WO2013178682A2 - Multicomponent process for the preparation of bicyclic compounds - Google Patents

Description

MULTICOMPONENT PROCESS FOR THE PREPARATION OF BICYCLIC COMPOUNDS

Field of the invention

The present invention relates to a multicomponent process for the preparation of N-acyl bicyclic prolinamides which can be easily converted into one of the HCV protease inhibitors, particularly Telaprevir or Boceprevir, or the salts and the intermediates useful in the synthesis thereof.

Background of the invention

Hepatitis C virus (HCV) is a (+)-sense single-stranded RNA virus that has been implicated as the major causative agent in non-A, non-B hepatitis (NANBH), particularly in blood-associated NANBH. NANBH is to be distinguished from other types of viral-induced liver disease, such as hepatitis A virus (HAV), hepatitis B virus (HBV), delta hepatitis virus (HDV), cytomegalovirus (CMV) and Epstein-Barr virus (EBV), as well as from other forms of liver diseases such as alcoholism and primary biliary cirrhosis.

Recently, a HCV protease necessary for polypeptide processing and viral replication has been identified, cloned and expressed. This approximately 3000 amino acid polyprotein contains, from the amino terminus to the carboxy terminus, a nucleocapsid protein C, envelope proteins (El and E2) and several non-structural proteins (NS 1, 2, 3, 4a, 5a and 5b). NS3 is an approximately 68 KDa protein, encoded by approximately 1893 nucleotides of the HCV genome and has two distinct domains: (a) a serine protease domain consisting of approximately 200 of the N-terminal amino acids; and (b) an RNA- dependent ATPase domain at the C-terminus of the protein. The HCV NS3 serine protease is responsible for proteolysis of the polypeptide (polyprotein) at the NS3/NS4a, NS4a/NS4b, NS4b/NS5a and NS5a/NS5b junctions and is thus responsible for generating four viral proteins during viral replications. This has made the HCV NS3 serine protease an attractive target for antiviral chemotherapy.

Boceprevir and Telaprevir, depicted below, are two of the most interesting serine protease inhibitors, disclosed respectively in international patent applications WO 2003/062265 Al and WO 2002/018369 Al .

The preparation methods described in said applications include the preparation of three key intermediates (Fragment A, B and C for Telaprevir; Fragment A', B' and C for Boceprevir), as illustrated below:

Fragment A gment B Fragment C

Fragment A" Fragment B" Fragment C

The most interesting synthetic routes described include the preparation of the intermediates B, C, B' and C (fragments A and A' are prepared through ordinary peptide synthesis).

Fragment B synthesis (according to WO 2002/018369 Al and WO 2007/022459 Al) entails preparing octahydrocyclopenta[c]pyrrole-l-carboxylic acid from the corresponding symmetrical (achiral) bicyclic amine by forming the N-Boc derivative, and reacting it with sec-butyllithium (a pyrophoric agent) in the presence of an excess of bulky chelating diamine (preparation described in WO 2007/022459 Al), followed by addition of C0₂. All these operations are carried out below -70 °C to produce the racemic N-Boc amino acids as depicted below:

Racemic Mixture

The (lR,3aS,6aR) (undesired) and (!S,3aR,6aS) (desired) stereoisomers are then separated by diastereomeric salt resolution using a homochiral base.

(35)-3-Amino-2-hydroxyhexanoic cyclopropylamide (fragment C) preparation, according to WO 2002/018369 Al, requires adding potassium cyanide to the aldehyde derived from L-N-Boc norvaline. The Boc group is then removed and the cyano group is hydrolyzed to give the 3-amino-2-hydroxyhexanoic acid; the nitrogen is protected with Cbz group; the acid is then condensed with cyclopropylamine using a peptide coupling agent and the Cbz group is removed by hydrogenolysis.

Another method for producing fragment C is described in patent applications WO 2005/058821 Al and WO 2005/087730 Al ; in this method, L-N-(tert-butoxycarbonyl)- norvaline is reacted with N,O-dimethylhydroxylamine to obtain a Weinreb amide; the amide is reduced to an aldehyde; cyclopropylisocyanide and acetic acid are added thereto to give (25',35)-3-N-tert-butoxycarbonylamino-2-acetoxyhexanoic cyclopropylamide; finally, the acetyl group and the tert-butoxycarbonyl group are cleaved. Disadvantage of this path is the high number of the process steps because of the protection/deprotection of functional groups and redox reactions.

Fragment C preparation, in accordance with WO 2003/062265 A2, entails adding acetone cyanohydrin to an aldehyde derived from 2-((tert-butoxycarbonyl)amino)-3- cyclobutylpropanoic acid; the a-hydroxynitrile is subsequently hydrolyzed to yield tert- butyl (4-amino-l-cyclobutyl-3-hydroxy-4-oxobutan-2-yl)carbamate and the Boc group is removed.

Fragment B' (according to WO 2003/062265 A2) is prepared reacting (3R,7aS)-3- phenyl-l,7a-dihydropyrrolo[l,2-c]oxazol-5(3H)-one (prepared according to J. Org. Chem. (1999), 64(2), 547) with n-butyllithium and isopropyl triphenylposphonium iodide to yield the corresponding dimethyl cyclopropane, which is subsequently reduced and hydrogenated to obtain ((li?,25',55)-6,6-dimethyl-3-azabicyclo[3.1.0]hexan-2- yl)methanol. Said amino alcohol is protected with benzyl chloroformate and oxidized to give the desired amino acid.

Although stereoselective, the synthetic routes proposed are multistep, complex, expensive, inefficient and low yielding. Furthermore they include the use of cryogenic temperatures and employ dangerous reagents, such as cyanides or sec-butyllithium. Fragment B' can also be produced according to the method described in international patent application WO 2004/113295 Al . The synthetic route entails the asymmetric opening of caronic anhydride mediated by quinidine, a cinchona alkaloid, followed by a diasteromeric salt resolution via the formation of a salt with a single enatiomer of a chiral amine (probably due to low enantiomeric purity of the product). The proposed synthetic path is very long and complex, including several steps of protection and deprotection and in some cases the use of highly toxic reagents, such as trimethylsilyl cyanide or boron trifluoride etherate.

A further method of producing fragment B' is disclosed in patent application WO 2007/075790 Al . This method involves the production of the methyl ester of the bicyclic proline analogue (li?,25',55)-6,6-dimethyl-3-azabicyclo[3.1.0]hexane-2-carboxylic acid from the corresponding symmetrical (achiral) bicyclic amine (li?,5S)-6,6-dimethyl-3- azabicyclo[3.1.0]hexane (prepared from caronic anhydride in 2 steps), beginning with its oxidation to the corresponding racemic imine, which is subsequently reacted with cyanide to provide the racemic aminonitrile; the aminonitrile is reacted with acid and methanol to give the racemic amino acid methyl ester of the following structural formula:

Racemic Mixture

Finally, the (IR,2S,5S) (undesired) and (1S,2R,5R) (desired) stereoisomeric methyl esters are separated by diastereomeric salt resolution. This method achieves the desired result, but the resolution of a mixture of enantiomers of these bicyclic proline analogues inherently involves the waste of at least one half of all of the material (e.g. reagents, solvents, catalysts) used in the production of the racemic mixture.

Still another synthetic path for the preparation of fragments B and B' is described in international patent application WO 2010/008828 Al : bicyclic imines (depicted below), prepared through an enzymatic desymmetrization of the corresponding meso- pyrrolidines by means of a monoamine oxidase N (MAO-N) from Aspergillus niger, are reacted with sodium bisulfite and then with cyanide to yield the corresponding trans- nitriles, which are finally hydro lysed to fragments B and B' :

Bicyclic imine Fragment B

N CN N C0 H

H H

Bicyclic imine Fragment B'

Nevertheless, the biocatalysis processes require additional steps for preparing and maintaining the bacterial cultures or for the isolation of the enzymes from this cultures. Another very interesting synthetic path proposed for the synthesis of Telaprevir is described in Chemical Communications (2010), 46(42), 7918-7920 and in the corresponding international application WO 2011103933 Al, wherein the desired product is obtained through a multicomponent Ugi reaction between Fragment A, a bicyclic imine and an isocyanide, as depicted below:

imine

The required isocyanide is prepared by reacting (5)-N-(l-oxopentan-2-yl)formamide with cyclopropylisocyanide in a Passerini reaction, followed by dehydration of the formamide. Although the route described therein is interesting, the present inventors, performing the synthesis described in Chemical Communications, have found that the isocyanide and its precursors required for the Ugi reaction are very unstable and difficult to analyze. Their instability causes a drastic decrease of the overall yield.

For the above reasons said synthesis is not particularly suited for a practical industrial application. An object of the invention is therefore to provide an alternative synthetic route for the industrial preparation of N-acyl bicyclic prolinamides which can be easily converted into one of the HCV protease inhibitors, particularly Telaprevir or Boceprevir, their salts, or the intermediates useful for the synthesis thereof, characterized by a lower number of steps, a high overall yield and an excellent diasteroisomeric and optical purity. A further object of the invention is to provide novel compounds that can be used in the processes. Summary of the invention

These and other objects are achieved within the present invention which, in a first aspect, regards a process for the preparation of N-acyl bicyclic prolinamides of general formula (IX), or their salts:

wherein, if n = 0, then R⁸ and R⁹ are C¾, and if n = 1 , then R⁸ and R⁹ are hydrogen; said process comprising the following operations:

a) preparing a δ-acylamino-a-hydroxyamide of formula (VIII):

b) cyclizing a δ-acylamino-a-hydroxyamide of formula (VIII) to provide a N-acyl bicyclic prolinamide of formula (IX);

wherein:

- R² is

- R⁵ is Ci-C₆ linear or branched alkyl optionally substituted with a Ci-C₆ cyclic alkyl (preferably n-propyl or cyclobutylmethyl);

- R¹⁰ is cyclopropyl, or one of the removable groups of the convertible isocyanide as detailed hereinafter;

- R is NH₂; NH-Pg; or NH-R ,

- R¹⁶ is OH; OPg;

- ¹⁷ is hydrogen or cyclopropyl;

- R¹⁹ is OH; a Ci-C₆ linear or branched alkoxy optionally substituted with a C₆-Cio aryl; NH-R¹⁰; or NH-R¹⁷;

- R²⁰ is hydrogen or a Ci-C₆ linear or branched alkyl, optionally substituted with a

C₆-Cio aryl group; and

- Pg is a protecting group; in the group -OPg in R¹⁶, it is an alcohol protecting group, while in the group -NH-Pg in R¹³ or in R¹⁵ it is a nitrogen protecting group.

Useful alcohol protecting groups are known in the field and comprise, e.g., esters (e.g. acetate, phenylacetate or benzoates optionally substituted, such as /?-nitrobenzoate), silyl ethers (for example trimethylsilyl (TMS), triisopropylsilyl (TIPS), tert- butyldimethylsilyl (TBDMS), tert-butyldiphenylsilyl (TBDPS)), or ethers (such as benzyl, /?-methoxybenzyl, allyl, tetrahydropyranyl (THP), 1-ethoxyethyl, methoxymethyl, /?-methoxybenzyloxymethyl, or 2-trimethylsilylethyl). Nitrogen protecting groups useful for the invention are, e.g., tert-butyloxycarbonyl (Boc), benzyloxycarbonyl (Cbz), and 9-fluorenylmethyloxycarbonyl (Fmoc).

The prolinamide of formula (IX) can be further transformed into one of the serine protease inhibitors, their salts, or one of the intermediates useful in the synthesis thereof. Detailed description of the invention

All terms as used in this application, unless otherwise stated, shall be understood in their ordinary meaning as known in the art. Other more specific definitions for certain terms used in the present application are set forth below and are intended to apply uniformly throughout the specification and claims unless otherwise expressly stated.

The compounds prepared by the processes of the present invention may have one or more stereogenic centers and may exist and may be used or isolated in optically active or racemic forms as well as in diastereomerically pure forms or as diastereomeric mixtures. It is to be understood that the processes of the present invention can give rise to any racemic- or optically-active forms, or mixture thereof. It is to be further understood that the products of the processes described herein, can be isolated as racemic, or optically active forms, or mixtures thereof. Purification and characterization procedures for such products are known to those of ordinary skill in the art, and include recrystallization techniques, chiral chromatographic separation procedures, as well as other methods. The sign "*" (asterisk) present in some formulae of this description indicate stereogenic (asymmetric) center, although the absence of asterisks does not necessarily imply that the compound lacks a stereocenter. Such formulae may refer to the racemate or to individual enantiomers or diastereomers, which may or may not be substantially pure. A mixture of (R,S) enantiomers can contain the two single enantiomers in any ratio to each other. The enantiomeric purity is generally expressed as "enantiomeric excess" or e.e. and is defined, for example for the (S) enantiomer, as [(S-R)/(R+S)]xl00, wherein S and R are respectively the amounts of the (S) and (R) enantiomers (as determined for example by GC or HPLC on a chiral stationary phase or polarimetry).

The term "aryl" refers to any substituent derived from a monocyclic or a polycyclic aromatic hydrocarbon by removal of an hydrogen atom from a ring carbon atom (i.e. phenyl, tolyl, 1-naphtyl or 2-napthyl).

The term "racemic" refers to a sample of a chiral compound which contains both the (+) and (-) isomers in equal amount.

