WO2008143996A1

WO2008143996A1 - New chemical processes

Info

Publication number: WO2008143996A1
Application number: PCT/US2008/006325
Authority: WO
Inventors: Keqiang Li
Original assignee: Scynexis Inc
Current assignee: Scynexis Inc
Priority date: 2007-05-18
Filing date: 2008-05-16
Publication date: 2008-11-27
Anticipated expiration: 2009-11-18

Abstract

Provided herein are processes for the preparation of cyclosporin derivative substituted in the 3-position by an ether group -OR1, wherein R1 is an amine-bearing alkyl group, which comprises the reductive amination of a cyclosporin substituted in the 3-position by an ether group -OR1 1, wherein R11 is an alkyl group substituted by a carbonyl group. These compounds are useful as pharmaceuticals or as intermediates in the preparation of biologically active compounds.

Description

NEW CHEMICAL PROCESSES

1 CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of priority of U.S. Provisional Application No. 60/931 ,024, filed May 18, 2007, the content of which is hereby incorporated by reference in its entirety.

2 FIELD OF THE INVENTION

[0002] This invention relates to new methods for the preparation of 3 -substituted cyclosporin derivatives. These compounds are useful as pharmaceuticals or as intermediates in the preparation of biologically active compounds.

3 BACKGROUND

[0003] Cyclosporins are a group of non-polar cyclic oligopeptides with immunosuppressant, anti-inflammatory, and anti-parasitic properties. 3 -Ether substituted cyclosporin derivatives are known from European Patent No. EP 1086124, WO2006/039668 and WO2007/041631 and are described as having various pharmaceutical properties. EP 1086124 describes processes for the preparation of compounds of formula (I) that involve the treatment of a 3-sulfide substituted cyclosporin derivative with a suitably protected amino alcohol which result in a diastereomeric mixture of 3-ether cyclosporins that are frequently difficult to purify.

[0004] In the pharmaceutical industry, it is desirable to prepare compounds in enantiomerically or diastereomerically pure form. In some cases this can be achieved using purification techniques such as crystallization or chromatography, but these can add to the cost of manufacturing the pharmaceutical as they can involve expensive specialized methods, such as super critical fluid chromatography or countercurrent chromatography, as well as roughly half of the material in the form of the non-required isomer being lost where a reaction takes place in a non-stereoselective manner. The ability to prepare compounds that are completely, or substantially, isomerically pure can favor crystallization. 4 SUMMARY

[0005] Provided herein are processes for the preparation of a cyclosporin derivative substituted in the 3-position by an ether group -OR¹, wherein R¹ is an amine-bearing alkyl group, which comprises the reductive amination of a cyclosporin derivative bearing an ether group in the 3-position, wherein said 3-substituted ether contains a carbonyl group, e.g., a cyclosporin derivative substituted in the 3-position by an ether group -OR¹¹, wherein R¹¹ is an alkyl group substituted by a carbonyl group. In particular, the invention provides a process for the preparation of a cyclosporin derivative of general formula (I):

(I) wherein R¹ is (Ak)NR⁵R⁶;

Ak is alkylene;

R⁵ and R⁶ are each independently hydrogen or straight- or branched- chain alkyl comprising from one to six carbon atoms; alkylaryl; alkylheteroaryl; aryl; heteroaryl; or R⁵ and R , together with the nitrogen atom to which they are attached, form a saturated or unsaturated heterocyclic ring containing from four to six ring atoms, which ring may optionally contain another heteroatom selected from the group consisting of nitrogen, oxygen and sulfur and may be optionally substituted by one to four groups which may be the same or different selected from alkyl, hydroxyl, amino, N-alkylamino and N,N-dialkylamino;

R² is isobutyl or 2-methyl-2-(OR¹²)propyl, where R¹² is hydrogen or a protecting group;

R³ is (E)-2-butenyl-l or n-butyl;

R⁴ is ethyl, 1-hydroxyethyl, isopropyl or n-propyl;

R¹⁰ is hydrogen or a protecting group;

[0006] comprising the reaction of a compound of formula (II): 1

(H) wherein R², R³, R⁴ and R¹⁰ are as defined above, R^{1 1} is (Ak)-C(=O)R⁷ and R⁷ is selected from hydrogen, lower alkyl, aryl and heteroaryl;

[0007] with an amine of formula H-NR⁵R⁶, wherein R⁵ and R⁶ are as defined above, in the presence of a reducing agent.

