidified to pH 2 using 6 M MCI. The layers were separated and the aqueous layer was extracted with dichloromethane (3 x 125 mL). The combined organic layers were washed with brine (250 mL), dried over magnesium sulfate, filtered and concentrated in vacuo. The resulting crude product was recrystallised from hexane to give the title compound as a white solid (1.69 8, 9.9 mmol) in 77% yield.

m p 98 -101 °C 111 NMR (300 MHz, Chlorofonn-d) 6 3.95 (app. td, = 10.7, 3J.3-°y = 4.4 Hz, 1H, C3H), 2.43 (br s, 2H, 2 x OH), 2.17 -2.04 (m, 1H, Cl H), 1.85 -1.74 (m, 1H, C21-1), 1.57 -1.45 (m, 4H, C2Hh and C5EL. and C6H2), 1.41 (m, 1H, C4H), 1.25 (s, 3H, C9H3), 1.23 (s, 3H, Cl OHO, 1.21 -1.07 (rn, 1H, C5Hh), 0.98 (d, J = 7.3 Hz, 3H, C7H3).

13C NMR (101 MHz, Chloroform-d) 6 75.3 (C8), 68.9 (C3), 54.8 (C4), 41.7 (C2), 31.4 (C6), 30.2 (C10), 28.3 (C1), 24.0 (C9), 22.3 (C5), 18.4 (C7).

I.R. (thin film) vin,,,c (cm-1): 3255 (0-H), 2967, 2930, 2874.

FIRMS (ESI): m/z calculated for Clotho02. requires 173.1536 for [M+H] ; found 173.1540. [a]i °: +4 (c = 1.0, CHC13).

(-)-trans-Verbenyl acetate (89) A stirred solution of (-)-a-pinene (7.42 g, 54.5 mmol) in toluene (200 mL) was heated to 65 °C. Lead (IV) acetate (26.5 g, 59.6 mmol) was added over 15 minutes and the resulting slurry heated for 90 minutes before being cooled to room temperature. The reaction was filtered to remove the resulting brown precipitate and then washed with water (2 x 100 mL) and brine (2 x 100 mL) The organic layer was dried over magnesium sulfate, filtered and the solvent removed in vacuo. To the resulting colourless oil was added acetic acid (35 mL) and the reaction was stirred at room temperature for 45 minutes before diluting with water (150 mL) The aqueous solution was extracted with hexane (2 x 150 mL) and the combined organic layers were washed with water (2 x 150 mL), 5% aq. NaHCO3 (2 x 150 mL) and brine (150 mL). The organic layers were dried over magnesium sulfate, filtered and concentrated in lucre() to give the title compound as a colourless oil (6.72 g, 34.6 mmol) in 64% yield.

1H NMR (400 MHz, Chloroform-d) 6 5.33 (m, 2H, CH(OAc) and C=CH), 2.32 -2.18 (m, 2H), 2.05 -2.00 (m, 4H), 1.73 (s, 3H), 1.44 (d, J = 8.9 Hz, 2H), 1.33 (s, 3H, CH3), 0.90 (s, 314, CH3).

13C NMR (101 MHz, Chloroform-d) 6 171.1 150.8 115.3, 73.9, 47.8 46.4 44.5, 29.5, 26.6, 22.9, 21.6, 20.8.

(-)-trans-Verbenol (71) A stirred solution of (-)-trans-Verbenyl acetate (2.00 g, 10.3 mmol) in dry diethyl ether (100 mL) was cooled to 0 °C. Lithium aluminium hydride (20.7 mL of 1.0 M solution in THF) was added over 30 minutes and the reaction gradually warmed to room temperature before being stirred for 2 hours. The reaction was quenched by slow addition of water (1 mL), followed by 2 M NaOH (2 mL) and water (2 mL) After warming to room temperature and stirring for 15 minutes, the reaction was dried over MgSO4 and filtered before evaporating the solvent under reduced pressure. The resulting oil was purified by silica gel column chromatography (petroleum ether: ethyl acetate (85:15), Rr= 0.45) to give the title compound as a colourless oil (0.91 g, 6.0 mmol) in 58% yield.

NMR, (300 MHz, Chloroform-0 5.39 -5.28 (m, 111, C=CH), 4.26 (s, 1H, CHOH), 2.25 (dt, 1 = 9.0, 5.6 Hz, 11-), 2.20 -2.13 (m, 1H), 2.02 (td, 1 = 5.6, 1.5 Hz, 1H), 1.71 (t, J = 1.5 Hz, 3H, CH3), 1.49 (br s, tH, OH), 1.35 -1.28 (m, 4H, CH3), 0.86 (s, 3H, CH3).

13C NMR (76 MHz, Chloroform-d) 6 149.0, 118.9, 70.6, 48.2, 47.2, 46.4, 28.8, 26.8, 22.8, 20.6.

(4aR,8aS)-8-bromo-2,2,4,4,7-pentamethyl-4a,5,8,8a-tetrahydro-4Hbenzo[d] [1,3]dioxine (92) To a stirred solution of N-bromosuccinimide (0.85 g, 4.93 mmol) in acetone (10 mL) at room temperature in the dark was added (-)-trans-verbenol (0.75 g, 4.93 mmol) in acetone (10 mL) dropwise over 30 minutes. The reaction was stirred at room temperature for 24 hours at which point it had turned pale yellow. The solvent was removed in vacuo to give a pale yellow slurry. To this was added hexane (20 mL) and the white precipitate was removed via filtration. The filtrate was concentrated in vacno to give the crude product as a pale yellow oil (1.39 g). This was used without further purification due to its propensity to degrade when handled for extended periods of time at room temperature. ITT NMR spectra of the crude product was in agreement with previously published data.