The term "enantiomerically enriched" as used herein means that one of the enantiomers of a compound is present in excess compared to the other enantiomer.

The term "single (S)- or ( ?)-enantiomer" means that the enantiomeric purity is usually at least about 96%, preferably at least 99%, more preferably at least 99.5%.

The sign (dotted line bond) present in some formulae of this description and of the claims indicate that the substituent is directed below the plane of the paper.

The sign— (wedged line bond) present in some formulae of this description and of the claims indicate that the substituent is directed above the plane of the paper.

The compounds obtained by the chemical transformations of the present invention can be used for the following steps without further purification or can be separated and purified by employing conventional methods well known to those skilled in the art, such as recrystallization, column chromatography, or by transforming them into a salt or in a co-crystal with an appropriate co-former, or by washing with an organic solvent or with an aqueous solution, optionally adjusting pH.

It will be understood that any compound described herein may also describe any salts or co-crystals thereof.

In its broadest embodiment, the process of the invention comprises, as a first operation, the preparation of a δ-acylamino-a-hydroxyamide of formula (VIII) given above. The desired compound of formula (VIII) can be prepared, in operation a) of the process of the invention, according to two alternative synthetic routes, a.i) and a.ii).

The reaction pathway a.i) comprises the following steps:

a.i. l) conversion of an azido aldehyde of formula (VI) into a δ-azido-a- acyloxyamide of formula (VII) by treatment with an isocyanide (R³NC) and a carboxy

a.i.2)

a.i.3)

In step a.i.l), an azido aldehyde of formula (VI) is reacted with a carboxylic acid of general formula (R²C0₂H) and an isocyanide of formula (R³NC), wherein the substituents R² and R³ assume the meanings given above, according to Passerini reaction conditions in a chlorinated solvent, preferably dichloromethane, or in an aprotic polar solvent, such as, an ether (preferably tetrahydroiuran), an ester (preferably ethyl acetate), acetonitrile (ACN) or a mixture thereof, at a temperature comprised in the range between 0 and 60 °C (preferably at 20 °C), to yield a δ-azido-a-acyloxyamide of formula (VII). The amount of the carboxylic acid of general formula (R²C0₂H) and of the isocyanide of formula (R³NC) are comprised between 1 and 1.5 equivalents, preferably 1 equivalent, compared to the molar quantity of the azido aldehyde of formula (VI).

In step a.i.2), the δ-azido-a-acyloxyamide of formula (VII) is reduced to the amine of formula (Vlld). The reduction reaction can be carried out using one of the methods generally known in the field for example using borane-dimethylsulfide, borane- tetrahydrofuran, tin dichloride, hydrogenation using as catalysts, for example, palladium on calcium carbonate (lead poisoned), palladium on carbon, palladium (II) hydroxide on carbon, platinum (IV) oxide, rhodium on alumina; the reaction takes place in a polar protic solvent, preferably ethanol, or in an aprotic polar solvent, as tetrahydroiuran, or a mixture thereof.

Alternatively and preferably, said reduction can be performed by treating the δ-azido-a- acyloxyamide of formula (VII) with a trivalent phosphorus compound (according to Staudinger reaction conditions), such as a trialkyl- or triarylphosphine (e.g. tris(3- hydroxypropyl)phosphine or preferably triphenylphosphine) optionally supported, in a polar aprotic solvent, such as ethers (preferably tetrahydroiuran) in the presence of water to yield the corresponding amine, at a temperature comprised in the range between 40 and 80 °C, preferably 60 °C.

In step a.i.3), the amine of formula (Vlld) (optionally isolated) is subjected to an 0→N acyl migration to yield the δ-acylamino-a-hydroxyamide of formula (VIII) with one of the known methods, optionally by means of base catalysis; an organic base, such as a tertiary amine, is optionally added to increase the reaction rate of the 0^→N acyl migration. Normally this step occurs in the same solvent used for the reduction, at a temperature comprised in the range between 20 and 80 °C (preferably 60 °C).

The alternative reaction pathway a.ii) comprises the following steps:

a.ii. l) reacting an azido aldehyde of formula (VI) with an isocyanide (R³NC) and an acid (as detailed hereinafter) to obtain a δ-azido-a-hydroxyamide of formula

(Vllb):

a.ii.2) reducing the azido group to yield the amine of formula (Vile);

a.ii.3) N-acylation to provide a δ-acylamino-a-hydroxyamide of formula (VIII):

Step a.ii. l) entails the preparation of the δ-azido-a-hydroxyamide of formula (Vllb) via a truncated Passerini reaction (i.e. a variation of the Passerini reaction where the final product is an a-hydroxyamide rather than an a-acyloxyamide, see for example Organic Reactions, Volume 65, Chapter 1 "The Passerini Reaction") by treating the azido aldehyde of formula (VI) with an isocyanide of formula (R³NC) and an acid as detailed below, in a chlorinated solvent (preferably dichloromethane) or in an aprotic polar solvent, such as, ethers (preferably tetrahydroiuran), esters (alkylacetates, such as ethyl acetate), acetonitrile, amides (such as dimethylformamide (DMF), dimethylacetamide (DMA) or N-methyl pyrrolidone), or a mixture thereof, at a temperature comprised in the range between 0 and 60 °C (preferably at 20 °C). Suitable acids for the aim are, for example, trifluoroacetic acid (TFA), pyridinium trifluoroacetate or, preferably, boric acid, used in an amount comprised between 1 and 2 equivalents, preferably 1 equivalent, compared to the molar quantity of the azido aldehyde of formula (VI). The amount of the isocyanide of formula (R³NC) is comprised between 1 and 1.5 equivalents, preferably 1.2 equivalent, compared to the molar quantity of the azido aldehyde of formula (VI).

Step a.ii.2) is the reduction of the azido group, for example with one of the methods mentioned above in step a.i.2.

Step a.ii.3) is the N-acylation of the amine of formula (Vile) obtained in step a.ii.2 with a carboxylic acid of formula (R²C0₂H) as defined above, to yield said δ-acylamino-a- hydroxy amide of formula (VIII).

N-acylation is carried out using one of the peptide coupling reagents generally known in the field (e.g. see Valeur E. et ah : Chem. Soc. Rev., (2009), 38, 606-631), preferably 1- ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), benzotriazol- 1 -yl- oxytripyrrolidino phosphonium hexafluorophosphate (PyBOP), O-(7-Azabenzotriazol-l- yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate (HATU) or 6-chloro-l- ((dimethylamino)(morpho lino)-methylene)- 1 H-benzotriazo hum hexafluorophosphate 3 - oxide (6-HDMCB) and a tertiary amine (cyclic or acyclic), such as triethylamine, N,N- diisopropylethylamine, N,N-diisopropylmethylamine, N-methylpyrrolidine, N- methylmorpholine, N,N-dicyclohexylmethylamine, N,N-diethylaniline, 2,6- dimethylpyridine or 2,4,6-trimethylpyridine; the reaction is optionally carried out in the presence of an additive, such as N-hydroxybenzotriazole (HOBT), 5-aza-l- hydroxybenzotriazole (5-HOAT), N-hydroxysuccinimide (HOSu), l-hydroxy-2- phenylbenzimidazole (HOBI) and ethyl 2-cyano-2-(hydroxyimino)acetate (Oxyma); and in a polar aprotic solvent such as dichloromethane, acetonitrile, dimethylacetamide, dimethylformamide, tetrahydrofuran, alkyl acetates or a mixture thereof.

The second operation of the process of the invention, b), is the cyclization of a δ- acylamino-a-hydroxyamide of formula (VIII) to yield the N-acyl bicyclic prolinamide of formula (IX).

This operation comprises two reactions steps:

b.l) preparation, starting from a compound of formula (VIII), of an a-activated-δ- acylamino amide of formula (VHIb):

(Vlllb) wherein the substituents have the meanings given above and R¹¹ represents one of the leaving groups, known to the person skilled in the art, able to undergo a nucleophilic substitution, such as for example, a mesylate, a tosylate, a halogen, a triflate, a nonaflate, a fluorosulfonate, or a nosylate; b.2) cyclization of the a-activated-5-acylamino amide of formula (Vlllb) to produce the prolinamide of formula (IX).

In step b.l) a compound of formula (VIII) is converted into the corresponding a-activated-5-acylamino amide of formula (Vlllb).

When in the compound of formula (Vlllb) R¹¹ is a sulphonate, such as mesylate, trifluoromethanesulfonate (triflate) or tosylate, its preparation can be performed with one of the methods generally known in the field, for example by treating the substrate with the corresponding sulfonyl halide or sulfonyl anhydride, in presence of an organic base in a suitable solvent. Preferably the base is a tertiary amine (cyclic or acyclic), such as triethylamine, N,N-diisopropylethylamine, N,N-diisopropylmethylamine, N- methylpyrrolidine, N-methylmorpholine, N,N-dicyclohexylmethylamine, N,N- diethylaniline, pyridine, 2-methylpyridine, 2,6-dimethylpyridine, 2,4,6-trimethylpyridine or 4-dimethylaminopyridine. Solvents useful for the aim are, for example, chlorinated solvent, e.g. dichloromethane, or a polar aprotic solvent, such as an ether, or a mixture thereof. The quantity of sulfonyl halide or of sulfonyl anhydride used is comprised between 1 and 1.5 equivalents, preferably 1.2 equivalents, compared to the molar quantity of the δ-acylamino-a-hydroxyamide of formula (VIII). The amount of the organic base used is comprised between 1 and 3 equivalents, preferably 2 equivalents, compared to the molar quantity of the δ-acylamino-a-hydroxyamide of formula (VIII). Alternatively, when in the a-activated-5-acylamino amide of formula (Vlllb) R¹¹ is a halogen, said compound can be prepared by treating the δ-acylamino-a-hydroxyamide of formula (VIII) with a halogenating agent such as CX₄ (preferably CBr₄, CC ), in presence of a stoichiometric amount of a phosphine (preferably triphenylphosphine) in a chlorinated solvent, for example dichloromethane, or in an aprotic polar solvent, such as an ether (preferably tetrahydrofuran) or a mixture thereof, at a temperature in the range comprised between -10 °C and 10 °C, preferably 0 °C. The quantity of the halogenating agent is comprised between 1 and 2 equivalents, preferably 1.5 equivalents, compared to the molar quantity of the δ-acylamino-a-hydroxyamide of formula (VIII). The quantity of the phosphine is comprised between 1 and 2 equivalents, preferably 1.5 equivalents, compared to the molar quantity of the δ-acylamino-a-hydroxyamide of formula (VIII). Alternatively said activated compound of formula (Vlllb) can be prepared by treating the δ-acylamino-a-hydroxyamide of formula (VIII) with thionyl chloride, thionyl bromide, phosphoryl chloride, or phosphorus tribromide in a chlorinated solvent, such as dichloromethane, in a polar aprotic solvent, as acetates (preferably alkylacetates, such as ethyl acetate), ethers (preferably tetrahydrofuran or 1,4-dioxane), in a hydrocarbon, as toluene, or a mixture thereof, optionally in presence of an organic base (preferably pyridine).

In step b.2), said a-activated-5-acylamino amide of formula (Vlllb) is cyclized by treatment in a dipolar aprotic solvent, such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone or a mixture thereof, at a temperature between -30 °C and 40 °C (preferably at 0 °C), with an organic or inorganic base capable to promote said cyclization step, optionally in the presence of a halide salt such as a tetraalkylammonium halide (preferably tetrabutylammonium iodide or bromide) or an alkali metal halide (preferably Nal, NaBr, KI or KBr).

Bases useful for the aim are strong bases, for example hydrides (preferably sodium, lithium or potassium hydrides), alkaline amides (preferably lithium bis(trimethylsilyl)amide (LiHMDS)) or alkaline tert-butoxides (such as sodium or potassium tert-butoxide). The amount of the base used is comprised between 1 and 2 equivalents, preferably 1.2 equivalents, compared to the molar quantity of the a-activated-5-acylamino amide of formula (Vlllb).

Preferably, the starting material for either operation a.i. l) or a.ii. l) described above, is an enantiomerically enriched azido aldehyde having the following structure (VI'):

In this case, the process leads to the enantiomerically enriched N-acyl bicyclic prolinamide of formula (IX') below:

Even more preferably, the process is such to lead to an N-acyl bicyclic prolinamide (IX) having one of the following formulae (A) and (B), in which the substituents assume the meanings given above:

The starting compound for the synthetic routes of the invention is an azido aldehyde of formula (VI):

The azido aldehyde (VI) can be prepared according to the following synthetic scheme:

(I) (II) _R4 (ill) 4

Path 2 consists in an enzymatic desymmetrization of a meso-diol of formula (I), by treating it with a vinyl alkanoate or a linear isopropenyl alkanoate of formula (XV), preferably vinyl acetate, to yield a monoalkanoate of formula (II), as detailed below:

wherein the substituents assume the meanings given above, R⁴ is a C1 -C5 linear alkyl, and R¹² is methyl or hydrogen.

The amount of the vinyl alkanoate or of the linear isopropenyl alkanoate (XV) is comprised between 1 and 1.5 equivalents, preferably 1.2 equivalents, compared to the molar quantity of the diol of formula (I).

When the vinyl alkanoate or the linear isopropenyl alkanoate of formula (XV) are vinyl acetate or isopropenyl acetate, they can also perform the function of solvent for the reaction.

