The dimerization of Δ ⁹-tetrahydrocannabinolic acid A (THCA-A)

The renewed interest in dimeric salicylates as broad-spectrum anti-inflammatory and anti-diabetic agents provided a rationale to investigate the dimerization of the substituted salicylate Δ ⁹-tetrahydrocannabinolic acid (THCA-A, 3a) as a strategy to solve its instability to decarboxylation and to generate analogues and/or pro-drugs of this native pre-cannabinoid. Activation of the carboxylic group with the DCC-HOBt-DMAP protocol afforded a high yield of the OBt ester 4, that was next converted into the highly crystalline di-depsidic dimer 5 upon treatment with DMAP. The mono-depsidic dimer 6 was also formed when the reaction was carried out with partially decarboxylated THCA-A samples. The structure of the depsidic dimers was established by spectroscopic methods and by aminolysis of 5 into the pre-cannabinoid amide 7. Both dimers showed excellent shelf stability and did not generate significant amounts of Δ ⁹-THC upon heating. However, only the didepsidic dimer 5 activated PPAR-γ, the major target of pre-cannabinoids, but strong binding to serum proteins abolished this activity, also shielding it from the action of esterases.