1,721,025 research outputs found
γ-Glutamyl transpeptidase-catalyzed synthesis of naturally occurring flavor enhancers
No full textγ-Glutamyl derivatives of S-substituted cysteines are naturally occurring flavor enhancers found in garlic and in other plants of the genus Allium. In this paper we describe a straightforward enzymatic synthesis of γ-glutamyl-S-allylcysteine, γ-glutamyl-S-methylcysteine and γ-glutamylmethionine based on a transpeptidation reaction involving glutathione as the γ-glutamyl donor and catalyzed by a commercially available γ-glutamyl transpeptidase (EC 2.3.2.2). Reaction conditions have been optimized with respect to pH, temperature, reactants molar ratio and enzyme concentration using a method based on TLC technique and computer-assisted image analysis for the quantitative evaluation of the reaction mixtures composition. Preparative enzymatic syntheses of γ-glutamyl-S- allylcysteine, γ-glutamyl-S-methylcysteine and γ-glutamylmethionine were carried out at 1 mmol scale. The method is suited for the laboratory scale synthesis of reference compounds for quality control assay, in that it avoids laborious and low-yielding isolation procedures from natural sources or complicated protection and deprotection steps required for chemical synthesis
New guanosine 5’-phosphate derivatives as flavor enhancers
No full textA number of N2 -alkyl and N2 -acyl derivatives of guanosine 5’-phosphate (2 and 3) have been synthesized as potential flavor enhancers and tested for their synergistic effect with monosodium-L-glutamate (MSG), the prototypical substance imparting umami taste to savory-based foods
Stereoselective TiCl4-promoted nucleophilic substitution at C-2 of (4S,5S)-2-alkyl-4-methyl-5-trifluoromethyl-1,3-dioxolanes
No full textTiCl4-mediated nucleophilic ring-opening reactions of chiral acetals derived from (2S,3S)-1,1,1-trifluorobutane-2,3-diol proceed in a completely regioselective manner, leading to the break of the O1-C2 bond accompanied by a high degree of stereoselectivity. The use of triethylsilyl deuteride or allyltributyltin as nucleophiles gives access, after removal of the chiral auxiliary, to stereoselectively deuterated primary alcohols or homoallylic secondary alcohols, respectively, with high enantiomeric excesses
Chemistry of α-mangostin : studies on the semisynthesis of minor xanthones from Garcinia mangostana
Full text linkα-Mangostin is the major prenylated xanthone from Garcinia mangostana and it has been used also in recent times as starting material for the semisynthetic preparation of various biologically active derivatives. Its structure is characterised by the presence of few functional groups amenable to chemical manipulations, but present in the molecule in multiple instances (three phenolic hydroxyl groups, two prenyl chains and two unsubstituted aromatic carbons). This study represents a first approach to the systematic investigation of the reactivity of α-mangostin and describes the semisynthesis of some minor xanthones isolated from G. mangostana
Expeditious solid-phase synthesis of pyrazoledicarboxylic acid derivatives by functionalization of resin-bound cyanoformate
No full textEsterification of the Wang resin 5 with the monoamide of oxalic acid (oxamic acid, 7) followed by dehydration of the amide function furnishes the resin-bound cyanoformate 9, which can be elaborated by zinc-catalyzed reaction with beta-keto esters. The obtained enamino keto diesters 10a-d react with hydrazines affording, after removal from the solid support, fully substituted pyrazoledicarboxylic acids 12a-n, Optimization of the above sequence and the solid-phase synthesis of a small test-library of 1,5-disubstituted pyrazole-3,4-dicarboxylic acid derivatives are described. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Evidence for a nucleophilic anti-attack on the cleaved C(2)-oxygen bond in Cl2AlH-catalyzed ring-opening of 2-substituted 1,3-dioxolanes
No full textThe Cl2AlH-mediated ring-opening of 2-substituted cis-4-methyl-5-trifluoromethyl-1,3-dioxolanes was found to occur with regioselective cleavage of the O1-C2 bond by attack of the aluminum hydride from the direction anti to the departing oxygen. This stereochernical outcome, which appears to be unprecedented in the reductive cleavage of chiral acetals by aluminum reagents, is interpreted on the basis of theoretical calculations. (C) 2005 Elsevier Ltd. All rights reserved
Attività anti-infiammatoria degli estratti di radice di Maytenus senegalensis e di acido maitenoico
No full textAloeresin I, an anti-inflammatory 5-methylchromone from Cape aloe
No full textA new diglucoside having a 5-methylchromone moiety was isolated from a commercial sample of Cape aloe, the dried exudate from Aloe ferox Miller, and named aloeresin I. Its structure was established as 1 on the basis of spectral and chemical evidence. Aloeresin I (1) (1 mumol/cm(2)) reduces in vivo the oedematous response (39%) induced by Croton oil in the mouse ear with the same potency as aloesin, one of the most abundant Cape aloe constituents, and to a higher extent than aloeresin H (2). Indomethacin (0.3 mumol/cm(2)), the reference anti-inflammatory compound, provokes 61% oedema inhibition
Immobilized purine nucleoside phosphorylase from Aeromonas hydrophila as an on-line enzyme reactor for biocatalytic applications
No full textWe described the development of a biochromatog. system which uses a purine nucleoside phosphorylase from Aeromonas hydrophila (AhPNP) for the evaluation of the substrate specificity on nucleoside libraries. AhPNP has been covalently immobilized on a fused silica Open Tubular Capillary (OTC) via Schiff base chem. The resulting bioreactor has been characterized by the detn. of kinetic consts. (Km and Vmax) for a natural substrate (inosine) and then assayed vs. all natural purine (deoxy)ribonucleosides and a small library of 6-substituted purine ribosides. Characterization of the bioreactor has been carried out through a bidimensional chromatog. system with the sample online transfer from the bioreactor to the anal. column for the sepn. and quantification of substrate and product. Comparison with the sol. enzyme showed that the AhPNP-based bioreactor is reliable as the same ranking order, with respect to the std. activity assay, was obtained. The stability of the IMER was also assessed and the system was found to be stable up to 60 reactions
Antiproliferative activity of Aloe arborescens leaf skin extracts tested on murine myeloma cells: cytological studies and chemical investigations
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