A New Cucurbitane Glycoside from Siraitia grosvenorii.

A systematic phytochemical study of the commercial extract of Luo Han Guo (Siraitia grosvenorii) resulted in the isolation of an additional minor new cucurbitane glycoside, mogroside V Al (1). The structure of the new compound was characterized on the basis of 1D (1H and 13C NMR) and 2D (COSY, HMQC, HMBC and NOESY) NMR and high resolution mass spectral (HRMS) data, as well as hydrolysis studies.

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-ß-D-glucopyranosyl-3-O-(4-O-α-D-glucopyranosyl)-ß-D-glucopyranosyl-ß-D-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid-[(4-O-α-D-glucopyranosyl-ß-D-glucopyranosyl) ester] (1), 13-[(2-O-ß-D-glucopyranosyl-ß-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)-ß-D-glucopyranosyl ester] (2), 13-[(2-O-ß-D-glucopyranosyl-3-O-(4-O-(4-O-(4-O-α-D-glucopyranosyl)-α-D-glucopyranosyl)-α-D-glucopyranosyl)-ß-D-glucopyranosyl-ß-D-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid ß-D-glucopyranosyl ester (3), and 13-[(2-O-ß-D-glucopyranosyl-3-O-(4-O-(4-O-(4-O-α-D-glucopyranosyl)-α-D-glucopyranosyl)-α-D-glucopyranosyl)-ß-D-glucopyranosyl- ß-D-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid-[(4-O-α-D-glucopyranosyl-ß-D-glucopyranosyl) ester] (4) on the basis of extensive NMR and mass spectral (MS) data as well as hydrolysis studies.

Additional new minor cucurbitane glycosides from Siraitia grosvenorii.

Continuous phytochemical studies of the crude extract of Luo Han Guo (Siraitia grosvenorii) furnished three additional new cucurbitane triterpene glycosides, namely 11-deoxymogroside V, 11-deoxyisomogroside V, and 11-deoxymogroside VI. The structures of all the isolated compounds were characterized on the basis of extensive NMR and mass spectral data as well as hydrolysis studies. The complete ¹H- and ¹³C-NMR spectral assignments of the three unknown compounds are reported for the first time based on COSY, TOCSY, HSQC, and HMBC spectroscopic data.

Structural characterization of the degradation products of a minor natural sweet diterpene glycoside Rebaudioside M under acidic conditions.

Degradation of rebaudioside M, a minor sweet component of Stevia rebaudiana Bertoni, under conditions that simulated extreme pH and temperature conditions has been studied. Thus, rebaudioside M was treated with 0.1 M phosphoric acid solution (pH 2.0) and 80 °C temperature for 24 h. Experimental results indicated that rebaudioside M under low pH and higher temperature yielded three minor degradation compounds, whose structural characterization was performed on the basis of 1D (1H-, 13C-) & 2D (COSY, HSQC, HMBC) NMR, HRMS, MS/MS spectral data as well as enzymatic and acid hydrolysis studies.

Isolation and structural characterization of a new minor diterpene glycoside from Stevia rebaudiana.

From the commercial extract of the leaves of the sweet plant Stevia rebaudiana Bertoni obtained from Sinochem Qingdao Co. Ltd., a new diterpene glycoside having three ß-D-glucopyranosyl units of which two of them were connected in a relatively rare linkage of 3-ß-D-glucobiosyl substitution at C-19 position of the aglycone steviol. The structure of the new compound has been characterized as 13-ß-D-glucopyranosyloxy ent-kaur-16-en-19-oic acid-[(3-O-ß-D- glucopyranosyl-ß-D-glucopyranosyl) ester (1) on the basis of extensive 1D (1H and 13C) and 2D NMR (TOCSY, HMQC, and HMBC), and High Resolution mass spectroscopic data as well as hydrolysis studies.

Additional minor diterpene glycosides from Stevia rebaudiana Bertoni.

Two additional novel minor diterpene glycosides were isolated from the commercial extract of the leaves of Stevia rebaudiana Bertoni. The structures of the new compounds were identified as 13-{ß-D-glucopyranosyl-(1 → 2)-O-[ß-D-glucopyranosyl-(1 → 3)-ß-D-glucopyranosyl-oxy} ent-kaur-16-en-19-oic acid {ß-D-xylopyranosyl-(1 → 2)-O-[ß-D-glucopyranosyl-(1 → 3)]-O-ß-D-glucupyranosyl-ester} (1), and 13-{ß-D-6-deoxy-glucopyranosyl-(1 → 2)-O-[ß-D-glucopyranosyl-(1 → 3)-ß-D-glucopyranosyl-oxy} ent-kaur-16-en-19-oic acid {ß-D-glucopyranosyl-(1 → 2)-O-[ß-D-glucopyranosyl-(1 → 3)-ß-D-gluco-pyranosyl-ester} (2), on the basis of extensive 1D (1H- and 13C-) 2D NMR (COSY, HSQC and HMBC) and MS spectroscopic data as well as chemical studies.

