STEREOCONTROLLED SYNTHESIS OF BETA-HYDROXYPHENYLALANINE AND BETA-HYDROXYTYROSINE DERIVATIVES

Side-chain bromination of N-phthaloyl-(S)-phenylalanine and tyrosine d erivatives, followed by treatment of the product bromides with silver nitrate in aqueous acetone, affords the corresponding (2S,3R)-beta-hyd roxy-alpha-amino acids, enantiospecifically and diastereoselectively. The diastereoselectivity depends on the carboxyl protecting group, ter t-Butyl esters display greater stereoselectivity than the correspondin g methyl esters, presumably as a result of a steric effect, while N-te rt-butylamides react diastereospecifically due to a combination of ste ric and electronic effects.