title: New anthocyanidin and anthocyanin pigments from blue plumbago.
abstract: Phytochemical investigations of blue plumbago ( Plumbago auriculata  Poir. syn.  Plumbago capensis  Thunb.) flowers have led to the isolation of six new anthocyanins based on three new anthocyanidins with 5,7-dimethoxylated A-rings. Their structures were identified by 2D nuclear magnetic resonance and high-resolution mass spectrometry as the 3-O-β-galactopyranosides (1,2,4) and 3-O-α-rhamnopyranosides (3,5,6) of 5,7-dimethyldelphinidin, 5,7-dimethylpetunidin, and 5,7-dimethylmalvidin. Identification of 1-6 implies new structures for the previously reported anthocyanidins pulchellidin, europinidin, and capensinidin to be 5,7-dimethoxy-3,3',4',5'-tetrahydroxyflavylium, 5,7,3'-trimethoxy-3,4',5'-trihydroxyflavylium, and 5,7,3',5'-tetramethoxy-3,4'-dihydroxyflavylium cations, respectively. The anthocyanins (0.4 mg/g flowers) were accompanied by the dihydroflavonol taxifolin 3'-O-β-glucopyranoside (1.4 mg/g) and the flavonols 5-methylquercetin 3-O-α-rhamnopyranoside (8.8 mg/g) and 5-methylquercetin (0.4 mg/g). The anthocyanins 1-6 are the first reported natural anthocyanins with no free hydroxyl groups in their 5- and 7-positions on their A-rings. They have thus no possibility of forming the tautomeric quinonoidal bases (anhydrobases), which are related to the free hydroxyl groups in the 5- and 7-positions of previously reported anthocyanins. The genes behind the 5,7-dimethoxylated anthocyanins might be useful for making anthocyanins with special properties (colors, etc.).
authors.affiliation: Department of Chemistry, University of Bergen, Allégt. 41, 5007 Bergen, Norway.
authors.forename: Irene
authors.initials: I
authors.lastname: Skaar
authors.forename: Monica
authors.initials: M
authors.lastname: Jordheim
authors.forename: Robert
authors.initials: R
authors.lastname: Byamukama
authors.forename: Angella
authors.initials: A
authors.lastname: Mbabazi
authors.forename: Sileshi G
authors.initials: SG
authors.lastname: Wubshet
authors.forename: Bernard
authors.initials: B
authors.lastname: Kiremire
authors.forename: Oyvind M
authors.initials: OM
authors.lastname: Andersen
mesh_terms: D000872:Anthocyanins / Q000737:chemistry / Q000302:isolation & purification*; D002851:Chromatography, High Pressure Liquid; D005419:Flavonoids / Q000737:chemistry / Q000302:isolation & purification; D035264:Flowers / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D029606:Plumbaginaceae
chemical_list: D000872:Anthocyanins; D005419:Flavonoids