Abstract
Rebaudioside D3, a novel steviol glycoside, is produced by specific UDP-glycosyltransferase of rebaudioside E, a minor steviol glycoside of Stevia rebaudiana Bertoni. The complete proton and carbon NMR spectral assignments of rebaudioside D3, 13-[(2-O-β-D-glucopyranosyl-6-O-β-D-glucopyranosyl-β-D-glucopyranosyl) oxy] ent-kaur-16-en-19-oic acid-(2-O-β-D-glucopyranosyl-β-D-glucopyranosyl) ester, was achieved by the extensive 1D and 2D NMR (1H and 13C, TOCSY, HMQC, HMBC) as well as mass spectral data. Further, hydrolysis studies were performed on rebaudioside D3 using acid and enzymatic studies to identify aglycone and sugar residues in its structure. Rebaudioside D3 is detected in the commercial extract of the leaves of Stevia rebaudiana by LC-MS analysis, suggesting rebaudioside D3 is a natural steviol glycoside.
Highlights
Stevia rebaudian Bertoni (Bertoni), a perennial shrub of Asteraceae (Compositae) family member native to South America, has been historically utilized to produce sweet beverages
The commercial extract of S. rebaudiana leaves were supplied by Blue California (Rancho Santa Margarita, CA) and the authenticity of the commercial extract was confirmed by performing its retention time comparison with the internal standard compounds of known JECFA steviol glycosides using the preparative HPLC method as reported earlier [4] [5] [6]
The molecular formula of compound 1 has been deduced as C50H80O28 on the basis of its positive high resolution mass spectrum (HRMS) which showed adduct ions corresponding to [M + NH4]+ and [M+ Na]+ at m/z 1146.5169 and 1151.4721 respectively (Figure 2); this composition was supported by the 13C NMR spectral data
Summary
Stevia rebaudian Bertoni (Bertoni), a perennial shrub of Asteraceae (Compositae) family member native to South America, has been historically utilized to produce sweet beverages. Recent studies reported identification and structural characterization of several minor diterpene glycoside compounds from various commercial stevia extracts [9] [10]. The majority of steviol glycosides are formed by a series of glycosylation reactions of steviol, the backbone molecule of the majority of isolated steviol glycosides. These glycosylation are typically catalyzed by the UDP-glycosyltransferases (UGTs) using uridine 5’-diphosphoglucose (UDP-glucose) as a donor of the sugar moiety [11] [12]. Rebaudioside E is treated with this UGT to produce a novel steviol glycoside, named here as rebaudioside D3 (Reb D3 (1), Figure 1). We are describing the production, isolation, characterization, and complete 1H and 13C NMR spectral assignments for the diterpene glycoside of Reb D3 which was assigned as 13-[(2-O-β-D-glucopyra-
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