5 DETAILED DESCRIPTION

5.1 Definitions

[0008] When referring to the compounds and complexes provided herein, the following terms have the following meanings unless indicated otherwise.

[0009] "Cyclosporin" refers to any cyclosporin compound known to those of skill in the art, or a derivative thereof. See, e.g., Ruegger et al., 1976, HeIv. Chim. Acta. 59:1075-92; Borel et al., 1977, Immunology 32:1017-25; the contents of which are hereby incorporated by reference in their entireties. Exemplary compounds for use in the methods provided herein are cyclosporin derivatives. Unless noted otherwise, a cyclosporin described herein is a cyclosporin A, and a cyclosporin derivative described herein is a derivative of cyclosporin A.

[0010] The cyclosporin nomenclature and numbering systems used hereafter are those used by J. Kallen et al., "Cyclosporins: Recent Developments in Biosynthesis, Pharmacology and Biology, and Clinical Applications," Biotechnology, second edition, H.-J. Rehm and G. Reed, ed., 1997, p535-591 and are shown below:

- 3 - Position Amino acid in cyclosporin A

1 N-Methyl-butenyl-threonine (MeBmt)

2 [alpha] -aminobutyric acid (Abu)

3 Sarcosine (Sar)

4 N-Methyl-leucine (MeLeu)

5 Valine (VaI)

6 N-Methyl-leucine (MeLeu)

7 Alanine (Ala)

8 N-Methyl-leucine (MeLeu)

9 (D)-Alanine ((D)-AIa)

10 N-Methyl-leucine (MeLeu)

11 N-Methylvaline (MeVaI)

[0011] "Alkyl" refers to monovalent saturated aliphatic hydrocarbyl groups, particularly having up to about 11 carbon atoms, more particularly as a lower alkyl, from 1 to 8 carbon atoms and still more particularly, from 1 to 6 carbon atoms. The hydrocarbon chain may be either straight-chained or branched. This term is exemplified by groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, iso-butyl, tert-butyl, n-hexyl, n-octyl, tert-octyl and the like. The term "lower alkyl" refers to alkyl groups having 1 to 6 carbon atoms.

[0012] "Alkylene" refers to divalent saturated aliphatic hydrocarbyl groups particularly having up to about 1 1 carbon atoms and more particularly 1 to 6 carbon atoms which can be straight-chained or branched. This term is exemplified by groups such as methylene (-CH₂-), ethylene (-CH₂CH₂-), the propylene isomers (e.g., -CH₂CH₂CH₂- and -CH(CH₃)CH₂-) and the like.

[0013] "Aryl" refers to a mono or bicyclic aromatic ring which can be optionally substituted by alkyl, halo, hydroxyl, amino or carboxyl groups. Preferred aryl groups are phenyl and naphthyl.

[0014] "Heteroaryl" refers to a mono or bicyclic aromatic group containing 5-9 atoms in which at least one of the atoms is nitrogen, sulfur or oxygen. Examples of preferred heteroaryl groups include, but are not limited to, furan, thiophene, pyrrole, indole, benzothiophene and the like.

[0015] "Amino" refers to the radical -NH₂. [0016] "Hetero" when used to describe a compound or a group present on a compound means that one or more carbon atoms in the compound or group have been replaced by a nitrogen, oxygen, or sulfur heteroatom. Hetero may be applied to any of the hydrocarbyl groups described above such as alkyl, for example, heteroalkyl, aryl, for example, heteroaryl, and the like, having from 1 to 5, and especially from 1 to 3 heteroatoms.