Hydrolases useful for the aim are, for example, lipases, such as a pig pancreatic lipase (PPL), a lipase SAM-2, a lipase from Candida Antarctica, or preferably the lipase PS "Amano" SD or the lipase A "Amano", optionally adsorbed on celite , at a temperature comprised in the range between -20 and 20 °C, preferably at 0 °C. Such desymmetrization step can be performed in a polar aprotic solvent, preferably ethers, such as isopropyl ether, tetrahydrofuran or methyl tert-butyl ether, or a mixture thereof, optionally in presence of molecular sieves.

Alternatively, path 3 entails the preparation of the monoalkanoate of formula (II) through the preparation of a dialkanoate formula (Ha) (step A), followed by an enzymatic hydrolysis (step B).

Step A can be carried out with one of the methods generally known in the field (see e.g. Theodora W. Green, Protective Groups in Organic Synthesis, John Wiley & Sons (1999)), for example by treating diol (I) with an anhydride or an acyl halide in presence of a tertiary amine.

Hydrolases useful in step B for the aim are, for example, lipases, such as a pig pancreatic lipase (PPL), a lipase SAM-2, a lipase from Candida Antarctica, or preferably the lipase PS "Amano" SD or the lipase AK "Amano", in presence of a pH buffer and a variable amount (comprised between 0 and 20%) of an organic co-solvent, such as a protic polar solvent, preferably an alcohol, or an aprotic polar solvent, such as an ether, dimethylformamide, dimethylsulfoxide, or an apolar solvent, such as a hydrocarbon at a temperature comprised in the range between 5 and 30 °C.

The next step of the synthetic route described herein is the transformation of the monoalkanoate of formula (II) into an azido alkanoate of formula (IV), according to the scheme shown below:

wherein the substituents assume the meanings given above.

Path 1 step A foresees the preparation of an activated monoalkanoate of formula (III), wherein the substituents have the meanings given above and R¹ represents one of the leaving groups, known to the person skilled in the art, able to undergo a nucleophilic substitution, such as for example, a mesylate, a tosylate, a halogen, a triflate, a nonaflate, a fluorosulfonate, or a nosylate.

Such step can be performed using one of the methods known to the ordinary skilled person, as for example those described in operation b. l to prepare an a-activated-δ- acylamino amide of formula (VHIb).

Path 1 step B entails the preparation of the azido alkanoate of formula (IV) by a displacement of the leaving group (namely R¹) by treating with an azide, preferably lithium, sodium, or potassium azide, in an aprotic polar solvent such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran or a mixture thereof.

The quantity of the azide used is comprised between 1 and 1.5 equivalents, preferably 1.2 equivalents, compared to the molar quantity of the activated monoalkanoate of formula (III).

Alternatively the azido alkanoate of formula (IV) can be prepared by treating the activated monoalkanoate of formula (III) with an azide and a catalytic amount of an alkaline halide (Finkelstein reaction), such as sodium iodide or bromide, in an aliphatic ketone (e.g. methylethylketone or acetone), dimethylformamide, dimethylacetamide, N- methylpyrrolidone, tetrahydrofuran or a mixture thereof.

The following step is the preparation of an azido alcohol of formula (V) through hydrolysis of the ester with one of the suitable methods known to a skilled person.

Preferably, the hydrolysis is carried out by contacting the azido alkanoate of formula (IV) with a hydroxide or a carbonate of an alkaline metal (such as K₂CO₃, Na₂C0₃, L1₂CO₃, CS₂CO₃, KOH, NaOH, LiOH) in a water miscible solvent, such as methanol, ethanol, tetrahydrofuran, dioxane or a mixture thereof) in the presence of water.

The amount of the alkaline base used is comprised between 1 and 5 equivalents, preferably 3 equivalents, compared to the molar quantity of the azido alkanoate of formula (IV).

If the monoalkanoate of formula (II) is obtained as the undesired enantiomer according to formula (lib), as detailed below, it can be converted into the azido alcohol of formula (V) with one of the methods generally known in the field, such as, for example the one depicted in the following scheme:

wherein Pg is one of the protecting groups of the alcohols orthogonal to the acyl (namely Pv⁴CO) derived from the enzymatic desymmetrization.

Said azido alcohol of formula (V) is subsequently oxidized to an azido aldehyde of formula (VI), with one of the methods known in the field such as, for example, those reported in Burke-Danheiser, Handbook of Reagents for Organic Synthesis: Oxydizing and Reducing Agents, John Wiley & Sons (1999), or alternatively using one of the following methods:

employing the Swern oxidation (by treating with oxalyl chloride (COCl)₂ or trifluoroacetic anhydride (TFAA), dimethylsulfoxide (DMSO) and a tertiary amine) or one of its variation, such as the Corey- Kim oxidation (by treating with

N-chlorosuccinimide, dimethyl sulfide and a tertiary amine) or the Pfitzner- Moffat oxidation (by treating with dicyclohexyl carbodiimide (DCC), DMSO and a catalytic amount of phosphoric acid);

using bis(acetoxy)iodobenzene and 2,6,6-tetramethylpiperidin-l-oxyl (TEMPO) (see e.g. A. De Mico et al: Journal of Organic Chemistry (1997), 62(19), 6974-

6977);

treating with hypervalent iodine based oxidizing agents such as 2-iodoxybenzoic acid (IBX) or Dess-Martin periodinane (DMP);

using a catalytic amount of tetrapropylammonium perruthenate (TPAP) with a co-oxidant such as N-methylmorpholine-N-oxide (NMO) (referred to as the Ley oxidation);

treating with TEMPO, sodium hypochlorite (NaOCl) and optionally in the presence of sodium or potassium bromide (Anelli oxidation);

using dimethyl sulfoxide (DMSO) as the oxidant, activated by the sulfur trioxide pyridine complex in the presence of a tertiary amine (known as Parikh-Doering oxidation).

In a preferred embodiment, the prolinamides according to formulae (IX), (IX')_> (A) or (B) above, are further reacted to produce intermediates in the synthesis of the serine protease inhibitors described in the introduction of this description, their salts or their co- crystals.

Another preferred embodiment of the invention is directed to the preparation of an aldehyde of formula (XIa):

The process of this preferred embodiment comprises the following steps:

a') preparing a δ-acylamino-a-hydroxyamide of formula (Villa):

a wherein the substituents have the meanings given above;

b') cyclizing the δ-acylamino-a-hydroxyamide of formula (Villa) to provide a N- acyl bicyclic proline amide of formula (IXa):

optionally, when R¹⁶ is OPg, removing the protecting group (i.e., Pg) to obtain N-acyl bicyclic proline (hydroxyalkyl)amide of formula (Xa):

d) oxidizing the N-acyl bicyclic proline (hydroxyalkyl)amide of formula (Xa) to provide an aldehyde of formula (XIa).

Steps a') and b') correspond to steps a) and b) of the most general embodiment of the invention, carried out using, as the isocyanide of formula R³NC, the isocyanide of formula (XII):

in which the substituent assume the meanings given above. Preferably, the isocyanide of formula (XII) has one of the following formulae:

The optional step c) consists in deprotecting the N-acyl bicyclic proline amide of formula (IXa) obtained in step b') to provide the N-acyl bicyclic proline (hydroxyalkyl)amide of formula (Xa) with one of the suitable methods known to a skilled person, such as those reported in Theodora W. Green, Protective Groups in Organic Synthesis, John Wiley & Sons (1999), preferably, in the case when the protecting group is an ester, for instance benzoate, /?-nitrobenzoate or acetate, by means of an alkaline hydroxide (e.g. LiOH, KOH, NaOH) in water optionally using a water miscible co-solvent.

Then, in step d), compound (Xa) is oxidized to provide an aldehyde of formula (XIa). Said oxidation step can be performed using one of the oxidizing methods known in the field, such as, for example, those reported hereinbefore for the preparation of an azido aldehyde of formula (VI) starting from an azido alcohol of formula (V). Optionally this step can be performed under biocatalyzed conditions using one of the alcohol dehydrogenase enzymes generally known in the field. Preferred conditions entails the use of TEMPO and sodium hypochlorite (optionally in the presence of sodium or potassium bromide) or the use of dimethyl sulfoxide (DMSO) activated by the sulfur trioxide pyridine complex in the presence of a tertiary amine.

Similarly to the process comprising operations a) and b), the process defined by steps a') to d) is preferably carried out on the enantiomerically enriched azido aldehyde of formula (VI'), leading to an enantiomerically enriched aldehyde of formula (XIa'):

In an even more preferred embodiment, the aldehydes (XIa) or (XIa') may be further reacted to produce one of the serine protease inhibitors described in the introduction of this description, the salts, the co-crystals, or one of the intermediates useful in the synthesis thereof; this more preferred embodiment will be described hereinbelow with reference to aldehyde (XIa) as starting compound, but will be apparent that the same sequence of steps described below may be applied starting from an aldheyde (XIa'). According to this more preferred embodiment, starting from an aldehyde of formula (XIa), it is produced an a-ketoamide of formula (XVIIIa):

With the proper choice of the substituents and of configuration at the stereogenic centers present in the structure shown above, the a-ketoamide of formula (XVIIIa) can represent both Telaprevir and Boceprevir. In particular, with the stereogenic centers having the suitable configuration, Telaprevir is a compound of formula (XVIIIa) in which n = 1, R⁵ is /? -propyl, R⁸ = R⁹ are hydrogen, and R¹⁷ is cyclopropyl, while Boceprevir is a compound of formula (XVIIIa) in which n = 0, R⁵ is cyclobutylmethyl, R⁸ = R⁹ are methyl, and R¹⁷ is hydrogen, choosing the appropriate R².

An a-ketoamide of formula (XVIIIa) can be prepared from an aldehyde of formula (XIa) according to two alternative routes, the first one comprising operations e) and f), the second one comprising steps g) to j).

According to the first option, aldehyde (XIa) is transformed into an a-ketoamide (XVIIIa) via the following two operations:

e) preparing a hydroxyamide of formula (XHIa):

f) converting the hydroxyamide of formula (XHIa) into the α-ketoamide of formula (XVIIIa);

Operation e) can be carried out according to two alternative routes of synthesis, e.i) and e.ii).

The reaction pathway e.i) comprises the following steps:

e.i. l) conversion of the aldehyde of formula (XIa) into an acyloxyamide of formula (Xlla) by treatment with an isocyanide (R¹⁰NC) and a carboxylic acid of form ⁷C0₂H), via a Passerini reaction:

e.i.2) converting the acyloxyamide of formula (Xlla) into the hydroxyamide of formula (XHIa).

Step e.i. l) entails the preparation of an acyloxyamide of formula (Xlla) according to the Passerini reaction conditions as described above with reference to step a.i. l) of the process, replacing the carboxylic acid of formula (R²C0₂H) and the isocyanide of formula (R³NC) respectively with a carboxylic acid of formula (R⁷C0₂H) and an isocyanide of formula (R¹⁰NC), wherein R¹⁰ has the meaning given above and R⁷ is a Ci-C₆ linear or branched alkyl optionally substituted with a C₆-Cio aryl (such as, e.g. methyl or benzyl), or an optionally substituted C₆-Cio aryl (such as phenyl).

Step e.i.2) consists in the conversion of acyloxyamide (Xlla) into the hydroxyamide of formula (XHIa). Said step is carried out using one of the conditions generally known in the field, such as, for example, those described hereinbefore for the preparation of the azido alcohol of formula (V).

Reaction pathway e.ii) is a single-step reaction, and involves the preparation of the hydroxyamide of formula (XHIa) through a truncated Passerini reaction by treating the aldehyde of formula (XIa) with an isocyanide of formula (R¹⁰NC) in presence of an acid, for instance pyridinium trifluoroacetate or, preferably, boric acid.

When n = 0 and R⁸ and R⁹ = C¾, the isocyanide of formula (R¹⁰NC) useful for the reaction is one of the convertible isocyanides (i.e. an isocyanide wherein R¹⁰ is a group that can be easily transformed into H after the multicomponent reaction, such as Passerini or Ugi reaction) known to the skilled person such as, for example, tert- butylisocyanide (as described in Organic & Biomolecular Chemistry, 2010, 8(16), 3631- 3634), the l-(acyloxy)-2-isocyanobenzenes (as detailed in Journal of American Chemical Society, 2006, 128(36), 1 1772-1 1773), l-(silyloxymethyl)-2-isocyanobenzene (as detailed in Journal of Organic Chemistry, 1999, 64(2), 336-337) or one of the convertible isocyanides as described in Topics Heterocyclic Chemistry, 2010, 23, 1-39. The thus obtained hydroxyamide (XHIa) is then converted, in operation f) of the method, into the a-ketoamide of formula (XVIIIa), according to three possible synthesis routes f.i), f.ii) and f.iii).

Synthetic route f.i) may be followed when n = 0, R⁸ = R⁹ = C¾ and R¹⁰ is not cyclopropyl, and comprises two steps:

f.i. l) oxidation of the hydroxyamide of formula (XHIa) to yield an α-ketoamide of formula (XlVa):

f.i.2) deprotection of the α-ketoamide of formula (XlVa) to yield an α-ketoamide of formula (XVIIIa). The oxidation of step f.i. l) may be achieved with a variety of known oxidizing reagents, such as, for example, Dess-Martin periodinane ( 1,1 -dihydro- 1,1,1 -triacetoxy- 1,2- benzoiodooxol-3(lH)-one), TEMPO and sodium hypochlorite (optionally in the presence of sodium or potassium bromide) or the use of dimethyl sulfoxide (DMSO) activated by the sulfur trioxide pyridine complex in the presence of a tertiary amine. Step f.i.2) entails the deprotection of a-ketoamide of formula (XlVa) to yield the a- ketoamide (XVIIIa), by removing the substituent derived by the convertible isocyanides used, with one of the methods known in the field, such as those described in the documents cited above.

