Synthesis of Designed Acylquinic Acid Derivatives Involved in Blue Color Development of Hydrangea and Their Co-pigmentation Effect

The blue sepal color of hydrangea may be developed by an unstable supramolecular metal-complex pigment composed of delphinidin 3-glucoside (1), 5-O-caffeoylquinic acid (2) and 5-O-p-coumaroylquinic acid (3) as co-pigments and Al 3+ in aqueous solution.To clarify the structure of blue pigment and the role of co-pigments, various acylquinic acid derivatives were designed and synthesized.As a result of reproduction experiment using the synthesized co-pigments, it was revealed that 1-COOH, 1-OH and 5-O-ester of quinic acid moiety was essential for blue color development.The aromatic plane of the 5-O-acyl moiety contributes to the stability of the blue complex.