"Carba" peptide bond surrogates. Different approaches to Gly-psi(CH2-CH2)-D,L-Xaa pseudo-dipeptide units.

Racemic "carba" pseudo-dipeptide units such as Gly-psi(CH2-CH2)-D,L-Xaa were obtained either through the Horner-Emmons condensation of N-tert.-butyloxycarbonyl-beta alaninal with the appropriate substituted triethyl phosphonacetate, or from commercially available 3-carbethoxy-2-piperidone.