Rebaudiosides T and U, minor C-19 xylopyranosyl and arabinopyranosyl steviol glycoside derivatives from Stevia rebaudiana (Bertoni) Bertoni

Two diterpene glycosides were isolated from a commercial Stevia rebaudiana leaf extract. One was found to be 13-[(2-O-β-d-glucopyranosyl-3-O-β-d-glucopyranosyl-β-d-glucopyranosyl)oxy]ent-kaur-16-en-19-oic acid-(2-O-β-d-xylopyranosyl-3-O-β-d-glucopyranosyl- β-d-glucopyranosyl) ester (rebaudioside T), whereas the other was determined to be 13-[(2-O-β-d-glucopyranosyl-3-O-β-d-glucopyranosyl-β-d-glucopyranosyl)oxy]ent-kaur-16-en-19-oic acid-(6-O-α-l-arabinopyranosyl-β-d-glucopyranosyl) ester (rebaudioside U). In addition, five C-19 sugar free derivatives were prepared and identified as follows: 13-[(2-O-α-l-rhamnopyranosyl-β-d-glucopyranosyl)]oxy]kaur-16-en-19-oic acid (dulcoside A₁); 13-[(2-O-β-d-xylopyranosy-3-O-β-d-glucopyranosyl-β-d-glucopyranosyl)oxy]kaur-16-en-19-oic acid; 13-[(2-O-β-d-xylopyranosyl-β-d-glucopyranosyl-)oxy]kaur-16-en-19-oic acid; 13-[(2-O-β-d-glucopyranosyl-3-O-β-d-glucopyranosyl-β-d-xylopyranosyl-)oxy]kaur-16-en-19-oic acid (rebaudioside R₁) and 13-[(2-O-6-deoxy-β-d-glucopyranosyl-3-O-β-d-glucopyranosyl-β-d-glucopyranosyl)oxy]kaur-16-en-19-oic acid, respectively. Chemical structures were determined by NMR experiments. HPLC analyses were also useful to differentiate different steviol-C13 sugar substituent patterns by elution position.