Uncovering the psychoactivity of a cannabinoid from liverworts associated with a legal high

Phytochemical studies on the liverwort genus have previously identified the bibenzyl (-)--perrottetinene (-PET), which structurally resembles (-)-Δ--tetrahydrocannabinol (Δ--THC) from L. preparations are sold as cannabinoid-like legal high on the internet, even though pharmacological data are lacking. Herein, we describe a versatile total synthesis of (-)--PET and its (-)- diastereoisomer and demonstrate that both molecules readily penetrate the brain and induce hypothermia, catalepsy, hypolocomotion, and analgesia in a CB1 receptor-dependent manner in mice. The natural product (-)--PET was profiled on major brain receptors, showing a selective cannabinoid pharmacology. This study also uncovers pharmacological differences between Δ-THC and PET diastereoisomers. Most notably, (-)--PET and (-)--PET significantly reduced basal brain prostaglandin levels associated with Δ--THC side effects in a CB1 receptor-dependent manner, thus mimicking the action of the endocannabinoid 2-arachidonoyl glycerol. Therefore, the natural product (-)--PET is a psychoactive cannabinoid from bryophytes, illustrating the existence of convergent evolution of bioactive cannabinoids in the plant kingdom. Our findings may have implications for bioprospecting and drug discovery and provide a molecular rationale for the reported effects upon consumption of certain preparations as moderately active legal highs.