Hydrogenation of the exocyclic olefinic bond at C-16/C-17 position of ent-kaurane diterpene glycosides of Stevia rebaudiana using various catalysts.

Catalytic hydrogenation of the exocyclic double bond present between C16 and C17 carbons of the four ent-kaurane diterpene glycosides namely rebaudioside A, rebaudioside B, rebaudioside C, and rebaudioside D isolated from Stevia rebaudiana has been carried out using Pt/C, Pd(OH)2, Rh/C, Raney Ni, PtO2, and 5% Pd/BaCO3 to their corresponding dihydro derivatives with 17α and 17ß methyl group isomers. Reactions were performed using the above-mentioned catalysts with the solvents methanol, water, and ethanol/water (8:2) under various conditions. Synthesis of reduced steviol glycosides was performed using straightforward chemistry and their structures were characterized on the basis of 1D and 2D NMR spectral data, including a comparison with reported spectral data.

Isolation, characterization and sensory evaluation of a Hexa beta-D-glucopyranosyl diterpene from Stevia rebaudiana.

From the extract of the leaves of Stevia rebaudiana Bertoni, a diterpene glycoside was isolated which was identified as 13-[(2-O-beta-D-glucopyranosyl-3-O-beta-D-glucopyranosyl-beta-D-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid-(2-O-beta-D-glucopyranosyl-3-O-beta-D-glucopyranosyl-D-glucopyranosyl) ester (1). The complete 1H and 13C NMR assignment of 1 is reported for the first time, from extensive NMR (1H and 13C, COSY, HSQC, and HMBC) and mass spectral data. Also, we report the sensory evaluation of 1 against sucrose for the sweetness property of this molecule.

Isolation, NMR Spectral Analysis and Hydrolysis Studies of a Hepta Pyranosyl Diterpene Glycoside from Stevia rebaudiana Bertoni.

From the commercial extract of the leaves of Stevia rebaudiana Bertoni, a minor steviol glycoside, 13-[(2-O-ß-D-glucopyranosyl-3-O-ß-D-glucopyranosyl-ß-D-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid-[(2-O-(3-O-ß-D-glucopyranosyl-α-L-rhamnopyranosyl)-3-O-ß-D-glucopyranosyl-ß-D-glucopyranosyl) ester] (1); also known as rebaudioside O having seven sugar units has been isolated. Its structural characterization has been achieved by the extensive 1D (1H and 13C), and 2D NMR (COSY, HMQC, HMBC) as well as mass spectral data. Further, hydrolysis studies were performed on rebaudioside O using acid and enzymatic methods to identify aglycone and sugar residues in its structure as well as their configurations.

Catalytic hydrogenation of the sweet principles of Stevia rebaudiana, Rebaudioside B, Rebaudioside C, and Rebaudioside D and sensory evaluation of their reduced derivatives.

Catalytic hydrogenation of rebaudioside B, rebaudioside C, and rebaudioside D; the three ent-kaurane diterpene glycosides isolated from Stevia rebaudiana was carried out using Pd(OH)(2). Reduction of steviol glycosides was performed using straightforward synthetic chemistry with the catalyst Pd(OH)(2) and structures of the corresponding dihydro derivatives were characterized on the basis of 1D and 2D nuclear magnetic resonance (NMR) spectral data indicating that all are novel compounds being reported for the first time. Also, the taste properties of all reduced compounds were evaluated against their corresponding original steviol glycosides and sucrose.

Synthesis and sensory evaluation of ent-kaurane diterpene glycosides.

Catalytic hydrogenation of the three ent-kaurane diterpene glycosides isolated from Stevia rebaudiana, namely rubusoside, stevioside, and rebaudioside-A has been carried out using Pd(OH)2 and their corresponding dihydro derivatives have been isolated as the products. Synthesis of reduced steviol glycosides was performed using straightforward chemistry and their structures were characterized on the basis of 1D and 2D NMR spectral data and chemical studies. Also, we report herewith the sensory evaluation of all the reduced compounds against their corresponding original steviol glycosides and sucrose for the sweetness property of these molecules.

Synthesis of ent-kaurane diterpene monoglycosides.

Synthesis of two ent-kaurane diterpene glycosides, steviol 19-O-ß-D-glucopyranosiduronic acid (steviol glucuronide, 5), and 13-hydroxy ent-kaur-16-en-19-oic acid-ß-D-glucopyranosyl ester (7) has been achieved from a common starting material, steviol, using phase transfer catalyst. Also, synthesis of an additional 17-nor-ent-kaurane glycoside, namely 13-methyl-16-oxo-17-nor-ent-kauran-19-oic acid-ß-D-glucopyranosyl ester (10) was performed using the starting material isosteviol and similar synthetic methodology. Synthesis of all three steviol glycosides was performed using straightforward chemistry and their structures were characterized on the basis of 1D and 2D NMR as well as mass spectral (MS) data.

