Synthesis Of Alkyl Glycosides Research Articles

Engineering CGTase to improve synthesis of alkyl glycosides.

Alkyl glycoside surfactants with elongated carbohydrate chains are useful in different applications due to their improved biocompatibility. Cyclodextrin glucanotransferases can catalyze the elongation process through the coupling reaction. However, due to the presence of a hydrophobic tail, the interaction between an alkyl glycoside acceptor and the active site residues is weaker than the interaction with maltooligosaccharides at the corresponding site. Here we report the mutations of F197, G263 and E266 near the acceptor subsites in the CGTase CspCGT13 from Carboxydocella sp. The results showed that substitutions of both F197 and G263 were important for the binding of acceptor substrate dodecyl maltoside during coupling reaction. The double mutant F197Y/G263A showed enhanced coupling activity and displayed a 2-fold increase of the primary coupling product using γ-cyclodextrin as donor when compared to wildtype CspCGT13. Disproportionation activity was also reduced, which was also the case for another double mutant (F197Y/E266A) that however not showed the corresponding increase in coupling. A triple mutant F197Y/G263A/E266A maintained the increase in primary coupling product (1.8-fold increase) using dodecyl maltoside as acceptor, but disproportionation was approximately at the same level as in the double mutants. In addition, hydrolysis of starch was slightly increased by the F197Y and G263A substitutions, indicating that interactions at both positions influenced the selectivity between glycosyl and alkyl moieties.

Increased yield of enzymatic synthesis by chromatographic selection of different N-glycoforms of yeast invertase.

Invertases are glycosidases applied for synthesis of alkyl glycosides that are important and effective surfactants. Stability of invertases in the environment with increased content of organic solvent is crucial for increase of productivity of glycosidases. Their stability is significantly influenced by N-glycosylation. However, yeast N-glycosylation pathways may synthesize plethora of N-glycan structures. A total natural crude mixture of invertase glycoforms (EINV) extracted from Saccharomyces cerevisiae was subfractionated by anion-exchange chromatography on industrial monolithic supports to obtain different glycoforms (EINV1-EINV3). Separated glycoforms exhibited different stabilities in water-alcohol solutions that are in direct correlation with the amount of phosphate bound to N-glycans. Observed differences in stability of different invertase glycoforms were used to improve productivity of methyl β-d-fructofuranoside (MF) synthesis. The efficiency and yield of MF synthesis were improved more than 50% when the most stabile glycoform bearing the lowest amount of phosphorylated N-glycans is selected and utilized. These data underline the importance of analysis of glycan structures attached to glycoproteins, demonstrate different impact of N-glycans on the surface charge and enzyme stability in regard to particular reaction environment, and provide a platform for improvement of yield of industrial enzymatic synthesis by chromatographic selection of glycoforms on monolithic supports.

A Novel Dimeric Exoglucanase (GH5_38): Biochemical and Structural Characterisation towards its Application in Alkyl Cellobioside Synthesis.

An exoglucanase (Exg-D) from the glycoside hydrolase family 5 subfamily 38 (GH5_38) was heterologously expressed and structurally and biochemically characterised at a molecular level for its application in alkyl glycoside synthesis. The purified Exg-D existed in both dimeric and monomeric forms in solution, which showed highest activity on mixed-linked β-glucan (88.0 and 86.7 U/mg protein, respectively) and lichenin (24.5 and 23.7 U/mg protein, respectively). They displayed a broad optimum pH range from 5.5 to 7 and a temperature optimum from 40 to 60 °C. Kinetic studies demonstrated that Exg-D had a higher affinity towards β-glucan, with a Km of 7.9 mg/mL and a kcat of 117.2 s−1, compared to lichenin which had a Km of 21.5 mg/mL and a kcat of 70.0 s−1. The circular dichroism profile of Exg-D showed that its secondary structure consisted of 11% α-helices, 36% β-strands and 53% coils. Exg-D performed transglycosylation using p-nitrophenyl cellobioside as a glycosyl donor and several primary alcohols as acceptors to produce methyl-, ethyl- and propyl-cellobiosides. These products were identified and quantified via thin-layer chromatography (TLC) and liquid chromatography–mass spectrometry (LC-MS). We concluded that Exg-D is a novel and promising oligomeric glycoside hydrolase for the one-step synthesis of alkyl glycosides with more than one monosaccharide unit.

Deep Eutectic Solvents as New Reaction Media to Produce Alkyl-Glycosides Using Alpha-Amylase from Thermotoga maritima.

