SciCombinator

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Concept: Glycoside

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O-linked glycosylation is one of the most abundant post-translational modifications of proteins. Within the secretory pathway of higher eukaryotes, the core of these glycans is frequently an N-acetylgalactosamine residue that is α-linked to serine or threonine residues. Glycoside hydrolases in family 101 are presently the only known enzymes to be able to hydrolyze this glycosidic linkage. Here we determine the high-resolution structures of the catalytic domain comprising a fragment of GH101 from Streptococcus pneumoniae TIGR4, SpGH101, in the absence of carbohydrate, and in complex with reaction products, inhibitor, and substrate analogues. Upon substrate binding, a tryptophan lid (residues 724-WNW-726) closes on the substrate. The closing of this lid fully engages the substrate in the active site with D764 positioned directly beneath C1 of the sugar residue bound within the -1 subsite, consistent with its proposed role as the catalytic nucleophile. In all of the bound forms of the enzyme, however, the proposed catalytic acid/base residue was found to be too distant from the glycosidic oxygen (>4.3 Å) to serve directly as a general catalytic acid/base residue and thereby facilitate cleavage of the glycosidic bond. These same complexes, however, revealed a structurally conserved water molecule positioned between the catalytic acid/base and the glycosidic oxygen. On the basis of these structural observations we propose a new variation of the retaining glycoside hydrolase mechanism wherein the intervening water molecule enables a Grotthuss proton shuttle between E796 and the glycosidic oxygen, permitting this residue to serve as the general acid/base catalytic residue.

Concepts: Enzyme, Starch, Polysaccharide, Cellulose, Glycosylation, Carbohydrate chemistry, Glycoside, Carbohydrates

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The LC-MS/MS technique was applied to the stability study of several flavonoids and phenolic acids in honey samples during the ultrasonic extraction (USE) and microwave-assisted extraction (MAE). Phenolic compounds from the standard mixture were stable under ultrasounds action with the mean recovery of (90.4%±7.1%), but during microwave-assisted extraction the benzoic acid derivatives and aglycones of flavonoids showed lower recovery (70-80%). In honey matrix, the phenolic acids and the glycosides exhibited the high stability for MAE and USE treatments. However, the recoveries of tested aglycones were below 10%. In the presence of an artificial sugar matrix, flavonols were almost completely degraded after successive treatment under MAE and USE conditions. The obtained results indicated that standard addition method for flavonoids quantification in honey samples should not be recommended. Application of the USE conditions provided higher and/or similar extraction yields for phenolic acids than usually applied shaking with solvent. It also allowed shortening the time required for the whole sample preparation procedure. Phenolic acids and glycosides such as quercetrin, rutin and hesperidin appeared to be stable under such conditions.

Concepts: Catechin, Quercetin, Flavonoid, Glycoside, Phenols, Myricetin, Standard addition, Rutin

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New derivatives of steviol 1, the aglycone of the glycosides of Stevia rebaudiana, including a novel class of semisynthetic diterpenoids, namely macrocyclic ent-kauranes were synthesized. These compounds possess antituberculosis activity inhibiting the in vitro growth of Mycobacterium Tuberculosis (H37R(V) strain) with MIC 5-20μg/ml that is close to MIC 1μg/ml demonstrated by antituberculosis drug isoniazid in control experiment. For the first time it was found that the change of ent-kaurane geometry (as in steviol 1) of tetracyclic diterpenoid skeleton to ent-beyerane one (as in isosteviol 2) influences on antituberculosis activity.