114 NMR (400 MHz, Chloroform-d) 6 5.49 (m, 1H, C=CH), 4.55 (d, J = 3.9 Hz, 1 H, CHOH), 3.76 (dd, J= 11.2, 3.9 Hz, 111, CHBr), 2.31 -2.08 (m, 2H), 2.02-1.90 (m, 1H), 1.86 (s, 3H, CH3), 1.50 (s, 3H, CH3), 1.46 (s, 3H, CH3), 1.32 (s, 3H, CH3), 1.25 (s, 3H, CH-3).

(4aR,8aR)-2,2,4,4,7-pentamethy1-4a,5,8,8a-tetrahydro-4H-benzo[d][1,3] dioxine (93a/b) To a stirred solution of lithium aluminium hydride (9.0 mL of 1.0 M in THF) at 0 °C was added 92 (1.39 g, 4.80 mmol) in dry diethyl ether (10 mL) dropwise over 30 minutes. The reaction was stirred at 0 °C for 30 minutes, and then at room temperature for 4 hours. The reaction was cooled to 0 °C and quenched via slow addition of water (0.4 mL), 2 M NaOH (0.8 mL) and water (0.8 mL). The reaction was warmed to room temperature and stirred for 30 minutes, at which point a white precipitate had formed Magnesium sulfate was added and the reaction stirred for 10 minutes before being filtered and concentrated in vacua The crude product was purified using silica gel column chromatography (petroleum ether: diethyl ether (19:1), Rf= 0.40) to give the mixture of isomers shown as a colourless oil (0.57 g, 2.71 mmol) in 55% overall yield over two steps from (-)-trans-verbenol. Subsequent column chromatography in 2% diethyl ether in petroleum ether allowed a small amount of the major isomer to be separated from the minor isomer.

Major somer data 1H NMR (400 MHz, Chloroform-d) S 5.33 (s, 111, C=CH), 3.95 (m, 1H, CHOH), 2.302.16(m, 1H), 2.10 -1.91 (m, 2H), 1.81 -1.59 (rn, 51-I), 1.49 (s, 3H), 1.39 (s, 3H), 1.28 (s, 3H), 1.21 (s, 314).

13C NMR (101 MHz, Chloroform-a) S 131.6, 119.8, 97.8, 73.6, 65.5, 44.6, 373, 323, 31.4, 25.8, 24.9, 24.5, 23.3.

p-Menthane-3,8-diol (mixture of diastereomers PMD 1 and PMD 7) To a stirred solution of 93a/b (0.53 g, 2.50 mmol) in hexane (20 mL) at room temperature was added platinum (IV) oxide (0.029 g, 0.13 mmol). The reaction was purged with nitrogen gas before having hydrogen bubbled through for 15 minutes and then being left to stir under a hydrogen atmosphere for 4 hours. Nitrogen was then bubbled through the reaction for 5 minutes, before filtering through celite and removing the solvent in vacua To the residue was added ethanol (50 mL) and pyridiniumpara-toluenesulfonate (0.063 g, 0.25 mmol) and the reaction stirred for 16 hours. The solvent was then removed in vacuo before adding hexane (50 mL) and filtering off the resulting white precipitate. Removal of the solvent in vacuo gave the mixture of isomers shown as a white solid (0.301 g, 1.75 mmol) in 70% yield.

Spectra of the mixed product matched with authentic samples of each isomer prepared using other methods.

(S)-(-)-3-methylcyclohexanone (101) ao A stirred solution of 98 (0.510 g, 3.0 mmol) was heated in 3M HCl (2 mL) at 110 °C for 4 hours. After cooling to room temperature, the reaction mixture was poured into saturated 1: 1 NaHCO3 (20 mL) and extracted with diethyl ether (2 x 20 mL) The combined organic extracts were washed with brine (20 mL) before being dried over magnesium sulfate, filtered and the solvent removed in vactio to yield the title compound as a spectroscopically pure pale yellow oil (0.265 g, 2.37 mmol) in 79% yield.

H NMR (400 MHz, Chloroform-d) 6 2.41 -2.30 (m, 2H), 2.29 -2.18 (m, 1H), 2.08 -1.96 (m, 2H), 1.95 -1.82 (m, 2H), 1.73 -1.60 (m, 1H), 1.39 -1.24 (m, 111), 1.02 (d, .1= 6.4 Hz, 3H).

13C NMR (101 MHz, CDC13) 6 212.1, 50.2, 41.3, 34.3, 33.5, 25.5, 22.2.

(-)-Isopulegol epoxide (54a/b)

OH OH 54a

PW4024[PTC]3 (0.226 g, 0.10 mmol) was dissolved in a solution of (-)-isopulegol (1.54 g, 10.0 mmol) and toluene (2.1 mL, 20.0 mmol). The resulting solution was heated to 35 °C and stirred at 150 rpm. Na2SO4 (0.43 g, 3.0 mmol) was dissolved in 50 wt% aqueous H202 (0.57 mL, 10 mmol) and the resulting solution was basified to pH 7-8 using 3 M NaOH. The aqueous solution was added dropwise to the stirred organic solution and the resulting biphasic reaction stirred for 5 minutes. After this time, the stirring was increased to 500 rpm and the reaction stirred for a further 5 hours before removing the organic layer and purifying via flash column silica gel chromatography (petroleum ether: ethyl acetate (7:3), = 0.40) to give the title compound as a colourless oil (1.54 g, 9.1 mmol) in 91% yield.