[0017] "Heterocycle" or "heterocyclic ring" refers to any heterocycle known to those of skill in the art. As used herein, a heterocycle can be a heteroaryl group or a cycloheteroalkyl group, as will be recognized by those of skill in the art. In certain embodiments, heterocyclyl refers to a 4, 5, or 6 membered saturated heterocyclic ring containing one or more heteroatoms in the ring.

[0018] "Dialkylamino" means a radical -NRR' where R and R' independently represent an alkyl, substituted alkyl, aryl, substituted aryl, cycloalkyl, substituted cycloalkyl, cycloheteroalkyl, substituted cycloheteroalkyl, heteroaryl, or substituted heteroaryl group as defined herein.

[0019] "Halogen" or "halo" refers to chloro, bromo, fluoro or iodo. [0020] "Sarcosine" refers to N-methyl glycine (CH₃NHCH₂CO₂H).

[0021] It is to be understood that compounds having the same molecular formula but differing in the nature or sequence of bonding of their atoms or in the arrangement of their atoms in space are termed "isomers." Isomers that differ in the arrangement of their atoms in space are termed "stereoisomers."

[0022] Stereoisomers that are not mirror images of one another are termed "diastereomers" and those that are non-superimposable mirror images of each other are termed "enantiomers". When a compound has an asymmetric center, for example, when it is bonded to four different groups, a pair of enantiomers is possible. An enantiomer can be characterized by the absolute configuration of its asymmetric center and is designated (R) or (S) according to the rules of Cahn and Prelog (Cahn ef α/., 1966, Angew. Chem. 78:413-447, Angew. Chem., Int. Ed. Engl. 5:385- 414 (errata: Angew. Chem., Int. Ed. Engl. 5:51 1); Prelog and Helmchen, 1982, Angew. Chem. 94:614-63 \, Angew. Chem. Internal. Ed. Eng. 21 :567-583; Mata and Lobo, 1993, Tetrahedron: Asymmetry 4:657-668) or can be characterized by the manner in which the molecule rotates the plane of polarized light and is designated dextrorotatory or levorotatory (i.e., as (+)- or (-)- isomers, respectively). A chiral compound can exist as either individual enantiomer or as a mixture thereof. A mixture containing equal proportions of enantiomers is called a "racemic mixture." [0023] In certain embodiments, the compounds for use in the methods provided herein may possess one or more asymmetric centers; such compounds can therefore be produced as the individual (R)- or (5)-enantiomer or as a mixture thereof. Unless indicated otherwise, for example by designation of stereochemistry at any position of a formula, the description or naming of a particular compound in the specification and claims is intended to include both individual enantiomers and mixtures, racemic or otherwise, thereof. Methods for determination of stereochemistry and separation of stereoisomers are well-known in the art. In particular embodiments, provided herein are the stereoisomers of the compounds depicted herein upon treatment with base.

[0024] In certain embodiments, the compounds for use in the methods provided herein are "stereochemically pure." A stereochemical^ pure compound or has a level of stereochemical purity that would be recognized as "pure" by those of skill in the art. Of course, this level of purity will be less than 100%. In certain embodiments, "stereochemically pure" designates a compound that is substantially free of alternate isomers. In particular embodiments, the compound is 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.5% or 99.9% free of other isomers.

5.2 Embodiments of the Invention

[0025] Provided herein are processes for the preparation of cyclosporin derivatives substituted in the 3-position by an ether group -OR¹, wherein R¹ is an amine-bearing alkyl group, such as compounds of formula (I). In certain embodiments the reaction of a compound of formula (II) with an amine under reducing conditions gives compounds of formula (I). Typically the reaction is carried out by treating the compound of formula (II) with an appropriate amine and a reducing agent, optionally in the presence of an acid catalyst such as acetic acid, in an appropriate solvent. The presence of an acid catalyst is particularly desirable where the 3-substituted ether contains a carbonyl group which is not an aldehyde (e.g., compounds of formula (II) above in which R⁷ is not hydrogen). In one embodiment the reaction is performed at a temperature from about -1O⁰C to about 8O⁰C. In another embodiment the reaction is performed at a temperature from about O⁰C to about 8O⁰C. In another embodiment the reaction is performed at a temperature from about O⁰C to about 4O⁰C. In a further embodiment the reaction is performed at about room temperature. In one embodiment the acid catalyst is acetic acid. In a further embodiment the acid catalyst is a Lewis acid, for example, titanium isoproxide.

