Antioxidant flavan derivatives from the leaves of Morus alba

Two pairs of new flavans, moracinflavan A and B (1a/1b and 2a/2b), together with another five new flavan derivatives moracinflavan C-G (3-7), and three known flavans (8-10) were isolated from the leaves of Morus alba. Their structures were elucidated by detailed analyses based on spectroscopic data. Separation of the stereoisomeric mixtures of 1a and 1b, 2a and 2b was achieved using chiral HPLC, and the absolute configurations of the respective stereoisomers were determined based on comparison of experimental and calculated electronic circular dichroism (ECD) spectra. Using an ARE-dependent luciferase reporter assay, we identified that these flavans were capable of increasing ARE-luciferase activities. This indicated that these flavans are potential Nrf2 activators.