Synthesis and equilibrium multistate of new pyrano-3-deoxyanthocyanin-type pigments in aqueous solutions

Pyrano-flavylium compounds are flavylium derivatives with occurrence in processed foodstuffs such as wine and red fruit juices. In this work, the chemical equilibria of bio-inspired pyrano-3deoxyanthocyanin dyes (4-8), presenting different substituent groups in D ring (10-methyl, 10-catechol, 10-dimethylaminophenyl, 10-carboxy) as well as in B ring (3',4'-dihydroxy, 4'-carboxy), were studied for the first time in aqueous solutions by UV-Vis spectroscopy. The presence of a methyl group at C-10 (pigment 4) seems to stabilize the flavylium cation (AH(+)) shifting the deprotonation of 7-OH to a higher pK(a1) (pK(a1) = 5.0 0.1). On the other hand, the quinoidal bases (A, A(-)) were more stabilized for the pigments which undergo the first acid-base equilibrium at C-10 substituent, as could be observed by the pICa2 constants (pK(a2) = 8.4 +/- 0.1 and pK(a2) = 8.1 +/- 0.1, pigments 6 and 8, respectively). (C) 2017 Elsevier Ltd. All rights reserved.