1H NMR (300 MHz, Chloroform-d) 6 3.71 (td, J= 10.5, 4.4 Hz, 1H, 54a), 3.35 (d, J= 2.0 Hz, 1H, Mb), 3.28 (td, .1= 10.5, 4.6 Hz, 1H, 54b), 2.92 (d, J= 4.1 Hz, 1H, 54b), 2.81 (d,./ = 2.4 Hz, 1H, 54a), 2.66 (d, J = 4.1 Hz, 1H, 54b), 2.59 (d, J= 4.6 Hz, 1H, 54a), 2.53 (dq, J= 4.6, 0.7 Hz, 1H, 54a), 2.08 -1.98 (m, 1H, 54a), 1.97 -1.81 (m, 2H, Mb), 1.75 -1.61 (m, 3H, 2 x Ma and 1 x 54b), 1.54 -1.38 (m, 3H, 1 x Ma and 2 x 54b), 1.36 (d, J= 0.7 Hz, 311, 54b), 1.31 (d, J= 0.7 Hz, 3H, 54a), 1.26 -1.05 (m, 2H, 1 x 54a and 1 x 54b) 1.03 -0.80 (in, 11 H, 6 x 54a and 5 x 54b) 13C NMR (126 MHz, Chloroform-d) 71.4, 70.6, 60.5, 59 3, 53.0, 52.3, 51.3 49.0, 43.6, 42.9, 34.0, 34.0, 31.3, 31.0, 27.8, 22.2, 21.1, 17.0.

I.R (thin film) vinax (cm-1): 3421 (0-H), 2921, 2867 (C-11), 1450 FIRMS (ESI): tri/z calculated for CloH1802 requires 193.1199 for [M+Na]+ found 193.1202 Two-step catalytic PMD synthesis (1R, 3R, 4R)-p-Menthane-3,8-diol (PMD 1) To a stirred solution of (-)-isopulegol (0.770 g, 5.00 mmol) in toluene (1.05 mL, 10.00 mmol) was added PW4024[PTC]3 (0.113 g, 2259 gmoti, 0.05 mmol, 1 mol%) and the resulting mixture was heated to 35 °C and stirred for 15 minutes. Na2SO4 (0.211 g, 1.50 mmol) was dissolved in a solution of 50 wt% aqueous 11202 (0.290 mL, 5 05 mmol) before adjusting the pH of this solution to pH 7 with 2 M NaOH. The aqueous solution was then added dropwi se over 5 minutes to the stirred organic solution and the resulting biphasic mixture stirred rapidly (500 rpm) for 5 hours. The organic layer was then removed and dissolved in methanol (25 mL) before adding NaOH (0.040 g, 1.00 mmol) and 10% Pd/C (0.530 g, 0.50 mmol of Pd). Nitrogen was bubbled through the resulting suspension for 5 minutes before bubbling hydrogen through it for 15 minutes. The reaction was sealed under an atmosphere of hydrogen and stirred for 24 hours. Nitrogen was then bubbled through the reaction for 5 minutes before filtering through celite and removing the solvent in vaczto The crude product was purified by silica gel flash column chromatography (petroleum ether: ethyl acetate (7:3), R = 0.3) to afford the title compound as a white solid (0.62 g, 3.61 mmol) in 72% yield over two steps.

PTC = mixture of MeN I(C8H17)3 and MeN' (CioH203 m.p. 72 -74 °C 11-1NIVIR (300 MHz, Chloroform-d) S 3.72 (1H, td, J = 10.6, 4.4 Hz, CHOH), 3.22 (211, br s, 2 x OH), 2.00 -1.89 (1H, m), 1.75 -1.60 (2H, m), 1.51 -1.31 (2H, m), 1.23 (6H, s, C(CH3)20H), 1.10 -0.98 (1H, m), 0.96 -0.86 (5H, m).

13C NAIR (126 MHz, Chloroform-d) 75.1, 72.9, 53.5, 44.7, 34.7, 31.4, 30.2, 27.2, 23.8, 22.0 I.R. (thin film) vim, (cm): 3257 (0-H), 2975, 2952, 2920, 2843 FIRMS (ESI): natz calculated for C1012002 requires 195.1356 for [M+Na] ; found 195.1356 [ct]f: -11 (c = 1.0, CHC13) Dose Response Test Results The aim of the tests described below was to provide dose response data for eight (PMD) stereoisomers required to prevent probing of Aedes ctegypti (most domesticated and widespread in areas of human habitation, vector of Dengue and Yellow Fever) and Anopheles gat-tibiae mosquitoes (most important mosquito vector for malaria) and also pyrethroid-insensitive Anopheles gambiae and DEET-insensitive Aedes aegypti.

Test Conditions and Set-Up One cage (30 x 30 x 30 cm) was set up in the test room at least 30 minutes before testing, containing a batch of either 50 Ae. Aegypti or An. gctnibicte female mosquitoes, 5-7 days old.

