3-Indolyl-1-naphthylmethanes: New Cannabimimetic Indoles. Provide Evidence for Aromatic Stacking Interactions with the. CB1 Cannabinoid Receptor

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A series of 1-pentyl-1H-indol-3-yl-(1-naphthyl)methanes (911) and 2-methyl-1-pentyl-1H-indol-3-yl-(1-naphthyl)methanes (1214) have been synthesized to investigate the hypothesis that cannabimimetic 3-(1-naphthoyl)indoles interact with the CB1 receptor by hydrogen bonding to the carbonyl group. Indoles 911 have significant (Ki=17–23 nM) receptor affinity, somewhat less than that of the corresponding naphthoylindoles (5, 15, 16). 2-Methyl-1-indoles 1214 have little affinity for the CB1 receptor, in contrast to 2-methyl-3-(1-naphthoyl)indoles 1719, which have affinities comparable to those of 5, 15, 16. A cannabimimetic indene hydrocarbon (26) was synthesized and found to have Ki=26±4 nM. Molecular modeling and receptor docking studies of naphthoylindole 16, its 2-methyl congener (19) and indolyl-1-naphthylmethanes 11 and 14, combined with the receptor affinities of these cannabimimetic indoles, strongly suggest that these cannabinoid receptor ligands bind primarily by aromatic stacking interactions in the transmembrane helix 3-4-5-6 region of the CB1 receptor.