Fully deprotected phosphonamidate dipeptides, predicted as effective inhibitors of cytosolic leucine aminopeptidase, showed unexpected instability in water solution at pH below 12. Their hydrolysis rate was strictly correlated with basicity of the N-terminal amino group. To improve this feature a phosphonamidate analogue containing less basic, aromatic 2- aminophenylphosphonate residue in P1 position of the inhibitor was designed. The target ...