[0026] In one embodiment the molar ratio of cyclosporin to reducing agent is from about 1 : 1 to about 1 :8. In another embodiment the molar ratio of cyclosporin to reducing agent is from about 1 : 1 to about 1 :2. In a still further embodiment the molar ratio of cyclosporin to reducing agent is from about 1 : 1.3 to about 1 : 1.6.

[0027] In one embodiment Ak is methylene, ethylene or propylene. In another embodiment Ak is ethylene. In another embodiment R² is isobutyl. In another embodiment R² is 2-methyl-2- hydroxypropyl. In a further embodiment R³ is (E)-2-butenyl-l. In a still further embodiment R⁴ is ethyl. In a still further embodiment R⁵ and R⁶ are lower alkyl, or R⁵ and R⁶, together with the nitrogen to which they are attached, form a ring selected from the group consisting of azetidine, pyrrolidine, piperazine, morpholine, imidazole, said ring optionally bearing one or two groups selected from alkyl and hydroxyl. In a still further embodiment R⁷ is hydrogen.

[0028) When R¹⁰ is a protecting group it is generally an acid stable protecting group, such as an allyl or benzyl ether, a trichloroacetate, benzoate, or methyl, allyl or benzyl carbonate.

[0029] In one embodiment the reducing agent contains boron. In another embodiment the reducing agent is a cyanoborohydride, for example, sodium cyanoborohydride, sodium acetoxyborohydride and the like. In another embodiment the reducing agent is selected from a borane in pyridine, titanium isoproxide with sodium cyanoborohydride, a borohydride exchange resin, zinc in acetic acid, sodium borohydride with magnesium pechlorate, and zinc tetrahydroborate with zinc chloride. In a further embodiment the solvent is an alcohol (e.g., methanol or ethanol), a chlorinated solvent (e.g., dichloromethane or dichloroethane), tetrahydrofuran or acetonitrile. In another embodiment the hydroxyl group at the 1 -MeBmt position of the cyclosporin ring is protected, for example, in formula (I) R¹¹ is a protecting group. In a further embodiment where the 4-position of the cyclosporin ring bears a hydroxyl group said hydroxyl group is unprotected, for example, in formula (I) R¹² is hydroxyl. In a further embodiment where the 4-position of the cyclosporin ring bears a hydroxyl group said hydroxyl group is protected, for example, in formula (I) in which R² is 2-methyl-2-(OR^l2)propyl and R¹² is a protecting group. In a further embodiment each protecting group (where present) is removed by hydrolysis using an alkoxide in an alcohol under conditions typical for such a reaction, for example, an alkali metal alkoxide such as sodium methoxide in methanol; or an alkaline earth metal salt such as potassium carbonate in methanol. In one embodiment each protecting group is an acetate. In a further embodiment where one or more protecting groups are present and each protecting group is acetate, each protecting group may be removed by treatment with a base. In a further embodiment the base is an alkoxide, for example, an alkali metal alkoxide such as sodium methoxide, and the solvent is an alcohol, for example, methanol, as described in the reaction sequence below for the conversion of a compound of formula (III) into a compounds of formula (Ia), which is a compound of formula (I) above in which R¹⁰ is hydrogen. It will be understood by one skilled in the art that the acetate protecting group may be replaced with a different group that is compatible with the conditions described in these procedures.

