Common anionic receptor site hypothesis: its relevance to the antagonist action of naloxone.

Appropriate modification of 14 beta-methoxy- and 14 beta-ethoxycodeinone (prepared by alkylation of 14 beta-hydroxycodeinone) has generated four alkoxy analogues (3a-d) of naloxone and naltrexone. These agents were pure narcotic antagonists in contradiction to the predictions of the common anionic receptor site hypothesis, postulated to be of importance in the enhanced antagonism of naloxone. The molecular change from allyl to cyclopropylmethyl on the N atom increased selectivity of these antagonists for the mu receptor to the same extent as found for naloxone. Increase in the length of the C14 O-substituent had no effect on receptor selectivity, and either formation in most cases did not significantly alter oral/parenteral ratios of durations of action.