Natural Acylated Anthocyanins and Other Related Flavonoids: Structure Elucidation of Ipomoea cairica Compounds and QSAR Studies Including Multidrug Resistance

Structure elucidation of new acylated anthocyanins is a challenging task because of molecule complexity, sensitivity to light, atmospheric oxygen, pH, and temperature. The type, number, and position of the acyl moieties should be carefully assessed. New anthocyanins acylated with cinnamic acid derivatives attached to the disaccharide sophorose have been recently isolated, purified, and completely identified in our research group. Structure determination was performed by chemical methods, and spectroscopic techniques, including 1H and 13C NMR, 2D NMR, and MS. Connection relationships between an aglycone moiety, three sugars, and one and two acyl groups, respectively, for each compound were also confirmed by HMBC and NOESY measurements. Therefore, six structures of cyanidin sophorosides acylated with caffeoyl and p-coumaroyl residues, isolated from Ipomoea cairica (family: Convolvulaceae), were fully elucidated. These acylated anthocyanins showed antioxidant activity and antimutagenicity. Quantitative structure–activity relationship studies of flavonoids and biflavonoids as enzyme inhibitors are discussed, e.g., inhibiting influenza H1N1 virus neuraminidase, and as inhibitors of P-glycoprotein in multidrug resistance.