Flavonoids of the rose-pink, blue, and white flowers of Nigella damascena L. (Ranunculaceae)

Nigella damascena L. is an annual plant belonging to the buttercup family Ranunculaceae, commonly known as love-in-a-mist. It is used as a garden plant. The flowers are blue, pink, or white. In order to determine the pigments responsible for the flower colors of N. damascena, the anthocyanins and flavonols in the rose-pink, blue, and white flowers of N. damascena were investigated using cultivars of the 'Miss Jekyll' series. The identities and structures of compounds were determined by chemical and spectroscopic analyses. Four cyanidin 3-glycosides were detected and identified from the rose-pink flowers. In the blue flowers, one major anthocyanin and several minor anthocyanins were detected. The identities of the major and one minor anthocyanin were determined. The main anthocyanins in the rose-pink and the blue flowers were cyanidin 3-[2-(xylosyl)-6-(rhamnosyl)-glucosidel and 7-methyldelphinidin 3-[2-(xylosyl)-6-(rhamnosyl)-glucoside], respectively. Petunidin 3[2-(zylosyl)-6-(rhamnosyl)-glucoside] had been previously reported as the major anthocyanin from the blue flowers, however, any petunidin-type anthocyanins were not found from the blue flowers. Cyanidin 3-[2-(glucuronosyl)-6-(rhamnosyl)-glucosidel, one of minor anthocyanins in the rose-pink flowers, and 7-methyldelphinidin 3-[2-(xylosyl)-6-(rhamnosyl)-glucoside] are reported for the first time. This is the second report of an anthocyanin of the 7-methyldelphinidin type, following that from Catharanthus roseus flowers. The white-flower cultivar contained anthocyanins analogous to those of the blue flowers but at very low levels. The same three flavonols were detected in the rose-pink, blue, and white flowers.