Acylated cyanidin 3,7-Diglucosides in the red-purple flowers of Sophronitis wittigiana (Orchidaceae)

Three new acylated cyanidin 3,7-diglucosides (1-3) were isolated from the red-purple flowers of Sophronitis wittigiana as its main floral anthocyanins. These three pigments were based on cyanidin 3,7-diglucoside as the deacylanthocyanin, and their structures were determined to be cyanidin 3-O-[6-O-(malonyl)-β-glucopyranoside)]- 7-O-[6-O-(trans-caffeoyl)-β-glucopyranoside] as pigment 1, its demalonyl anthocyanin as pigment 2, and cyanidin 3-O-[6-O-(malonyl)-glucoside]-7-O-glucoside as pigment 3 by chemical and spectroscopic methods. On the other hand, five known acylated cyanidin 3,7,3'-triglucosides (4-8) were isolated from orange-red or red flowers of S. acuensis, S. brevipedunculata, S. cernua, S. coccinea var. xanthoglossa, and S. grandiflora as well as those of S. coccinea, and identified to be pigment 4 as Sophronitis coccinea anthocyanin 1 (SCA 1), pigment 5 as SCA 2, pigment 6 as SCA 3, pigment 7 as SCA 4, and pigment 8 as SCA 5 in comparison of the TLC, HPLC, and UVVis properties with standard samples of SCAs 1-5. These results showed that the three 3,7,3'-O-hydroxy groups of anthocyanins were all substituted with acylglucose and/or glucose residues in the orange-red or red flowers of six taxa of Sophronitis, whereas the 3'-O-hydroxy group was free from glucose in the red-purple flowers of S. wittigiana. Thus, the inactivation of 3'-O-glycosylation in cyanidin units might be involved in causing the blue color direction shift from orange-red or red to red-purple flower color of S. wittigiana.