Flavonoid Diglycosides from Dendrobium officinale Leaves and Their Tyrosinase Inhibitory Activity

Four flavonoid C-glycosides, including two new diglycosides, dendrodiglycosides A (1) and B (2), along with known isoviolanthin (3) and apigenin 6-C-β-D-glucopyranosyl-(1→2)-α-L-arabinopyranoside (4), were isolated from the leaves of Dendrobium officinale (Orchidaceae). Their structures were elucidated by NMR and MS. Apigenin 6-C-β-D-glucopyranosyl-(1→2)-α-L-arabinopyranoside exhibited an inhibitory effect against tyrosinase with an IC50 value of 146.5 μg/mL.