All four stereoisomers of the highly constrained novel amino acid, bet
a-isopropyltyrosine, have been synthesized with high stereoselectiviti
es (> 90% de) and in 40-50% overall yields by using the optically pure
4-phenyloxazolidinone as a chiral auxiliary via asymmetric Michael ad
dition, direct or indirect azidation, hydrogenolysis and demethylation
reactions. (C) 1997 Elsevier Science Ltd.