Δ9-cis-Tetrahydrocannabinol: Natural Occurrence, Chirality, and Pharmacology.

The cis-stereoisomers of Δ9-THC [(-)-3 and (+)-3] were identified and quantified in a series of low-THC-containing varieties of Cannabis sativa registered in Europe as fiber hemp and in research accessions of cannabis. While Δ9-cis-THC (3) occurs in cannabis fiber hemp in the concentration range of (-)-Δ9-trans-THC [(-)-1], it was undetectable in a sample of high-THC-containing medicinal cannabis. Natural Δ9-cis-THC (3) is scalemic (ca. 80-90% enantiomeric purity), and the absolute configuration of the major enantiomer was established as 6aS,10aR [(-)-3] by chiral chromatographic comparison with a sample available by asymmetric synthesis. The major enantiomer, (-)-Δ9-cis-THC [(-)-3], was characterized as a partial cannabinoid agonist in vitro and elicited a full tetrad response in mice at 50 mg/kg doses. The current legal discrimination between narcotic and non-narcotic cannabis varieties centers on the contents of "Δ9-THC and isomers" and needs therefore revision, or at least a more specific wording, to account for the presence of Δ9-cis-THCs [(+)-3 and (-)-3] in cannabis fiber hemp varieties.