Studies on Nepalese crude drugs. XXV. Phenolic constituents of the leaves of Didymocarpus leucocalyx C. B. Clarke (Gesneriaceae)

Seven new phenolic compounds (814) 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 814 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-phenyl-prop-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.