Aminophosphinic inhibitors as transition state analogues of enkephalin-degrading enzymes: A class of central analgesics

Abstract

Inhibition of aminopeptidase N and neutral endopeptidase-24.11, two zinc metallopeptidases involved in the inactivation of the opioid peptides enkephalins, produces potent physiological analgesic responses, without major side-effects, in all animal models of pain in which morphine is active. Dual inhibitors of both enzymes could fill the gap between opioid analgesics and antalgics. Until now, attempts to find a compound with high affinity both for neutral endopeptidase and aminopeptidase N have failed. We report here the design of dual competitive inhibitors of both enzymes with K_I values in the nanomolar range. These have been obtained by selecting R₁, R_2, and R₃ determinants in aminophosphinic-containing inhibitors: NH₂—CH(R₁)P(O)—(OH)CH₂—CH(R₂)CONH—CH(R₃)COOH, for optimal recognition of the two enkephalin inactivating enzymes, whose active site peculiarities, determined by site-directed mutagenesis, have been taken into account. The best inhibitors were 10× more potent than described dual inhibitors in alleviating acute and inflammatory nociceptive stimuli in mice, thus providing a basis for the development of a family of analgesics devoid of opioid side effects.