Dysosmaflavonoid A-F, new flavonols with potent DPPH radical scavenging activity from Dysosma versipellis.

Six new flavonols, including four glucosylated flavonols (dysosmaflavonoid A-D), one phenylpropanoid-substituted flavonol (dysosmaflavonoid E), and one phenyl-substituted flavonol (dysosmaflavonoid F), together with five known analogues, were isolated from the roots and rhizomes of Dysosma versipellis. Their structures were elucidated by comprehensive analysis of their NMR, IR, UV, HRESIMS, and HPLC data. The antioxidant activities of all isolated compounds were examined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. Compounds 2, 3, 5-8, and 12 exhibited significant DPPH scavenging capacity with IC50 values of 33.95, 39.02, 31.17, 32.79, 31.85, 30.48, and 23.75 µM, respectively, in comparison with Trolox (IC50, 15.80 µM). Compound 12 displayed more potent DPPH radical scavenging activity than prenylated and (or) glucosided derivatives (2-4, or 10). The preliminary structure-activity relationship showed that the catechol structure in flavonol is essential for DPPH radical scavenging effect.

Structurally diverse biflavonoids from Dysosma versipellis and their bioactivity.

Five pairs of new biflavonoid enantiomers, (±)-dysosmabiflavonoids A-E (1-5), two new biflavonoids, dysosmabiflavonoids F-G (6-7), and four biosynthetically related precursors (8-11) were isolated from the roots and rhizomes of Dysosma versipellis. Their structures were elucidated by extensive spectroscopic analysis, including HR-ESI-MS and 2D NMR. Their absolute configurations were determined by comparison of the calculated and experimental ECD spectra. All isolated compounds were evaluated for AChE inhibitory activity. Compounds 6 and 7 exhibited more potent inhibitory activities with IC50 values of 1.42 and 0.73 µM, respectively, than their biosynthetically related precursors kaempferol (8, 17.90 µM) and quercetin (9, 3.96 µM). The preliminary structure-activity relationship study indicated that the connection mode of biflavonoid subunits, oxidation degree of the C ring, and 3,4-dihydroxy group of the B ring were important structural factors for AChE inhibitory activity. Racemates 1-5 and their corresponding levorotatory and dextrorotatory enantiomers were tested for their potential to impede the generation of NO in lipopolysaccharide-stimulated RAW264.7 cells, and their mushroom tyrosinase inhibitory effect. Racemate 1 displayed more potent mushroom tyrosinase inhibitory activity (IC50, 28.27 µM) than the positive control kojic acid (IC50, 32.59 µM). D. versipellis may have therapeutic potential for melanogenesis disorders and neurodegenerative diseases.