(III)

(Ia)

R²² = CH₂CH(CH₃)₂ or CH₂C(OH)(CH₃)₂

[0030] Compounds of formula (III) can be prepared by treating an alcohol compound of formula (IV) with an oxidizing agent known by those of skill in the art to convert an alcohol to an aldehyde or a ketone. Typically the reaction is carried out by treating the alcohol of formula (IV) with an oxidant, such as Dess-Martin periodinane, in a suitable solvent, such as dichloromethane or dichloroethane. A molar excess of oxidizing agent is generally used, for example, up to five molar equivalents of oxidizing agent or more preferably up to two molar equivalents. The reaction is generally performed at a temperature from O⁰C to 4O⁰C. The reaction scheme is illustrated for compounds of formula (III) [i.e., a compound of formula (II) in which R⁷ is hydrogen]:

M (in)

[0031] Compounds of formula (IV) in which R¹⁰ is a protecting group can be obtained by treatment of the diastereomeric mixture of an acetate compound of formula (V) with an appropriate alcohol in a solvent, optionally in the presence of an acid catalyst, and heating. The alcohol is a dihydroxy compound such as 1 ,2-dihydroxyethane, 1,3-dihydroxypropane, 1,4- dihydroxybutane and the like. The acid catalyst can be a sulfonic acid, such as camphorsulfonic acid and toluenesulfonic acid; hydrochloric acid, sulphuric acid and the like. The preferred solvents include, but are not limited to, tetrahydrofuran, 1,4-dioxane, and 1 ,2-dimethoxyethane, and the reaction is preferably heated to 50 to 80⁰C. Compounds of formula (IV) are isolated completely, or substantially as a single isomer with stereochemistry as indicated.

(V) (IV)

[0032] Compounds of formula (V) can be prepared from compounds of formula (VI) by treatment of said mixture with an acetate salt in acetic acid with optional heating. The acetate salt is preferably mercury acetate and the reaction is heated at about 40 to 80⁰C. Compounds of formula (VI) are described in EP 1086124.

(VI) (V)

[0033] The cyclosporin derivative in which the 3-position is a carbonyl-bearing alkyl group may be prepared by the reaction of the corresponding cyclosporin derivative in which the 3-position is substituted by a sulfide with an acetate salt, followed by treatment with a dihydroxy compound.

5.2.1 Compounds that may be prepared using the processes

[0034] Among the compounds that may be prepared by in the process provided herein are the cyclosporin compounds listed below. Note that in general the process of the invention is performed on the corresponding compound bearing a protecting group on the hydroxyl present in the 1 -position of the cyclosporin ring, and this protecting group is subsequently removed.

A 3-[2-(N,N-dimethylamino)ethoxy]cyclosporin.

B 3-[2-(azetidin-l-yl)ethoxy]cyclosporin.

C 3-[2-(pyrrolidin- 1 -yl)ethoxy]cyclosporin. D 3-[2-(piperidin-l-yl)ethoxy]cyclosporin.

E 3-[2-(4-methylpiperazin-l-yl)ethoxy]cyclosporin.

F 3-[2-(moφholin-4-yl)ethoxy]cyclosporin.

G 3-[2-(2,6-dimethylmorpholin-4-yl)ethoxy]cyclosporin.

H 3-[2-(3-hydroxypyrrolidin- 1 -yOethoxyJcyclosporin.

I 3-{2-[(4-dimethylamino)piperidin-l -yljethoxy} cyclosporin.

J 3-[2-(4-hydroxypiperidin- 1 -yl)ethoxy]cyclosporin.

K 3-[2-(imidazol-l-yl)ethoxy]cyclosporin.

L 3-[2-(N-methylamino)ethoxy]cyclosporin.

M 3-[2-(N-isopropyl-N-methylamino)ethoxy]cyclosporin.

N 3-[2-(aminopropoxy)]cyclosporin.

O 3-[2-(N,N-dimethylamino)ethoxy]-4-(gamma-hydroxy- methylleucine)cyclosporin P 3-[2-(N,N-dimethylamino)propoxy]-4-(gamma-hydroxy- methylleucine)cyclosporin The Compound Letters A to P are used hereafter.

6 EXAMPLES

[0035] The following Example illustrates the process of the present invention. Numerous modifications and variations of the claimed subject matter are possible in view of the teachings herein and, therefore, are within the scope of the claimed subject matter.

