Defining Steric Requirements at CB and CB Cannabinoid Receptors Using Synthetic Cannabinoid Receptor Agonists 5F-AB-PINACA, 5F-ADB-PINACA, PX-1, PX-2, NNL-1, and Their Analogues.

Synthetic cannabinoid receptor agonists (SCRAs) are a diverse class of new psychoactive substances (NPS). They commonly comprise -alkylated indole, indazole, or 7-azaindole scaffolds with amide-linked pendant amino acid groups. To explore the contribution of the amino acid side chain to the cannabinoid pharmacology of SCRA NPS, a systematic library of side chain-modified SCRAs was prepared based on the recent detections of amino acid derivatives (5F-AB-PINACA), (5F-ADB-PINACA), (PX-1), (PX-2), and (NNL-1). In vitro binding affinities and functional activities at cannabinoid type 1 and 2 receptors (CB and CB, respectively) were determined for all the library members using radioligand competition experiments and a fluorescence-based membrane potential assay. Binding affinities and functional activities varied widely across compounds ( = 0.32 to >10 000 nM, EC = 0.24-1259 nM), with several clear structure-activity relationships (SARs) emerging. Affinity and potency at CB changed as a function of the heterocyclic core (indazole > indole > 7-azaindole) and the pendant amino acid side chain (-butyl > -propyl > -butyl > benzyl > ethyl > methyl > hydrogen). Ensemble docking at CB revealed a clear steric basis for observed SAR trends. Interestingly, although (PX-1) and (PX-2) have been detected in recreational drug markets, they failed to induce centrally CB-mediated effects (e.g., hypothermia) in mice using radiobiotelemetry. Together, these data provide insights regarding structural contributions to the cannabimimetic profiles of (5F-AB-PINACA), (5F-ADB-PINACA), (PX-1), (PX-2), (NNL-1), and other SCRA NPS.