Patent ID: 7767826

Claim:
A process for preparing the compounds of Formula (I): wherein R and R 1 are independently chosen from hydrogen, C 1 -C 8 alkyl, C 3 -C 8 alkenyl, C 3 -C 8 alkynyl, C 3 -C 7 cycloalkyl, cycloalkyl-lower alkyl aryl-lower alkyl or substituted aryl-lower alkyl; comprising the following successive steps: a) reacting L-histidine alkyl ester with an acid halide, chloroformate or pyrocarbonate in the presence of a base thereby obtaining an alkyl-(S,Z)-2,4,5 triamidopent-4-enoate; b) hydrolysis of the alkyl-(S,Z)-2,4,5-triamidopent-4-enoate to obtain a (S)-alkyl 2,5-diamido-4-oxopentanoate; c) acid catalyzed hydrolysis of the (S)-alkyl 2,5-diamido-4-oxopentanoate followed by reaction with a metal thiocyanate to obtain a thiohistidine, (S)-2-amino-3-(2-thioxo-2,3-dihydro-1H-imidazol-4-yl)propanoic acid; d) protection of the sulfur of the thiohistidine by the addition of tert-butyl protecting group to obtain (S)-2-amino-3-(2-(tert-butylthio)-1H-imidazol-5-yl)propanoic acid; e) dialkylation of the primary amine to obtain a tertiary amine (S)-3-(2-(tert-butylthio)-1H-imidazol-5-yl)-2-(dialkylamino)propanoic acid; f) quaternization of the tertiary amine; and g) removal of the protecting group to obtain the desired (S)-3-(2-mercapto-1H-imidazol-5-yl)-2-(trialkylammonio)propanoate (I).