Synthesis and functional evaluation of proteinogenic amino acid-derived synthetic cannabinoid receptor agonists...

Synthetic cannabinoid receptor agonists (SCRAs) comprise the second largest class of new psychoactive substances (NPS), and typically α-amino acid moieties are incorporated as part of their design. Limited investigation has been performed into elucidating structure-activity relationships around commonly used α-amino acid-derived head groups, mainly with valine and tert-leucine-derived compounds previously described. As such, proactive synthesis, characterisation and pharmacological evaluation were performed to explore structure-activity relationships of 15 α-amino acid derivatives, with both the natural isomers and their enantiomers at CB₁ and CB₂ investigated using a fluorescence-based membrane potential assay. This library was based around the detected SCRAs MPP-5F-PICA, MMB-5F-PICA, and MDMB-5F-PICA, with the latter showing significant receptor activation at CB₁ (pEC₅₀ = 8.34 ± 0.05 M; E _max = 108 ± 3%) and CB₂ (pEC₅₀ = 8.13 ± 0.07 M; E _max = 99 ± 2%). Most valine and leucine derivatives were potent and efficacious SCRAs, while smaller derivatives generally showed reduced activity at CB₁ and CB₂, and larger derivatives also showed reduced activity. SAR trends observed were rationalised via in silico induced fit docking. Overall, while natural enantiomers showed equipotent or greater activity than the unnatural isomers in most cases, this was not universal. As such, a number of these compounds should be monitored as emerging NPS, and various substituents described herein.