SYNTHESIS OF 3-METHOXY-FLAVYLIUM AND 3-(BETA-D-GLUCOPYRANOSYLOXY)FLAVYLIUM IONS - INFLUENCE OF THE FLAVYLIUM SUBSTITUTION PATTERN ON THE REACTIVITY OF ANTHOCYANINS IN AQUEOUS-SOLUTION

The synthesis of 3-glycosyloxylated flavylium ions (anthocyanins), in particular of callistephin (4), a natural anthocyanin, is described. T he structural transformations in aqueous solution and molecular comple xation with chlorogenic acid (7) and caffeine (8) of the synthesized p igments 3 and 4 are investigated and compared to those of the correspo nding 3-methoxyflavylium ions 1 and 2 and to those of oenin (5) and ma lvin (6), two very common natural anthocyanins. The results are discus sed in terms of the role played by the glycosyloxy residues in the che mical properties of anthocyanins. Anthocyanin molecular complexation ( copigmentation) is quantitatively investigated by UV/VIS spectroscopy and H-1-NMR. In particular, the UV/VIS spectroscopic data are interpre ted using a general theoretical treatment, which, e.g., allows to demo nstrate the formation of molecular complexes between the colourless fo rms of an anthocyanin and 8.