Structures of Some Novel α-Glucosyl Diterpene Glycosides from the Glycosylation of Steviol Glycosides

Four new minor diterpene glycosides with a rare α-glucosyl linkage were isolated from a cyclodextrin glycosyltransferase glucosylated stevia extract containing more than 98% steviol glycosides. The new compounds were identified as 13-[(2-O-β-d-glucopyranosyl-3-O-(4-O-α-d-glucopyranosyl)-β-d-glucopyranosyl-β-d-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid-[(4-O-α-d-glucopyranosyl-β-d-glucopyranosyl) ester] (1), 13-[(2-O-β-d-glucopyranosyl-β-d-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid-[(4-O-(4-O-(4-O-α-d-glucopyranosyl)-α-d-glucopyranosyl)-α-d-glucopyranosyl)-β-d-glucopyranosyl ester] (2), 13-[(2-O-β-d-glucopyranosyl-3-O-(4-O-(4-O-(4-O-α-d-glucopyranosyl)-α-d-glucopyranosyl)-α-d-glucopyranosyl)-β-d-glucopyranosyl-β-d-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid β-d-glucopyranosyl ester (3), and 13-[(2-O-β-d-glucopyranosyl-3-O-(4-O-(4-O-(4-O-α-d-glucopyranosyl)-α-d-glucopyranosyl)-α-d-glucopyranosyl)-β-d-glucopyranosyl-β-d-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid-[(4-O-α-d-glucopyranosyl-β-d-glucopyranosyl) ester] (4) on the basis of extensive NMR and mass spectral (MS) data as well as hydrolysis studies.