Concepts: Tuberculosis, Mycobacterium, Mycobacterium tuberculosis, Glycoside, Isoniazid, Stevia, Steviol glycoside, Glycosides

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INTRODUCTION: Propolis is a chemically complex resinous substance collected by honeybees (Apis mellifera) from tree buds, comprising plant exudates, secreted substances from bee metabolism, pollen and waxes. Its chemical composition depends strongly on the plant sources available around the beehive, which have a direct impact in the quality and bioactivity of the propolis. Being as Portugal is a country of botanical diversity, the phenolic characterisation of propolis from the different regions is a priority. OBJECTIVE: Extensive characterisation of the phenolic composition of Portuguese propolis from different continental regions and islands. METHOD: Forty propolis ethanolic extracts were analysed extensively by liquid chromatography with diode-array detection coupled to electrospray ionisation tandem mass spectrometry (LC-DAD-ESI-MS(n) ). RESULTS: Seventy-six polyphenols were detected in the samples and two groups of propolis were established: the common temperate propolis, which contained the typical poplar phenolic compounds such as flavonoids and their methylated/esterified forms, phenylpropanoid acids and their esters, and an uncommon propolis type with an unusual composition in quercetin and kaempferol glycosides - some of them never described in propolis. CONCLUSION: The method allowed the establishment of the phenolic profile of Portuguese propolis from different geographical locations, and the possibility to use some phenolic compounds, such as kaempferol-dimethylether, as geographical markers. Data suggest that other botanical species in addition to poplar trees can be important sources of resins for Portuguese propolis. Copyright © 2012 John Wiley & Sons, Ltd.

Concepts: Mass spectrometry, Honey bee, Beekeeping, Catechin, Quercetin, Flavonoid, Glycoside, Myricetin

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O-Picolinyl and O-picoloyl groups at remote positions (C-3, C-4, and C-6) can mediate glycosylation reactions by providing high or even complete facial selectivity for the attack of the glycosyl acceptor. The set of data presented herein offers a strong evidence of the inter-molecular H-bond tethering between the glycosyl donor and glycosyl acceptor counterparts while providing a practical new methodology for the synthesis of either 1,2-cis or 1,2-trans linkages. Challenging glycosidic linkages including α-gluco, β-manno, and β-rhamno have seen obtained with high or complete stereocontrol.

Concepts: Chemical reaction, Carbohydrate chemistry, Chemical glycosylation, Glycosyl acceptor, Glycosyl donor, Glycoside, Carbohydrates, Attack

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Given that harvesting time has a great impact on the quality of herbal medicine, knowing the ontogenesis in the chemical profile aspect is essential to determine the optimal harvesting season. A high-throughput and versatile approach (herbal infrared macro-fingerprinting) harmonizing with the character of herbal medicine and providing the whole chemical profile (entirety), group analogues (part), and single compounds (major components) is developed to rapidly disclose the variation rule of the full chemical profile of herbal medicine over a growing season without extraction pretreatments, and thus to determine the optimal harvesting period in respect to groups of chemical compounds using Scutellaria baicalensis as a demonstration. IR macro-fingerprints of Scutellaria baicalensis harvested in the same period have a high similarity (> 0.91) despite small variations, suggesting that IR macro-fingerprinting can faithfully reflect the spectacle of “disordered order” in nature. From Year-1 spring to Year-3 autumn, general contents (%, w/w) of total flavonoids fluctuate up and down with a maximum value in Year-2 spring, and that of saccharides is relatively stable except for the attenuation from Year-2 autumn to Year-3 spring. From Year-1 autumn to Year-2 spring, flavonoid aglycones initially produced in Scutellaria baicalensis are extensively transformed to responding flavonoid glycosides. From Year-2 spring to Year-3 autumn, flavonoid glycosides are converted back to their corresponding aglycones. The best seasons for collecting Scutellaria baicalensis with a high content of flavonoid glycosides and aglycones would be Year-2 spring and Year-3 spring, respectively.

