Antioxidant phenolic compounds and flavonoids of Mitragyna rotundifolia (Roxb.) Kuntze in vitro

Different solvent extracts of leaves and bark of Mitragyna rotundifolia (Roxb.) Kuntze were evaluated by DPPH, ABTS, and FRAP assays, respectively, for antioxidant properties. Total phenolic and flavonoid content was determined as pyrocatechol and rutin equivalents, respectively, and correlated with antioxidant activities. More polar solvent extracts (n-butanol and ethyl acetate) had relatively higher antioxidant activity than nonpolar solvent extracts (petroleum ether). The n-butanol extract also exhibited a higher phenolic and flavonoid content than the other solvent extracts did. The DPPH assay was highly correlated with the ABTS assay (R (2) = 0.9628, P < 0.0001). Two phenolic and four flavonoid compounds were isolated from the ethyl acetate leaf extracts. Compounds 3-6 were isolated for the first time from the genus of Mitragyna and compound 5 showed the highest antioxidant activity.