THE FIRST SYNTHESIS OF 3-O-METHYLCYANIDIN AND THE EFFECT OF 3-O-SUBSTITUTION ON STABILITY UNDER ACIDIC CONDITIONS

摘要

The simplest and most common anthocyanin in nature is 3-O-glucosylcyanidin (1), and 3-O-glucosylation is believed to stabilize the chromophore. To clarify the effect of the glucose residue we compared the stability of 1 with its aglycone, cyanidin (2), and newly synthesized 3-O-methylcyanidin (3). In an aqueous solution at pH 1, 1 and 3 showed similar stabilities, and 2 was less stable than 1 and 3, indicating that 3-O-substituion does enhance stability. We also analyzed the co-pigmentation effect of flavocommelin (4) and rutin (5), on the color and stability of 3-O-substituted cyanidins and cyanidin. The bathochromic shift of lambda vismax and stability of the color by addition of 4 was greater than that of rutin (5). 4 might stack closer and stronger to the anthocyanidin chromophore than 5.