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

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)-alpha-L-rhamnopyranoside (9) and 11 known compounds. The known compounds quercetin 3-O-(3 '',4 ''-di-O-acetyl)-alpha-L-rhamnopyranoside (8), rutin (10), quercetin 3-O-alpha-L-rhamnopyranoside (11), and myricetin 3-O-alpha-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 (IC50 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 IC50 values ranging 1.90 to 3.90 mu M.