Kelatorphan: a full inhibitor of enkephalin degrading enzymes. Biochemical and pharmacological properties, regional distribution of enkephalinase in rat brain by use of a tritiated derivative

New potent inhibitors of enkephalin degrading enzymes were obtained by synthesis of compounds bearing a bidentate group. Among these bidentates, Kelatorphan, N-[(R)-3-(N-hydroxy)-carboxamido-2-benzylpropanoyl]-L-alanine, is in vitro a full inhibitor of enkephalinase, dipeptidylaminopeptidase and Aminopeptidase. In vivo Kelatorphan (i.c.v. administered in mice) prevents exogenous enkephalin from peptidase degradation. The analgesic effect of Kelatorphan is at least equal to that of the association of bestatin and thiorphan. An analogue of Kelatorphan was tritiated and was used as a specific marker of enkephalinase. Thus the distribution of enkephalinase in rat brain was studied: striatum corpus and substantia nigra were particularly labelled.