The radical scavenging activity of glycozolidol in physiological environments: a quantum chemical study

Glycozolidol was isolated from the root of Glycosmis pentaphylla (6-hydroxy-2-methoxy-3-methylcarbazole, GLD). This molecule attracted considerable interest due to its beneficial biological activities that likely stem from its antioxidant activity; yet, the radical scavenging action of GLD has not been investigated thus far. In this study, DFT calculations were used to estimate the radical scavenging activity of GLD against a variety of biologically significant radical species in physiological environments. The findings demonstrated that GLD exerts significant antiradical activity in water at pH = 7.40 and in pentyl ethanoate (as a model of lipidic media) with k _overall = 8.23 × 10⁶ and 3.53 × 10⁴ M^-1 s^-1, respectively. In aqueous solution, the sequential proton-loss electron transfer mechanism made the highest contribution to the activity, whereas in nonpolar solvents the formal hydrogen transfer mechanism dominated the activity. GLD is predicted to have strong antiradical activity against CH₃O˙, CH₃OO˙, CCl₃OO˙, NO₂, SO₄˙^-, DPPH and ABTS⁺˙ k _app ≈ 10⁹ M^-1 s^-1 and k _f ≈ 10⁶ M^-1 s^-1. The results suggest that GLD is a good radical scavenger in physiological environments.