Isolation and structural characterization of new anthocyanin-alkyl-catechin pigments

A condensation reaction between malvidin 3-glucoside (mv3gl) and catechin (cat) mediated by acetaldehyde and propionaldehyde was conducted in model solutions at two pH values (at 1.5 and 3.2). Acetaldehyde led to the formation of mv3gl-8-ethyl-8-cat (m/z at 809) widely reported in the literature, whereas propionaldehyde led to the formation of mv3gl-8-propyl-8-cat (m/z at 823) and its structural characterization is elucidated herein for the first time by 1D and 2D NMR. The formation of these alkyl-linked pigments is favoured at lower pH value as the alkyl linkage requires the formation of an aldehyde carbocation for a further condensation.