The peptide H-D-Pro-Pro-Glu-NH2 is a highly effective catalyst for conjugate addition reactions between aldehydes and nitroethylene. Only 1 mol % of H-D-Pro-Pro-Glu-NH2 and a 1.5-fold excess of aldehyde with respect to nitroethylene suffice to obtain Y-nitroaldehydes and, after reduction, monosubstituted Y-nitroalcohols in excellent yields and optical purities. The products can be readily converted into Y-2-amino acids, thereby opening an effective direct entry into this important class of compounds.