Copigmentation with Acylated Anthocyanin and Kaempferol Glycosides in Violet and Purple Flower Cultivars of Aubrieta ^|^times; cultorum (Brassicaceae)

Abstract

Flavonoid pigments and flower colors of the violet and purple flower cultivars ‘Royal Violet’ and ‘Royal Red’, respectively, of Aubrieta × cultorum in the family Brassicaceae were investigated. Three acylated cyanidin 3-sambubioside-5-glucosides (1–3) were isolated as the main anthocyanins from violet and purple flowers of both cultivars. In particular, 1 was the dominant anthocyanin in both cultivars. Furthermore, an acylated flavonol glycoside (4) and another acylated flavonol glycoside (5) were isolated as the main flavonol pigments from flowers of ‘Royal Violet’ and ‘Royal Red’, respectively. The structures of 1–5 were elucidated by chemical and spectroscopic methods. Pigments 1, 2, 4, and 5 were found to be new flavonoid pigments. The structures of 1 and 2 were determined to be cyanidin 3-O-[2-O-(β-xylopyranosyl)-6-O-(trans-sinapoyl)-β-glucopyranoside]-5-O-[6-O-(malonyl)-β-glucopyranoside] and its demalonyl derivative, respectively. The structures of 4 and 5 were determined to be kaempferol 3-O-[2-O-(β-glucopyranosyl)-6-O-(trans-sinapoyl)-β-glucopyranoside]-7-O-[4-O-(β-glucopyranosyl)-6-O-(trans-sinapoyl)-β-glucopyranoside] and its desinapoyl-cellobiosyl derivative, respectively. Pigment 3 was identified to be the known compound cyanidin 3-O-[2-O-(β-xylopyranosyl)-6-O-(trans-p-coumaroyl)-β-glucopyranoside]-5-O-[6-O-(malonyl)-β-glucopyranoside]. The flower color of ‘Royal Violet’ was Violet 87A and that of ‘Royal Red’ was Purple 78A according to the R.H.S. Color Chart. On the visible absorption spectral curve, fresh petals and pressed petal juices of ‘Royal Violet’ in pH 5.0 buffer solution showed two characteristic absorption maxima at 560 and 604 nm and those of ‘Royal Red’ showed a single broad absorption maximum near 546 nm. In the reproducible experiments of their flower colors in pH 5.0 buffer solution, the violet solution was produced by the mixture of 1 and 4 (1 : 2) and exhibited characteristic absorption maxima at 560 and 604 nm, similar to those of the flower of ‘Royal Violet’. In contrast, a mixture of 1 and 5 or that of 1 and other common copigments produced a purple solution with only one absorption maximum near 547 nm. From these results, it was revealed that 4 was more appropriate for the bluing effect of A. × cultorum cultivars by intermolecular copigmentation with 1 than 5.