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[en] Subsequent to our previous report describing several novel carbohydrate α-amino acid dipeptides (and the structural characterization of one of those), and their extension to higher peptides, a synchrotron radiation study of one of those - a pentapeptide - showing its structure to be a well-defined helical array in each of two independent molecules, stabilized by internal hydrogen bonds, is reported.
Journal
[en] Direct and unified synthetic routes to ophiocerin A, B, C, and D have been successfully developed. These syntheses are based on ring-closing metathesis and non-carbohydrate starting materials and are simpler and more efficient than the previous syntheses, as demonstrated in the case of ophiocerin B (2) (eleven steps from methyl α-D-glucopyranoside vs. four steps from 4-penten-2-ol) and ophiocerin A (1) (twelve steps from methyl α-D-glucopyranoside vs. three steps from 4-penten-2-ol). These routes will be useful for the practical synthesis of related natural products. Ophiocerins are comprised of four compounds isolated from the aqueous fungi Ophioceras venezuelense, each bearing a tetrahydropyran ring with an interesting array of substituents (Figure 1). Since substituted tetrahydropyran rings are found in many biologically important natural products, ophiocerins have attracted the attention of synthetic chemists
Journal
Bulletin of the Korean Chemical Society; ISSN 0253-2964; 
; v. 31(3); p. 555-556
; v. 31(3); p. 555-556
[en] Food irradiation has anomalously been classified as a food additive rather than as a processing method. The justification for this is that chemical changes take place during the process. However, most foodstuffs consist of a large number of constituents, most of which are present in small concentrations. As a result, the amounts of radiolysis products which may be formed are far too low for identification and measurement, even by conventional analytical methods. Radiation-chemical knowledge is applied to determine the probable nature and concentration of reaction products produced in fruits. Fruits consist mainly of water and carbohydrates, with small amounts of protein, fat, inorganic material and vitamins as 'contaminants'. The real situation is exceedingly complex, but, using this simple model as a first approximation, predictions which may be verified in a relatively simple experimental scheme are made on the radiation stability of a typical fruit. Calculations using known radiation-chemical data show that, in the case of the mango, only carbohydrates are present in sufficient concentration and of sufficient sensitivity to merit attention from a toxicological viewpoint. Experimentally, the radiation sensitivity of numerous constituents of the fruit has been compared with that of glucose and, apart from a few exceptions whose concentrations are minimal, results obtained agree well with predicted values
[af]
Voedselbestraling word verkeerdelik as 'n byvoegsel tot voedsel in plaas van 'n voorbereidingsmetode beskou. Die regverdiging hiervoor is dat daar chemiese veranderinge gedurende die proses plaasvind. Die meeste voedselsoorte bestaan uit 'n groot aantal bestanddele waarvan die meerderheid in klein konsentrasies teenwoordig is. Die hoeveelheid radioliseprodukte wat gevorm mag word is reeds te laag vir identifikasie asook vir kwantitatiewe bepalings, selfs met gebruiklike analitiese metodes. Stralingschemiese kennis word gebruik om die moontlike aard en konsentrasie van reaksieprodukte te bepaal wat in vrugte ontstaan. Vrugte bestaan in hoofsaak uit water en koolhidrate, en klein hoeveelhede proteine, vette, anorganiese materiaal en vitamiene wat as 'kontaminante' optree. In werklikheid is die toestand geweldig ingewikkeld maar deur hierdie eenvoudige model as 'n eerste benadering te gebruik, kan voorspellings in verband met die stralingsstabiliteit van 'n tipiese vrug gemaak word. Berekeninge wat met behulp van bekende stralingschemiegegewens gedoen is, toon dat alleenlik koolhidrate in genoegsame konsentrasie in die geval van die mango teenwoordig is, en dat hulle voldoende sensitief is, om uit 'n toksikologiese standpunt aandag te geniet. Die stralingssensiwiteit van baie van die vrugbestanddele is eksperimenteel met die van glukose vergelyk. Behalwe in die geval van 'n paar uitsonderings wat in minimale hoeveelhede teenwoordig is, het die resulte met die voorspelde waardes ooreengestemSource
Jun 1977; 26 p; ISBN 0 86960 659 X;
[en] Stereoselective synthesis of α-sialosides by the glycosylation reaction (sialylation) is an important task in carbohydrate chemistry. Using quantum chemical calculations, the conformations of the sialyl cation formed from the sialyl donor under conditions of sialylation reaction were studied. Although the "axial conformation" of sialyl cation itself is energetically unfavorable, it is possible to stabilize it through the participation of O- and N-acyl protective groups. The obtained results open the possibility to modulate the stereoselectivity of sialylation by directed variation of the nature of protective groups in the sialyl donor molecule. 2
Journal
[en] Using first-principles calculations, we show that the formation of carbohydrates directly from carbon and water is energetically favored when graphene is subjected to an unequal chemical environment across the two sides, with a difference in the chemical potential of protons and hydroxyl groups. The resultant carbohydrate structure is two-dimensional (2D), with the hydrogen atoms exclusively attached on one side of the graphene and the hydroxyl groups on the other side, the latter forming a herringbone reconstruction that optimizes hydrogen bonding. We show that graphene undergoes a metal-insulator transition upon hydration that is readily detectable from the significant shift in the vibration spectrum. The hydrate form of graphene offers new applications for graphene in electronics, either deposited on a substrate or in solution.