Example 1

[0036] [3'-Acetoxy-N-MeBmt] ' [(R)-2'-formylmethoxy-Sar]³cyclosporin A (290 mg), was dissolved in methanol (15 mL) and to this solution were added acetic acid (30 μL), pyrrolidine (50 μL), and sodium cyanoborohydride (30 mg). The resulting mixture was stirred at room temperature overnight. The solvent was removed and the residue was purified using silica gel column chromatography to yield 154 mg of [3'-acetoxy-N-MeBmt]'[(R)-2'-(2-pyrrolidin-l- yl)ethoxy-Sar]³cyclosporin A. ¹H NMR peaks at 5.95, 7.08, 7.16, 7.60 and 7.90 ppm.

Reference Example 1

[0037] To a suspension of Dess-Martin periodinane (300 mg) in dichloromethane (30 mL) was added [3'-acetoxy-N-MeBmt]^J[(R)-2'-hydroxymethylmethoxy-Sar]³cyclosporin A (600 mg) in dichloromethane (15 mL) and the resulting mixture was stirred at room temperature for 1 hour. The reaction mixture was diluted with methyl t-butyl ether, washed with a 1 : 1 (volume/volume) mixture of 10% sodium thiosulfate and saturated sodium hydrogen carbonate, saturated brine solution, and dried over anhydrous sodium sulphate. After solvent removal, 580 mg of [3'-acetoxy-N-MeBmt]'[(R)-2'-formylmethoxy-Sar]³cyclosporin A was obtained.

Reference Example 2

[0038] Camphor sulfonic acid (1.0 g) was added to a solution of [3'-acetoxy-N-methyl- Bmt]'[2'-acetoxy-Sar]³cyclosporin A (5.14 g) in a solvent mixture of tetrahydrofuran (10 mL) and dry ethylene glycol, and the resulting mixture was stirred at 50⁰C for 5 hours. The reaction mixture was diluted with saturated sodium hydrogen sulfate, water, and extracted with ethyl acetate. The combined organic extracts were washed with water, saturated sodium chloride solution, and dried over anhydrous sodium sulphate. After solvent removal, 2.66 g of [3'-acetoxy-N-MeBmt]'[(R)-2'-hydroxymethylmethoxy-Sar]³cyclosporin A was obtained. ¹H NMR peaks at 5.90, 7.26, 7.46, 8.03 and 8.55 ppm.

[0039] Mercury acetate (4.4 g) was added to a solution of [3'-acetoxy-N-MeBmt]¹[(R)-2'- thiophenyl-Sar]³cyclosporin A (4.4 g) in glacial acetic acid (90 mL) and the resulting mixture was stirred for 3 hours at 50⁰C. The solvent was then removed and the residue dissolved in ethyl acetate (300 mL), washed with a saturated solution of sodium hydrogen carbonate (150 mL) and then brine (150 mL), and dried over anhydrous sodium sulphate. After removal of the solvent, the crude product was purified using silica gel column chromatography to yield 5.14 g of [3 ' -acetoxy-N-MeBmt] ' [2 ' -acetoxy-Sar]³cyclosporin A.

[0040] The compound obtained in Example 1 above was de-protected as follows: to a solution of [3'-acetoxy-N-MeBmt]^l[(R)-2'-(2-pyrrolidin-l-yl)ethoxy-Sar]³cyclosporin A (150 mg) in methanol (10 mL) was added 25 wt % sodium methoxide in methanol (0.04 mL) and the resulting mixture was stirred at room temperature for 24 hours under nitrogen. Methanol was removed under reduced pressure and the residue was diluted with ethyl acetate, washed with saturated ammonium chloride, brine, and dried over anhydrous sodium sulfate. After solvent removal, the residue was purified using preparative liquid chromatography to yield 33 mg of 3- [2-(pyrrolidin-l-yl)ethoxy]cyclosporin (Compound C). ¹H NMR peaks at 5.89, 7.10, 7.15, 7.64 and 7.96 ppm. LCMS (ESI): calculated for C₆₈H₁₂₂Ni₂O_n: 1314, found 1315.2 (M+H)⁺. [0041] By proceeding in a similar manner to the reaction described in Example 1 and subsequent deprotection the following compounds were also prepared:

