Sesquiterpene lactone glucosides and alkyl glycosides from the fruit of cumin

From the polar portion of the methanolic extract of cumin (fruit of Cuminum cyminum L.), two sesquiterpenoid glucosides, cuminoside A and B, and two alkyl glycosides were isolated together with five known compounds. Their structures were established as (1S,5S,6S,10S)-10-hydroxyguaia-3,7(11)-dien-12,6-olide beta-D-glucopyranoside, (1R,5R,6S,7S,9S,10R,11R)-1,9-dihydroxyeudesm-3-en-12,6-olide 9-O-beta-D-glucopyranoside, methyl beta-D-apiofuranosyl-(1-->6)-beta-D-glucopyranoside and ethane-1,2-diol 1-O-beta-D-apiofuranosyl-(1-->6)-beta-D-glucopyranoside, respectively.     

Glycosides of 2-C-methyl-D-erythritol from the fruits of anise,coriander and cumin

Eight glycosides of 2-C-methyl-D-erythritol (1) were isolated from the fruit of anise, and their structures were clarified as 1-O-beta-D-glucopyranoside, 3-O-beta-D-glucopyranoside, 4-O-beta-D-glucopyranoside, 1-O-beta-D-fructofuranoside, 3-O-beta-D-fructofuranoside, 4-O-beta-D-fructofuranoside, 1-O-beta-D-(6-O-4-hydroxybenzoyl)-glucopyranoside and 1-O-beta-D-(6-O-4-methoxybenzoyl)-glucopyranoside of 2-C-methyl-D-erythritol (2-9), respectively. Furthermore, 2 and 4 were isolated from the fruit of coriander, and 2, 3 and 4 were isolated from the fruit of cumin. Though the phosphate of 1 was known to be one of the first precursors of isoprenoids in the non-mevalonate pathway, and 1 is considered to be a common constituent in Umbelliferous plants, the glycosides of 1 are found for the first time.     

Structural and functional analyses of catalytic domain of GH10 xylanase from Thermoanaerobacterium saccharolyticum JW/SL‐YS485

Xylanases are capable of decomposing xylans, the major components in plant cell wall, and releasing the constituent sugars for further applications. Because xylanase is widely used in various manufacturing processes, high specific activity, and thermostability are desirable. Here, the wild‐type and mutant (E146A and E251A) catalytic domain of xylanase from Thermoanaerobacterium saccharolyticum JW/SL‐YS485 (TsXylA) were expressed in Escherichia coli and purified subsequently. The recombinant protein showed optimal temperature and pH of 75°C and 6.5, respectively, and it remained fully active even after heat treatment at 75°C for 1 h. Furthermore, the crystal structures of apo‐form wild‐type TsXylA and the xylobiose‐, xylotriose‐, and xylotetraose‐bound E146A and E251A mutants were solved by X‐ray diffraction to high resolution (1.32–1.66 Å). The protein forms a classic (β/α)₈ folding of typical GH10 xylanases. The ligands in substrate‐binding groove as well as the interactions between sugars and active‐site residues were clearly elucidated by analyzing the complex structures. According to the structural analyses, TsXylA utilizes a double displacement catalytic machinery to carry out the enzymatic reactions. In conclusion, TsXylA is effective under industrially favored conditions, and our findings provide fundamental knowledge which may contribute to further enhancement of the enzyme performance through molecular engineering. Proteins 2013; 81:1256–1265. © 2013 Wiley Periodicals, Inc.     

C andH NMR spectroscopy as a tool in the configurational analysis of iridoid glucosides

The ¹³C NMR data of 51 iridoid glucosides or glucoside acetates are tabulated. The collection includes 20 pairs of C-6, C-7 or C-8 epimers. Three parameters in using the data for the configurational assignment of 6-O-substituents are given. The chemical shift for C-9 in a range of substituted compounds is shown to be numerically related to the stereochemistry at C-8. This allows the determination of the configuration at this centre for most types of substitution patterns by calculation of the C-9 shift using increments for each substituent. Such increments are given for 25 substituents in three different solvents. A method for simulation of spectra of unknown iridoid glucosides is presented. By this method, the structures of five novel iridoid glucosides have been elucidated, and that of tecomoside has been revised. The methods used to assign the configurations to C-6 and C-8 epimeric iridoid glucosides by ¹H NMR spectroscopy are discussed and a table with selected data is presented. It is suggested that the structures in the literature for ajugol and myoporoside should be interchanged. Consequently, Horeau's method has failed in these instances. Finally, the differences in the ¹³C NMR spectra of pairs of C-6 and C-8 epimeric iridoid glucosides have been interpreted as originating from cis/trans-interactions.     

