Synthesis of [13C4]-labeled Δ9-tetrahydrocannabinol and 11-nor-9-carboxy-Δ9-tetrahydrocannabinol as internal standards for reducing ion suppressing/alteration effects in LC/MS-MS quantification

Abstract

(-)-Δ9-Tetrahydrocannabinol is the principal psychoactive component of the cannabis plant and also the active ingredient in some prescribed drugs. To detect and control misuse and monitor administration in clinical settings, reference samples of the native drugs and their metabolites are needed. The accuracy of liquid chromatography/mass spectrometric quantification of drugs in biological samples depends among others on ion suppressing/alteration effects. Especially, 13C-labeled drug analogues are useful for minimzing such interferences. Thus, to provide internal standards for more accurate quantification and for identification purpose, synthesis of [13C4]-Δ9-tetrahydrocannabinol and [13C4]-11-nor-9-carboxy-Δ9-tetrahydrocannabinol was developed via [13C4]-olivetol. Starting from [13C4]-olivetol the synthesis of [13C4]-11-nor-9-carboxy-Δ9- tetrahydrocannabinol was shortened from three to two steps by employing nitromethane as a co-solvent in condensation with (+)-apoverbenone.