DIPEPTIDE-DERIVED DIPHENYL PHOSPHONATE ESTERS - MECHANISM-BASED INHIBITORS OF DIPEPTIDYL PEPTIDASE-IV

A number of dipeptide diphenyl phosphonate esters were studied as inhi bitors of dipeptidyl peptidase IV, focusing on the role of the P2 resi due in the inactivation process. The active compounds were slow irreve rsible inhibitors of the catalytic activity of the enzyme. With prolin e (or alanine) in the Pi position, the rate constants of inactivation correlated with the acylation rate constants reported for homologous d ipeptide derived substrates. The kinetic data indicate that the mechan ism of inhibition consists of the formation of a fairly weak initial c omplex, followed by a slow irreversible inactivation step. This indica tes that, as in the case of trypsin-like proteinases, dipeptide diphen yl phosphonate eaters form a covalent adduct with the catalytic site o f DPP IV, even though this enzyme belongs to a completely distinct cla ss of serine peptidases. Enantioselectivity and secondary specificity further support the evidence that diphenyl phosphonate eaters are mech anism-based inhibitors, The dipeptide diphenyl phosphonate esters had a half-life of 3-10 h at 37 degrees C in Tris buffer. The inhibitors w ere degraded in human plasma, depending on the type of amino-terminal amino acid, The compound with proline in the P2 position was the most resistant to degradation in plasma. Due to their stability and the irr eversible nature of the inhibition, the diphenyl phosphonate esters pr omise to be useful tools in the continuing investigation of the physio logical function of dipeptidyl peptidase IV.