Product Application The volunteer's arm was measured and the surface area calculated. One of the repellent formulations was applied at the standard WHO repellent application rate of 1.67 pil/cm2 onto one forearm. The formulations were measured using a Gilson pipette (P1000). The measured doses were applied evenly using a single gloved finger to the forearm to completely cover the skin from the wrist to the elbow. The arm was allowed to dry for one minute after application before use in testing.

Product Concentration Product was applied at a dose of 0.2% (0.002g/ml), and at ongoing increments of 0.2% were applied until 100% protective efficacy was reached.

Arm-in-cage Procedure A combined fitness check and control test was conducted by placing a bare arm (without product) into the cage while wearing a nitrite glove to protect the hand (any attempted probing on the glove was excluded from the test). The number of mosquitoes probing the forearm was recorded after 30 seconds, then they were then shaken off and the arm removed from the cage. Only cages with at least ten mosquitoes probing at the end of the exposure time were used in subsequent testing. If fewer than 10 mosquitoes were recorded probing the arm, the cage was activated by breathing on it, and control tests carried out again. If this failed, additional mosquitoes were added to the cage, and a further check conducted. If the cage continued to fail the fitness check, it was discarded and a fresh cage set up. The treated arm was then inserted into the cage for 30 seconds and the number of mosquitoes probing/probing on the arm was counted and recorded. If any mosquitoes probed the treated arm (i.e. 100% protective efficacy was not recorded), the arm was withdrawn, and an additional dose of the product was applied. The treated arm was then re-tested. This method was repeated until no mosquitoes probed/bite the arm within the exposure period. When this point was reached, a further test was carried out using the control arm to verify probing avidity in the test cage. At this pilot stage, only one replicate was completed per dose.

Effective dose of products Test Conditions and Set-Up Three cages (30 x 30 x 30 cm) were set up in the test room at least 30 minutes before testing, each containing a batch of either 50 Ae. aesopti or An. gamblue female mosquitoes, 5-7 days old.

Product Application Product application was conducted as in pilot testing (section 1.2). The volunteer's arm was measured to calculate surface area, and the repellent applied at a dose equivalent to 1.67 p1/cm2. Application was conducted using a Gilson pipette (P1000), and products rubbed into the volunteer's arm using a single gloved finger to ensure complete even coverage from wrist to elbow. At least one minute was allowed on each application for the product to dry before testing.

Effective Dose Product Concentration Data from the pilot study determined the dose range. Depending on the stereoisomer, product was applied at an initial dose of 0.05% (0.0005g/ml) or 0.1% (0.001g/m1) for the first 3 applications to provide less than 50% protective efficacy. A higher concentration, either 0.01% or 0.02% dependent on the stereoisomer was applied for the next 10 applications. If 100% efficacy was not achieved the dose was upped to 0.02% for some stereoisomers. Incremental dosing was adjusted until 100% protective efficacy was reached.

Arm-in-Cage Procedure Methods were conducted as per pilot but in triplicate. A combined fitness check and control test was conducted by placing an untreated arm (without product) into the cage, the number of probing mosquitoes on the forearm after 30 seconds was recorded. A minimum of ten mosquitoes probing per cage were required to pass the fitness check.

Once the fitness test check had been passed, the treated arm with the first dose of the assigned stereoisomer was inserted into the cage for 30 seconds and the number of mosquitoes probing/probing the forearm were recorded. If any mosquitoes probed the treated arm (i.e. 100% protective efficacy was not recorded), the arm was withdrawn, and an additional dose of the product was applied. The treated arm was then tested against the three mosquito cages.

This method was repeated until no mosquitoes were probing/probing the treated arm at the end of the exposure time or until an unsafe number of doses had been applied to the treated arm. When this point was reached, a further test was carried out using the control arm to verify probing avidity in each test cage.

Methods are based on WHO testing procedures for topical repellents.

Statistical Analysis The percent protective efficacy (PE) was calculated from the pooled data, using the formula below.

PE = 100 x (mosquitos probing on control -mosquitos probing on treatment) / mosquitos probing on control Analysis was conducted to calculate product dose needed to achieve 50%, 95% and 99% protective efficacy (PE). Method analysed protective efficacy per cage (i.e. three data points per dose), using natural log transformation, as per methods outlined in WHO guidelines (World Health Organization. Guidelines for efficacy testing of mosquito repellents for human skin. No. WHO/HTM/NTD/WHOPES/2009.4. World Health Organization, 2009).

Results of the pilot test are presented in Table 1, below: PMD Stereoisomer Concentration (g/ml) Ae. An. gambiae aegypti 1-cis-3-trans-4 (PMD 1) 0.017 0.01 1-cis-3-trans-4 (PMD 2) 0.003 0.006 1-trans-3-cis-4 (PMD 3) 0.006 0.023 1-trans-3-cis-4 (PMD 4) 0.01 0.006 1-cis-3-cis-4 (PAID 5) 0.007 0.014 1-cis-3-cis-4 (PAID 6) 0.012 0.018 1-trans-3-trans -4 (PMD 7) 0.01 0.002 1-trans-3-trans 4 (PMD 8) 0.002 0.024 Table 1. Concentration of the 8 PMD stereoisomers which gave 100% protective efficacy against An. gamlnae and Ae. aegypti in an arm-in-cage pilot dose response test.

