We have developed a versatile new synthesis of the Psi[CH2O] pseudopep
tides from N-protected 5-substituted morpholin-3-ones. This approach f
ocuses on a stereoselective alkylation of the morpholin-3-ones. The re
sulting alkylation products were used in the synthesis of some previou
sly unavailable Psi[CH2O] dipeptides.