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 IC 50 value of 146.5 μg/mL.