8 9 10 17

Synthetic route f.ii) may be followed when n = 0, R = R = C¾ and R and R are not cyclopropyl, and comprises two steps:

f.ii.l) deprotection of the hydroxyamide of formula (Xllla) to yield a hydroxyamide of formula (XVIIa):

f.ii.2) oxidation of the hydroxyamide of formula (XVIIa) to yield a a-ketoamide of formula (XVIIIa).

The conditions for carrying out the deprotection and oxidation reactions of synthesis route f.ii) are the same as in synthesis route f.i).

8 9 10 17

Finally, synthetic route f.iii) may be followed when n = l, R = R = H and R = R are cyclopropyl, and consists in a single-step oxidation below:

carried out with one of the methods detailed above.

The alternative synthetics route for converting aldehyde (XIa) into an a-ketoamide (XVIIIa) comprises steps g) to j), and is summarized in the scheme below:

In step g), the preparation of the cyanohydrin of formula (XVa) is achieved by reacting the aldehyde of formula (XIa) with a cyanide, such as sodium or potassium cyanide and optionally in the presence of an acid, organic or inorganic, such as hydrochloric acid or acetic acid. Alternatively the cyanohydrin of formula (XVa) can be prepared reacting the aldehyde of formula (XIa) with a trialkylsilyl cyanide, optionally generated in situ, such as trimethylsilyl cyanide, or by treatment with a cyanohydrin, such as, for example, acetone cyanohydrin, in the presence of a base.

In step h), the cyanohydrin of formula (XVa) is converted into the a-hydroxyacid of formula (XVIa) using one of the generally known methods, for example, in the presence of HC1 in a suitable solvent, such as dioxane, at a temperature comprised in the range between 50 and 110 °C.

Alternatively said step can be carried out using a biocatalyst, such as a nitrilase (i.e. an enzyme that transforms directly a nitrile into the corresponding carboxylic acid).

In step i), the a-hydroxyacid (XVIa) is coupled with an amine of general formula (R¹⁷NH₂) to yield the hydroxy amide of formula (XVIIa) using one of the conditions generally known in the field, such as, e.g. those reported to perform operation a.ii.3) to prepare a δ-acylamino-a-hydroxyamide of formula (VIII).

Finally, in step j), the hydroxyamide of formula (XVIIa) is oxidized with one of the methods described hereinbefore to provide the a-ketoamide of formula (XVIIIa).

When the N-acyl bicyclic prolinamides of formula (IX), or anyone of the compounds described herein, is obtained with a chemical and/or isomeric purity not satisfactory for the purpose of being included in a medicament, the synthetic pathway of the invention includes a purification step, for example by chromatographic purification or by crystallization, optionally after formation of an addition compound, such as a salt or a co-crystal.

Another embodiment of the present invention is the preparation of the isocyanide of formula (R¹⁰NC) suitable for steps e.i. l) and e.ii) described above. When R¹⁰ = cyclopropyl, the isocyanide can be prepared via dehydration of N-cyclopropylformamide, reacting it with methyl N-(methoxycarbonyl)-N- [(triethylammonium)sulfonyl]azanide (commonly referred to as the Burgess reagent) or one of the Burgess-type reagents of general formula (XIX):

( ix)

wherein R²¹ is a Ci-C₆ linear or branched alkyl optionally halogen substituted (preferably methyl ethyl, isopropyl, tert-butyl and 2,2,2-trifluoroethyl); and R²² is a cyclic or acyclic tertiary amine such as tributylamine, triethylamine, 1 ,4- diazabicyclo[2.2.2]octane (DABCO), N,N-diisopropylethylamine, N-methylmorpholine, N-methylpiperidine.

The Burgess or Burgess-type reagents can be prepared using, for instance, the procedure described in the Journal of the American Chemical Society (2004), 126(20), 6234.

Such reagents can be used in the subsequent dehydration (i.e. the reaction with N- cyclopropylformamide leading to cyclopropyl isocyanide) in isolated and purified form; or, alternatively, in mixture with the hydrochloride of the tertiary amine used for their preparation or without isolation in a one-pot operation.

Such dehydration is normally carried out in an aprotic solvent, such as a chlorinated solvent (preferably dichloromethane), an ester, such as ethyl acetate or isopropyl acetate, or a nitrile (preferably acetonitrile) at a temperature comprised in the range between 0 °C and the reflux temperature of the solvent, preferably at room temperature.

The reaction mixture resulting from the dehydration step can be conveniently used as such in the Passerini reaction as described in the steps e.i. l) and e.ii) without the isolation of the cyclopropyl isocyanide.

Further embodiments of the present invention are the compound (VII), (Vila), (Vllb), (Vlld), (Vile), (VIII), (Villa), (Vlllb), (IXa), (Xa), (XIa) and (XII), as defined above and the enantiomerically enriched isomers thereof.

The invention will be further illustrated by means of the following examples.

EXAMPLE 1

Preparation of ((15',2i?)-2-(hydroxymethyl)cyclopentyl)methyl acetate (2).

HO AcO

meso-(l) (2)

To a solution of meso-diol (1) (obtained by LiAlH₄ reduction of cz^'s-cyclopentane-1,2- dicarboxylic anhydride¹) (5.00 g, 38.4 mmol, 87% GC purity) in vinyl acetate (190 mL) cooled to 0 °C, powered 3 A molecular sieves (0.50 g) and Lipase Amano PS supported on Celite^® as described in the literature² (3.25 g, 1 g of this supported enzyme corresponds to 0.23 g of crude Lipase) are added. The reaction mixture is stirred at 0 °C for 17 h, then filtered through a sintered funnel and washed with CH₂CI₂ (100 mL). The filtrate is concentrated and the residue is purified by flash chromatography eluting with hexanes-Et₂0 (2: 1→1 :3) to give (2) (5.83 g, 88 %, e.e. 97%) as an oil. R_f = 0.36 (hexanes:Et₂0 1 :2).

GC-MS (HP-1 column, 12 m long, 0.2 mm wide, flow: 1 mL/min) (initial T: 70 °C, initial time: 2 min; rate: 20 °C/min): R_t 5.77 min.

The e.e. (97%) is determined by 1H-NMR by Mosher ester analysis.

1H-NMR (CDCI₃): 1.36-1.87 (6 H, m), 1.98 (1 H, broad s), 2.07 (3 H, s), 2.23 (1 H, hexuplet, J = 7.4), 2.35 (1 H, hexuplet, J = 7.2), 3.56 and 3.66 (2 H, AB part of an ABX system, J_AB = 10.9, J_AX = 6.8; J_BX = 7.5), 4.03 and 4.12 (2 H, AB part of an ABX system, J_AB = 11.0, J_Ax = 6.9; J_BX = 7.4).

¹³C-NMR (CDCI₃): 21.0, 23.0, 27.9, 28.8, 39.7, 44.0, 63.2, 65.2, 171.2.

1 Padwa A. et al., J. Org. Chem. (1989), 54, 817-824

2 Banfi L. et al, Tetrahedron: Asymmetry (1995), 6, 1345.

EXAMPLE 2

Preparation of ((15',2i?)-2-(azidomethyl)cyclopentyl)methyl acetate (4).

(2) (3) (4)

A solution of monoacetate (2) (5.75 g, 33.4 mmol) in dry CH₂CI₂ (80 mL) is cooled to 0 °C and treated with Et₃N (6.0 mL, 43.0 mmol) and methanesulfonyl chloride (3.1 mL, 40.1 mmol). The mixture is allowed to reach room temperature, kept 1 h at this temperature, then quenched with a saturated aqueous solution of NH₄CI and extracted with CH₂CI₂. The combined organic phases are washed with water, brine, dried over anhydrous sodium sulfate, and concentrated to give the crude mesylate (3) (8.35 g) as an oil. R_f = 0.51 (Hexane/CH₂C1₂/Et₂0 2:2: 1). The latter is taken up in dry DMF (60 mL), treated with NaN₃ (5.42 g, 83.4 mmol), stirred for 17 h at 90 °C, then diluted with H₂0 and extracted with Et₂0. The combined organic phases are washed with brine, dried over anhydrous sodium sulfate and concentrated. The crude product (4) (6.4 g, 97%) could be used in the next step without further purification. An analytical sample (50 mg) is purified by flash chromatography eluting with hexanes:Et₂0 (7:2) to give (4) (48 mg) as an oil. Rf = 0.51 (hexanes:Et₂0 3: 1).

GC-MS (HP-1 column, 12 m long, 0.2 mm wide, flow: 1 mL/min) (initial T: 70 °C, initial time: 2 min; rate: 20 °C/min): R_t 6.28 min.

1H-NMR (CDCI3): 1.40-1.91 (6 H, m), 2.07 (3 H, s), 2.26 (1 H, hexuplet, J = 7.3), 2.34 (1 H, hexuplet, J = 7.0), 3.22 and 3.37 (2 H, AB part of an ABX system, J_AB = 12.2, J_AX = 8.0; J_BX = 6.7), 4.03 (2 H, apparent d, J = 7.2).

1³C-NMR (CDC1₃): 20.9, 22.8, 28.3, 29.2, 40.1, 41.1, 52.2, 64.6, 171.0.

EXAMPLE 3

Preparation of ((15',2i?)-2-(azidomethyl)cyclopentyl)methanol (5).

AcO HO

(4) (5)

To a solution of (4) (6.35 g, 32.2 mmol) in MeOH (60 mL) is added a 1 M solution of KOH in MeOH (48.5 mL, 48.5 mmol) at room temperature. The reaction mixture is stirred at room temperature for 1 h, then treated with a saturated aqueous NH₄CI and most of the MeOH is evaporated. The pH is adjusted to 5-6 by addition of 1 N HCl, then the aqueous phase is extracted with AcOEt, washed with brine, dried over anhydrous sodium sulfate and concentrated to give the azidoalcohol (5) (4.90 g, 98%). The crude product could be used in the next step without further purification. An analytical sample is purified by flash chromatography eluting with with 3: 1 hexanes:Et₂0 to give (5) as an oil. R_f = 0.2 (hexanes:Et₂O 3:l).

[a]_D = +2.69 (c = 1.45, CHCI3)

GC-MS (HP-1 column, 12 m long, 0.2 mm wide, flow: 1 mL/min) (initial T: 70 °C, initial time: 2 min.; rate: 20 °C/min): R_t 5.44 min.

1H-NMR (CDCI3): 1.31-1.90 (7 H, m), 2.22 (1 H, centre of m), 2.28 (1 H, hexuplet, J = 7.2), 3.29 and 3.45 (2 H, AB part of an ABX system, J_AB = 12.3, J_AX = 6.9; J_BX = 7.8), 3.54-3.67 (2 H, m).

¹³C-NMR (CDCI3): 23.1, 27.8, 29.7, 40.9, 44.0, 52.6, 63.1.

EXAMPLE 4

Preparation of (15',2i?)-2-(azidomethyl)cyclopentanecarbaldehyde (6).

(5) (6)

To a solution of DMSO (0.6 mL, 8.4 mmol) in dry CH₂C1₂ (20 ml), at -78 °C under nitrogen atmosphere, a solution of oxalyl chloride in dry CH₂C1₂ (1.43 M, 4.7 mL, 6.7 mmol) is added. The solution is stirred for approx. lO min, until effervescence ceased. A solution of (5) (0.50 g, 3.2 mmol) in dry CH₂C1₂ is added dropwise, and the solution is stirred for 10 min at -78 °C. Triethylamine (2.1 mL, 15.1 mmol) is then added and the solution is stirred for 1 h at the same temperature. After this time the reaction mixture at -78 °C is poured into a 5% aqueous solution of (NH₄)H₂P0₄ (100 mL + 5 mL 1 N HCl solution) to have a final pH = 4, and the product is extracted with Et₂0. The organic layer is washed with a saturated aqueous solution of NaHC0₃, followed by water and brine, dried over anhydrous sodium sulfate and co-evaporated with CH₂C1₂ to have a final solution of (6) (3.22 mmol) in ca. 1.1 mL of CH₂C1₂.

EXAMPLE 5

Preparation of (25)-2-(2-((15',2i?)-2-(azidomethyl)cyclopentyl)-2-hydroxyacetamido) pentyl benzoate (7).

To a stirred solution of aldehyde (6) (0.4 mL of a 2.92 M solution in CH₂C1₂, 1.2 mmol) and (iS)-2-isocyanopentyl benzoate (15) (300 mg, 1.4 mmol) in dry CH₃CN (0.5 mL) is added boric acid (85 mg, 1.4 mmol). The reaction mixture is stirred at room temperature for 15 h, then concentrated. The residue is purified by flash chromatography eluting with hexanes-AcOEt (3 : 1→2: 1) to give (7) (431 mg, 92% combined yield) as a mixture of diastereoisomers (Ratio a/b = 66.3 : 33.7 by HPLC analysis). (7a) R_f = 0.34 (hexanes:AcOEt 3 : 1), (7b) R_f = 0.23 (hexanes:AcOEt 3 : 1).

