Flowering Blues

Today I was weeding a bed of roses, and pulled out many handsful of Veronica persica Poiret. The flowers are small, but a beautiful shade of blue that comes from an excessively complex form of delphinidin [delphinidin 3-O-(2-O-(6-O-p-coumaroyl-glucosyl)-6-O-p-coumaroyl-glucoside)-5-O-glucoside] and a complex form of apigenin [apigenin 7-O-(2-O-glucuronosyl)-glucuronide]. Such complexity for a tiny flower!

In the summer I expect to find another of my favorite weeds, Commelina communis L. This also relies on a very complex pigment called commelinin, which is composed of Malonylawobanin [delphinidin 3-O-(6-O-p-coumaroylglucoside)-5-O-(6-O-malonylglucoside)] and Flavocommelin [swertisin 4-O-glucoside].

Even the blue delphinium relies on a complex delphinidin derivative called violdelphin: delphinidin 3-rutinoside-7-O-(6-O-(4-(6-O-(4-hydroxybenzoyl)-beta-D-glucosyl)oxybenzoyl)-beta-D-glucoside).

Delphinin has already been added to roses, with results that are less than dazzling. It might take a while to get from introduced delphinidin to a genuine blue.

The Heavenly Blue morning glory flowers are colored by peonidin 3-(dicaffeylsophoroside)-5-glucoside in a highly alkaline solution.

Roses already produce cyanidin 3-sophoroside, which suggests that a peonidin 3-sophoroside would be possible by breeding rather than by gene transplanting. [e.g., by crossing the peonin-rich 'Hansa' with Rosa rugosa 'Salmon Pink', which is colored by cyanidin 3-sophoroside.]

And the existence in roses of peonidin 3-ρ-coumaroylglucoside-5-glucoside, suggests the possibility of getting to peonidin 3-ρ-coumaroylsophoroside, though without the 5-glucoside part because in roses the 5 position is populated before the 3 in the 3,5 diglucosides. I don't know that the addition of one molecule of ρ-coumaric acid would have the same effect as two caffeic acid molecules, but it's worth investigating.
Mikanagi (2000)

Phytochemistry. 67(10):992-8. (May 2006)
Ferric ions involved in the flower color development of the Himalayan blue poppy, Meconopsis grandis.
Yoshida K, Kitahara S, Ito D, Kondo T.

The Himalayan blue poppy, Meconopsis grandis, has sky blue-colored petals, although the anthocyanidin nucleus of the petal pigment is cyanidin. The blue color development in this blue poppy involving ferric ions was therefore studied. We analyzed the vacuolar pH, and the organic and inorganic components of the colored cells. A direct measurement by a proton-selective microelectrode revealed that the vacuolar pH value was 4.8. The concentrations of the total anthocyanins in the colored cells were around 5mM, and ca. three times more concentrated flavonols were detected. Fe was detected by atomic analysis of the colored cells, and the ratio of Fe to anthocyanins was ca. 0.8 eq. By mixing the anthocyanin, flavonol and metal ion components in a buffered aq. solution at pH 5.0, we were able to reproduce the same blue color; the visible absorption spectrum and CD were identical to those in the petals, with Fe(3+), Mg(2+) and flavonol being essential for the blue color. The blue pigment in Meconopsis should be a new type of metal complex pigment that is different from a stoichiometric supramolecular pigment such as commelinin or protocyanin.

Phytochemistry. 2011 Dec;72(17):2219-29.

The blue anthocyanin pigments from the blue flowers of Heliophila coronopifolia L. (Brassicaceae).
Saito N1, Tatsuzawa F, Toki K, Shinoda K, Shigihara A, Honda T.

