Synthesis ofthreo-3-Methylcysteine from Threonine

threo-3-Methyl-D-cysteine as a moiety of β-methyllanthionine in the peptide antibiotic nisin was synthesized stereospecifically. The reaction of (2R,3R)-3-methyl-2-aziridinecarboxylic acid derivative prepared from D-threonine with thiobenzoic acid gave the β-mercapto α-amino acid derivative of the same configuration as the starting material. A stereochemistry of the product was retained as a result of double inversion mechanism through the reactions. Thus, we could prepare threo-3-methyl-D-cysteine, i.e., (2S,3S)-2-amino-3-mercaptobutanoic acid which is required for the synthetic study of nisin.