Journal
New Journal of Physics; ISSN 1367-2630; ; v. 12(12); [7 p.]
; v. 12(12); [7 p.]
[en] Grewia asiatica (Phalsa) is indigenous to Pakistan and is most commonly used in summer season, but it could not be kept for long. For this reason dried phalsa powder was prepared and its nutritional value was investigated to assess the numerous potential of this plant fruit. The results exhibited that the dried powder contains nutritional value (carbohydrates, protein, fat, fiber, minerals and energy) four times as compared to phalsa fruit. For acute oral toxicity test, the dried phalsa powder was tested on healthy laboratory animals in a dose of 0.45g/kg body weight and 0.90g/kg body weight and compared with the standard marketed product Tang (orange) in recommended dose. The test drink passed acute oral toxicity test showing no sign of toxicity within 72 hours claimed period. The gross behavioral observation of animals showed that the drink is energizing and CNS stimulant and no mortality was recorded during experimental period. Autopsy findings showed no gross changes. All vital organs i.e. heart, liver, spleen, lungs and kidneys were found normal as a result of which it can be concluded that during processing of fresh fruit in dried powder and addition of preservatives no hazardous material like toxins were produced. So it can be used safely. (author)
Journal
Journal of the Chemical Society of Pakistan; ISSN 0253-5106; ; v. 35(2); p. 321-324
; v. 35(2); p. 321-324
[en] Pharmacophore of kojic acid is enolic hydroxyl group in 5-position. To enhance biological activities of kojic acid, we increased hydrophobicity by introduction of 3,4-methylenedioxy cinnamate moiety in 2-position which is not pharmacophore. Its potent activities may be due to balance between hydrophilic and hydrophobic character. Kojic acid, 5-hydroxy-2-(hydroxymethyl)-4H-pyran-4-one, is produced from carbohydrate sources in an aerobic process by a variety of microorganisms. It showed broad biological activities such as inhibition of tyrosinase, scavenging of the free radicals, chelating activity of metal ions and prevention of photodamage. Its various activities are due to γ-pyranone structure having enolic hydroxyl group. Recently, enolic hydroxyl group of kojic acid has been focused as an alternative of carboxylic acid in retinoid structure. We synthesized 3,4-methylenedioxy cinnamic acid ester of kojic acid as a new retinoidal compound. In this study, we evaluated biological activities of new kojic acid derivative 1, 2-((3E)-4(2H,3H-benzo[3,4-d]1,3-dioxolan-5- yl)-2-oxo-but-3-enyloxy)-5-hydroxy-4H-pyran-4-one
Journal
Bulletin of the Korean Chemical Society; ISSN 0253-2964; ; v. 28(3); p. 471-473
; v. 28(3); p. 471-473
[en] Data on the main approaches to preparation of mono- and oligodentate glycoconjugates based on porphyrin scaffolds are surveyed. The prospects for using these compounds as sensitizers for photodynamic therapy of cancer and for suppression of bacterial and viral pathogens are considered. Data on the synthesis of oligodentate blocking agents for carbohydrate-binding proteins (lectins) based on porphyrin scaffolds are discussed. The bibliography includes 161 references
Journal
Russian Chemical Reviews (Print); ISSN 0036-021X; ; v. 83(6); p. 523-554
; v. 83(6); p. 523-554
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