A simple synthesis of 3-deoxyanthocyanidins and their O-glucosides

This work deals with the chemical synthesis of simple analogs of anthocyanins, the main class of water-soluble natural pigments. Flavylium ions with hydroxyl, methoxyl and β-D-glucopyranosyloxyl substituents at positions 4′ and 7 have been prepared by straightforward chemical procedures. Moreover, the two 3-deoxyanthocyanidins of red sorghum apigeninidin (4′,5,7-trihydroxyflavylium) and luteolinidin (3′,4′,5,7-tetrahydroxyflavylium) were synthesized in a one-step protocol. Attempts to synthesize luteolinidin O-β-D-glucosides resulted in a mixture of the 5-O- and 7-O-regioisomers in low yield. A preliminary study of the 4′-β-D-glucopyranosyloxy-7-hydroxyflavylium and 7-β-D-glucopyranosyloxy-4′-hydroxy-flavylium ions shows that simply changing the glucosidation site can profoundly affect the color intensity and stability.