The identification of the CB2 cannabinoid receptor has provided a novel target for the development of therapeutically useful cannabinergic molecules. We have synthesized benzo[ c]chromen-6-one analogs possessing high affinity and selectivity for this receptor. These novel compounds are structurally related to cannabinol (6,6,9-trimethyl-3-pentyl-6 H-benzo[ c]chromen-1-ol), a natural constituent of cannabis with modest CB2 selectivity. Key pharmacophoric features of the new selective agonists include a 3-(1',1'-dimethylheptyl) side chain and a 6-oxo group on the cannabinoid tricyclic structure that characterizes this class of compounds as "cannabilactones." Our results suggest that the six-membered lactone pharmacophore is critical for CB2 receptor selectivity. Optimal receptor subtype selectivity of 490-fold and subnanomolar affinity for the CB2 receptor is exhibited by a 9-hydroxyl analog 5 (AM1714), while the 9-methoxy analog 4b (AM1710) had a 54-fold CB2 selectivity. X-ray crystallography and molecular modeling show the cannabilactones to have a planar ring conformation. In vitro testing revealed that the novel compounds are CB2 agonists, while in vivo testing of cannabilactones 4b and 5 found them to possess potent peripheral analgesic activity.

The cannabinoid CB1 receptor is involved in complex physiological functions. The discovery of CB1 allosteric modulators generates new opportunities for drug discovery targeting the pharmacologically important CB1 receptor. 5-chloro-3-ethyl-N-(4-(piperidin-1-yl)phenethyl)-1H-indole-2-carboxamide (ORG27569; 1) represents a new class of indole-2-carboxamides that exhibit allostery of CB1. To better understand the SAR, a group of indole-2-carboxamide analogs were synthesized and assessed for allostery of the CB1 receptor. We found that within the structure of indole-2-carboxamides, the presence of the indole ring is preferred for maintaining the modulator's high binding affinity for the allosteric site, but not for generating allostery on the orthosteric site. However, the C3 substituents of the indole-2-carboxamides significantly impact the allostery of the ligand. A robust CB1 allosteric modulator 5-chloro-N-(4-(dimethylamino)phenethyl)-3-pentyl-1H-indole-2-carboxamide (11j) was identified. It showed an equilibrium dissociation constant (KB) of 167.3 nM with a markedly high binding cooperativity factor (α=16.55) and potent antagonism of agonist-induced GTPγS binding.

Allosteric modulation of G-protein coupled receptors (GPCRs) represents a novel approach for fine-tuning GPCR functions. The cannabinoid CB1 receptor, a GPCR associated with the CNS, has been implicated in the treatment of drug addiction, pain, and appetite disorders. We report here the synthesis and pharmacological characterization of two indole-2-carboxamides: 5-chloro-3-ethyl-1-methyl-N-(4-(piperidin-1-yl)phenethyl)-1H-indole-2-carboxamide (ICAM-a) and 5-chloro-3-pentyl-N-(4-(piperidin-1-yl)phenethyl)-1H-indole-2-carboxamide (ICAM-b). While both ICAM-a and ICAM-b enhanced CP55,940 binding, ICAM-b exhibited the strongest positive cooperativity thus far demonstrated for enhancing agonist binding to the CB1 receptor. Although it displayed negative modulatory effects on G-protein-coupling to CB1, ICAM-b induced β-arrestin-mediated downstream activation of ERK signaling. These results indicate that this compound represents a novel class of CB1 ligands that produce biased signaling via CB1.