Purpose This work reports the synthesis and pharmacological and analytical data for a new series of recently identified azaindole-adamantyl-derived synthetic cannabinoids (SCs). Methods Each SC was synthesised using an efficient and divergent synthesis, and assessed by electron ionisation mass spectrometry (EIMS). The cannabimimetic activity of each compound was conducted using a fluorometric imaging plate reader (FLIPR) assay. Results The described EIMS method and retention time by gas chromatography were able to effectively differentiate each of the analogues regardless of the bicyclic core. For the first time in these SC structures, the bicyclic ring system was shown to have an impact on the cannabimimetic activities in the fluorometric assay of membrane potential. Analogues ranged from moderately potent at both CB 1 and CB 2 (e.g., AP4AIC EC 50 = 160 nM and EC 50 = 64 nM, respectively) to not active at either cannabinoid receptor (AP4AICA, AP5AICA, and APIC). Conclusions Further investigation into receptor selectivity surrounding these bicyclic cores could prove useful for future therapeutic applications. Keywords Synthetic cannabinoid • Azaindole • Adamantyl • CB 1 and CB 2 • APICA • Gas chromatography-mass spectrometry Electronic supplementary material The online version of this article (
Synthetic cannabinoid receptor agonists
(SCRAs) remain a prolific
class of new psychoactive substances (NPS) and continue to expand
rapidly. Despite the recent identification of hydroxybenzotriazole
(HOBt) containing SCRAs in synthetic cannabis samples, there is currently
no information regarding the pharmacological profile of these NPS
with respect to human CB1 and CB2 receptors.
In the current study, a series consisting of seven HOBt indole-, indazole-,
and 7-azaindole-carboxylates bearing a range of N-alkyl substituents were synthesized and pharmacologically evaluated.
Competitive binding assays at CB1 and CB2 demonstrated
that all analogues except a 2-methyl-substituted derivative had low
affinity for CB1 (K
i = 3.80–43.7
μM) and CB2 (K
i = 2.75–18.2
μM). A fluorometric functional assay revealed that 2-methylindole-
and indole-derived HOBt carboxylates were potent and efficacious agonists
of CB1 (EC50 = 12.0 and 63.7 nM; E
max = 118 and 120%) and CB2 (EC50 = 10.9 and 321 nM; E
max = 91 and 126%).
All other analogues incorporating indazole and 7-azaindole cores and
bearing a range of N1-substituents showed relatively low potency for
CB1 and CB2. Additionally, a reporter assay
monitoring β-arrestin 2 (βarr2) recruitment to the receptor
revealed that the 2-methylindole example was the most potent and efficacious
at CB1 (EC50 = 131 nM; E
max = 724%) and the most potent at CB2 (EC50 = 38.2 nM; E
max = 51%). As with the
membrane potential assay, the indazole and other indole HOBt carboxylates
were considerably less potent at both receptors, and analogues comprising
a 7-azaindole core showed little activity. Taken together, these data
suggest that NNL-3 demonstrates little CB1 receptor activity and is
unlikely to be psychoactive in humans. NNL-3 is likely an unintended
SCRA manufacturing byproduct. However, the synthesis of NNL-3 analogues
proved simple and general, and some of these showed potent cannabimetic
profiles in vitro, indicating that HOBt esters of
this type may represent an emerging class of SCRA NPS.
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