[0042] The compounds prepared by the processes of the present invention are useful either as pharmaceutical compounds, as intermediates in the preparation of biologically active compounds (e.g., protected intermediate forms of pharmaceutically active compounds), for example, as described in European Patent No. EP 1086124, and International Patent Publication No. WO2006/039668 and WO2007/041631.

[0043] In the preparation of compounds all publications and patent applications cited in this specification are herein incorporated by reference as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. While the invention has been described in terms of various preferred embodiments, the skilled artisan will appreciate that various modifications, substitutions, omissions, and changes may be made without departing from the spirit thereof. Accordingly, it is intended that the scope of the claimed subject matter be limited solely by the scope of the following claims, including equivalents thereof.

Claims

WHAT WE CLAIM IS:

1. A process for the preparation of a cyclosporin derivative substituted in the 3 -position by an ether group -OR¹, wherein R¹ is an amine-bearing alkyl group, which comprises the reductive amination of a cyclosporin substituted in the 3 -position by an ether group -OR¹¹, wherein R¹¹ is an alkyl group substituted by a carbonyl group.

2. The process according to Claim 1 for the preparation of a cyclosporin derivative of general formula (I):

(I) wherein R¹ is (Ak)NR » 5³R_n6⁰.;

Ak is alkylene;

R⁵ and R⁶ are each independently hydrogen or straight- or branched- chain alkyl comprising from one to six carbon atoms; alkylaryl; alkylheteroaryl; aryl; heteroaryl; or R and R , together with the nitrogen atom to which they are attached, form a saturated or unsaturated heterocyclic ring containing from four to six ring atoms, which ring may optionally contain another heteroatom selected from the group consisting of nitrogen, oxygen and sulfur and may be optionally substituted by one to four groups which may be the same or different selected from alkyl, hydroxyl, amino, N-alkylamino and N,N-dialkylamino;

R² is isobutyl or 2-methyl-2-(OR^l2)propyl, where R¹² is hydrogen or a protecting group;

R³ is (E)-2-butenyl-l or n-butyl;

R⁴ is ethyl, 1 -hydroxyethyl, isopropyl or n-propyl;

R¹⁰ is hydrogen or a protecting group; comprising the reaction of a compound of formula (II):

(II) wherein R², R³, R⁴ and R¹⁰ are as defined above, and R¹ ' is (Ak)-C(=O)R⁷, wherein R⁷ is selected from hydrogen, lower alkyl, aryl and heteroaryl; with an amine of formula H-NR⁵R⁶, wherein R⁵ and R⁶ are as defined above, in the presence of a reducing agent.

3. The process according to Claim 2, wherein the reaction is performed in the presence of an acid catalyst.

4. The process according to Claim 2, wherein Ak is methylene, ethylene or propylene; R² is isobutyl or 2-methyl-2-hydroxypropyl; R³ is (E)-2-butenyl-l; R⁴ is ethyl; R⁵ and R⁶ are lower alkyl, or R⁵ and R⁶, together with the nitrogen to which they are attached, form a ring selected from the group consisting of azetidine, pyrrolidine, piperazine, morpholine, imidazole, said ring optionally bearing one or two groups selected from alkyl and hydroxyl; and R⁷ is hydrogen.

5. The process according to Claim 4, wherein the reaction is performed in the presence of an acid catalyst.

6. The process according to any one of Claims 2 to 5, wherein the reducing agent contains boron.

7. The process according to Claim 6, wherein the reducing agent is a cyanoborohydride.

8. The process according to any one of Claims 2 to 5, wherein the R 10 is a protecting group

9. The process according to Claim 8, wherein the protecting group is stable under acidic conditions.

10. The process according to Claim 8, wherein the protecting group is acetate.