Preparations of Optically Active Homocysteine and Homocystine by Asymmetric Transformation of (RS)-1,3-Thiazane-4-carboxylic Acid

DL-Homocysteine [DL-Hcy] from (RS)-homocysteine thiolactone hydrochloride [(RS)-HTL·HCl] was subjected to reaction with formaldehyde in acetic acid to give (RS)-1,3-thiazane-4-carboxylic acid monohydrate [(RS)-THA·H2O]. An asymmetric transformation of (RS)-THA·H2O was achieved via salt formation with optically active tartaric acid in the presence of salicylaldehyde in acetic acid. The (R)- and (S)-THA obtained, respectively, from the salt of (R)-THA with (2R, 3R)-tartaric acid and its enantiomeric salt were treated with hydroxylamine hydrochloride to give D- and L-Hcy of 100% optical purity, respectively, in 50% yield from (RS)-HTL·HCl. Oxidation of D- and L-Hcy with hydrogen peroxide gave D- and L-homocystine, respectively, in 47% yield.