7 research outputs found
Isolation and Characterization of a Novel Rebaudioside M Isomer from a Bioconversion Reaction of Rebaudioside A and NMR Comparison Studies of Rebaudioside M Isolated from Stevia rebaudiana Bertoni and Stevia rebaudiana Morita
A minor product, rebaudioside M2 (2), from the bioconversion reaction of rebaudioside A (4) to rebaudioside D (3), was isolated and the complete structure of the novel steviol glycoside was determined. Rebaudioside M2 (2) is considered an isomer of rebaudioside M (1) and contains a relatively rare 1â6 sugar linkage. It was isolated and characterized with NMR (1H, 13C, COSY, HSQC-DEPT, HMBC, 1D-TOCSY, and NOESY) and mass spectral data. Additionally, we emphasize the importance of 1D and 2D NMR techniques when identifying complex steviol glycosides. Numerous NMR spectroscopy studies of rebaudioside M (1), rebaudioside D (3), and mixture of 1 and 3 led to the discovery that SG17 which was previously reported in literature, is a mixture of rebaudioside D (3), rebaudioside M (1), and possibly other related steviol glycosides
Small Molecule Suppression of Carbapenem Resistance in NDM-1 Producing <i>Klebsiella pneumoniae</i>
The already considerable global public health threat
of multidrug-resistant Gram-negative bacteria has become even more
of a concern following the emergence of New Delhi metallo-β-lactamase
(NDM-1) producing strains of <i>Klebsiella pneumoniae</i> and other Gram-negative bacteria. As an alternative approach to
the traditional development of new bactericidal entities, we have
identified a 2-aminoimidazole-derived small molecule that acts as
an antibiotic adjuvant and is able to suppress resistance of a NDM-1
producing strain of <i>K. pneumoniae</i> to imipenem and
meropenem, in addition to suppressing resistance of other β-lactam
nonsusceptible <i>K. pneumoniae</i> strains. The small molecule
is able to lower carbapenem minimum inhibitory concentrations by up
to 16-fold, while exhibiting little bactericidal activity itself
A Novel Diterpene Glycoside with Nine Glucose Units from Stevia rebaudiana Bertoni
Following our interest in new diterpene glycosides with better taste profiles than that of Rebaudioside M, we have recently isolated and characterized Rebaudioside IXâa novel steviol glycosideâfrom a commerciallyâsupplied extract of Stevia rebaudiana Bertoni. This molecule contains a hexasaccharide group attached at Câ13 of the central diterpene core, and contains three additional glucose units when compared with Rebaudioside M. Here we report the complete structure elucidationâbased on extensive Nuclear Magnetic Resonance (NMR) analysis (1H, 13C, Correlation Spectroscopy (COSY), Heteronuclear Single Quantum CoherenceâDistortionless Enhancement Polarization Transfer (HSQCâDEPT), Heteronuclear Multiple Bond Correlation (HMBC), 1D Total Correlation Spectroscopy (TOCSY), Nuclear Overhauser Effect Spectroscopy (NOESY)) and mass spectral dataâof this novel diterpene glycoside with nine sugar moieties and containing a relatively rare 16 Îąâlinked glycoside. A steviol glycoside bearing nine glucose units is unprecedented in the literature, and could have an impact on the natural sweetener catalog
Bioconversion of Rebaudioside I from Rebaudioside A
To supply the increasing demand of natural high potency sweeteners to reduce the calories in food and beverages, we have looked to steviol glycosides. In this work we report the bioconversion of rebaudioside A to rebaudioside I using a glucosyltransferase enzyme. This bioconversion reaction adds one sugar unit with a 1â3 linkage. We utilized 1D and 2D NMR spectroscopy (1H, 13C, COSY, HSQC-DEPT, HMBC, 1D TOCSY and NOESY) and mass spectral data to fully characterize rebaudioside I