PHOSPHONAMIDATE PEPTIDE ANALOGUES AS INHIBITORS OF ENKEPHALINASE AND ANGIOTENSIN-CONVERTING ENZYME (TRANSITION-STATE INHIBITORS, METALLOENDOPEPTIDASE)

The effectiveness of phosphonamidate peptide analogues as inhibitors of enkephalinase and angiotensin-converting enzyme has been explored with a series of enkephalin analogues in which the scissile Gly('3)-Phe('4) amide bond has been replaced with a phosphonamide bond. In addition, the effect of these modifications on the opioid activity of these compounds has been investigated.; Incorporation of the aminomethylphosphino moiety into the enkephalin analogues was accomplished by conversion of the phthaloyl-protected aminomethylphosphonate diester to the corresponding phosphonochloridate, followed by coupling with the appropriate dipeptide to provide the phosphonamidate tripeptide analogues. Extension of the molecule in the N-terminal direction to afford the target compounds was accomplished via standard peptide chemistry. The inhibitory potency of these compounds was evaluated against rat kidney metalloendopeptidase (enkephalinase, E.C. 3.4.24.11) and angiotensin-converting enzyme (ACE, 3.4.15.1) from rat brain. The opioid activity was evaluated on the electrically stimulated guinea pig ileum and mouse vas deferens preparations.; The phosphonamidate inhibitors demonstrated good inhibitory potency against both enzymes, having K(,i) values in the (mu)M range. Enkephalinase exhibited an intolerance towards large alkaryl groups at the P(,1) position and the ethyl phosphonamidate moiety at the Gly('3) amide bond position. The high inhibitory potencies of the pentapeptide analogues against enkephalinase suggests that ancillary sites in addition to the S(,1)' and S(,2)' sites are involved in the binding of larger peptides. Likewise, the inhibitory potency of the N-(acyl)-aminomethylphosphonamidates against ACE was attenuated by larger alkaryl functionalities, although not to the same degree as with enkephalinase. The two pentapeptide analogues were devoid of any opioid activity on both the guinea pig ileum and mouse vas deferens preparations.; These results have shown that phosphonamidate peptide analogues are effective inhibitors of enkephalinase and angiotensin-coverting enzyme, and have defined some of the differences between the active sites of these enzymes. The absence of any opioid activity of the pentapeptide analogues indicates that the opioid receptors cannot tolerate a tetrahedral phosphonamidate moiety in place of the Gly('3) amide bond. This inactivity may be due to the inability of critical pharmacophores to interact effectively with the receptor.