title: C-glycosylanthocyanidins synthesized from C-glycosylflavones.
abstract: Nine C-glycosyldeoxyanthocyanidins, 6-C-beta-glucopyranosyl-7-O-methylapigeninidin, 6-C-beta-glucopyranosyl-7-O-methylluteolinidin, 6-C-beta-(2''-O-beta-glucopyranosylglucopyranosyl)-7-O-methylapigeninidin, 6-C-beta-(2''-O-beta-glucopyranosylglucopyranosyl)-7,4'-di-O-methylapigeninidin, 8-C-beta-glucopyranosylapigeninidin, 8-C-beta-(2''-O-alpha-rhamnopyranosylglucopyranosyl)apigeninidin, 8-C-beta-(2''-O-alpha-(4'''-O-acetylrhamnopyranosyl)glucopyranosyl)apigeninidin, 6,8-di-C-beta-glucopyranosylapigeninidin (8), 6,8-di-C-beta-glucopyranosyl-4'-O-methylluteolinidin (9), have been synthesized from their respective C-glycosylflavones (yields between 14% and 32%) by the Clemmensen reduction reaction using zinc-amalgam. The various precursors (C-glycosylflavones) of the C-glycosylanthocyanidins were isolated from either flowers of Iris sibirica L., leaves of Hawthorn 'Crataegi Folium Cum Flore', or lemons and oranges. This is the first time C-glycosylanthocyanidins have been synthesized. The structures of all flavonoids including the flavone rotamers were elucidated by 2D NMR techniques and high-resolution electrospray MS. The distribution of the various structural forms of 8 and 9 are different at pH 1.1, 4.5, and 7.0, however, the two pigments undergoes similar structural transformations at the various pH values. Pigments 8 and 9 with C-C linkages between the sugar moieties and the aglycone, were found to be far more stable towards acid hydrolysis than pelargonidin 3-O-glucoside, which has the typical anthocyanidin C-O linkage between the sugar and aglycone. This stability may extend the present use of anthocyanins as nutraceuticals, pharmaceuticals or colorants.
authors.affiliation: Department of Chemistry, University of Bergen, Allégt. 41, N-5007 Bergen, Norway.
authors.forename: Orjan
authors.initials: O
authors.lastname: Bjorøy
authors.forename: Saleh
authors.initials: S
authors.lastname: Rayyan
authors.forename: Torgils
authors.initials: T
authors.lastname: Fossen
authors.forename: Kjersti
authors.initials: K
authors.lastname: Kalberg
authors.forename: Oyvind M
authors.initials: OM
authors.lastname: Andersen
mesh_terms: D000143:Acids / Q000737:chemistry; D000872:Anthocyanins / Q000138:chemical synthesis* / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D047309:Flavones; D005419:Flavonoids / Q000737:chemistry*; D006031:Glycosylation; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D013053:Spectrophotometry
chemical_list: D000143:Acids; D000872:Anthocyanins; D047309:Flavones; D005419:Flavonoids; C017154:cyanidin; C043562:flavone