Analytical data for diastereoisomer (7a):

[<x]_D = +13.9 (c = 1.09, CHC1₃)

1H-NMR (CDCI3): 0.96 (3 H, t, J = 7.2), 1.33-1.79 (10 H, m), 2.29 (1 H, centre of m), 2.45 (1 H, dq, J = 8.4, 2.7), 3.30 (1 H, centre of m), 3.50 and 3.51 (2 H, AB part of an ABX system, J_AB = 12.6, J_AX = 3.3; J_BX = 9.6), 4.27-4.39 (4 H, m), 6.64 (1 H, broad d, J = 7.5), 7.45 (2 H, centre of m), 7.57 (1 H, tt, J = 7.4, 1.4), 8.02-8.05 (2 H, m).

1³C-NMR (CDCI3): 13.9, 19.1 , 23.4, 23.8, 30.3, 33.8, 41.6, 44.4, 48.1 , 52.8, 66.4, 71.4, 128.4, 129.7, 129.8, 133.2, 166.6, 173.0.

EXAMPLE 6

Preparation of (5)-2-((i?)-2-((l_lS,2i?)-2-(((5)-2-((tert-butoxycarbonyl)amino)-3,3- dimethylbutanamido)methyl)cyclopentyl)-2-hydroxyacetamido)pentyl benzoate (8a).

To a stirred solution of (7a) (163 mg, 0.42 mmol) in dry THF (4 mL) at 70 °C triphenylphosphine (121 mg, 0.46 mmol) is added. After 1 hour, H₂0 (160 μί) is added and stirring is continued for 2 h. Then the solution is cooled at room temperature, treated with N-methylmorpho line (NMM) (184 μί, 1.67 mmol), L-Boc-t-Leucine (107 mg, 0.46 mmol) and PyBOP (241 mg, 0.46 mmol). The reaction mixture is stirred at room temperature for 24 h, then quenched with a saturated aqueous solution of NH₄C1 and most of the THF is evaporated. The aqueous phase is extracted with AcOEt, washed with saturated aqueous NaHC0₃, brine, dried (Na₂S04), and concentrated. The crude product is purified by flash chromatography eluting with 1 : 1 hexanes: AcOEt to give (8a) (188 mg, 78%) as an amorphous solid. R_f = 0.46 (hexanes: AcOEt 1 : 1).

[a]_D = +8.47 (c = 1.075, CHC1₃)

1H-NMR (CDC1₃): 0.94 (3 H, t, J = 7.2), 0.99 (9 H, s), 1.34-1.68 (10 H, m), 1.41 (9 H, s), 2.19 (1 H, centre of m), 2.29 (1 H, m), 3.22 (1 H, centre of m), 3.49 (1 H, centre of m), 3.73 (1 H, d, J = 9.0), 4.22 (1 H, t, J = 5.1), 4.27-4.39 (3 H, m), 4.48 (1 H, d, J = 5.1), 5.46 (1 H, broad d, J = 9.0), 6.85-6.96 (2 H, m), 7.44 (2 H, centre of m), 7.57 (1 H, tt, J = 7.2, 1.5), 8.01-8.06 (2 H, m).

¹³C-NMR (CDC1₃): 13.9, 19.1, 23.3, 24.6, 26.6, 28.3, 30.7, 33.6, 34.2, 40.3, 41.5, 44.6, 48.1, 62.9, 66.4, 71.4, 79.9, 128.4, 129.7, 129.8, 133.1, 156.2, 166.5, 171.1, 174.3.

EXAMPLE 7

Preparation of (5)-2-((i?)-2-((l_lS,2i?)-2-(((5)-2-((t-butoxycarbonyl)amino)-3,3- dimethylbutanamido) methyl) cyclopentyl)-2-((methylsulfonyl) oxy) acetamido) pentyl benzoate (9a).

A solution of (8a) (99 mg, 0.17 mmol) in dry CH₂C1₂ (2 mL) is cooled to 0 °C and treated with Et₃N (62 μΕ, 0.44 mmol) and methanesulfonyl chloride (32 μΕ, 0.41 mmol). The mixture is allowed to warm to room temperature in 1 h, then is quenched with a saturated aqueous solution of NH₄CI and extracted with CH₂C1₂. The combined organic phases are washed with brine, dried (Na₂S04), and concentrated to give the crude mesylate (9a) (120 mg, quant, yield) as an amorphous solid. R_f = 0.67 (hexanes: AcOEt 1 : 1). The crude product could be used in the next step without further purification. Selected data:

1H-NMR (CDC1₃): 0.95 (3 H, t, J = 7.2), 0.97 (9 H, s), 1.36-1.82 (10 H, m), 1.43 (9 H, s), 2.19 (2 H, centre of m), 3.07 (3 H, s), 3.24 (2 H, centre of m), 3.81 (1 H, d, J = 9.0), 4.30-4.47 (3 H, m), 5.11 (1 H, d, J = 8.1), 5.19 (1 H, broad d, J = 9.0), 6.65 (1H, broad d, J = 7.8), 7.22 (1 H, broad s), 7.45 (2 H, centre of m), 7.58 (1 H, tt, J = 7.5, 1.2), 8.01- 8.06 (2 H, m).

EXAMPLE 8

Preparation of (5)-2-((15',3ai?,6a5)-2-((5)-2-((tert-butoxycarbonyl)amino)-3,3- dimethylbutanoyl) octahydrocyclopenta[c]pyrrole-l-carboxamido) pentyl benzoate (10a

To a solution of crude mesylate (9a) (112 mg, 0.17 mmol) in dry DMF (1.7 mL) at 0 °C, sodium hydride (14 mg, 0.34 mmol, 60% of a dispersion in mineral oil) is added. The mixture is stirred for 1 h at 0 °C, then treated with saturated aqueous NH₄C1 and extracted with CH₂CI₂. The combined organic phases are washed with brine, dried (Na₂S0₄), and concentrated. The crude product is purified by flash chromatography eluting with hexanes-AcOEt (4: 1→3: 1) to give (10a) (74 mg, 78%) as an amorphous solid. R _f = 0.65 (hexanes:AcOEt 2: 1).

[a]_D = -24.2 (c = 1.06, CHC1₃)

1H-NMR (CDCI₃): 0.91 (3 H, t, J = 7.2), 0.99 (9 H, s), 1.33-1.72 (8 H, m), 1.42 (9 H, s), 1.75-1.89 (2 H, m), 2.80 (1 H, centre of m), 2.95 (1 H, centre of m), 3.67-3.78 (2 H, m), 4.26-4.42 (5 H, m), 5.22 (1 H, d, J = 9.9), 6.85 (1 H, broad d, J = 8.1), 7.42-7.48 (2 H, m), 7.57 (1 H, tt, J = 7.5, 1.2), 8.05-8.09 (2 H, m).

¹³C-NMR (CDCI₃): 13.8, 19.1, 25.4, 26.3, 28.2, 31.8, 32.1, 33.9, 35.2, 43.1, 44.7, 48.1, 54.2, 58.2, 66.2, 66.4, 79.6, 128.4, 129.7, 129.9, 133.1, 155.8, 166.4, 170.8, 171.8.

EXAMPLE 9

Preparation of tert-butyl ((5)-l-((15',3ai?,6a5)-l-(((5)-l-hydroxypentan-2-yl) carbamoyl) hexahydrocyclopenta[c]pyrrol-2( 1 H)-yl) -3 ,3-dimethyl- 1 -oxobutan-2-yl) carbamate (11a).

To a solution of (10a) (126 mg, 0.22 mmol) in MeOH (2 mL) at room temperature, potassium carbonate (37 mg, 0.27 mmol) is added. The reaction mixture is stirred at room temperature for 2 h, then quenched with saturated aqueous NH₄C1 and extracted with AcOEt. The combined organic phases are washed with brine, dried over anhydrous Na₂S0₄, and concentrated. The crude product is purified by flash chromatography eluting with 3: 1 AcOE hexanes to give (11a) (94 mg, 94%) as an amorphous solid. R_f = 0.32 (AcOEthexanes 3:1).

[<x]_D = -95.39 (c = 1.11, CHCI3)

1H-NMR of major conformer (major/minor ~ 10: 1) (CDC1₃): 0.89 (3 H, t, J = 7.2), 0.99 (9 H, s), 1.29-1.76 (8 H, m), 1.42 (9 H, s), 1.82-1.95 (2 H, m), 2.86 (1 H, centre of m),

2.99 (1 H, centre of m), 3.54-3.78 (5 H, m), 3.82-3.90 (2 H, m), 4.30 (1H, d, J = 10.2),

4.40 (1 H, d, J = 2.7), 5.22 (1 H, d, J = 9.9), 6.78 (1 H, broad d, J = 7.2).

¹³C-NMR (CDCI3): 13.9, 19.3, 25.4, 26.3, 28.2, 31.7, 32.1, 33.1, 35.3, 43.1, 45.1, 52.1,

53.0, 58.3, 65.4, 66.6, 79.7, 155.8, 171.8, 171.9.

EXAMPLE 10

Preparation of tert-butyl ((5)-3,3-dimethyl-l-oxo-l-((15',3ai?,6a5)-l-(((5)-l-oxopentan- 2-yl) carbamoyl) hexahydrocyclopenta[c]pyrrol-2(lH)-yl) butan-2-yl) carbamate (12a).

A solution of alcohol (lla) (60 mg, 132 μιηοΐ) in dry CH₂C1₂ (1.2 mL) is cooled to 0 °C and treated with Dess-Martin periodinane (62 mg, 146 μιηοΐ). The mixture is stirred at 0 °C for 2 h, then treated with a saturated aqueous solution of NaHCC>3 and 0.5 M solution of Na₂S₂03, and extracted with CH₂C1₂. The combined organic phases are dried over anhydrous Na₂S0₄ and concentrated. The crude product is purified by flash chromatography eluting with 1 : 1 AcOEthexanes to give (12a) (51 mg, 85%) as an oil . R_f = 0.77 (AcOEthexanes 3: 1)

1H-NMR of major conformer (major/minor ~ 20: 1) (CDC1₃): 0.91 (3 H, t, J = 7.2), 0.98 (9 H, s), 1.33-1.97 (10 H, m), 1.43 (9 H, s), 2.83 (1 H, centre of m), 2.99 (1 H, centre of m), 3.51-3.79 (2 H, m), 4.31 (1H, d, J = 10.2), 4.42 (1 H, centre of m), 4.48 (1 H, d, J = 3.0), 5.25 (1 H, broad d, J = 9.9), 7.20 (1 H, broad d, J = 6.6), 9.55 (1 H, d, J = 0.6).

¹³C-NMR (CDC1₃): 13.8, 18.5, 25.3, 26.3, 28.2, 31.0, 31.7, 32.1, 35.3, 43.1, 45.1, 54.2, 58.2, 58.5, 66.1, 79.6, 155.8, 171.6, 171.8, 199.5.

EXAMPLE 11

Preparation of (5)-N-( -hydroxypentan-2-yl)formamide (13).

A solution of L-Norvalinol (12) (14.90 g, 144.4 mmol) in ethyl formate (75 mL) is refluxed until complete disappearance of (12) monitoring the reaction by GC.

Ethyl formate is evaporated under reduced pressure and the residue is purified by crystallisation from AcOEt to give (13) (13.30 g, 70%) as colourless low-melting solid. GC method (HP-1 column, 30 m long, 0.3 mm wide, flow: 1 mL/min) (120 °C for 3 min, from 120 to 190 °C at 10 °C/min; from 190 to 250 °C at 30 °C/min): R_t (12) 3.4 min, R_t (13) 6.1 min.

EXAMPLE 12

Preparation of (5)-2-formamidopentyl benzoate (14).

A solution of (13) (4.30 g, 32.8 mmol) in dichloromethane (43 mL) is cooled to -15 °C and N-ethyldiisopropylamine (6.8 mL, 39.7 mmol) and 4-dimethyaminopyridine (0.20 g, 1.6 mmol) are consecutively added keeping the temperature below -10 °C. Afterwards, benzoic anhydride (7.40 g, 32.7 mmol) is added in small portions keeping the temperature below -10 °C. After complete addition the mixture is stirred overnight at -10 °C. After complete conversion (monitoring by GC using the method detailed in example 11, R_t 12.8 min) the mixture is cooled to room temperature and quenched with water and saturated aqueous NaHC0₃. The phases are separated and the organic phase is dried over anhydrous sodium sulfate and filtered. The solution obtained is concentrated under vacuum and the residue is crystallized from diisopropyl ether to afford (14) (6.96 g, 90%) as white solid.

1H NMR (CDCls) δ 8.20 & 8.10 (bs, d, J = 1 1.8 Hz, 1H overall, 2 NH rotamers), 8.05- 7.97 (m, 2H), 7.60-7.52 (m, 1H), 7.48-7.39 (m, 2H), 5.95-5.75 (m, 1H, 2 NH rotamers), 4.50-4.16 (m, 3H), 1.68-1.30 (m, 4H), 1.00-0.90 (m, 3H).

EXAMPLE 13

Preparation of (5)-2-isocyanopentyl benzoate (15).

A solution of (14) (37.00 g, 157.9 mmol) in dichloromethane (740 mL) is cooled to -40 °C. Triethylamine (TEA) (73.16 g, 723.0 mmol) and POCl₃ (36.18 g, 236.0 mmol) are successively added, keeping the temperature below -30 °C.

