a,b-Diamino acids are important structural fragments of biologically active compounds. syn-(2R,3S)-Diaminopropanoates were readily prepared by adding the prochiral lithium enolate of ethyl (dibenzylamino)acetate to various sulfinimines (N-sulfinyl imines). To demonstrate the efficiency of this new methodology, the formal synthsis of (+)-CP-99,994 and (+)-CP-122,721 will be presented.