Synthesis and pharmacological evaluation of newly detected synthetic cannabinoid receptor agonists AB-4CN-BUTICA, MMB-4CN-BUTINACA, MDMB-4F-BUTICA, MDMB-4F-BUTINACA and their analogs

Abstract

Synthetic cannabinoid receptor agonists (SCRAs) continue to make up a significant portion new psychoactive substances (NPS) detected and seized worldwide. Due to their often potent activation of central cannabinoid receptors in vivo, use of SCRAs can result in severe intoxication, in addition to other adverse health effects. Recent detections of AB-4CN-BUTICA, MMB-4CN-BUTINACA, MDMB-4F-BUTICA and MDMB-4F-BUTINACA mark a continuation in the appearance of SCRAs bearing novel tail substituents. The proactive characterization campaign described here has facilitated the detection of several new SCRAs in toxicological case work. Here we detail the synthesis, characterization, and pharmacological evaluation of recently detected SCRAs, as well as a systematic library of 32 compounds bearing head, tail, and core group combinations likely to appear in future. In vitro radioligand binding assays revealed most compounds showed moderate to high affinity at both CB1 (pKi = < 5 to 8.89 ± 0.09 M) and CB2 (pKi = 5.49 ± 0.03 to 9.92 ± 0.09 M) receptors. In vitro functional evaluation using a fluorescence-based membrane potential assay showed that most compounds were sub-micromolar to sub-nanomolar agonists at CB1 (pEC50 = < 5 to 9.48 ± 0.14 M) and CB2 (pEC50 = 5.92 ± 0.16 to 8.64 ± 0.15 M) receptors. An in silico receptor-ligand docking approach was utilized to rationalize binding trends for CB2 with respect to the tail substituent, and indicated that rigidity in this region (i.e., 4-cyanobutyl) was detrimental to affinity.

Synthesis and Functional Evaluation of Synthetic Cannabinoid Receptor Agonists Related to ADB-HEXINACA

“…Consistent with previous reports, to a stirred solution of the appropriate carboxylic acid (1-hexyl-1 H -indole-3-carboxylic acid, 1-(hex-5-en-1-yl)-1 H -indole-3-carboxylic acid, 1-hexyl-1 H -indazole-3-carboxylic acid, 1-(hex-5-en-1-yl)-1 H -indazole-3-carboxylic acid, 1-hexyl-1 H -pyrrolo­[2,3- b ]­pyridine-3-carboxylic acid, or 1-(hex-5-en-1-yl)-1 H -pyrrolo­[2,3- b ]­pyridine-3-carboxylic acid) in CH 2 Cl 2 was added to 1-hydroxybenzotriazole (0.1 equiv), 3-(((ethylimino)­methylene)­amino)- N , N -dimethylpropan-1-amine hydrochloride (1.2 equiv), triethylamine (3.3 equiv), and the appropriate amine (1.1 equiv). ,,,− The mixture was then stirred for 18–48 h, diluted with CH 2 Cl 2 , washed with H 2 O, with the organic layer collected and dried over Na 2 SO 4 . The solvent was then removed in vacuo, and the crude was purified via flash chromatography.…”

“…SCRAs with an APP ( 27 , 34 , 40 , 47 , 54 , and 61 ) headgroup were by far the least active, with only APP-5en-HEXINACA ( 47 ) achieving the activity cutoff for potency determination at CB 1 (CB 1 pEC 50 = 6.09 ± 0.15 nM; E max = 85 ± 8%; and CB 2 pEC 50 = 7.09 ± 0.22 nM; E max = 86 ± 5%). These observations relating to the phenylalanine-derived headgroups align with previous SARs observed with related SCRAs. ,− Interestingly, both phenylalaninyl-derived headgroups, APP and MPP, tended to confer CB 2 preference in terms of potencies observed, potentially indicating the intolerance of the CB 1 receptor to the terminal amide present on the phenylalaninyl side chain of the headgroup, while tolerating the equivalent methyl ester.…”

“…The same trend was also seen for 7-azaindole analogues ADB-HEX7AICA ( 53 , CB 2 pEC 50 = 8.08 ± 0.21 nM; E max = 73 ± 5.92%) and ADB-5en-HEX7AICA ( 60 , CB 2 pEC 50 = 8.28 ± 0.20 nM; E max = 65 ± 3.72%). Notably, 7-azaindoles were partial agonists at CB 2 , but highly efficacious agonists relative to CP55,940 at CB 1 , supporting previous comparisons between these scaffolds in analogous compound series. , Compared with evaluation via the MPA assay, indole and 7-azaindole derivatives followed similar trends, and the indazole analogues showed slightly smaller difference in potencies.…”

“…It was in this compound that a significant change in the position of the core indazole scaffold was observed, indicating less interaction with Phe200. MPP-HEXINACA (43) was observed to bind in a similar fashion as the MDMB compounds (29,36,42,49,56, and 63, Figure 7c); however, the increased length of the benzyl side chain makes it less able to be stabilized by the surrounding residues and more likely to result in unfavorable steric clashes, a potential reason for its decreased potency at CB 1 relative to its MDMB counterpart. Finally, CUMYL-HEXINACA (44) bound in a similar fashion to MPP-HEXINACA (43); however, the smaller cumyl headgroup experiences fewer clashes with surrounding residues Binding modes observed for CB 2 were similar to those observed for CB 1 .…”

“…Notably, 7-azaindoles were partial agonists at CB 2 , but highly efficacious agonists relative to CP55,940 at CB 1 , supporting previous comparisons between these scaffolds in analogous compound series. 48,49 Compared with evaluation via the MPA assay, indole and 7-azaindole derivatives followed similar trends, and the indazole analogues showed slightly smaller difference in potencies.…”