After 2 hours the mixture is warmed to room temperature and quenched with a saturated aqueous solution of NaHC0₃. The phases are separated and the organic phase is dried over anhydrous sodium sulfate, the solvent is concentrated under vacuum to give the crude product (15) (quantitative yield) as an orange oil.

1H NMR (CDCI3) δ 8.12-8.0 (m, 2H), 7.64-7.56 (m, 1H), 7.51-7.42 (m, 2H), 4.47-4.30 (m, 2H), 3.94 (bs, 1H), 1.83-1.41 (m, 4H), 0.99 (t, J = 6.5 Hz, 3H).

HPLC method

Column: XBridge BEH130 C18 150 x 4.6mm, 5μιη

Flow rate: 1.0 mL/min

Injection volume: 10 μΐ,

Wavelength channels A 210 nm & 340 nm

Column temperature: 40 °C

Mobile phase:

Phase A: H₂0-ACN-TFA Phase B: H₂0-ACN-TFA 10:90:0.1

Gradient:

Time Phase A (%) Phase B (%)

0 100 0

15 0 100

5 0 100

21 100 0

Equilibration time: 9 minutes

Run time: 21 minutes

Total analysis time: 30 minutes

Diluting solution: Acetonitrile/Water (1 : 1)

Retention times (min): (14) 9.40; (15) 12.66

EXAMPLE 14

Preparation of 2-((15',2i?)-2-(azidomethyl)cyclopentyl)-N-butyl-2-hydroxyacetamide (16).

To a stirred solution of aldehyde (6) (1.2 mL of a 0.6 M solution in CH₂C1₂, 0.70 mmol) and n-butyl isocyanide (88 μΐ,, 0.84 mmol) in dry CH₃CN (600 μΐ,) is added boric acid (52 mg, 0.84 mmol). The reaction mixture is stirred at room temperature for 48 h, then concentrated. The residue is purified by flash chromatography eluting with hexanes- AcOEt (2: 1→1 : 1) to give (16) (1 19 mg, 67% combined yield) as a mixture of diastereoisomers (Ratio a/b = 59.1 : 40.1).

(16a) R_f = 0.73 (hexanes :AcOEt 1 : 1); (16b) R_f = 0.59 (hexanes :AcOEt 1 : 1).

Analytical data for diastereoisomer 16a:

[<x]_D = +63.1 (c = 1.025, CHC1₃)

1H-NMR (CDC1₃): 0.93 (3 H, t, J = 7.2), 1.29-1.63 (8 H, m), 1.77 (2 H, centre of m), 2.31 (1 H, hexuplet, J = 7.5), 2.48 (1 H, dq, J = 8.4, 2.7), 3.28 (2 H, nonuplet, J = 6.6), 3.52 (2 H, centre of m), 3.59 (1 H, broad m), 4.31 (1 H, broad m), 6.62 (1 H, broad s).

13

C-NMR (CDC1₃): 13.7, 20.0, 23.5, 23.8, 30.4, 31.6, 38.9, 41.6, 44.2, 52.8, 71.2, 173.2. EXAMPLE 15

Preparation of (3S)-3 (lS a^,6aS)-2-((S)-2 (S)-2-cyclohexyl-2-( yrazine-2- carboxamido) acetamido) -3,3-dimethylbutanoyl) octahydrocyclopenta[c]pyrrole-l- carboxamido)-l-(cyclopropylamino)-l-oxohexan-2-yl acetate (19).

To a solution of alcohol (17) (3.00 g, 5.0 mmol) in dichloromethane (DCM; 30 mL), cooled at 0 °C, bis(acetoxy) iodobenzene (1.61 g, 5.0 mmol) and TEMPO (62 mg, 0.4 mmol) are added, keeping the temperature below 5 °C. The mixture is then allowed to warm to room temperature and stirred until complete conversion into aldehyde (18). To the above mixture are subsequently added acetic acid (286 μί, 5.0 mmol) and cyclopropyl isocyanide (402 mg, 6.0 mmol) and the mixture is stirred at room temperature overnight. When the reaction is judged completed (monitoring by TLC, DCM-MeOH 95:5 and HPLC), water is added. The phases are separated and the organic phases are dried over anhydrous sodium sulfate, and filtered.

The solution obtained is concentrated under vacuum to give the crude product (19) as a pale green oil as ca. 2: 1 mixture of acetate epimers by HPLC. The residue is purified by flash chromatography eluting with n-Hexane-AcOEt (60:40— 0: 100) to give (19) (1.95 g, 54%) as a colourless solid with spectral data in accordance with those reported by Orru et al. in Chemical Communications, 2010, 46(42), 7918-7920.

HPLC method

Column: Gemini NX 5μιη 110A C18 250x4,6mm Flow rate: l .O mL/min

Injection volume: 10 μΐ

Wavelength channel A: 210 nm

Wavelength channel B: 232 nm

Column temperature: 40 °C

Mobile phase:

Phase A: H7O-ACN-NH4OH 90: 10:0.1

Phase B: H20-ACN-NH₄OH 10:90:0.1

Gradient:

Time

(min) Phase A (%) Phase B (%)

0 100 0

25 0 100

35 0 100

36 100 0 Equilibration time: 9 minutes

Run time: 36 minutes

Total analysis time: 45 minutes

Diluting solution: Acetonitrile /Water (1 : 1)

Retention times (min): (17) 12.10; (18) 16.10; (19) 16.01 & 16.29 (acetate epimers) EXAMPLE 16

Preparation of tert-butyl ((25)-l-((((li?,25)-2-(2-(butylamino)-l-hydroxy-2-oxoethyl) cyclopentyl)methyl)amino)-3,3-dimethyl-l-oxobutan-2-yl)carbamate (21).

To a stirred solution of (16) (100 mg, 0.39 mmol) in dry THF (3 mL) at 70 °C triphenylphosphine (113 mg, 0.43 mmol) is added. After 2 h H₂0 (140 μί) is added and stirring is continued for 3 h. After this time the solution is cooled at room temperature, and treated with NMM (108 uL, 0.98 mmol), L-Boc-t-Leucine (99 mg, 0.43 mmol) and PyBOP (224 mg, 0.43 mmol). The reaction mixture is stirred at room temperature for 60 h, then treated with a saturated aqueous NH₄C1 and most THF is evaporated. The aqueous phase is extracted three times with AcOEt, washed with saturated aqueous NaHCC"3 and brine. The collected organic phases are dried over anhydrous sodium sulfate, and filtered. The solution obtained is concentrated under vacuum to give the crude product (21) which is purified by flash chromatography eluting with 1 : 1 hexanes:AcOEt with 1% MeOH to give (21) (104 mg, 60%) as an amorphous solid. Analytical data for diastereoisomer (21a):

[a]_D = +29.9 (c = 1.14, CHC1₃)

1H-NMR (CDCI₃): 0.92 (3 H, t, J = 7.2), 0.99 (9 H, s), 1.28-1.77 (10 H, m), 1.41 (9 H, s), 2.24 (1 H, centre of m), 2.33 (1 H, centre of m), 3.16-3.36 (3 H, m), 3.51 (1 H, centre of m), 3.76 (1 H, d, J = 9.0), 4.20 (1 H, t, J = 4.2), 4.64 (1 H, d, J = 5.1), 5.50 (1 H, broad d, J = 9.0), 6.92 (1 H, broad t, J = 5.7), 7.01 (1 H, broad s).

¹³C-NMPv (CDCI₃): 13.8, 20.0, 23.4, 24.6, 26.6, 28.3, 30.7, 31.6, 34.2, 38.9, 40.3, 41.6, 44.4, 62.9, 71.3, 79.9, 156.2, 171.1, 174.5.

EXAMPLE 17

Preparation of (25)-l-((15',2i?)-2-(azidomethyl)cyclopentyl)-2-(butylamino)-2-oxoethyl 2-((tert-butoxycarbonyl)amino)-3,3-dimethylbutanoate (23).

To a stirred solution of aldehyde (6) (2.0 mL of a 0.25 M solution in CH₂CI₂, 0.50 mmol), L-Boc-t-Leucine (127 mg, 0.55 mmol) and n-butyl isocyanide (58 μί, 0.55 mmol) are added. The reaction mixture is stirred at room temperature for 20 h, then concentrated. The residue is purified by flash chromatography eluting with hexanes- Et₂0 (3: 1→1 : 1) to give (23) (as an oil, 137 mg, 59%) as a mixture of diastereoisomers (Ratio a/b = 1 : 1.4). (23a) R_f = 0.61 (hexanes:Et₂0 1 : 1), (23b) R_f = 0.51 (hexanes:Et₂0 1 : 1).

Analytical data for diastereoisomer (23a): Ή-NMR (CDCls): 0.91 (3 H, t, J = 7.2), 1.04 (9 H, s), 1.32 (2 H, hexuplet, J = 7.2), 1.43 (9 H, s), 1.45-1.87 (8 H, m), 2.35-2.53 (2 H, m), 3.02 (1 H, centre of m), 3.17 (1 H, A part of an ABX system, J_AB = 12, J_AX = 9.3), 3.37 (1 H, centre of m), 3.74 (1 H, B part of an ABX system, J_AB = 12, J_BX = 5.4), 3.94 (1 H, d, J = 7.5), 5.02 (1 H, broad d, J = 7.5), 5.08 (1 H, d, J = 8.1), 6.90 (1 H, broad s).

1³C-NMR (CDCI3): 13.7, 20.0, 22.4, 26.7, 27.8, 28.2, 29.5, 31.4, 33.3, 39.0, 40.9, 44.3, 51.7, 62.8, 75.3, 80.7, 156.3, 169.1, 171.8.

Analytical data for diastereoisomer (23b):

1H-NMR (CDCI3): 0.91 (3 H, t, J = 7.2), 1.05 (9 H, s), 1.33 (2 H, hexuplet, J = 7.5), 1.43-1.83 (8 H, m), 1.46 (9 H, s), 2.34 (1 H, centre of m), 2.56 (1 H, centre of m), 3.10 (1 H, A part of an ABX system, J_AB = 12, J_Ax = 9.3), 3.25 (2 H, centre of m), 3.44 (1 H, B part of an ABX system, J_AB = 12, J_BX = 5.1), 4.02 (1 H, d, J = 8.1), 4.97 (1 H, d, J = 8.1), 5.02 (1 H, broad d, J = 8.1), 6.42 (1 H, broad s).

¹³C-NMR (CDCI3): 13.7, 19.9, 26.8, 28.3, 29.2, 31.3, 33.8, 39.1, 39.9, 43.7, 51.8, 62.6, 75.6, 80.5, 156.3, 168.7, 171.0.

EXAMPLE 18

Preparation of tert-butyl ((25)-l-((((li?,25)-2-(2-(butylamino)-l-hydroxy-2-oxoethyl) cyclopentyl)methyl)amino)-3,3-dimethyl-l-oxobutan-2-yl)carbamate (21).

To a stirred solution of (23) (40 mg, 85 μιηοΐ) in dry THF (1 mL) at 60 °C triphenylphosphine (25 mg, 95 μιηοΐ) is added. After 1 h H₂0 (10 μί) is added and stirring is continued for 4 h. After this time the solution is cooled at room temperature, and treated with Et₃N (2.5 μί, 18 μιηοΐ). The reaction mixture is stirred at room temperature for 60 h, then concentrated. The crude product is purified by flash chromatography eluting with 1 :3 hexanes:AcOEt to give (21) (11 mg, 29%) as an amorphous solid.

EXAMPLE 19

Preparation of l-((15',2i?)-2-(((5)-2-((tert-butoxycarbonyl)amino)-3,3- dimethylbutanamido)methyl)cyclopentyl)-2-(butylamino)-2-oxoethyl methanesulfonate (2

b=— OMs

A solution of (21) (83 mg, 19 μηιοΐ) in dry CH2CI2 (2 mL) is cooled to 0 °C and treated with Et₃N (68 μί, 49 μηιοΐ) and methanesulfonyl chloride (35 μί, 45 μmol). The mixture is allowed to reach room temperature in 2 h, then it is quenched with a saturated aqueous solution of NH₄C1 and extracted with CH2CI2. The organic phases are washed with brine, dried over anhydrous sodium sulfate, filtered and concentrated to give the crude mesylate (24) (110 mg, quant. Yield, ratio a:b = 58:42) as an amorphous solid. The crude product could be used in the next step without further purification.

EXAMPLE 20

Preparation of tert-butyl ((5)-l-((lS,3ai?,6a5)-l-(butylcarbamoyl) hexahydrocyclopenta[c]pyrrol-2(lH)-yl)-3,3-dimethyl-l-oxobut -2-yl)carbamate (25).

To a solution of crude mesylate (24) (19 μιηοΐ) in dry DMF (1 mL) at 0 °C is added sodium hydride (12 mg, 30 μιηοΐ, 60% of a dispersion in mineral oil). After 1 h the solution is quenched with a saturated aqueous of NH₄CI and extracted three times with CH2CI2. The combined organic phases are washed with brine, dried over anhydrous sodium sulfate, filtered and concentrated. The crude product is purified by flash chromatography eluting

with hexanes-AcOEt (2: 1→1 : 1) to give (25a) (30 mg, 37%) as an oil. R_f = 0.66 (hexanes:AcOEt 1 : 1). Analytical data for diastereoisomer 25a:

1H-NMR of major conformer (major/minor ~ 94:6) (CDC1₃): 0.89 (3 H, t, J = 7.2), 0.98 (9 H, s), 1.26-1.74 (8 H, m), 1.42 (9 H, s), 1.81-1.96 (2 H, m), 2.82 (1 H, centre of m), 3.03 (1 H, centre of m), 3.20 (2 H, centre of m), 3.67-3.78 (2 H, m), 4.31 (1 H, d, J = 10.1), 4.41 (1 H, d, J = 2.7), 5.20 (1 H, broad d, J = 10.1), 6.80 (1 H, broad s).

