Abstract: Pure enantiomers of N (benzyloxycarbony1) serine (Za) or N-(tert-butoxycarbony1) serine (Zb) are cyclized without racemization to N-protected a-amino@-lactones 3a and 3b in 60-72% yield by using modified Mitsunobu conditions (Ph3P, dimethyl azodicarboxylate). Treatment of the &lactones with a variety of halogen, oxygen, sulfur, or nitrogen nucleophiles gives pure enantiomers of N-protected &substituted alanines 4-14a and 4b in high yield. ...