β-Lactam derivatives as enzyme inhibitors: Peptidic derivatives of (RS)-2-oxo-4-phenylazetidine-1-alkanoic acids
4-Phenylazetidine-2-one was transformed into 4-phenylazetidine-1-alkanoic acids, which were reacted in the presence of diphenylphosphoroazidate with amino acid esters and dipeptide esters yielding β-lactam peptides with different spacers between the lacta