Synthesis of α-methyl- and β-methyl-dl-cystine

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Abstract
A synthesis of [beta]-methyl-DL-cystine from DL-allothreonine is described. Cyclization of N-thiobenzoylal-lothreonine ethyl ester with thionylchloride gave 4-carboxy-5-methyl-2 phenylthiazoline, which was hydrolyzed by acid to ft-methyl-DL-cysteine (thiothreonine, [alpha]-amino-[beta]-mercaptobutyric acid). This amino acid was identical with isomer B of thiothreonine, previously synthesized by Carter et al (1941). By a similar series of reactions DL-threonine was also converted into isomer B of thiothreonine. The significance of formation of the same isomer of thiothreonine from both threonine and allothreonine is discussed. It is suggested that isomers A and B of thiothreonine have the erythro- and threo-configuration respectively. The synthesis of [alpha]-methyl-DL-cystine is reported. The preparation of DL-carboxy-C14-allothreonine, [beta]-methyl-DL-carboxy-C14-cystine and [alpha]-methyl-DL-carboxy-C14-cystine is also described.

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