Six acylated delphinidin glycosides (pigments 1-6) and one acylated kaempferol glycoside (pigment 9) were isolated from the blue flowers of cape stock (Heliophila coronopifolia) in Brassicaceae along with two known acylated cyanidin glycosides (pigments 7 and 8). Pigments 1-8, based on 3-sambubioside-5-glucosides of delphinidin and cyanidin, were acylated with hydroxycinnamic acids at 3-glycosyl residues of anthocyanidins. Using spectroscopic and chemical methods, the structures of pigments 1, 2, 5, and 6 were determined to be: delphinidin 3-O-[2-O-(β-xylopyranosyl)-6-O-(acyl)-β-glucopyranoside]-5-O-[6-O-(malonyl)-β-glucopyranoside], in which acyl moieties were, respectively, cis-p-coumaric acid for pigment 1, trans-caffeic acid for pigment 2, trans-p-coumaric acid for pigment 5 (a main pigment) and trans-ferulic acid for pigment 6, respectively. Moreover, the structure of pigments 3 and 4 were elucidated, respectively, as a demalonyl pigment 5 and a demalonyl pigment 6. Two known anthocyanins (pigments 7 and 8) were identified to be cyanidin 3-(6-p-coumaroyl-sambubioside)-5-(6-malonyl-glucoside) for pigment 7 and cyanidin 3-(6-feruloyl-sambubioside)-5-(6-malonyl-glucoside) for pigment 8 as minor anthocyanin pigments. A flavonol pigment (pigment 9) was isolated from its flowers and determined to be kaempferol 3-O-[6-O-(trans-feruloyl)-β-glucopyranoside]-7-O-cellobioside-4'-O-glucopyranoside as the main flavonol pigment. On the visible absorption spectral curve of the fresh blue petals of this plant and its petal pressed juice in the pH 5.0 buffer solution, three characteristic absorption maxima were observed at 546, 583 and 635 nm. However, the absorption curve of pigment 5 (a main anthocyanin in its flower) exhibited only one maximum at 569 nm in the pH 5.0 buffer solution, and violet color. The color of pigment 5 was observed to be very unstable in the pH 5.0 solution and soon decayed. In the pH 5.0 solution, the violet color of pigment 5 was restored as pure blue color by addition of pigment 9 (a main flavonol in this flower) like its fresh flower, and its blue solution exhibited the same three maxima at 546, 583 and 635 nm. On the other hand, the violet color of pigment 5 in the pH 5.0 buffer solution was not restored as pure blue color by addition of deacyl pigment 9 or rutin (a typical flower copigment). It is particularly interesting that, a blue anthocyanin-flavonol complex was extracted from the blue flowers of this plant with H(2)O or 5% HOAc solution as a dark blue powder. This complex exhibited the same absorption maxima at 546, 583 and 635 nm in the pH 5.0 buffer solution. Analysis of FAB mass measurement established that this blue anthocyanin-flavonol complex was composed of one molecule each of pigment 5 and pigment 9, exhibiting a molecular ion [M+1] (+) at 2102 m/z (C(93)H(105)O(55) calc. 2101.542). However, this blue complex is extremely unstable in acid solution. It really dissociates into pigment 5 and pigment 9.

The Flavonoids: Advances in Research since 1980 (1988) pp. 5, 7-8
J. B. Harborne
1.3.4 Zwitterionic anthocyanins

Until recently, acylated anthocyanins were known to be substituted by hydroxycinnamic acids ( ρ-coumaric, caffeic, ferulic or sinapic), by ρ-hydroxybenzoic acid or by acetic acid. However, it is now apparent from extensive electrophoretic surveys (Harborne and Boardley, 1985; Harborne, 1986) and from detailed investigations of individual pigments (e.g. Cornuz et al., 1981) that anthocyanins are also acylated in nature with aliphatic dicarboxylic acids, such as malonic, malic, oxalic and succinic. Such acylation renders the cationic anthocyanin a zwitterion, which means that it is possible to distinguish these pigments from other anthocyanins by paper electrophoresis in a weakly acidic buffer.

Bot. Mag. Tokyo 96, 359. (1983)
The anthocyanin in blue flowers of Centaurea cyanus.
Takeda, K. and Tominaga, S.

The anthocyanin in the blue cornflower (Centaurea cyanus) has been known for many years to be cyanidin 3,5-diglucoside, namely cyanin. However, in the course of this study, it became evident that the major anthocyanin in the blue cornflower is not cyanin but cyanidin 3-succinyl glucoside 5-glucoside. This anthocyanin has not been reported in the literature and is tentatively called “centaurocyanin”. Centaurocyanin is chromatographically identical with the anthocyanin contained in crystalline protocyanin, the blue pigment from the cornflower. Thus, there seems no doubt that this anthocyanin, but not cyanin, forms the blue complex pigment protocyanin.

Tetrahedron Lett. 24(51): 5749-5752 (1983)
Structures of a succinyl anthocyanin and a malonyl flavone, two constituents of the complex blue pigment of cornflower Centaurea cyanus
Tamura, H., Kondo, T., Kato, Y. and Goto, T.

Structures of a new anthocyanin and a new flavone isolated from the complex pigment of blue flower of cornflower Centaurea cyan's were determined to be 3-O-(6-O-succinyl-β-D-glucosyl)-5-O-(β-D-glucosyl)cyaniding (1) (succinylcyanin) and apigenin 4'-O-(6-O-malonyl-β-D-glucoside) 7-O-β-D-glucoronde (3), respectively.