Dose response against An. garnbiae As shown in Figure 2, and Table 2, all of the eight PMD stereoisomers achieved 100% protective efficacy. PMD 4 required the lowest concentration (0.005g/m1) to reach 100% PE, followed by PMD 8 (0.0045g/ml), PMD 1 (0.005g/m1), PMD 3 (0.0055g/ml), PMD 5 (0.0065g/ml), PMD 2 (0.0075g/m1) and PMD 6 (0.008g/ml). PMD 7 required the highest concentration (0.013g/ml) to reach 100% PE.

PMD Stereoisomer Concentration (g/ml) 1-cis-3-trans-4 (PMD 1) 0.005 1-cis-3-trans-4 (PMD 2) 0.0075 1-trans-3-cis-4 (PMD 3) 0.0055 1-trans-3-cis-4 (PMD 4) 0.002 1-cis-3-cis-4 (PMD 5) 0.0065 1-cis-3-cis-4 (PMD 6) 0.008 1-trans-3-trans-4 (PMD 7) 0.013 1-trans-3-trans 4 (PMD 8) 0.0045 Table 2. The concentration of each PMD stereoisomer required to reach 100% PE against An. gangnae (dose response test).

Dose response against Ae. aegypti As shown in Figure 3, and Table 3, seven out of the eight PMD stereoisomers achieved 100% protective efficacy. PMD 3 required the lowest concentration (0.0025g/ml) to reach 100% PE, followed by PMD 5 (0.0045g/m1), PMD 2 (0.009g/ml), PMD 6 (0.012g/ml), PMD 4 (0.014g/ml), PMD 1 (0.021g/ml), and PMD 8 (0.0445g/ml).

PMD 7 was stopped after 25 dose applications due to safety concerns on the level of exposure. After 25 applications, PMD 7 reached 87% PE at a dose of 0.0665g/ml. The highest PE that was reached during this test was 91.7% PE which was achieved at a concentration of 0.0225g/ml.

PMD Stereoisomer Concentration (g/m1) 1-cis-3-trans-4 (PMD 1) 0.021 1-cis-3-trans-4 (PMD 2) 0.009 1-trans-3-cis-4 (PMD 3) 0.0025 1-trans-3-cis-4 (PMD 4) 0.014 1-cis-3-cis-4 (PMD 5) 0.0045 1-cis-3-cis-4 (PMD 6) 0.012 1-trans-3-trans 4 (PMD 8) 0.0445 Table 3. The concentration in does response tests required to reach 100% PE for each PMD stereoisomer against Ae. aegvti.

Description of each PMD stereoisomer's odour

Table 4 summarises the descriptions of each stereoisomer during the pilot tests. Each tester was asked to describe the odour and any addition comments they had about the stereoisomer. The stereoisomers were smelled in anhydrous form and in solution, commercial PMD was only assessed in anhydrous form.

PMD Tester 1 Tester 2 Stereoisomer 1-cis-3-trans-4 Camphorwood, fruity (excluding Strong.

(PMD 1) citrus), pleasant, sweet.

Pleasant light feel, minimal scent and more pleasant at lower doses, began to smell a bit like petrol at higher doses 1-cis-3-trans-4 Musky, weak. Antiseptic, strong.

(PLAID 2) Herby kind of smell, similar to dill. Very overpowering antiseptic smell e.g. Crystallised solid smelt more A hospital smell citrusy.

1-trans-3-cis-4 Weak, woody. Antiseptic, citrus.

(PAID 3) Smells very mild, faint hint of None of the traditional PMD smell. No varnish. real feeling on the skin.

1-trans-3-cis-4 Camphorwood, musky. Minty.

(PAID 4) Smells kind of like damp Like spearmint sweets. Minty but sweet.

firewood/varnish. Feels tacky on the skin 1-cis-3-cis-4 Musky, woody. Sweet, toffee.

(PAID 5) Smells kind of musty, like damp Very sweet like toffee/caramel. Feels firewood? Crystals had a sharper normal on skin. Can smell it in ethanol scent. solution.

1-cis-3-cis-4 Very light-applies like Sweet.

(PMD 6) water/ethanol. Smells mostly of the Extremely sweet smell-borderline sickly alcohol.

smell.

1-trans-3-trans-Weak. Pleasant, sweet, weak.

4 (P1VID 7) Feels light, not remotely sticky/ greasy which is unusual for a repellent.

1-trans-3-trans Pleasant, sweet, weak. Sweet, toffee.

(PMD 8) Couldn't smell anything, light Pleasant smell, sort of a burnt formula as low concentration, so caramel/toffee smell. A light tacky pleasant feel. touch.

Table 4. A summary of the description of odour and/ or feel of each stereoisomer.

Discussion All isomers were shown to offer protection against both species of mosquito tested (Anopheles gambiae and Aedes aegypti) with higher concentrations required for Aedes aegypli (consistent with this species being a more aggressively feeding species).

100% protection was afforded with concentrations ranging between 0.2% (0.002 g/mL) and 5% (0.05 g/mL) depending on the isomer and species of mosquito used.

For each species tested, there was variation between protective efficacies of the eight isomers, with around an order of magnitude difference in concentration required for 100% protective efficacy between the best and worst performing isomers. The results in this study differ from existing literature in which four PMD stereoisomers, (-)-and (+)-cis-p-Menthane-3,8-diols and (+)-and (-)-trans-p-Menthane-3,8-diols were tested in a mosquito repellency assay against An. get:tibiae, found no significant difference in the level of repellency (Barasa, S. S., et al. (2002). Journal of medical entomology, 39(5), 736-741.) However, studies of other chemical repellents provide evidence that mosquitoes respond differently to different stereoisomers. For example, in a study of piperidine repellents, where some of the stereoisomers were up to 3.1 times more repellent than other stereoisomers (Klun, J. A., et al (2001) Journal of medical entomology, 38(6), 809-812).

