Rebaudiosides R and S, Minor Diterpene Glycosides from the Leaves of Stevia rebaudiana.

Two new diterpene glycosides have been isolated from a commercial extract of the leaves of Stevia rebaudiana. Compound 1 was shown to be 13-[(2-O-β-d-glucopyranosyl-3-O-β-d-glucopyranosyl-β-d-xylopyranosyl)oxy]ent-kaur-16-en-19-oic acid β-d-glucopyranosyl ester (rebaudioside R), while compound 2 was determined to be 13-[(2-O-α-d-glucopyranosyl-β-d-glucopyranosyl)oxy]ent-kaur-16-en-19-oic acid 2-O-α-l-rhamnopyranosyl-β-d-glucopyranosyl ester (rebaudioside S). Six additional known compounds were identified, dulcoside B, 13-[(2-O-β-d-xylopyranosyl-β-d-glucopyranosyl)oxy]ent-kaur-16-en-19-oic acid β-d-glucopyranosyl ester, eugenol diglucoside, rebaudioside G, 13-[(2-O-6-deoxy-β-d-glucopyranosyl-3-O-β-d-glucopyranosyl-β-d-glucopyranosyl)oxy]ent-kaur-16-en-19-oic acid β-d-glucopyranosyl ester, and rebaudioside D (3), respectively. The structures of 1 and 2 were determined based on comprehensive 1D and 2D NMR (COSY, HSQC, and HMBC) studies. A high-quality crystal of compound 3 allowed confirmation of its structure by X-ray diffraction.