In vitro cannabinoid activity profiling of generic ban-evading brominated synthetic cannabinoid receptor agonists and their analogs

Abstract

Following the enactment of a generic ban in China in 2021, the synthetic cannabinoid market has been evolving, now encompassing even wider structural diversity. Compounds carrying a brominated core such as ADB-5′Br-BUTINACA (ADMB-B-5Br-INACA) and tail-less analogs, such as ADB-5′Br-INACA (ADMB-5Br-INACA), MDMB-5′Br-INACA, and ADB-INACA (ADMB-INACA), have been detected since late 2021. This study investigated the cannabinoid receptor (CB) activation potential of synthesized (S)-enantiomers of these substances, as well as of two predicted analogs MDMB-5′Br-BUTINACA (MDMB-B-5Br-INACA) and ADB-5′F-BUTINACA (ADMB-B-5F-INACA), using CB₁ and CB₂ β-arrestin 2 recruitment assays and a CB₁ intracellular calcium release assay. Surprisingly, the tail-less (S)-ADB-5′Br-INACA and (S)-MDMB-5′Br-INACA retained CB activity, albeit with a decreased potency compared to their tailed counterparts (S)-ADB-5′Br-BUTINACA and (S)-MDMB-5′Br-BUTINACA, respectively, which were potent and efficacious CB₁ agonists. Also, at CB₂, tail-less analogs showed a lower potency but increased efficacy. Removing the bromine substitution ((S)-ADB-INACA) resulted in a reduced activity at CB₁; however, this effect was less prominent at CB₂. Looking at tailed analogs, replacing the bromine with a fluorine substitution ((S)-ADB-5′F-BUTINACA) resulted in an increased potency and efficacy at both receptors. Furthermore, as ADB-5′Br-INACA and MDMB-5′Br-INACA have been frequently detected together in Scottish prisons, this study also evaluated the CB₁ receptor activation potential of different mixtures of their respective reference standards, showing no unexpected cannabimimetic effect of combining both substances. Lastly, two powders seized by Belgian Customs and confirmed to contain ADB-5′Br-INACA and MDMB-5′Br-INACA, respectively, were assessed for CB activity. Based on the comparison with their reference standards, varying degrees of purity were suspected.