The two species showed different responses to the different isomers (e.g. order of most repellent to least repellent isomers was different for each species) suggesting opportunities for blending mixtures of isomers for use in commercial products.

Some isomers afforded high protection against both species.

The scents of each individual isomer were noted by all test volunteers and ranged from noting hardly any odour at all to strong citrus, mint or sweet odours.

Testing of PAID isomers against pyrethroid-insensitive Anopheles gambiae and DEET-insensitive Aedes aegypti Pyrethroid-insensitive Anopheles gambiae Test Insects and Method RSP is a pyrethroid-resistant strain of Anophele.s. gambioe. RSP (Reduced Susceptibility to Permethrin) have a number of upregulated genes compared to susceptible strains, including the GST TSTE2, two P450s, and two peroxidase genes3. This species of Anopheles is a major vector for the Plasmodium parasite that causes Malaria.

Mosquitoes were obtained from an insecticide-resistant lab strain held at Londoneast-UK. All mosquitoes were reared and housed under optimal environmental conditions of 27°C ± 2°C and 80% +10°C Relative Humidity with a 12: 12 hour photoperiod. Three cages (30 x 30 x 30 cm) were set up in the test room at least 30 minutes before testing, each containing a batch of 50 host-seeking Pyrethroid resistant female Anopheles gambiae, 2-5 days old.

Test methods were otherwise as described above.

Dose response against pyrethroid-resistant An. gambiae As shown in Figure 3, Table 5 and Appendix 1 (raw data set), all eight PMD stereoisomers achieved 100% protective efficacy. PMD 4 required the lowest concentration (0.0105g/m1) to reach 100% PE, followed by PMD 5 (0.0135g/m1), PMD 1 (0.014g/m1), PMD 8 (0.0155g/m1), PMD 6 (0.017g/m1), PMD 2 (0.0175g/m1), PMD 3 (0.0185g/m1), and finally PMD 7, which required the highest concentration (0.0235g/ml).

PMD Stereoisomer Concentration (g/m1) 1-cis-3-trans-4(PMD 1) 0.014 1-cis-3-trans-4 (PMD 2) 0.0175 1-trans-3-cis-4 (PMD 3) 0.0185 1-trans-3-cis-4 (PMD 4) 0.0105 1-cis-3-cis-4 (PMD 5) 0.0135 1-cis-3-cis-4 (PMD 6) 0.017 1-trans-3-trans-4 (PMD 7) 0.0235 1-trans-3-trans 4 (PMD 8) 0.0155 Table 5. The concentration required to reach 100% PE for each PMD stereoisomer against pyrethroid-resistant An. gandnae.

DEET-insensitive Aedes aegppti.

Test Insects Aedes aegmti is an important nuisance probing mosquito species found on most continents. It is the most domesticated of mosquito species and widespread in areas of human habitation. Feeds throughout the day and breeds in containers such as discarded car tyres, tin cans and pots. This zoophylic species is an important vector of Dengue and Yellow Fever.

Mosquitoes were obtained from an insecticide-susceptible lab strain held at LondoneastUK. All mosquitoes were reared and housed under optimal environmental conditions of 27°C ± 2°C and 80% +10°C Relative Humidity with a 12: 12 hour photoperiod.

During the selection method (see below), the DEET-insensitive colony of Aedes aegpyti was kept under the same environmental conditions of 27°C ± 2°C and 80% +10°C Relative Humidity with a 12:12 hour photoperiod.

DEET-insensitive Selection of Aedes aegypti Test Conditions and Set-Up One cage (30 x 30 x 30 cm) was set up in the test room at least 30 minutes before testing, containing a batch of 10-20 host-seeking Ae. aegypli female mosquitoes, 5-7 days old. Ae. aegvi females were checked for host-seeking behaviour by placing a hand next to the cage prior to selection.

Product Application The volunteer's arm was measured, and the surface area calculated. A 20% DEET solution was applied at the standard WHO repellent application rate of 1.67 ulicm2 onto one forearm. The solution was measured using a Gilson pipette (P1000). The measured dose was applied evenly using a single gloved finger to the forearm to completely cover the skin from the wrist to the elbow. The arm was allowed to dry for one minute after application before use in selection.

Exposing to DEET Once the DEET was applied to the forearm, the arm was placed over the top of the cage at a height of 1.5cm above the mesh, preventing the mosquitoes from contacting the arm or DEET.

Female mosquitoes that landed on the mesh and attempted to probe the arm were considered to be insensitive to DEET and removed using a mouth-aspirator into a separate cage, causing as little disturbance as possible to the other mosquitoes. At the end of the two-minute period, the mosquitoes that did not land were considered to be sensitive to the repellent and discarded.

All DEET-insensitive females from each test were placed into a single cage with the males from the same generation. Blood-feeding, using a Haemotech feeder, was allowed and egg papers were generated.

This selection was done over a 5-generation period to ensure the DEET-insensitivity was high enough for the numbers to be adequate for testing.

