All four isomers of a novel fl-branched unusual amino acid were designed and synthesized with high stereoselectivity （〉 90% de） and in 33%--44% overall yields by the use of 4（R/S）-5,5-dimethyl-4-phenyl-oxazolidin-2-one as the chiral auxiliary via asymmetric 1,4-Michael addition, direct or indirect azidation, hydrolysis and hydrogenation reactions.