Additional minor diterpene glycosides from Stevia rebaudiana.

From the commercial extract of the leaves of Stevia rebaudiana, two additional new diterpenoid glycosides were isolated and their structures were characterized as 13-[(2-O-beta-glucopyranosyl-3-O-beta-D-xylopyranosyl-beta-D-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid beta-D-glucopyranosyl ester (1) and 13-[(2-O-beta-D-xylopyranosyl-beta-D-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid beta-D-glucopyranosyl ester (2) on the basis of extensive spectral data (NMR and MS) and chemical studies.

Structures of the novel α-glucosyl linked diterpene glycosides from Stevia rebaudiana.

From the commercial extract of the leaves of Stevia rebaudiana, two new minor diterpene glycosides having α-glucosyl linkage were isolated besides the known steviol glycosides including stevioside, steviolbioside, rebaudiosides A-F, rubusoside and dulcoside A. The structures of the two compounds were identified as 13-[(2-O-(3-α-O-d-glucopyranosyl)-ß-d-glucopyranosyl-3-O-ß-d-glucopyranosyl-ß-d-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid ß-d-glucopyranosyl ester (1), and 13-[(2-O-ß-d-glucopyranosyl-3-O-(4-O-α-d-glucopyranosyl)-ß-d-glucopyranosyl-ß-d-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid ß-d-glucopyranosyl ester (2), on the basis of extensive NMR and MS spectral data as well as chemical studies.

Diterpene glycosides from Stevia rebaudiana.

Three novel diterpene glycosides were isolated for the first time from the commercial extract of the leaves of Stevia rebaudiana, along with several known steviol glycosides, namely stevioside, rebaudiosides A-F, rubusoside and dulcoside A. The new compounds were identified as 13-[(2-O-ß-D-glucopyranosyl-3-O-ß-D-glucopyranosyl-ß-D-glucopyranosyl)oxy] ent-kaur-15-en-19-oic acid, 13-[(2-O-ß-D-glucopyranosyl-3-O-ß-D-glucopyranosyl-ß-D-glucopyranosyl)oxy]-16ß-hydroxy-ent-kauran-19-oic acid and 13-methyl-16-oxo-17-nor-ent-kauran-19-oic acid-ß-D-glucopyranosyl ester on the basis of extensive 2D NMR and MS spectroscopic data as well as chemical studies.

Structures of the novel diterpene glycosides from Stevia rebaudiana.

From the commercial extract of the leaves of Stevia rebaudiana, two new diterpenoid glycosides were isolated besides the known steviol glycosides including stevioside, rebaudiosides A-F, rubusoside, and dulcoside A. The structures of the two new compounds were identified as 13-[(2-O-6-deoxy-ß-d-glucopyranosyl-ß-d-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid ß-d-glucopyranosyl ester (1), and 13-[(2-O-6-deoxy-ß-d-glucopyranosyl-3-O-ß-d-glucopyranosyl-ß-d-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid ß-d-glucopyranosyl ester (2), on the basis of extensive NMR and MS spectral data as well as chemical studies.

A new diterpene glycoside from Stevia rebaudiana.

From the commercial extract of the leaves of Stevia rebaudiana, a new diterpene glycoside was isolated besides the known steviol glycosides including stevioside, rebaudiosides A-F, rubusoside and dulcoside A. The new compound was identified as 13-[(2-O-ß-D-glucopyranosyl-3-O-ß-D-glucopyranosyl-ß-D-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid-(2-O-α-L-rhamnopyranosyl-ß-D-glucopyranosyl) ester (1) on the basis of extensive spectroscopic (NMR and MS) and chemical studies.

Two minor diterpene glycosides from the leaves of Stevia rebaudiana.

Two new new diterpene glycosides, 13-[(2-O-(6-O-beta-D-glucopyranosyl)-beta-D-glucopyranosyl-beta-D-glucopyranosyl)oxy] kaur-16-en-18-oic acid beta-D-glucopyranosyl ester (1) and 13-[(2-O-beta-D-glucopyranosyl-3-O-beta-D-fructofuranosyl-beta-D-glucopyranosyl)oxy] kaur-16-en-18-oic acid beta-D-glucopyranosyl ester (2) were isolated from the leaves of Stevia rebaudiana, along with the known steviol glycosides stevioside, rebaudiosides A-F and dulcoside A. The structures of the two new compounds were established on the basis of extensive 2D NMR (COSY, HSQC, and HMBC), MS and chemical studies.