Pharmacophoric requirements for cannabinoid side chains: multiple bond and C1'-substituted delta 8-tetrahydrocannabinols

Accumulated evidence indicates that within the cannabinoid structure the aliphatic side chain plays a pivotal role in determining cannabimimetic activity. We describe the synthesis and affinities for the CB1 and CB2 receptors of a series of novel delta 8-THC analogues in which the side-chain pharmacophores are conformationally more defined than in the parent molecule. No analogue has the side-chain pharmacophore in a fully restricted conformation. However, our design serves to narrow down the scope of options for conformational requirements at the receptor active sites. All the analogues tested showed nanomolar or subnanomolar affinities for the receptors; 2-(6a,7,10,10a-tetrahydro-6,6,9-trimethyl-1-hydroxy-6H- dibenzo[b,d]pyranyl)-2-hexyl-1,3-dithiolane was found to possess very high affinity for both cannabinoid receptors (CB1, Ki = 0.32 nM; CB2, Ki = 0.52 nM).