Drug design and synthesis of ε opioid receptor agonist:: 17-(cyclopropylmethyl)-4,5α-epoxy-3,6β-dihydroxy-6,14-endoethenomorphinan-7α-(N-methyl-N-phenethyl)carboxamide (TAN-821) inducing antinociception mediated by putative ε opioid receptor

Here we report the new drug design and synthesis of a series of 6,14-endoethenomorphinan-7-carboxamide derivatives as a putative E: opioid receptor agonist. One of these compounds, 17-(cyclopropylmethyl)-4,5alpha-epoxy-3,6beta-dihydroxy-6,14-endoethenomorphinan-7alpha-(N-methyl-N-phenethyl)carboxamide (TAN-821), showed agonistic activity for a putative E opioid receptor (IC50 = 71.71 nM) in the rat vas deferens (RVD) preparations. TAN-821 stimulated the binding of the nonhydrolyzable guanosine 5'-triphosphate analog, guanosine 5'-(gamma-thio)-triphosphate (GTPgammaS), to the mouse pons/medulla membrane via the activation of putative E: opioid receptor. Moreover, TAN-821 given intracerbroventricularly (i.c.v.) produced a marked antinociception in the tail-flick test (ED50 = 1.73 mug) and the hot-plate test (ED50 = 2.05 mug) in a dose-dependent manner. The antinociception induced by TAN-821 administered i.c.v. was blocked by the i.c.v.-pretreatment with a putative epsilon opioid receptor partial agonist beta-endorphin [1-27], but not a mu opioid receptor antagonist beta-FNA, a delta opioid receptor antagonist NTI, or a kappa opioid receptor antagonist nor-BNI. The present results suggest that TAN-821 may be a useful tool for the investigation on the pharmacological properties of the putative epsilon opioid receptor. (C) 2004 Elsevier Ltd. All rights reserved.