Nonenzymatic C-glycosylation of flavan-3-ols by oligo- and polysaccharides

Model reactions between the polysaccharide amylose and the polyphenol (-)-epicatechin followed by partial enzymatic hydrolysis of the reaction products formed led to the detection of mono- and oligo-C-glucosylated flavan-3-ols by means of LC-MS/MS experiments. To confirm the structure of these putative flavan-3-ol/oligosaccharide conjugates, (-)-epicatechin was reacted with maltose and maltotriose, respectively, giving rise to a series of previously unreported flavan-3-ol/maltose and flavan-3-ol/maltotriose conjugates, namely, (-)-epicatechin-8-C-β-D-glucopyranosyl-(4→1)-O- α-D-glucopyranoside, (-)-catechin-8-C-β-D-glucopyranosyl-(4→1)- O-α-D-glucopyranoside, (-)-catechin-6-C-β-D-glucopyranosyl-(4→1) -O-α-D-glucopyranoside, (-)-catechin-8-C-β-D-glucopyranosyl- (4→1)-O-α-D-glucopyranosyl-(4→1)- O-α-D-glucopyranoside, (-)-catechin-6-C-β-D-glucopyranosyl-(4→1)-O-α-D-glucopyranosyl- (4→1)-O-α-D-glucopyranoside, and (-)-epicatechin-6/8-C-β-D- glucopyranosyl-(4→1)-O-α-D-glucopyranosyl-(4→1) -O-α-D-glucopyranoside. Furthermore, quantitative analysis of flavan-3-ol-C-glucosides in an enzymatic total hydrolysate using a newly developed stable isotope dilution assay (SIDA) enabled a first insight into the yield of the formation of polyphenol/polysaccharide cross-links, for example, an amount of 14.0, 9.0, and 0.15 μmol of flavan-3-ol-6-C-β-D- glucopyranoside, flavan-3-ol-8-C-β-D-glucopyranoside, and flavan-3-ol-6-C,8-C-β-D-glucopyranoside were per mmol (-)-epicatechin when reacted with amylose.