Enzyme-catalysed synthesis of alkyl β-D-Glucosides in organic media

A selective and mild glycosylation method of natural phenolic alcohols

Several bioactive natural p-hydroxyphenylalkyl β-D-glucopyranosides, such as vanillyl β-D-glucopyranoside, salidroside and isoconiferin, and their glycosyl analogues were prepared by a simple reaction sequence. The highly efficient synthetic approach was achieved by utilizing acetylated glycosyl bromides as well as aromatic moieties and mild glycosylation promoters. The aglycones, p-O-acetylated arylalkyl alcohols, were prepared by the reduction of the corresponding acetylated aldehydes or acids. Various stereoselective 1,2-trans-O-glycosylation methods were studied, including the DDQ-iodine or ZnO-ZnCl2 catalyst combination. Among them, ZnO-iodine has been identified as a new glycosylation promoter and successfully applied to the stereoselective glycoside synthesis. The final products were obtained by conventional Zemplén deacetylation.

Enzyme-catalyzed synthesis of heptyl-β-glycosides: effect of water coalescence at high temperature

Alkyl glycosides can be synthesized by glycosidases in organic media with limited amounts of water. These systems, however, limit the solubility of the sugar substrates and decrease reaction yields. Herein we report the enzymatic synthesis of heptyl-β-glycosides in heptanol catalyzed by a hyperthermophilic β-glycosidase at 90°C. Our results indicate that dispersion of water in heptanol changes with time producing coalescence of water at the bottom of the reactor, playing a key role in the reaction yield. Water-soluble substrate, enzyme and products are concentrated in the aqueous phase, according to their partition coefficients, promoting side reactions that inactivate the enzyme. Reaction yield of heptyl-β-glycosides was 35% relative to lactose, at 7% water. The increase in the water phase to 12% diminished the enzyme inactivation and increased the heptyl-β-glycosides yield to 52%. Surface-active compounds, SDS and octyl glucoside, increased water dispersion but were unable to prevent coalescence.

The response of filamentous fungus Rhizopus nigricans to flavonoids

The saprophytic fungus Rhizopus nigricans constitutes a serious problem when thriving on gathered crops. The identification of any compounds, especially natural ones, that inhibit fungal growth, may therefore be important. During its life cycle, Rhizopus nigricans encounters many compounds, among them the flavonoids, plant secondary metabolites that are involved in plant defense against pathogenic microorganisms. Although not being a plant pathogen, Rhizopus nigricans may interact with these compounds in the same way as plant pathogens--in response to the fungitoxic effect of flavonoids the fungi transform them into less toxic metabolites. We have studied the interaction of R. nigricans with some flavonoids. Inhibition of hyphal spreading (from 3% to 100%) was observed by 300 μM flavones, flavanones and isoflavones, irrespective of their basic structure, oxidized or reduced C-ring, and orientation of the B-ring. However, a hydrophobic A-ring was important for the toxicity. R. nigricans transformed some of the flavonoids into glucosylated products. Recognition of substrates for glucosylating enzyme(s) did not correlate with their fungitoxic effect but depended exclusively on the presence of a free -OH group in the flavonoid A-ring and of a hydrophobic B-ring. Although the fungus produced glucosyltransferase constitutively, an additional amount of the enzyme was induced by the substrate flavonoid. Moreover, effective detoxification was shown to require the presence of glucose.

Studies on the transglucosylation reactions of cassava and Thai rosewood β-glucosidases using 2-deoxy-2-fluoro-glycosyl-enzyme intermediates

Beta-glucosidases from cassava and Thai rosewood can synthesize a variety of alkyl glucosides using various alcohols as glucosyl acceptors for transglucosylation. Both enzymes were inactivated by 2-deoxy-2-fluoro-sugar analogues to form the covalent glycosyl-enzyme intermediates, indicating that the reaction mechanism was of the double-replacement type. The trapped enzyme intermediates were used for investigating transglucosylation specificity, by measuring the rate of reactivation by various alcohols. The glucosyl-enzyme intermediate from the cassava enzyme showed a 20- to 120-fold higher rate of glucose transfer to alcohols than the glucosyl-enzyme intermediate from the Thai rosewood enzyme. Kinetic analysis indicated that the aglycone binding site of the cassava enzyme was hydrophobic, since the enzyme bound better to more hydrophobic alcohols and showed poor transfer of glucose to hydrophilic sugars. With butanol, transglucosylation was faster with the primary alcohols than with the secondary or tertiary alcohol. Studies with ethanol and chloro-substituted ethanols indicated that the rate of transglucosylation was significantly faster with alcohols with lower pKa values, where the reactive alkoxide was more readily generated, indicating that the formation of the alkoxide species was a major step governing the formation of the transition state in the cassava enzyme.

