The Oxidation of Phytocannabinoids to Cannabinoquinoids
Diego Caprioglio, Daiana Mattoteia, Federica Pollastro, Roberto Negri, Annalisa Lopatriello, Giuseppina Chianese, Alberto Minassi, Juan A. Collado, Eduardo Muñóz, Orazio Taglialatela‐Scafati, Giovanni Appendino
Abstract
Spurred by a growing interest in cannabidiolquinone (CBDQ, HU-313, 2) as a degradation marker and alledged hepatotoxic metabolite of cannabidiol (CBD, 1), we performed a systematic study on the oxidation of CBD (1) to CBDQ (2) under a variety of experimental conditions (base-catalyzed aerobic oxidation, oxidation with metals, oxidation with hypervalent iodine reagents). The best results in terms of reproducibility and scalability were obtained with λ5-periodinanes (Dess-Martin periodinane, 1-hydroxy-1λ5,2-benziodoxole-1,3-dione (IBX), and SIBX, a stabilized, nonexplosive version of IBX). With these reagents, the oxidative dimerization that plagues the reaction under basic aerobic conditions was completely suppressed. A different reaction course was observed with the copper(II) chloride-hydroxylamine complex (Takehira reagent), which afforded a mixture of the hydroxyiminodienone 11 and the halogenated resorcinol 12. The λ5-periodinane oxidation was general for phytocannabinoids, turning cannabigerol (CBG, 18), cannabichromene (CBC, 10), and cannabinol (CBN, 19) into their corresponding hydroxyquinones (20, 21, and 22, respectively). All cannabinoquinoids modulated to a various extent peroxisome proliferator-activated receptor gamma (PPAR-γ) activity, outperforming their parent resorcinols in terms of potency, but the iminoquinone 11, the quinone dimers 3 and 23, and the haloresorcinol 12 were inactive, suggesting a specific role for the monomeric hydroxyquinone moiety in the interaction with PPAR-γ.