A comparative study on the antioxidant properties of tetrahydrocurcuminoids and curcuminoids

Several curcuminoids and tetrahydrocurcuminoids (THCs), bearing various hydroxyl and/or methoxy groups on their benzene rings, have been synthesized to study their antioxidant and hydrogen donating capacities using the DPPH method at 25 °C in methanol. The results show that the tetrahydrocurcuminoids are in general much more efficient than their curcuminoid analogs if they include a phenol group in meta- or para-position of the linking chain and a neighboring phenol or methoxy group. This efficiency gain of THCs by comparison to curcuminoids was attributed to the presence of benzylic hydrogens involved in the oxidation process of these compounds and not to the beta-diketone moiety in the chain.

The antioxidant power of curcuminoids and tetrahydrocurcuminoids is due to phenol units and not the enolic part of the chain. The enhanced antioxidant power of tetrahydrocurcuminoids compared to curcuminoids is due to the presence of easily oxidizable benzylic hydrogens.