Test Conditions and Set-Up Three cages (30 x 30 x 30 cm) were set up in the test room at least 30 minutes before testing, each containing a batch of 50 host-seeking DEET-insensitive female Ae. etegypn, 5-7 days old. These had been selected for, prior to exposure to PMD, to ensure the test individuals were insensitive to DEET as discussed above. Other conditions were generally as set out for the other test, above.

DEET-Insensitivity Results The results for the DEET-insensitivity selection assays showed an incremental increase of DEET-insensitive females from 10.4% in the population drawn from a regular test cage, increasing to 55% after 5 generations of exposure to DEET as shown in Table 6, below.

In the PMD exposure, only individuals that had already been demonstrated to be DEBT-insensitive were used.

Generation No. DEET Insensitivity No. Tested DEET insensitive Gen 0 500 10.4% Gen 1 750 10.9% Gen 2 1453 18.4% Gen 3 1500 27% Gen 4 3158 38% Gen 5 2910 55% Table 6. Generational results for DEET insensitivity in Aedes aegypti.

Dose response against BEET-insensitive Ae. aegypti As shown in Figure 5 and Table 7, all eight PMD stereoisomers achieved 100% protective efficacy. PMD 1 required the lowest concentration (0.007g/m1) to reach 100% PE, followed by PMD 4 (0.0085g/m1), PMD 5 (0.0125g/ml), PMD 8 (0.0145g/ml), PMD 3 (0.018g/ml), PMD 6 (0.021g/m1), PMD 7 (0.255g/m1), and PMD2 (0.0335g/m1).

PMD Stereoisomer Concentration (g/m1) 1-cis-3-trans-4 (PMD 1) 0.007 1-cis-3-trans-4 (PMD 2) 0.0335 1-trans-3-cis-4 (PMD 3) 0.018 1-trans-3-cis-4 (PMD 4) 0.0085 1-cis-3-cis-4 (PMD 5) 0.0125 1-cis-3-cis-4 (PMD 6) 0.021 1-trans-3-trans-4 (PMD 7) 0.0255 1-trans-3-trans 4 (PMD 8) 0.0145 Table 7. The concentration required to reach 100% PE for each PMD stereoisomer against DEET-insensitive Ae. aegypti.

Discussion All isomers were shown to offer protection against both species of mosquito tested (pyrethroid-insensitive Anopheles gambiae and DEET-insensitive Aedes aegypti) with higher concentrations required for Aede.s. aegypti (consistent with this species being a more aggressively feeding species). 100% protection was afforded with concentrations ranging between 0.7% (0.002 g/mL) and 3% (0.03 g/mL) depending on the isomer and species of mosquito used. For each species tested, there was variation between protective efficacies of the eight isomers, with around an order of magnitude difference in concentration required for 100% protective efficacy between the best and worst performing isomers. The two species showed different responses to the different isomers (e.g. order of most repellent to least repellent isomers was different for each species) suggesting opportunities for blending mixtures of isomers for use in commercial products. Some isomers afforded high protection against both species.

All publications mentioned in the above specification are herein incorporated by reference. Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

