Two new lignans and melanogenesis inhibitors from Schisandra nigra

An acetone extract from the stems of Schisandra nigra M ax . (Schisandraceae) exhibited significant inhibition of 3-isobutyl-1-methylxanthine (IBMX)-stimulated melanogenesis in murine B16 melanoma F10 cells. Fractionation and purification of the extract led to the isolation of two new tetrahydrofuran-type lignans, (+)-5-methoxyzuonin A ( 2 ) and kadlongirin C ( 3 ), along with eight known compounds ( 1 , 4 – 10 ). The structures of the new compounds were determined by spectroscopic analyses. Of the isolated compounds ( 1 , 3 – 10 ), (+)-zuonin A ( 1 ) showed remarkable inhibition of melanogenesis at concentrations without cytotoxicity in B16 melanoma F10 cells. (+)-Zuonin A ( 1 ) did not inhibit tyrosinase; however, Western blot analysis revealed that it decreased protein levels of tyrosinase and tyrosinase-related proteins (TRP)-1 and TRP-2 without changing phosphorylation level of cAMP response element-binding protein.