Isolation of Flavonoids and Flavonoid Glycosides from i>Myrsine africana/i> and Their Inhibitory Activities against Mushroom Tyrosinase

摘要

Bioassay-guided fractionation of the methanol extract of the shoots of Myrsine africana led to the isolation of the new compound myricetin 3- O -(2″,4″-di- O -acetyl)-α-l-rhamnopyranoside ( 9 ) and 11 known compounds. The known compounds quercetin 3- O -(3″,4″-di- O -acetyl)-α-l-rhamnopyranoside ( 8 ), rutin ( 10 ), quercetin 3- O -α-l-rhamnopyranoside ( 11 ), and myricetin 3- O -α-l-rhamnopyranoside ( 12 ) are reported for the first time from the methanol extract of the shoots of M. africana. Compounds 10 and 12 showed significant inhibition of tyrosinase with 50% inhibition (IC_(50) values) of the enzyme at 0.13 ± 0.003 and 0.12 ± 0.002 mM, respectively, which was supported by the docking fitness scores obtained through molecular docking analysis. In addition, compounds 1 – 12 displayed significant antioxidant activity with IC_(50) values ranging 1.90 to 3.90 μM.