title: Flavonoids in translucent bracts of the Himalayan Rheum nobile (Polygonaceae) as ultraviolet shields.
abstract: UV-absorbing substances were isolated from the translucent bracts of Rheum nobile, which grows in the alpine zone of the eastern Himalayas. Nine kinds of the UV-absorbing substances were found by high performance liquid chromatography (HPLC) and paper chromatography (PC) surveys. All of the five major compounds are flavonoids, and were identified as quercetin 3- O-glucoside, quercetin 3- O-galactoside, quercetin 3- O-rutinoside, quercetin 3- O-arabinoside and quercetin 3- O-[6"-(3-hydroxy-3-methylglutaroyl)-glucoside] by UV, 1H and 13C NMR, mass spectra, and acid hydrolysis of the original glycosides, and direct PC and HPLC comparisons with authentic specimens. The four minor compounds were characterised as quercetin itself, quercetin 7- O-glycoside, kaempferol glycoside and feruloyl ester. Of those compounds, quercetin 3- O-[6"-(3-hydroxy-3-methylglutaroyl)-glucoside] was found in nature for the first time. The translucent bracts of R. nobile accumulate a substantial quantity of flavonoids (3.3-5 mg per g dry material for the major compounds). Moreover, it was clarified by quantitative HPLC survey that much more of the UV-absorbing substances is present in the bracts than in rosulate leaves. Although the flavonoid compounds have been presumed to be the important UV shields in higher plants, there has been little characterisation of these compounds. In this paper, the UV-absorbing substances of the Himalayan R. nobile were characterised as flavonol glycosides based on quercetin.
authors.affiliation: Tsukuba Botanical Garden, National Science Museum, 4-1-1 Amakubo, Tsukuba 305-0005, Japan. iwashina@kahaku.go.jp
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Iwashina
authors.forename: Yuji
authors.initials: Y
authors.lastname: Omori
authors.forename: Junichi
authors.initials: J
authors.lastname: Kitajima
authors.forename: Shinobu
authors.initials: S
authors.lastname: Akiyama
authors.forename: Toshisada
authors.initials: T
authors.lastname: Suzuki
authors.forename: Hideaki
authors.initials: H
authors.lastname: Ohba
mesh_terms: D002851:Chromatography, High Pressure Liquid; D002854:Chromatography, Paper; D005419:Flavonoids / Q000737:chemistry* / Q000302:isolation & purification; D015394:Molecular Structure; D019664:Polygonaceae / Q000737:chemistry*; D014466:Ultraviolet Rays
chemical_list: D005419:Flavonoids