Synthesis of enantiomerically enriched beta,gamma-unsaturated-alpha-amino acids

A variety of enantiomerically enriched beta,gamma -unsaturated-alpha -amino acids are synthesized by olefination of a Cbz-protected serine aldehyde eq uivalent, readily prepared from serine. A cyclic ortho ester protecting gro up is employed to minimize racemization. The deprotected amino acids are ob tained in good yield, ranging from 70-95% ee, with double-bond geometry det ermined by the type of Wittig reagent used. Isotopically labeled side chain s are readily introduced by this procedure, and free gamma-C-13-vinylglycin e was prepared in 44% yield from the protected serine aldehyde synthon. (C) 2001 Elsevier Science Ltd. All rights reserved.