Simple Synthesis of .BETA.-D-Glycopyranosides Using .BETA.-Glycosidase from Almonds

Enzymatic glycosidation of twenty-one kinds of alcohols (n-hepanol, n-octanol, 2-phenylethanol, 3-phenylpropanol, 4-phenylbutanol, 5-phenylpentanol, 6-phenylhexanol, furfury alcohol, 2-pyridinemethanol, isobutanol, isopentanol, p-methoxycinnamylalcohol) including secondary alcohols (isopropanol, cyclohexanol, 1-phenylethanol) and 1,omega-alkanediols (1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol), salicyl alcohol and 4-nitrophenyl beta-D-glucopyranoside (5) using beta-glucosidase from almonds stereoselectively gave the corresponding beta-D-glucopyranosides in moderate yield.

Aromatic compound glucosides, alkyl glucoside and glucide from the fruit of anise

From the polar portion of the methanolic extract of the fruit of anise (Pimpinella anisum L.), which has been used as a spice and medicine since antiquity, four aromatic compound glucosides, an alkyl glucoside and a glucide were isolated together with 24 known compounds. The structures of the new compounds were clarified as (E)-3-hydroxyanethole beta-D-glucopyranoside, (E)-1'-(2-hydroxy-5-methoxyphenyl)propane beta-D-glucopyranoside, 3-hydroxyestragole beta-D-glucopyranoside, methyl syringate 4-O-beta-D-glucopyranoside, hexane-1,5-diol 1-O-beta-D-glucopyranoside and 1-deoxy-L-erythritol 3-O-beta-D-glucopyranoside by spectral investigation.

Efficient synthesis of glyceroyl beta-lactoside and its derivatives through a condensation reaction by cellulase

Condensation reaction between lactose and glycerol was effectively catalyzed by utilizing a commercially available cellulase preparation from Trichoderma reesei. The enzyme induced the formation of 1-O-beta-lactosyl-(R,S)-glycerol (1) and 2-O-beta-lactosyl glycerol (2) in a molar ratio of 7:3 and in a 20% yield based on lactose added. The enzyme also induced the condensation of lactose with 1,3-propanediol to produce O-beta-lactosyl propanediol (3) in a yield of 15%. When various alkanols (N: 2-8) and allyl alcohol were used in the condensation reaction, the corresponding alkyl and allyl beta-lactoside were obtained in the yields of 0.9-3.8% of the desired compounds.

Glycosidases and glycosyl transferases in glycoside and oligosaccharide synthesis

Remarakable advances in glycobiology in recent years have stimulated a resurgence of interest in carbohydrate chemistry. The challenge of producing the complex glycosides and oligosaccharides needed for research in glycobiology has led to the development of enzymatic methods that are now firmly established as part of the synthetic repertoire of the carbohydrate chemist.

Thermodynamic predictions for biocatalysis in nonconventional media: theory, tests, and recommendations for experimental design and analysis

This article discusses the application of thermodynamic and related analysis to reaction systems for enzymic or whole cell catalysis, in which there are high proportions of organic liquid, gas, or supercritical fluid. A variety of predictions may be made, especially based on the partitioning of components between the different phases normally present. In many cases, observed behavior can be explained without invoking any direct molecular effects on the biocatalyst. The predictable changes should always be allowed for before seeking explanations for the residual effects, which are often very different from the crude observations. A summary of the general thermodynamics of multiphase systems is presented, and then the main classes of component that distribute between the phases are discussed in turn. Thermodynamic water activity (aw) determines the mass action effects of water on hydrolytic equilibria. It also describes the distribution of water between the various phases that can compete in binding water. Because catalytic activity is very sensitive to the hydration of the enzyme molecules, aw often predicts an unchanging optimum as other aspects of the system are changed. Hence the aw should be measured and/or controlled in these systems, whether the primary aim is to study the effects of water or of other changes. The methods available for measurement and control of aw are discussed. Adverse effects of organic solvents or similar nonpolar species partly reflect their tendency to partition into the relatively polar phase around the biocatalyst, especially when this is dilute aqueous. The well-established log P parameter is a measure of this. But other mechanisms of inactivation can occur: directly through contact of the biocatalyst with the phase interface, or indirectly via hydration changes. In these cases the molecular property log P is probably not the best solvent parameter. In low-water systems the biocatalyst remains in a separate phase even when water-miscible solvents are used. Hence, the categorization of solvents in terms of miscibility becomes less relevant. This accounts for the "two peak" dependence of catalytic activity on water content in some miscible systems. Differential solvation of reactants and products, as the bulk phase is altered, causes changes in concentration-based equilibrium constants and yields. These changes in solvation may be monitored through partition coefficient or solubility measurements. Reactant solvation can also account for differences in biocatalyst kinetics, whether or not partitioning into a dilute aqueous phase is involved. These predictable effects should be allowed for when studying effects of solvent or similar changes on activity or specificity.(ABSTRACT TRUNCATED AT 400 WORDS)