Acylated flavonol glycosides and δ-truxinate derivative from the aerial parts of Lysimachia clethroides

Phytochemical investigation of the aerial parts of Lysimachia clethroides led to the isolation of a new acylated flavonol glycoside (1) and a new δ-truxinate derivative (2), together with three known acylated flavonol glycosides. The structures of the new compounds were determined by spectroscopic methods and chemical evidence as quercetin-3-O-β-d-(6-O-Z-p-coumaroyl)glucopyranoside (1) and monomethyl 3,3′,4,4′-tetrahydroxy-δ-truxinate (2), respectively. All of the isolates were evaluated for their in vitro inhibitory activity against aldose reductase.     

Inhibition of α-Glycosidase by Lippia dulcis Trevir. (Verbenaceae) Preparations,Quantification of Verbascoside,and Study of Its Molecular Docking

This study aimed to quantify verbascoside (VEB), perform molecular docking studies of VEB with the α-glucosidase (GL) of Bacillus stearothermophilus, and evaluate the inhibition of the enzyme by L. dulcis preparations. The substrate concentration and presence of reduced glutathione were evaluated for their effect on the in vitro inhibition of the GL enzyme. Assays were also performed in the presence and absence of simulated gastric fluid. The antidiabetic fractions 2 and 3 were the most inhibited GL, but their activity were significantly decreased in the presence of gastric fluid. Chromatographic analyses confirmed the predominant presence of VEB in the samples. The samples had VEB concentrations between 49.9 and 243.5 mg/g. Simulation of the molecular docking of VEB were consistent with its GL-inhibitory activity. It can conclude that the crude ethanol extract and fractions show inhibitory activity against the GL enzyme.     

Streptococcus pneumoniae NanC: STRUCTURAL INSIGHTS INTO THE SPECIFICITY AND MECHANISM OF A SIALIDASE THAT PRODUCES A SIALIDASE INHIBITOR*

Streptococcus pneumoniae is an important human pathogen that causes a range of disease states. Sialidases are important bacterial virulence factors. There are three pneumococcal sialidases: NanA, NanB, and NanC. NanC is an unusual sialidase in that its primary reaction product is 2-deoxy-2,3-didehydro-N-acetylneuraminic acid (Neu5Ac2en, also known as DANA), a nonspecific hydrolytic sialidase inhibitor. The production of Neu5Ac2en from α2–3-linked sialosides by the catalytic domain is confirmed within a crystal structure. A covalent complex with 3-fluoro-β-N-acetylneuraminic acid is also presented, suggesting a common mechanism with other sialidases up to the final step of product formation. A conformation change in an active site hydrophobic loop on ligand binding constricts the entrance to the active site. In addition, the distance between the catalytic acid/base (Asp-315) and the ligand anomeric carbon is unusually short. These features facilitate a novel sialidase reaction in which the final step of product formation is direct abstraction of the C3 proton by the active site aspartic acid, forming Neu5Ac2en. NanC also possesses a carbohydrate-binding module, which is shown to bind α2–3- and α2–6-linked sialosides, as well as N-acetylneuraminic acid, which is captured in the crystal structure following hydration of Neu5Ac2en by NanC. Overall, the pneumococcal sialidases show remarkable mechanistic diversity while maintaining a common structural scaffold.     

Characterization of surface binding sites in glycoside hydrolases: A computational study

Structural properties of carbohydrate surface binding sites (SBSs) were investigated with computational methods. Eighty‐five SBSs of 44 enzymes in 119 Protein Data Bank (PDB) files were collected as a dataset. On the basis of SBSs shape, they were divided into 3 categories: flat surfaces, clefts, and cavities (types A, B, and C, respectively). Ligand varieties showed the correlation between shape of SBSs and ligands size. To reduce cut‐off differences in each SBSs with different ligand size, molecular docking were performed. Molecular docking results were used to refine SBSs classification and binding sites cut‐off. Docking results predicted putative ligands positions and displayed dependence of the ligands binding mode to the structural type of SBSs. Physicochemical properties of SBSs were calculated for all docking results with YASARA Structure. The results showed that all SBSs are hydrophilic, while their charges could vary and depended to ligand size and defined cut‐off. Surface binding sites type B had highest average values of solvent accessible surface area. Analysis of interactions showed that hydrophobic interactions occur more than hydrogen bonds, which is related to the presence of aromatic residues and carbohydrates interactions.     

Mono- and triglycosylsterols from the leafy stem of rice

Two sterylglycosides have been isolated from rice plants and identified as β-d-glucopyranosyl (1 → 3)-sitosterol and β-d-glucopyranosyl(1