Melanogenesis inhibitory pregnane glycosides from Cynanchum atratum

Abstract Bioassay-guided fractionation of the methanolic extract from the roots of Cynanchum atratum has resulted in the isolation of three new pregnane glycosides ( 1 – 3 ) along with four known compounds ( 4 – 7 ). Their structures were identified by analysis of the spectroscopic data including extensive 2D NMR. All of the isolates were evaluated for their potential to inhibit the melanin production in α-melanocyte stimulating hormone (α-MSH)-activated B16 melanoma cells. Of these, compounds 4 – 7 dose-dependently inhibited the melanin production with the IC 50 values ranging from 4 μM to 33 μM.