Concepts: Harvest, Chemical compound, Season, Flavonoid, Glycoside, Infrared, Viticulture, Scutellaria baicalensis

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In this study, we reported the phytochemical composition of the aerial parts of Atriplex halimus L. collected from Sardinia. This species is a halophytic shrub, typical of the Mediterranean Basin. Four new glycosylated flavonoids were isolated and their structures were elucidated on the basis of 1D, 2D NMR and MS spectra as 3',5'-dimethoxymyricetin-3-O-β-d-xylopyranosyl-7-O-fucopyranosyl-(1 → 3)-β-d-glucopyranoside (1), 3'-methoxyquercetin-7-O-β-d-fucopyranosyl-(1 → 3)-β-d-glucopyranosyl-3-O-β-xylopyranosyl-(1 → 4)-β-xylopyranoside (2), 3'-methoxyquercetin-7-O-α-l-rhamnopyranosyl-3-O-α-arabinofuranosyl-(1 → 6)-β-d-glucopyranoside (3) and 3',5'-dimethoxymyricetin-7-O-fucopyranosyl-(1 → 3)-β-d-glucopyranoside (4). LC-MS (n) analysis on the extract revealed the presence of other myricetin, quercetin, isorhamnetin glycosides, simple phenolic acids and esters.

Concepts: Mediterranean Sea, Quercetin, Flavonoid, Glycoside, Flavonols, Myricetin, Shrubland, Atriplex

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A new acetylated chalcone glycoside, trans-2',6'-dihydroxy-4'-O-(4″-acetyl-rhamnoside)-4-methoxychalcone (1) and a new biflavonoid glycosides, 5,3',5″,4″'-tetrahydroxy-3″',5″'dimethoxy-biflavone (4' → 8″)-7-O-((2-rhamnoside) rhamnoside) (2) were isolated from the ethyl acetate soluble fraction of the methanol extract obtained from Trigonosciadium brachytaenium and have been purified by column chromatography and preparative TLC. Those structures were elucidated by UV, (1)H NMR and (13)C NMR, HMBC, EI-MS and IR spectra. The antioxidant activity of ethyl acetate extract was evaluated by 1,1-diphenyl-2-picrylhydrazyl method. The results indicate that ethyl acetate extract from aerial part of T. brachytaenium possesses considerable antioxidant activity.

Concepts: Chromatography, Acetic acid, Solvent, Glycoside, Infrared, Ethyl acetate, Silica gel, Rhamnose

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The tyrosine-derived cyanogenic di-glucoside proteacin and related mono-glucoside dhurrin were identified as the cyanogens in foliage of the tropical tree species Polyscias australiana, present in the approximate ratio 9:1. To date cyanogenic glycosides have not been characterised from the Araliaceae or the Apiales. Concentrations of cyanogenic glycosides varied significantly between plant parts and with leaf age, with the highest concentrations in young emerging leaves (mean 2217.1μgCNg(-1) dry wt), petioles (rachis; 1487.1μgCNg(-1) dry wt) and floral buds (265.8μgCNg(-1) dry wt). Between 2% and 10% of nitrogen in emerging leaves and petioles was present as cyanogenic glycosides. With the exception of floral buds, all tissues apparently lack a specific cyanogenic β-glucosidase to catalyse the first step in the breakdown of these cyanogenic glycosides. Only with the addition of emulsin, an exogenous non-specific β-glucosidase from almonds, were high concentrations of cyanogenic glycosides detected, as much as 20-fold greater than the low to negligible cyanogenic glycoside concentrations determined in the absence of exogenous enzyme. High concentrations of cyanogens in young tissues may confer protection, but may also be a nitrogen source during leaf expansion.

Concepts: Cyanide, Glycoside, Leaf, Plant morphology, Almond, Rhubarb, Cardiac glycoside

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Five new phenolic glycosides, hedyotosides A-E (1-5), including a new cyanogenic glycoside (1), along with 10 known compounds (6-15) were isolated from the whole plants of Hedyotis scandens. The structures of compounds 1-5 were established by extensive spectroscopic analyses and acid hydrolysis. All the isolated compounds were evaluated for their in vitro antiviral activity against respiratory syncytial virus (RSV) with cytopathic effect (CPE) reduction assay. Compounds 6 and 15 showed anti-RSV effects with IC(50) values of 20 and 25μg/mL, respectively.

Concepts: Protein, Microbiology, Cyanide, Quercetin, Glycoside, Human respiratory syncytial virus, Cardiac glycoside, Glycosides