Di-and tripeptide analogues containing (2-amin0ethyl) phosphonic acid [HA~ P (OH)~], which has been discovered in a wide variety of living organisms, were prepared. As starting materials for incorporating the amino phosphonic acid into a peptide chain, the N- phthalylated diethyl ester [Pht-Ae~(OEt)~ l and the N-carbobenzyloxylated monoalkyl ester [Cbz-Aep (OR)(OH), R= Me, Et, and Bzl] were used. A phosphonamide bond between the ...