¹³C-NMR (CDCls): 13.7, 20.1, 25.5, 26.3, 28.2, 31.5, 31.9, 32.3, 35.3, 39.1, 43.1, 44.6, 54.2, 58.1, 66.2, 79.6, 155.7, 170.8, 171.6.

EXAMPLE 21

Preparation of (5)-2-((l_lS,3ai?,6a5)-2-((_lS)-2-((_lS)-2-cyclohexyl-2-(pyrazine-2- carboxamido) acetamido) -3,3-dimethylbutanoyl) octahydrocyclopenta[c]pyrrole-l- carboxamido) pentyl benzoate (26a).

To a solution of (10a) (74 mg, 0.13 mmol) cooled (0 °C) in CH₂C1₂ (2 mL) is added dropwise CF₃C0₂H (1 mL). The solution is allowed to reach room temperature in 1 h, then concentrated. The solution of the crude trifluoroacetate salt in dry CH₂C1₂ (2 mL) is treated with NMM (100 μί, 0.92 mmol), L-Boc-cyclohexylglycine (37 mg, 0.14 mmol) and PyBOP (83 mg, 0.16 mmol). The reaction mixture is stirred at room temperature for 2 h, then treated with a saturated aqueous NH₄CI and extracted with AcOEt, washed with a saturated aqueous NaHC0₃ and brine (20 mL), dried over anhydrous sodium sulfate, filtered and concentrated. The crude is purified by flash chromatography eluting with 2: 1 hexanes:AcOEt to give the coupling product (81 mg, 89%) as an amorphous solid. R_f = 0.43 (hexanes: AcOEt 2: 1). To a cooled (0 °C) solution of the coupling product in CH₂C1₂ (2 mL) is added dropwise CF₃C0₂H (1 mL). The solution is allowed to reach room temperature in 1 h, then concentrated. The solution of the crude trifluroacetate salt in dry CH₂C1₂ (2 mL) is treated with NMM (88 μί, 0.82 mmol), pyrazinecarboxylic acid (16 mg, 0.13 mmol) and PyBOP (73 mg, 0.14 mmol). The reaction mixture is stirred at room temperature for 2 h, then treated with a saturated aqueous NH₄C1 and extracted with AcOEt, washed with saturated aqueous NaHC0₃ and brine, dried over anhydrous sodium sulfate, filtered and concentrated. The crude is purified by flash chromatography eluting with 1 :2 hexanes:AcOEt to give the coupling product (26a) (69 mg, overall yield: 75%) as an amorphous solid. R_f = 0.4 (hexanes: AcOEt 1 :2). Ή-NMR (CDCls, 313 K): 0.89 (3 H, t, J = 7.2), 0.94-1.25 (6 H, m), 0.98 (9 H, s), 1.23-

1.74 (12 H, m), 1.85 (3 H, centre of m), 2.83 (1 H, centre of m), 2.94 (1 H, centre of m),

3.75 (2 H, centre of m), 4.29-4.39 (3 H, m), 4.42 (1 H, d, J = 2.4), 4.55 (1 H, dd, J = 9.0, 6.9), 4.76 (1 H, d, J = 9.6), 6.75 (1 H, broad d, J = 9.6), 6.85 (1 H, broad d, J = 8.1), 7.45 (2 H, tt, J = 8.1 , 1.2), 7.59 (1 H, tt, J = 7.5, 2.1) 8.06 (2 H, centre of m), 8.36 (1 H, broad d, J = 9.3), 8.55 (1 H, dd, J = 2.5, 1.5), 8.76 (1 H, d, J = 2.5), 9.43 (1 H, d, J = 1.5).

¹³C-NMR (CDCI₃, 313 K): 13.8, 19.1 , 25.5, 25.8, 25.9, 26.0, 26.4, 28.7, 29.6, 32.2, 32.4, 33.9, 35.7, 41.2, 43.0, 44.9, 48.08, 54.6, 56.6, 58.0, 66.3, 128.4, 129.7, 129.8, 133.1 , 142.7, 144.1 , 144.5, 147.4, 162.9, 166.5, 170.5, 170.6, 170.7.

EXAMPLE 22

Preparation of (15',3ai?,6a5)-2-((5)-2-((5)-2-cyclohexyl-2-(pyrazine-2-carboxamido) acetamido)-3,3-dimethylbutanoyl)-N-((5)-l-hydroxypentan-2-yl)octahydrocyclopenta

[c] pyrrole- 1-carboxamide (17).

To a solution of (26a) (59 mg, 0.08 mmol) in MeOH (2 mL) at room temperature, potassium carbonate (14 mg, 0.10 mmol) is added. The reaction mixture is stirred at room temperature for 3 h, then treated with a saturated aqueous solution of NH₄CI and extracted three times with AcOEt. The combined organic phases are washed with brine, dried over anhydrous sodium sulfate, filtered and concentrated. The crude product is purified by flash chromatography eluting with AcOEt-hexanes (5 : 1→ AcOEt) to give (17) (43 mg, 90%) as amorphous solid.

1H-NMR of major conformer (major/minor - 8 : 1) (CDC1₃, 313 K): 0.89 (3 H, t, J = 7.2), 0.95-1.97 (21 H, m), 0.98 (9 H, s), 2.88 (1 H, centre of m), 3.03 (1 H, centre of m), 3.58 (1 H, centre of m), 3.66-3.77 (3 H, m), 3.88 (1 H, m), 4.50 (1 H, d, J = 2.4), 4.66 (1 H, centre of m), 4.79 (1 H, d, J = 9.6), 6.87 (1 H, broad d, J = 6.3), 7.02 (1 H, broad s), 8.41 (1 H, broad d, J = 9.3), 8.54 (1 H, dd, J = 2.5, 1.5), 8.74 (1 H, d, J = 2.5), 9.52 (1 H, d, J = 1.5).

¹³C-NMPv (CDCI₃): 13.9, 19.3, 25.6, 25.8, 25.9, 26.0, 26.5, 28.8, 29.4, 32.4, 32.5, 33.2, 35.7, 41.4, 42.8, 44.8, 51.3, 54.9, 56.5, 57.5, 64.6, 66.1 , 142.7, 144.3, 144.8, 147.2, 162.8, 170.9, 171.0, 171.4.

HPLC method

Column: XBridge BEH130 C18 150x4,6mm 5μιη

Flow rate: 1.0 mL/min

Injection volume: 10 μΐ

Wavelength channels A: 210 nm & 232 nm

Column temperature: 40 °C

Mobile phase:

Phase A: H7O-ACN-TFA 90: 10:0.1

Phase B: H₂0-ACN-TFA 10:90:0.1

Gradient:

Time Phase A (%) Phase B (%)

0 100 0

25 0 100

35 0 100

36 100 0

Equilibration time: 9 minutes

Run time: 36 minutes

Total analysis time: 45 minutes

Diluting solution: Acetonitrile /Water (1 : 1)

Retention times (min): (17) 15.05; (26a) 20.60

EXAMPLE 23

Preparation of (5)-2-((15',3ai?,6a5)-2-((5)-2-((tert-butoxycarbonyl)amino)-3,3- dimethylbutanoyl) octahydrocyclopenta[c]pyrrole-l -carboxamido) pentyl benzoate (10a).

A solution of the bicyclic imine (28) (1.50 g, 13.7 mmol) in CH₂CI₂ (10 mL) is cooled to 0 °C. L-Boc-t-Leucine (3.17 g, 13.7 mmol) and (S)-2-isocyanopentyl benzoate (15) (2.98 g, 13.7 mmol) are added. The reaction mixture is warmed to room temperature and stirred for 18 h, then concentrated. The residue is purified by flash chromatography eluting with hexanes- AcOEt (4: 1→3 : 1) to give (10a) (6.05 g, 79%) as an amorphous solid.

The spectral data are identical to those recorded for the product obtained in Example 8.

EXAMPLE 24

Preparation of (15',3ai?,6a5)-N-butyl-2-((5)-2-((5)-2-cyclohexyl-2-(pyrazine-2- carboxamido)acetamido)-3 ,3-dimethylbutanoyl)octahydrocyclopenta[c]pyrrole- 1 - carboxamide (29a).

To a cooled (0 °C) solution of (25a) (84 mg, 200 μπιοΐ) in CH₂C1₂ (2 mL) is added dropwise CF₃C0₂H (1 mL). The solution is allowed to reach room temperature in 1 h, then concentrated. The solution of the crude trifluoroacetate salt in dry CH₂C1₂ (2 mL) is treated with NMM (152 μί, 1.4 mmol), L-Boc-cyclohexylglycine (56 mg, 220 μιηοΐ) and PyBOP (124 mg, 240 μιηοΐ). The reaction mixture is stirred at room temperature for 3.5 h, then treated with a saturated aqueous NH₄CI and extracted with AcOEt, washed with a saturated aqueous NaHC0₃ and brine dried over anhydrous sodium sulfate, filtered and concentrated. The crude product is purified by flash chromatography eluting with hexanes- AcOEt (2: 1→3 :2) to give the coupling product (101 mg, 90%) as an amorphous solid. R_f = 0.62 (hexanes: AcOEt 1 : 1). To a cooled (0 °C) solution of the coupling product in CH₂C1₂ (2 mL) is added dropwise CF₃C0₂H (1 mL). The solution is allowed to reach room temperature in 1 h, then concentrated. The solution of the crude trifluoroacetate salt in dry CH₂C1₂ (2 mL) is treated with NMM (139 μί, 1.24 mmol), pyrazinecarboxylic acid (24 mg, 190 μιηοΐ) and PyBOP (112 mg, 220 μιηοΐ). The reaction mixture is stirred at room temperature for 2 h, then treated with a saturated aqueous solution of NH₄C1 and extracted with AcOEt, washed with a saturated aqueous solution of NaHC0₃ and brine, dried over anhydrous sodium sulfate, filtered and concentrated. The crude is purified by flash chromatography eluting with hexanes- AcOEt (1 :2→1 :4) to give the coupling product (29a) (102 mg, 98%) as an amorphous solid. R_f = 0.28 (hexanes: AcOEt 1 : 1).

1H-NMR (CDC1₃): 0.89 (3 H, t, J = 7.2), 0.97 (9 H, s), 1.01-1.76 (18 H, m), 1.91 (3 H, centre of m), 2.85 (1 H, centre of m), 3.06 (1 H, centre of m), 3.21 (2 H, centre of m),

3.73 (2 H, centre of m), 4.44 (1 H, d, J = 2.7), 4.56 (1 H, dd, J = 9.0, 6.9), 4.74 (1 H, d, J

= 9.6), 6.68 (1 H, broad t, J = 5.4), 6.76 (1 H, broad d, J = 9.6), 8.35 (1 H, broad d, J =

9.0), 8.56 (1 H, dd, J = 2.5, 1.5), 8.76 (1 H, d, J = 2.5), 9.43 (1 H, d, J = 1.5).

¹³C-NMR (CDC1₃): 13.7, 20.1, 25.6, 25.8, 25.9, 26.0, 26.4, 28.7, 29.6, 31.6, 32.3, 32.5, 35.7, 39.2, 41.2, 43.0, 44.6, 54.6, 56.6, 57.9, 66.2, 142.7, 144.1, 144.5, 147.4, 162.9,

170.6, 170.7.

EXAMPLE 25

One-pot preparation of cyclopropyl isocyanide with in-situ formed Burgess reagent

Solution in DCM To a 0 °C solution of chlorosulfonyl isocyanate (582 mg, 4.1 mmol) in dichloromethane (1 mL) is added a solution of methanol (175 μΐ_^, 4.3 mmol) in dichloromethane (1 mL). After 30 minutes a solution of triethylamine (1.3 mL, 9.33 mmol) in dichloromethane (5 mL) is added during 30 minutes. To the resulting solution of the Burgess reagent is added a solution of cyclopropylformamide (350 mg, 4.1 mmol) in dichloromethane (1.5 mL) and the mixture is stirred at room temperature for 2 hours to obtain a solution in dichloromethane of cyclopropyl isocyanide. This solution can be used without any further purification in the procedure described in Example 15 in place of neat cyclopropyl isocyanide.

EXAMPLE 26

Preparation of (35)-3-((l_lS,3ai?,6a5)-2-((5)-2-((5)-2-cyclohexyl-2-(pyrazine-2- carboxamido) acetamido) -3,3-dimethylbutanoyl) octahydrocyclopenta[c]pyrrole-l- carboxamido -l-(cyclopropylamino)-l-oxohexan-2-yl acetate (19).

Alcohol (17) (4.48 g, 7.48 mmol) is dissolved in DCM (25 niL). To this solution DMSO (19 mL) and triethylamine (5.22 mL, 37.3 mmol) are added. The mixture is cooled to - 10 °C and a solution of S0₃-Pyridine complex (5.82 g, 36.6 mmol) in DMSO (18 mL) is added dropwise, keeping the temperature between -12 °C and -10 °C. After complete reaction (monitoring by HPLC) the reaction mixture is diluted with DCM and washed with water then with 0.1 N HCl, then water. The organic layer is dried over sodium sulphate and evaporated to a residue.

