Structure of tecophilin, a tri-caffeoylanthocyanin from the blue petals of Tecophilaea cyanocrocus, and the mechanism of blue color development

The pigment, tecophilin, in blue flowers of Tecophilaea cyanocrocus was isolated and the structure was determined to be 3-O-(6-O-α-l-rhamnopyranosyl-β-d-glucopyranosyl)-7-O-(6-O-(4-O-(2-O-(4-O-β-d-glucopyranosyl-(E)-caffeoyl)-6-O-(4-O-β-d-glucopyranosyl-(E)-caffeoyl)-β-d-glucopyranosyl)-(E)-caffeoyl)-β-d-glucopyranosyl)delphinidin. The reproduction experiment of the same color as petals according to the results of chemical analysis and measurement of vacuolar pH of blue cells clarified that the blue color solely develops by tecophilin without interaction of metal ions nor co-pigments. 1H NMR analysis and CD spectrum indicate the co-existence of clockwise intermolecular self-association of the delphinidin nuclei and intramolecular π-π stacking between the chromophore and caffeoyl residues to derive bathochromic shift of the absorption spectrum and stabilize the color by preventing hydration reaction.