Method for preparing chiral amino acids

Process for preparing chiral amino acids of formula (I):

• in which:
• R1 and R2 are different and are selected from:
• an alkyl or haloalkyl radical containing from 1 to 6 carbon atoms in a linear or branched chain;
• an alkoxyalkyl, alkylthioalkyl, alkylsulphonylalkyl, monoalkylaminoalkyl, alkenyl or alkynyl radical containing from 2 to 6 carbon atoms in a linear or branched chain;
• a dialkylaminoalkyl or cycloalkyl radical containing from 3 to 7 carbon atoms in a linear or branched chain;
• an aryl radical, optionally substituted by from 1 to 3 individually selected R6 groups;
• and
• an arylalkyl, aryloxyalkyl, arylthioalkyl or arylsulphonylalkyl radical;
• or else R1 and R2, together with the carbon atom to which they are attached on the ring, form a carbocycle or a heterocycle containing from 5 to 7 atoms, including these rings being fused with a phenyl optionally substituted by from 1 to 3 individually selected R6 groups;
• R6 represents a radical selected from:
• a halogen atom;
• an alkyl, haloalkyl, alkoxy, haloalkoxy, alkylthio, haloalkylthio or alkylsulphonyl radical containing from 1 to 6 carbon atoms;
• a cycloalkyl, halocycloalkyl, alkenyloxy, alkynyloxy, alkenylthio, alkynylthio radical containing from 3 to 6 carbon atoms;
• a nitro or cyano group;
• an amino radical optionally mono- or disubstituted by an alkyl or acyl radical containing from 1 to 6 carbon atoms or alkoxycarbonyl radical containing from 2 to 6 carbon atoms;
• and
• a phenyl, phenoxy or pyridyloxy radical, these radicals being optionally substituted by from 1 to 3 identical or different R7 groups;
• and
• R7 represents a radical selected from:
• a fluorine, chlorine, bromine or iodine atom;
• a linear or branched alkyl radical containing from 1 to 6 carbon atoms;
• a linear or branched alkoxy or alkylthio radical containing from 1 to 6 carbon atoms;
• a linear or branched haloalkoxy or haloalkylthio radical containing from 1 to 6 carbon atoms;
• a nitrile radical;
• and
• a nitro radical, said process comprising the steps of:
• (A) dissolving a racemic hydantoin of formula (II):
• in a basic medium used in an amount of from 0.2 to 0.8 equivalent of base relative to the amount of said racemic hydantoin;
• (B) adding an enantiomeric resolving agent in an amount of from 0.2 to 1.0 equivalent of resolving agent relative to the amount of said racemic hydantoin;
• (C) separating the resolving agent from the reaction mixture;
• and
• (D) hydrolysing the reaction mixture in a basic medium in order to liberate the basic salt of the desired chiral amino acid, which process is conducted in a water/co-solvent mixture.