Pentapeptides containing two dehydrophenylalanine residues--synthesis, structural studies and evaluation of their activity towards cathepsin C

Synthesis, structural and biological studies of pentapeptides containing two DeltaPhe residues (Z and E isomers) in position 2 and 4 in peptide chain were performed. All the investigated peptides adopted bent conformation and majority of them could exist as two different conformers in solution. Only pentapeptides, containing free N-termini appeared to act as weak inhibitors of cathepsin C with the slow-binding, competitive mechanism of inhibition, free acids being bound slightly better than their methyl esters. Results of molecular modeling suggested significant difference between peptides, depending of the type of amino acid residue in position 5 in peptide chain. Dehydropeptides containing Gly residue in this position may act as competitive slow-reacting substrates and therefore exhibit inhibitory-like properties.

A phosphonamidate containing aromatic N-terminal amino group as inhibitor of leucine aminopeptidase-design, synthesis and stability

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 compound was synthesised starting from diethyl 2-nitrophosphonate in several step procedure. The decrease in basicity of the terminal amino moiety of the modified analogue in fact resulted in satisfactory improvement of hydrolytic stability of the P-N bond. The developed phosphonamidate was proved to be fully resistant to hydrolysis above pH 7. Surprisingly, tested in enzymatic assays towards leucine aminopeptidase (optimum pH 8.5), it did not exhibit inhibition activity up to milimolar concentration. The explanation could be that diminishing the basic character of the terminal amino group may result in a change of its affinity towards the zinc ions.