Alkaloid constituents from flower buds and leaves of sacred lotus (Nelumbo nucifera, Nymphaeaceae) with melanogenesis inhibitory activity in B16 melanoma cells
摘要:
Methanolic extracts from the flower buds and leaves of sacred lotus (Nelumbo nucifera, Nymphaeaceae) were found to show inhibitory effects on melanogenesis in theophylline-stimulated murine B16 melanoma 4A5 cells. From the methanolic extracts, a new alkaloid, N-methylasimilobine N-oxide, was isolated together with eleven benzylisoquinoline alkaloids. The absolute stereostructure of the new alkaloid was determined from chemical and physicochemical evidence. Among the constituents isolated, nuciferine, N-methylasimilobine, (-)-lirinidine, and 2-hydroxy-1-methoxy-6a, 7-dehydroaporphine showed potent inhibition of melanogenesis. Comparison of the inhibitory activities of synthetic related alkaloids facilitated characterization of the structure-activity relationships of aporphine-and benzylisoquinoline-type alkaloids. In addition, 3-30 mu M nuciferine and N-methylasimilobine inhibited the expression of tyrosinase mRNA, 3-30 mu M N-methylasimilobine inhibited the expression of TRP-1 mRNA, and 10-30 mu M nuciferine inhibited the expression of TRP-2 mRNA. (C) 2012 Elsevier Ltd. All rights reserved.