"The structure can be represented as follows: ##STR1## wherein R represents any amino acid side chain and R' and R representhydrogen (in the case of a phosphonic acid) or a group such as alkyl or aryl (in the case of a phosphonate ester)..alpha.-Aminophosphonates are used in the synthesis of peptide analogues (peptidylphosphonates) possessing a phosphonate linkage in the place of at least one amid" . . . . . .