Browsing by Author "Kiremire, Bernard"

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    Anthocyanins from flowers of Hippeastrum cultivars
    (Elsevier, 2006) Byamukama, Robert; Jordheim, Monica; Kiremire, Bernard; Namukobe, Jane; Øyvind, M. Andersen
    The anthocyanins, cyanidin 3-O-(6″-O-α-rhamnopyranosyl-β-glucopyranoside) (1) and pelargonidin 3-O-(6″-O-α-rhamnopyranosyl-β-glucopyranoside) (2), were isolated from the ornamental flowers of a Ugandan Hippeastrum cultivar by a combination of chromatographic techniques, and their structures were elucidated mainly by the use of homo- and heteronuclear nuclear magnetic resonance spectroscopy and electrospray mass spectrometry. The same anthocyanins were found in six different Hippeastrum cultivars purchased in Norway. However, the absolute amount of the anthocyanins (0.08–1.79 mg/g, fresh weight) and the relative proportions of the individual anthocyanins varied from cultivar to cultivar (13.2–96.5% of 1). The colours of the fresh petals of the three cultivars ‘Red Lion’, ‘Royal Velvet’ and ‘Liberty’ were described by the CIELab coordinates L* (lightness), C* (chroma) and hab (hue angles). All the cultivars showed hue angles corresponding to scarlet nuances (hab = 22–35°), with the highest value in ‘Red Lion’. The most reddish petals (in ‘Royal Velvet’) contained the highest relative proportion of 1. Thus, the in vivo colours of these cultivars seem to be correlated with the relative proportions of individual anthocyanin in the petals.
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    Anthocyanins from leaf stalks of cassava (Manihot esculenta Crantz)
    (Byamukama, R., Namukobe, J., & Kiremire, B. (2009). Anthocyanins from leaf stalks of cassava (Manihot esculenta Crantz). African Journal of Pure and Applied Chemistry, 3(2), 020-025https://academicjournals.org/journal/AJPAC/article-abstract/1396EB61511., 2009) Byamukama, Robert; Namukobe, Jane; Kiremire, Bernard
    The anthocyanins, cyanidin 3-O-(6’’-O-a-rhamnopyranosyl-b-glucopyranoside) (1) and delphinidin 3-O-(6’’-O-a-rhamnopyranosyl-b-glucopyranoside) (2) isolated from the leaf stalks of cassava (Manihot esculenta Crantz) by a combination of chromatographic techniques, and their structures were elucidated mainly by the use of homo- and heteronuclear magnetic resonance spectroscopy. The relative amounts of 1 and 2 in the extracts were approximately 92 and 4%, respectively. The absolute amount was 124 mg/100 g.
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    Anthocyanins with Unusual Furanose Sugar (Apiose) from Leaves of Synadenium Grantii (Euphorbiaceae)
    (Elsevier, 2010) Andersen, Øyvind M.; Jordheim, Monica; Byamukama, Robert; Mbabazi, Angella; Ogweng, George; Skaar, Irene; Kiremire, Bernard
    Four anthocyanins, cyanidin 3-O-(200-(5000-(E-p-coumaroyl)-b-apiofuranosyl)-b-xylopyranoside)-5-O-bglucopyranoside, cyanidin 3-O-(200-(5000-(E-p-coumaroyl)-b-apiofuranosyl)-b-xylopyranoside), cyanidin 3-O-(200-(5000-(E-caffeoyl)-b-apiofuranosyl)-b-xylopyranoside) and cyanidin 3-O-(200-(5000-(E-feroyl)-bapiofuranosyl)- b-xylopyranoside) were isolated from leaves of African milk bush, (Synadenium grantii Hook, Euphorbiaceae) together with the known cyanidin 3-O-b-xylopyranoside-5-O-b-glucopyranoside and cyanidin 3-O-b-xyloside. The four former pigments are the first reported anthocyanins containing the monosaccharide apiose, and the three 5000-cinnamoyl derivative-200-(b-apiosyl)-b-xyloside subunits have previously not been reported for any compound.
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    New Anthocyanidin and Anthocyanin Pigments from Blue Plumbago
    (Journal of agricultural and food chemistry, 2012) Skaar, Irene; Jordheim, Monica; Byamukama, Robert; Mbabazi, Angella; Wubshet, Sileshi G.; Kiremire, Bernard; Andersen, Øyvind M.
    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.).
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    Purple anthocyanin colouration on lower (abaxial) leaf surface of Hemigraphis colorata (Acanthaceae)
    (Phytochemistry, 2014) Skaar, Irene; Adaku, Christopher; Jordheim, Monica; Byamukama, Robert; Kiremire, Bernard; Andersen, Øyvind M.
    The functional significance of anthocyanin colouration of lower (abaxial) leaf surfaces is not clear. Two anthocyanins, 5-O-methylcyanidin 3-O-(300-(b-glucuronopyranosyl)-b-glucopyranoside) (1) and 5-O-methylcyanidin 3-O-b-glucopyranoside (2), were isolated from Hemigraphis colorata (Blume) (Acanthaceae) leaves with strong purple abaxial colouration (2.2 and 0.6 mg/g fr. wt., respectively). The glycosyl moiety of 1, the disaccharide 300-(b-glucuronopyranosyl)-b-glucopyranoside), has previously been reported to occur only in a triterpenoid saponin, lindernioside A. The structural assignment of the aglycone of 1 and 2 is the first complete characterisation of a natural 7-hydroxy-5-methoxyanthocyanidin. Compared to nearly all naturally occurring anthocyanidins, the 5-O-methylation of this anthocyanidin limits the type of possible quinoidal forms of 1 and 2 to be those forms with keto-function in only their 7- and 40-positions