Synthesis and characterization of potent and selective agonists of the neuronal cannabinoid receptor (CB1)

Two subtypes of the cannabinoid receptor (CB1 and CB2) are expressed in mam malian tissues. Although selective antagonists are available for each of th e subtypes, most of the available cannabinoid agonists bind to both CB1 and CB2 with similar affinities. We have synthesized two analogs of N-arachido nylethanolamine (AEA), arachidonylcyclopropylamide (ACPA) and arachidonyl-2 -chloroethylamide (ACEA), that bind to the CB1 receptor with very high affi nity (K-I values of 2.2 +/- 0.4 nM and 1.4 +/- 0.3 nM, respectively) and to the CB2 receptor with low affinity (K-I values of 0.7 +/- 0.01 mu M and 3. 1 +/- 1.0 mu M, respectively). Both ACPA and ACEA have the characteristics of agonists at the CB1 receptor; both inhibit forskolin-induced accumulatio n of cAMP in Chinese hamster ovary cells expressing the human CB1 receptor, and both analogs increase the binding of [S-35]GTP gamma S to cerebellar m embranes and inhibit electrically evoked contractions of the mouse vas defe rens. ACPA and ACEA produce hypothermia in mice, and this effect is inhibit ed by coadministration of the CBI receptor antagonist SR141716A. Therefore, ACPA and ACEA are high-affinity agonists of the CBI receptor but do not bi nd the CB2 receptor, suggesting that structural analogs of AEA can be desig ned with considerable selectivity for the CB1 receptor over the CB2 recepto r.