Claims

CLAIMS1. A stereoselective method of producing a stereoisomer of p-menthane-3,8-diol, the method comprising the steps of: a. providing a stereoisomer of a compound of formula (I):
OH (1) ,b hydrating the alkene group of the compound of formula (I) to produce the stereoisomer of p-menthane-diol of formula (II): 2. A method as claimed in claim 1, wherein the step of hydrating the alkene of formula (1) comprises performing direct alkene hydration.
3. A method as claimed in claim 1, wherein the step of hydrating the alkene of formula (I) comprises epoxidizing the alkene to form an epoxide and then reducing the epoxide.
4. A method as claimed in any one of the preceding claims, wherein the stereoisomer of a compound of formula (I) is selected from a compound of formula (Ia; 53); a compound of formula (Ib; 56); a compound of formula (Ic; 63); or a compound of formula (Id; 66): OH /,, 'OH (la, 53) (Ib; 56) 1.0 (Ic; 63) (Id; 66).
5. A method as claimed in claim 4, wherein the stereoisomer of a compound of formula (I) is selected from a compound of formula (Ia; 53); a compound of formula (Ib; 56); a compound of formula (Ic; 63); or a compound of formula (Id; 66) and wherein the method thereby produces the stereoisomer of p-menthane-diol of formula (Ha, PMD 1); the stereoisomer of p-menthane-diol of formula (IIb; PMD 2); the stereoisomer of p-menthane-diol of formula (IIc; PMD 3) or the stereoisomer of pmenthane-diol of formula (Ild; PMD 4) respectively: 6.*OH 1/4/0HOH OH(Ha; PMD (IIb, PMD 2)OHOH or(Hc; PMD 3) (Hd, PMD 4).
6. A method as claimed in any one of the preceding claims, further comprising a step of alcohol inversion of the stereoisomer of p-menthane-diol of formula (II).
7. A method as claimed in claim 6, wherein the step of alcohol inversion comprises a step of oxidation of the secondary alcohol followed by a step of reduction.
8. A method as claimed in claim 7, wherein a step of oxidation of the secondary alcohol comprises treating the stereoisomer of p-menthane-diol of formula (II) with an oxidant selected from pyridinium chlorochromate (in CHCL3); or trichloroisocyanuric acid (TCICA). 7t
9. A method as claimed in either claim 7 or claim 8, wherein the step of selective reduction is performed by treating the product of the step of oxidation of the secondary alcohol with a reductant selected from hydrogen gas, NaBH4, LiAIH4, diisobutylaluminium hydride (DIBAL-H); or L-Selectride (lithium tri-sec-butyl(hydrido)borate(1-)).
10. A method as claimed in any one of claims 4 to 7, wherein the compound of formula (Ic; 63) or the compound of formula (Id; 66) is provided by a method comprising a step of alcohol inversion of the compound of formula (la; 53) or the compound of formula (Ib; 56) respectively.
11. A method as claimed in claim 10, wherein the step of alcohol inversion of the compound of formula (Ta; 53) or the compound of formula (ib; 56) is an oxidation/reduction alcohol inversion or a Mitsunobu-type inversion.
12. A method as claimed in any one of claims 3 to 11, wherein epoxidizing the alkene group of the compound of formula (I) comprises treatment of the compound of formula (I) with hydrogen peroxide or a peroxycarboxylic acid, optionally metachloroperoxybenzoic acid (mCPBA).
13. A method as claimed in any one of claims 3 to 12, wherein reducing the epoxide comprises treating the epoxide with a reducing agent selected from NaBH4, LiA1f14, diisobutylaluminium hydride (D1BAL-H); or L-Selectride (lithium tri-secbutyl(hydrido)borate(1-)) 14. A stereoselective method of producing a stereoisomer of p-menthane-3,8-diol, the method comprising the steps of: a. providing a stereoisomer of a compound of formula (III):OHb. performing a ring opening reaction on the compound of formula (III) in the presence of a carbonyl compound of formula RiC(0)R2 and a compound containing a source of halogen (X), to form a compound of formula (IV): R2 (IV) wherein Xis halo and RI and R2 are independently H, or a linear or branched CA-C9 alkyl chain which may be optionally substituted, c. dehalogenating the compound of formula (IV) to form a compound of formula (VI):, (VI) d. hydrogenating and deprotecting the diol of the compound of formula (VI), thereby producing the stereoisomer of p-menthane-diol of formula (I-):OH
OH (II)
15. A method as claimed in claim 14, wherein Ri and R2 are each CH3.
16. A method as claimed in either claim 14 or 15, wherein the stereoisomer of a compound of formula (III) is selected from a compound of formula (Ilia; 68); or a compound of formula (IIIb; 85): OH or OH (Ma; 68); (11Th; 85).
17. A method as claimed in claim 16, wherein the stereoisomer of a compound of formula (III) is a compound of formula (IIIc; 68) or (IIId; 85); (Inc, 68). (Hid; 85).
18. A method as claimed in claim 17, wherein the stereoisomer of a compound of formula (III) is selected from a compound of formula (Illa); a compound of formula to (IIlb; 85); a compound of formula (I tic; 68); or a compound of formula (111d; 85) and wherein the method thereby produces the stereoisomer of p-menthane-diol of formula (He, PMD 5); or the stereoisomer of p-menthane-diol of formula (IIf; PMD 6) respectively: or 11:111.41rOH OH (IIf; PMD 6). 1/10HH
(Ile, PMD 5) 19. A method as claimed in any one of claims 14 to 18, further comprising a step of alcohol inversion of the stereoisomer of p-menthane-diol of formula (II).
20. A method as claimed in claim 19, wherein alcohol inversion of the stereoisomer of p-menthane-diol of formula (Ile; PMD 5) or of formula (IIf; PMD 6): or 1/40H (IIe; PMD 5)OHOHPMD 6) produces the stereoisomer of p-menthane-diol of formula (11g, PMD 7); or the stereoisomer of p-menthane-diol of formula (IIh; PMD 8) respectively: CMOH or '11/40H 11:10H OH (IIh, PMD 8).
(IIg, PMD 7) 21. A method as claimed in any one of the preceding claims 14 to 20, wherein dehalogenating the compound of formula (IV) to form the compound of formula (VI) comprises treating the compound (IV) with a reducing agent, optionally Li Al 1-14.
22. A method as claimed in any one of the preceding claims 14 to 21, wherein hydrogenating the compound of formula (VI) comprises treating it with H2 in the presence of Pt02.
23. A composition comprising 95mo1% or greater of a stereoisomer of p-menthane- 3,8-diol selected from the stereoisomer of p-menthane-diol of formula (Ha, PMD 1); of formula (IIb; PMD 2); of formula (Hc; PMD 3) of formula (Hd, PMD 4); of formula (He; PMD 5), of formula (Hf; PMD 6), of formula (llg, PMD 7) or of formula (IIh; PMD 8):OH(Ha, PMD 1) 4,0HOH(llb, PMD 2) (Ile, PMD 3) (lid, PMD 4)OHOH(Iff; PMD 6) (fie; PMD 5) a. OH or (fig; PMD 7) (Ifh; PMD 8).
24. An insect repellent, a fragrance or a flavouring comprising at least one composition as claimed in claim 23.fo
25. A method of reducing resistance of a target insect or tick species to a p-menthane-diol repellent, the method comprising: identifying a measure of the degree of resistance of the target species to a composition comprising a first stereoisomer of p-menthane-diol; determining a second stereoisomer of p-menthane-diol with a lower degree of resistance of the target species than the first stereoisomer.
26. A compound of formula: 1/40H (IIe, PMD 5) PMD 6) aOH (IIg; PMD 7).