Facile syntheses of L-beta-haloalanine derivatives from L-cysteine or L-cystine.

L-beta-Haloalanines are physiologically active unnatural amino acids and they are useful intermediates for the synthesis of natural and unnatural amino acids, S-linked glycopeptides, and lanthionines. In general L-beta-haloalanines were prepared predominantly from L-serine via functional group transformation. Here we reported an alternative approach for the preparation of L-beta-haloalanines via halogenation of protected L-cysteine esters which was obtained from L-cysteine or L-cystine, respectively. The mercapto group of protected L-cysteine esters was efficiently transformed to halo groups by triphenylphosphine/N-halosuccinimides. It has been proved to be a versatile desulfurization strategy via this functional group transformation.