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 IX-a novel steviol glycoside-from a commercially-supplied extract of Stevia rebaudiana Bertoni. This molecule contains a hexasaccharide group attached at C-13 of the central diterpene core, and contains three additional glucose units when compared with Rebaudioside M. Here we report the complete structure elucidation-based on extensive Nuclear Magnetic Resonance (NMR) analysis (1H, 13C, Correlation Spectroscopy (COSY), Heteronuclear Single Quantum Coherence-Distortionless Enhancement Polarization Transfer (HSQC-DEPT), Heteronuclear Multiple Bond Correlation (HMBC), 1D Total Correlation Spectroscopy (TOCSY), Nuclear Overhauser Effect Spectroscopy (NOESY)) and mass spectral data-of this novel diterpene glycoside with nine sugar moieties and containing a relatively rare 16 α-linked glycoside. A steviol glycoside bearing nine glucose units is unprecedented in the literature, and could have an impact on the natural sweetener catalog.

A New Diterpene Glycoside: 15α-Hydroxy-Rebaudioside M Isolated from Stevia rebaudiana.

In a continued search for novel diterpenoid glycosides, we recently isolated and characterized a Rebaudioside M derivative with a hydroxyl group at position 15 in the central diterpene core from an extract of Stevia rebaudiana Bertoni. Here we report the complete structure elucidation of 15α-hydroxy-Rebaudioside M (2) on the basis of NMR (1H, 13C, COSY, HSQC-DEPT, HMBC, 1D TOCSY, NOESY) and mass spectral data. Steviol glycoside with a hydroxyl group at C-15 in the central diterpene core has not been previously reported.

Degradation products of rubusoside under acidic conditions.

A natural sweetener, Rubusoside (1), subjected to extreme pH and temperature conditions, resulted in the isolation and structural elucidation of one novel rubusoside degradant (7), together with seven known degradants (2-6 and 8-9). ID and 2D NMR spectroscopy (1H, 13C, COSY, HSQC-DEPT, HMBC, and NOESY) and mass spectral data were used to fully characterize the degradant 7.

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 1→3 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.

Isolation and structure elucidation of rebaudioside D2 from bioconversion reaction of rebaudioside A to rebaudioside D.

We report the isolation and complete structure of an isomer of rebaudioside D, known as rebaudioside D2. This novel steviol glycoside was isolated from a bioconversion reaction of rebaudioside A to rebaudioside D. Rebaudioside D2 possesses a relatively rare 1 --> 6 sugar linkage, which was discovered by extensive analysis of NMR (1H, 13C, COSY, HSQC-DEPT, HMBC, 1D TOCSY and NOESY) and mass spectral data.

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 1→6 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.

Development of Next Generation Stevia Sweetener: Rebaudioside M.

This work aims to review and showcase the unique properties of rebaudioside M as a natural non-caloric potential sweetener in food and beverage products. To determine the potential of rebaudioside M, isolated from Stevia rebaudiana Bertoni, as a high potency sweetener, we examined it with the Beidler Model. This model estimated that rebaudioside M is 200-350 times more potent than sucrose. Numerous sensory evaluations of rebaudioside M's taste attributes illustrated that this steviol glycoside possesses a clean, sweet taste with a slightly bitter or licorice aftertaste. The major reaction pathways in aqueous solutions (pH 2-8) for rebaudioside M are similar to rebaudioside A. Herein we demonstrate that rebaudioside M could be of great interest to the global food industry because it is well-suited for blending and is functional in a wide variety of food and beverage products.

Indole/triazole conjugates are selective inhibitors and inducers of bacterial biofilms.

Herein is described a method of accessing indole/triazole and benzothiophene/triazole analogues that selectively promote or inhibit biofilm formation by Gram-positive and Gram-negative bacteria. Structure/function studies revealed that the addition of a bromine atom at the 2-position of the indole/triazole scaffold altered activity against both Gram-negative and Gram-positive bacteria and could transform a biofilm inhibitor into a biofilm inducer. Isosteric replacement of the indole core by a benzothiophene significantly impaired anti-biofilm activity. A competition assay exposing Escherichia coli to the most potent biofilm inducer and an inhibitor of E. coli biofilm formation was performed. The inducer exhibited the ability to mute the effect of the anti-biofilm compound for this targeted bacterial population.

Small molecule suppression of carbapenem resistance in NDM-1 producing Klebsiella pneumoniae.

The already considerable global public health threat of multi-drug resistant Gram-negative bacteria has become even more of a concern following the emergence of New-Delhi metallo-ß-lactamase (NDM-1) producing strains of Klebsiella pneumoniae 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 K. pneumoniae to imipenem and meropenem, in addition to suppressing resistance of other ß-lactam non-susceptible K. pneumoniae strains. The small molecule is able to lower carbapenem minimum inhibitory concentrations by up to 16-fold while exhibiting little bactericidal activity itself.

Intercepting bacterial indole signaling with flustramine derivatives.

Indole signaling is one of the putative universal signaling networks in bacteria. We have investigated the use of desformylflustrabromine (dFBr) derivatives for the inhibition of biofilm formation through modulation of the indole-signaling network in Escherichia coli and Staphylococcus aureus . We have found dFBr derivatives that are 10-1000 times more active than indole itself, demonstrating that the flustramine family of indolic natural products represent a privileged scaffold for the design of molecules to control pathogenic bacterial behavior.

Flustramine inspired synthesis and biological evaluation of pyrroloindoline triazole amides as novel inhibitors of bacterial biofilms.

Anti-biofilm agents have been developed based upon the flustramine family of alkaloids isolated from Flustra foliacea. A Garg interrupted Fischer indolization reaction was employed to access a core pyrroloindoline scaffold that was subsequently employed to create a pyrroloindoline triazole amide library. Screening for the ability to modulate biofilm formation against strains of Gram-positive and Gram-negative bacteria identified several compounds with low micromolar, non-toxic IC(50) values.

Identification of aryl 2-aminoimidazoles as biofilm inhibitors in Gram-negative bacteria.

The synthesis and biofilm inhibitory activity of a 30-member aryl amide 2-aminoimidazole library against the three biofilm forming Gram-negative bacteria Escherichia coli, Psuedomonas aeruginosa, and Acinetobacter baumannii is presented. The most active compound identified inhibits the formation of E. coli biofilms with an IC(50) of 5.2 microM and was observed to be non-toxic to planktonic growth, demonstrating that analogues based on an aryl framework are viable options as biofilm inhibitors within the 2-aminoimidazole family.

The chemical synthesis and antibiotic activity of a diverse library of 2-aminobenzimidazole small molecules against MRSA and multidrug-resistant A. baumannii.

Multidrug-resistant bacterial infections continue to be a rising global health concern. Herein is described the development of a class of novel 2-aminobenzimidazoles with antibiotic activity. These active 2-aminobenzimidazoles retain their antibiotic activity against several strains of multidrug-resistant Staphylococcus aureus and Acinetobacter baumannii when compared to susceptible strains.