Tannins and Related Polyphenols of Melastomataceous Plants: I: Hydrolyzable Tannins from Tibouchina semidecandra Cogn

Abstract

Four new hydrolyzable tannins, methylvescalagin and nobotanins, A, D and F, along with eleven known polyphenolics, have been isolated from the leaves of Tibouchina semidecandra cogn. Based on spectral and chemical evidence, nobotanin D was characterized as l,6-di-0-galloyl-2,3-0-(*S 'x2018;)-hexahydroxydiphenoyl-/?-D-glucose (16), and the structures of nobotanins A (17) and F (18) were established as dimeric hydrolyzable tannins possessing a valoneoyl group as a linking unit between the monomers. © 1991, The Pharmaceutical Society of Japan. All rights reserved.