This residue is taken up in dichloromethane (7 mL) and added dropwise at 0 °C to a solution of cyclopropyl isocyanide (11.2 mmol) prepared according to the procedure described in Example 25. To the resulting reaction mixture is then added at 0 °C acetic acid (0.64 mL, 11.2 mmol). After 10 minutes the reaction mixture is warmed to room temperature and stirred at the same temperature for 18 hours. The reaction is diluted with DCM, then quenched adding a NaHC0₃ saturated solution. After phase separation the DCM solution is washed with a NaHC0₃ saturated solution followed by water. The organic phase is dried over sodium sulphate and concentrated to a residue, which is purified by flash chromatography eluting with n-Hexane-AcOEt (60:40— 0: 100) to give (19) (4.55 g, 84%) as a colourless solid.

EXAMPLE 27 Preparation of Burgess reagent in mixture with triethylamine hydrochloride

To a solution of chlorosulfonyl isocyanate (21.93 g, 154.95 mmol) in DCM (39 mL) at 0 °C is added a solution of MeOH (6.6 mL, 162.69 mmol) in DCM (39 mL) in about 1 hour.

When the addition is complete the reaction mixture is warmed to 20 °C and stirred for 30 minutes at the same temperature, then concentrated under vacuum to give the sulfamoyl chloride intermediate as a colorless solid which is taken up in toluene (305 mL) warming at 40 °C. This solution is added dropwise, in about 1 hour, to a solution of Et₃N (48.6 mL, 348.6 mmol) in toluene (105 mL) keeping the temperature between 25 -

30 °C.

After complete addition the suspension is cooled at 0 °C and after 1 hour filtered to give

53 g of the Burgess reagent containing 42% w/w of triethylamine hydrochloride by H

NMR.

EXAMPLE 28

Preparation of a solution of cyclopropyl isocyanide using Burgess reagent in mixture with triethylamine hydrochloride

To a solution of N-cyclopropylformamide (956 mg, 11.2 mmol) in DCM (6 mL) is added Burgess reagent in mixture with Et₃N-HCl prepared as described in Example 27 (4.67 g,l 1.24 mmoL).

The reaction is monitored by GC and complete conversion is achieved in about 2 hours. The DCM solution containing cyclopropyl isocyanide is used as such in the Passerini reaction with aldehyde (18).

GC Method: Column: DB 200, 30 m x 320 μιη x 0.5 μιη; Injector temp: 210 °C; Detector temp: 280 °C; Flow: 1 mL/min; Oven: 35 °C for 8 min, from 35 °C to 200 °C at 10 °C/min, from 200 °C to 280 °C at 40 °C/min, hold 8 min; Run time: 34.50 min; Split ratio: 50 : 1; Injection Volume: 1 uL R_t N-cyclopropylformamide: 19.35 min, R_t cyclopropyl isocyanide: 11.13 min.

Claims

1. Process for the preparation of N-acyl bicyclic prolinamides of general formula (IX), or their salts:

wherein, if n = 0, then R⁸ and R⁹ are C¾, and if n = 1, then R⁸ and R⁹ are hydrogen;

said process comprising the following operations:

a) preparing a δ-acylamino-a-hydroxyamide of formula (VIII):

cyclizing a δ-acylamino-a-hydroxyamide of formula (VIII) to provide a N- acyl bicyclic prolinamide of formula (IX) according to the following steps: b.l) preparing, starting from a compound of formula (VIII), an a-activated-5-acylamino amide of formula (Vlllb):

(Vlllb) b.2) cyclizing the a-activated-5-acylamino amide of formula (Vlllb) to produce the prolinamide of formula (IX),

wherein:

R is Ci-C₆ linear or branched alkyl or a Ci-C₆ linear or branched alkyl substituted with a Ci-C₆ cyclic alkyl;

R¹⁰ is cyclopropyl, or one of the removable groups of the convertible isocyanide;

R^{1 1} is a leaving group capable to undergo a nucleophilic substitution;

R¹⁵ is NH₂; NH-Pg; or NH-R ;

R¹⁶ is OH; OPg;

R¹⁷ is hydrogen or cyclopropyl;

R¹⁹ is OH; a Ci-C₆ linear or branched alkoxy; a Ci-C₆ linear or branched alkoxy substituted with a C₆-Ci₀ aryl; NH-R¹⁰; or NH-R¹⁷;

R²⁰ is hydrogen; a Ci-C₆ linear or branched alkyl; or a Ci-C₆ linear or branched alkyl substituted with a C₆-Cio aryl group; and

Pg is a protecting group; in the group -OPg in R¹⁶, it is an alcohol protecting group, while in the group -NH-Pg in R¹³ or in R¹⁵ it is a nitrogen protecting group.

Process according to claim 1 , wherein operation a) is carried out according to reaction pathway a.i), which comprises the following steps: conversion of an azido aldehyde of formula (VI) into a δ-azido-a- acyloxyamide of formula (VII) by treatment with an isocyanide (R³NC) and a carboxylic acid of formula (R²C0₂H), via a Passerini reaction:

a.i.2) reduction of the azido group to yield the compound of formula (Vlld); a.i.3) 0^→N acyl migration to provide a δ-acylamino-a-hydroxyamide of formula (VIII):

Process according to claim 1, wherein operation a) is carried out according to reaction pathway a.ii), which comprises the following steps:

a.ii. l) reacting an azido aldehyde of formula (VI) with an isocyanide (R³NC) and an acid to obtain a δ-azido-a-hydroxyamide of formula (Vllb):

(VI) (Vllb)

a.ii.2) reducing the azido group to yield the compound of formula (Vile);

a.ii.3) N-acylation to provide a δ-acylamino-a-hydroxyamide of formula (VIII):

Process according to any one of the preceding claims, in which it is prepared an aldehyde of formula (XIa):

according to the following steps:

a') preparing a δ-acylamino-a-hydroxyamide of formula (Villa):

a wherein the substituents have the meanings given above, using as the isocyanide R³NC, the isocyanide of formula (XII):

R 16

CN .

(XII)

b') cyclizing the δ-acylamino-a-hydroxyamide of formula (Villa) to provide a N-acyl bicyclic proline amide of formula (IXa):

c) when R¹⁶ is OPg, removing the protecting group Pg to obtain a N-acyl bicyclic proline (hydroxyalkyl)amide of formula (Xa):

d) oxidizing the N-acyl bicyclic proline (hydroxyalkyl)amide of formula (Xa) to provide an aldehyde of formula (XIa).

Process according to claim 4, in which the aldehyde (XIa) is further reacted to produce a a-ketoamide of formula (XVIIIa):

according to a synthetic route comprising the following operations

e) preparing a hydroxyamide of formula (Xllla):

f) converting the hydroxyamide of formula (Xllla) into the α-ketoamide of formula (XVIIIa).

Process according to claim 5 in which operation e) is carried out according to synthesis route e.i), comprising the following steps:

e.i. l) converting the aldehyde of formula (XIa) into an acyloxyamide of formula (Xlla) by treatment with an isocyanide (R¹⁰NC) and a carboxylic acid of formula (R⁷C0₂H), via a Passerini reaction:

converting the acyloxyamide of formula (Xlla) into the hydroxyamide of formula (Xllla),

wherein the substituents assume the meanings given above and R⁷ is a Ci-C₆ linear or branched alkyl, a Ci-C₆ linear or branched alkyl substituted with a C₆-Cio aryl, or a substituted C₆-Cio aryl

Process according to claim 5 in which operation e) is carried out according to the single-step synthesis route e.ii), comprising a truncated Passerini reaction by treating the aldehyde of formula (Xla) with an isocyanide of formula (R¹⁰NC) in presence of an acid.

Process according to any one of claims 5 to 7, in which operation f), when n = 0, R⁸ = R⁹ = CH₃ and R¹⁰ is not cyclopropyl, is carried out according to synthesis route f.i), comprising the following steps:

f.i. l) oxidation of the hydroxyamide of formula (Xllla) to yield an a- ketoamide of formula (XlVa):

f.i.2) deprotection of the a-ketoamide of formula (XlVa) to yield an a- ketoamide of formula (XVIIIa).

9. Process according to any one of claims 5 to 7, in which operation f) when n = 0, R⁸ = R⁹ = CH₃ and R¹⁰ and R¹⁷ are not cyclopropyl, is carried out according to synthesis route f.ii), comprising the following steps:

f.ii. l) deprotection of the hydroxyamide of formula (Xllla) to yield a hydroxyamide of formula (XVIIa):

f.ii.2) oxidation of the hydroxyamide of formula (XVIIa) to yield a a-ketoamide of formula (XVIIIa).

Process according to any one of claims 5 to 7 in which, when n = 1, R⁸ = R⁹ = H and R¹⁰ = R¹⁷ = cyclopropyl, operation f) is carried out according to the single-step oxidation f.iii) below:

11. Process according to claim 4, in which the aldehyde (XIa) is further reacted to produce a α-ketoamide of formula (XVIIIa):

according to a synthetic route comprising the following operations:

g) reacting the aldehyde of formula (XIa) with a cyanide, optionally

presence of an acid, obtaining a cyanohydrin of formula (XVa):

converting the cyanohydrin (XVa) to an a-hydroxyacid of formula (XVIa)

coupling the a-hydroxyacid (XVIa) with an amine of general formula (R¹⁷NH₂) to yield a hydroxyamide of formula (XVIIa):

j) oxidizing the hydroxyamide of formula (XVIIa) to provide the a-ketoamide of formula (XVIIIa).

Process according to any one of claims 2 to 11, in which the starting material for either operations a.i. l) or a.ii. l) is an enantiomerically enriched azido aldehyde having the following structure (VI'):

and the process leads to the enantiomerically enriched N-acyl bicyclic prolinamide of formula (IX') below:

Process according to any one of claims 2 to 11, in which the starting material for either operations a.i. l) or a.ii. l) is an enantiomerically enriched azido aldehyde having the following structure (VI'):

and the process leads to the enantiomerically enriched δ-acylamino-a- hydroxy amide of formula (Villa'):

which is further converted into an enantiomerically enriched aldehyde of formula (XIa') according to the procedure of steps a'), b'), c) and d) of claim 4:

Process according to claim 13, in which said enantiomerically enriched aldehyde of formula (XIa') is converted into an enantiomerically enriched a-ketoamide of formula (XVIIIa'):

following the procedure of claim 5 or claim 11.

Process according to any one of claims 12 to 14, in which said N-acyl bicyclic prolinamide of formula (IX') has one of the following formulae (A) and (B):

16. Process according to claim 4, in which said isocyanide of formula (XII) has one of the following formulae:

17. Process according to any one of the preceding claims, in which the -OPg group is selected among esters, silyl ethers or ethers.

18. Process according to any one of the preceding claims, in which the -NH-Pg group is selected among tert-butyloxycarbonyl (Boc), benzyloxycarbonyl (Cbz), and 9- fluorenylmethyloxycarbonyl (Fmoc).

19. Process according to any one of the preceding claims in which, in step b.2), said a-activated-5-acylamino amide of formula (VHIb) is cyclized by treatment in a dipolar aprotic solvent or a mixture of dipolar aprotic solvents, at a temperature between -30 °C and 40 °C, with an organic or inorganic base selected among hydrides, alkaline amides or alkaline tert-butoxides in an amount comprised between 1 and 2 equivalents compared to the molar quantity of the compound of formula (VHIb), optionally in the presence of a halide salt.

20. Process according to any one of claims 6 to 19, in which in said isocyanide (Pv¹⁰NC) the Pv¹⁰ group is cyclopropyl, and the isocyanide is prepared by dehydration of N-cyclopropylformamide with methyl N-(methoxycarbonyl)-N- [(triethylammonium)sulfonyl]azanide (Burgess reagent) or a reagent of general formula (XIX):

R is a cyclic or acyclic tertiary amine;

21. Process according to any one of claims 6 to 19, in which in said steps e.i. l) and e.ii), the reaction mixture resulting from the dehydration step of claim 20 is used directly in place of the isocyanide (R¹⁰NC).

22. A δ-azido-a-acyloxyamide of formula (VII) and the enantiomerically enriched isomers thereof:

23. A δ-azido-a-hydroxyamide of formula (Vllb) and the enantiomerically enriched isomers thereof:

(Vllb)

24. An amine of formula (Vlld) and the enantiomerically enriched isomers

25. An amine of formula (Vile) and the enantiomerically enriched isomers thereof:

26. A δ-acylamino-a-hydroxyamide of formula (VIII) and the enantiomerically enriched isomers thereof:

An a-activated-5-acylamino amide of formula (Vlllb) and the enantiomerically enriched isomers thereof:

28. A N-acyl bicyclic proline amide of formula (IXa) and the enantiomerically enriched isomers thereof:

29. A N-acyl bicyclic proline (hydroxy alkyl)amide of formula (Xa) and the enantiomerically enriched isomers thereof:

30. An aldehyde of formula (XIa) and the enantiomerically enriched isomers thereof:

31. An isocyanide according to formula (Xllb') or (XIIc'):

_R16 _R16

CN

(Xllb') (XIIc")