Flavonoid glycosides from the rhizomes of Pronephrium penangianum

Six flavonoid glycosides jixueqisus A-F, together with nine known flavonoids, were isolated from the rhizomes of the fern Pronephrium penangianum. Among them, two red pigments jixueqisus A and B possess the same rare 6,8-dimethyl-2-phenyl-7H-1-benzopyran-7-one skeleton (a long conjugated system). Jixueqisu Cwas a dihydrochalcone glycoside, jixueqisu D was a chalcone glycoside, jixueqisu E was an aurone glycoside, and jixueqisu F was a flavonone glycoside. Interestingly, jixueqisus D-F, (2S)-5,2',5'-trihydroxy-7-methoxyflavanone and 5,2',5'-trihydroxy-7-methoxyflavone possessed a 2,5-dihydroxy substituted benzene ring (B-ring). Their structures were elucidated by various spectroscopic and chemical methods. Furthermore, the plausible biosynthetic pathways of jixueqisus A-F were discussed, respectively. All isolated compounds were evaluated for their activities against the proliferation of MCF-7, HepG-2, HCT-116 and BGC-823 tumor cell lines, four known flavane-4-ol glycosides, abacopterins A and C, eruberin B and triphyllin A, exhibited moderate activities to various cell lines.