Studies on Nepalese Crude Drugs. XXV. Phenolic Constituents of the Leaves of Didymocarpus leucocalyx C. B. CLARKE (Gesneriaceae)

Seven new phenolic compounds (8-14) including three ones having unique structure named didymocalyxins A (12), B (13) and C (14) have been isolated from the leaves of Didymocarpus leucocalyx, along with five known flavonoids (5-hydroxy-6, 7-dimethoxyflavanone, 5, 8-dihydroxy-6, 7-dimethoxyflavanone, 2', 6'-dihydroxy-3', 4'-dimethoxychalcone, 3'-hydroxy-2', 4', 5', 6'-tetramethoxychalcone and 2', 5'-dihydroxy-4'-methoxy-3', 6'-dioxochalcone) and two known anthraquinoids (physcion and catenarin). The structures of 8-14 were determined to be 3', 4-dihydroxy-2', 4', 5', 6'-tetramethoxychalcone (8), 5, 8-dihydroxy-6, 7-dimethoxyisoflavone (9), 1, 6, 8-trihydroxy-4-benzoyloxy-3-methylanthraquinone (10), (2S)-2, 3-dihydroxypropyl 1, 6, 8-trihydroxy-3-methyl-9, 10-dioxoanthracene-2-carboxylate (11), (±)-1, 4-dihydroxy-2, 3, 6, 7-tetramethoxy-10-phenyl-9, 10-dihydrocyclohepta[2, 1-b]4H-chromene-8, 11-dione (12), 3-((1E, 2E)-1-hydroxy-3-phenylprop-2-enylidene)-7-((2E)-3-phenylprop-2-enoyl)-6-hydroxy-4, 5-dimethoxybenzo[b]furan-2-one (13) and 2((1E)-2-phenylvinyl)-5, 6-dihydroxy-7, 8-dimethoxy-4H-pyrano[3, 2-d]benzo[b]furan-4-one (14) on the basis of chemical and spectroscopic evidence and X-ray analysis.