Optimization of Chemical Functionalities of Indole-2-carboxamides To Improve Allosteric Parameters for the Cannabinoid Receptor 1 (CB1)

Abstract

5-Chloro-3-ethyl-N-(4-(piperidin-1-yl)phenethyl)-1H-indole-2-carboxamide (1; ORG27569) is a prototypical allosteric modulator for the cannabinoid type 1 receptor (CB1). Here, we reveal key structural requirements of indole-2-carboxamides for allosteric modulation of CB1: a critical chain length at the C3-position, an electron withdrawing group at the C5-position, the length of the linker between the amide bond and the phenyl ring B, and the amino substituent on the phenyl ring B. These significantly impact the binding affinity (KB) and the binding cooperativity (α). A potent CB1 allosteric modulator 5-chloro-N-(4-(dimethylamino)phenethyl)-3-propyl-1H-indole-2-carboxamide (12d) was identified. It exhibited a KB of 259.3 nM with a strikingly high binding α of 24.5. We also identified 5-chloro-N-(4-(dimethylamino)phenethyl)-3-hexyl-1H-indole-2-carboxamide (12f) with a KB of 89.1 nM, which is among the lowest KB values obtained for any allosteric modulator of CB1. These positive allosteric modulators of orthosteric agonist binding nonetheless antagonized the agonist-induced G-protein coupling to the CB1 receptor, yet induced β-arrestin mediated ERK1/2 phosphorylation.

Pyrimidinyl Biphenylureas: Identification of New Lead Compounds as Allosteric Modulators of the Cannabinoid Receptor CB1

“…Compound 2 exhibited a similar response shown for comparison. 37,38 These results, and the enhancement in binding of the orthosteric agonist CP55,940, suggest that these compounds are PAMs and promote an active state of the receptor that may be biased to signal via β -arrestin-1 (at least for ERK1/2 phosphorylation) and not G protein.…”

Structure–activity relationships of substituted 1H-indole-2-carboxamides as CB1 receptor allosteric modulators

“…Previous studies have focused on 4-substitutions on this phenyl ring, particularly 4-amino groups such as piperidinyl and dimethylamino. 25-27 Here we introduced a number of other amino groups at several positions. The activity of the piperidine ring-opened series (compounds 16 - 19 ) was found to be sensitive to the length of the alkyl substituent.…”

“…Hence, it appears that a flexible alkyl linker is important to CB1 activity, which is in agreement with Khurana et al who showed that the ethylene moiety was the optimal linker. 27 …”

“…29 Reduction of 9 by triethylsilane in trifluoroacetic acid at room temperature gave 10 which was hydrolyzed in aqueous sodium hydroxide and ethanol to furnish the intermediate 11 . 26, 27 Amide coupling between 11 and 4- or 3-nitrophenylethylamine in the presence of BOP provided 12 and 13 which were reduced by Raney nickel-catalyzed transfer hydrogenation using hydrazine in ethanol at 50 °C to give 14 and 15 . Reductive amination of amines 14 and 15 with the corresponding aldehydes provided the target compounds 16 - 20 .…”

Synthesis and biological evaluation of indole-2-carboxamides bearing photoactivatable functionalities as novel allosteric modulators for the cannabinoid CB1 receptor

“…To facilitate future proteomic study of allosteric sites on the CB1 receptor, we designed and synthesized several photoactivatable affinity ligands based on 1 and several other robust CB1 allosteric modulators (i.e. 7–9 , Figure 2) reported previously [31–33]. Compounds 7 [31], 8 [33] and 9 [32, 35] have been demonstrated to have either comparable or improved allosteric effects to 1 [31–33].…”