Patent ID: 7470525

Claim:
A process for producing an optically active 2-alkyl-L-cystein or a salt thereof from a 2-alkylcysteinamide or a salt thereof, which comprises allowing cells of microorganism or a treated product thereof having an activity of stereoselective hydrolysis of the amide bond of a 2-alkyl-L-cysteinamide or a salt thereof to act on a 2-alkylcysteinamide represented by the general formula (1) or a salt thereof, so as to generate a 2-alkyl-L-cysteine represented by the general formula (2) or a salt thereof; allowing the generated 2-alkyl-L-cysteine or salt thereof and an unreacted 2-alkyl-D-cysteinamide represented by the general formula (3) or a salt thereof to react with an aldehyde or ketone represented by the general formula (4), or an acetal or ketal thereof, so as to derive therefrom a 4-alkylthiazolidine-4-carboxylic acid represented by the general formula (5) or a salt thereof and a 4-alkylthiazolidine-4-carboxamide represented by the general formula (6) or a salt thereof, respectively; separating the 4-alkylthiazolidine-4-carboxylic acid represented by the general formula (5) or salt thereof from the mixture thereof; and hydrolyzing it for ring-opening to yield an optically active 2-alkyl-L-cysteine represented by the general formula (2) or a salt thereof, where in the general formulas (1), (2), (3), (5) and (6), R represents a C 1-4 lower alkyl; and in the general formulas (4), (5) and (6), each of R 1 and R 2 independently represents hydrogen or a C 1-4 lower alkyl, or R 1 and R 2 bind to each other to form a 5- to 8-membered alicyclic structure, provided that R 1 and R 2 do not simultaneously represent hydrogen.