Angew. Chem. Int. Ed. Engl 33(9): 978-979 (1994)
Composition of Protocyanin, A Self-Assembled Supramolecular Pigment from the Blue Cornflower, Centaurea cyanus

Prof. Dr. Tadao Kondo, Minoru Ueda, Dr. Hirotoshi Tamura, Dr. Kumi Yoshida, Prof. Dr. Minoru Isobe, Prof. Dr. Toshio Goto

Willstätter first isolated cyanin from the blue cornflower, Centaurea cyanus, in the early part of this century.[l,2] In 1958 Bayer isolated a blue pigment named protocyanin from the same flower.[3,4] Just after that, Hayashi obtained it as crystals,[5] as did Asen.[6-8] These three groups proposed protocyanin to be a metal complex, but the reported components contradicted each other, probably because of the complex properties of protocyanin. Protocyanin was described as a metalloanthocyanin analogous to another blue pigment, commelinin.[9] It is not dialyzable, migrates toward the anode on electrophoresis, and dissociates by dilution with water and then quickly decolorizes. We have already determined the complete structure of commelinin.[10] But pure protocyanin could not be obtained directly from cornflower petals since it is much less stable than commelinin. By acid dissociation of an extract, we found that the true anthocyanin and flavone components of protocyanin are succinylcyanin (Sucy, 1) and a malonylflavone (Mafl, 2).[11] From these components in addition to metal ions we first prepared the true blue pigment of the cornflower. In this paper we report the exact composition of protocyanin.

J. Agric. Food Chem. 60: 1510−1515 (2012)
New Anthocyanidin and Anthocyanin Pigments from Blue Plumbago
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.).

Phytochemistry. 2002 Jun;60(4):357-9.
Anthocyanins from flowers of Cichorium intybus.
Nørbaek R1, Nielsen K, Kondo T.

From the blue perianth segments of Cichorium intybus we isolated four anthocyanins. The pigments were identified as delphinidin 3,5-di-O-(6-O-malonyl-beta-D-glucoside) and delphinidin 3-O-(6-O-malonyl-beta-D-glucoside)-5-O-beta-D-glucoside and the known compounds were delphinidin 3-O-beta-D-glucoside-5-O-(6-O-malonyl-beta-D-glucoside) and delphinidin 3,5-di-O-beta-D-glucoside. In addition 3-O-p-coumaroyl quinic acid has been identified.

Phytochemistry. 2000 Mar;53(5):575-9.
Covalently linked anthocyanin-flavonol pigments from blue Agapanthus flowers.
Bloor SJ, Falshaw R.

The structures of the two major anthocyanins in blue Agapanthus flowers have been determined to be a p-coumaroylated delphinidin diglycoside attached to a flavonol triglycoside via a succinic acid diester link. The structure has been determined unambiguously through degradation studies, glycosidic analysis and NMR experiments. These compounds represent unique examples of anthocyanin pigments where both types of co-pigment, an aromatic acyl group and a flavonoid co-pigment, are attached covalently to the anthocyanin.

J. Jap. Soc. Hort. Sci. 83(3): 259-266 (2014)
Floral Pigments from the Blue Flowers of Nemophila menziesii ‘Insignis Blue’ and the Purple Flower of Its Variants
Fumi Tatsuzawa, Kenjiro Toki, Yuko Ohtani, Kazuhisa Kato, Norio Saito, Toshio Honda, Masahiro Mii

Two anthocyanins (pigments 1 and 2) were detected from the blue flowers of Nemophila menziesii ‘Insignis blue’ and the purple flowers of its variants as the main floral anthocyanins. These two anthocyanins were isolated from the blue flowers and elucidated to be petunidin 3-O-[6-O-(cis-p-coumaroyl)-β-glucopyranoside]-5-O-[6-O-(malonyl)-β-glucopyranoside] (1) and petunidin 3-O-[6-O-(trans-p-coumaroyl)- -glucopyranoside]-5-O-[6-O-(malonyl)-β-glucopyranoside] (2), respectively, by chemical and spectroscopic means, and pigment 1 was confirmed as a new anthocyanin in plants. Two flavonol glycosides (pigments 3 and 5) and two flavone glycosides (pigments 4 and 6) were also isolated from the blue flowers, and were identified to be kaempferol 3-(6-rhamnosyl)-glucoside-7-glucoside (3), apigenin 7,4 -di-glucoside (4), kaempferol 3-(2,6-di-rhamnosyl)-glucoside (5), and apigenin 7-glucoside-4 -(6-malonyl)-glucoside (6) as major flavonoids. Among these four flavonoids, however, pigments 4 and 6 (flavones) were not detected in the purple flowers. These results might be attributed to color production in blue and purple flowers.