Deep Eutectic Solvents (DES) were investigated as new reaction media for the synthesis of alkyl glycosides catalyzed by the thermostable α-amylase from Thermotoga maritima Amy A. The enzyme was almost completely deactivated when assayed in a series of pure DES, but as cosolvents, DES containing alcohols, sugars, and amides as hydrogen-bond donors (HBD) performed best. A choline chloride:urea based DES was further characterized for the alcoholysis reaction using methanol as a nucleophile. As a cosolvent, this DES increased the hydrolytic and alcoholytic activity of the enzyme at low methanol concentrations, even when both activities drastically dropped when methanol concentration was increased. To explain this phenomenon, variable-temperature, circular dichroism characterization of the protein was conducted, finding that above 60 °C, Amy A underwent large conformational changes not observed in aqueous medium. Thus, 60 °C was set as the temperature limit to carry out alcoholysis reactions. Higher DES contents at this temperature had a detrimental but differential effect on hydrolysis and alcoholysis reactions, thus increasing the alcoholyisis/hydrolysis ratio. To the best of our knowledge, this is the first report on the effect of DES and temperature on an enzyme in which structural studies made it possible to establish the temperature limit for a thermostable enzyme in DES.

Characterization of cyclodextrin glycosyltransferases (CGTases) and their application for synthesis of alkyl glycosides with oligomeric head group

Cyclodextrin glycosyltransferases (CGTases) from Paenibacillus macerans, Thermoanaerobacter sp. ATCC 53627, Bacillus stearothermophilus and a Carboxydocella sp. (phylogenetically identified from genomic DNA) were characterized with respect to their catalytic activity in different reactions, with emphasis on reactions useful for the elongation of the carbohydrate group of alkyl glycosides. All CGTases had activities between 95 and 115U/mg in the coupling reaction between α-cyclodextrin (α-CD) as glucosyl donor and β-dodecyl maltoside as glucosyl acceptor, but differed very much in the competing hydrolysis of α-CD. The α-CD hydrolysis activity ranged from 0.13U/mg for P. macerans CGTase to 10.5U/mg for the Carboxydocella sp. (CspCGT13). Furthermore, the disproportionation activity was much lower for the Paenibacillus CGTase compared to the other CGTases, and consequently this enzyme produced the highest yield of the primary coupling product β-dodecyl maltooctaoside, which is a valuable surfactant. For production of a polydisperse alkyl glycoside product, disproportionation reactions are useful and the other three CGTases of the current study are efficient catalysts. The newly discovered Carboxydocella sp. (CspCGT13) CGTase has the special feature to produce more of products with even longer carbohydrate groups than the primary coupling product.

ChemInform Abstract: Protection‐Free Synthesis of Alkyl Glycosides under Hydrogenolytic Conditions.

AbstractIn addition to the glycosylation of (II) and (V) using 4,6‐dibenzyloxy‐1,3,5‐triazin‐2‐yl‐β‐glucoside, the method is successfully applied to the corresponding acid sensitive 4,6‐dibenzyloxy‐1,3,5‐triazin‐2‐yl‐β‐melibioside and β‐maltopentaoside derivatives.

Hydrophobic Complexation Promotes Enzymatic Surfactant Synthesis from Alkyl Glucoside/Cyclodextrin Mixtures

The unique ability of cyclodextrin glycosyltransferase to form and utilize the cyclic maltooligosaccharide cyclodextrin (CD) makes this enzyme an attractive catalyst for the synthesis of alkyl glycosides. Here, we characterize the sugar headgroup elongation of alkyl glucosides (acceptor) via two transglycosylation reactions from either a linear (maltohexose) or a cyclic (CD) glycosyl donor. Inclusion complex formation overcomes both poor substrate solubility and aggregation. We have used pure alkyl glucosides and αCD as model compounds. The complex between CD and alkyl glucoside was efficiently used as a substrate. Kinetic and thermodynamic measurements allow the prediction of the optimal synthesis conditions. This optimum corresponds to the transition between a donor-limiting and an acceptor-limiting regime. The resulting rational design should lead to the practical development of a cost-efficient industrial synthesis. Our findings with respect to the importance of complexation should also readily apply to other enzymatic systems.

Preparation of two glycoside hydrolases for use in micro-aqueous media

Enzymatic synthesis of alkyl glycosides using glycoside hydrolases is well studied, but has yet to reach industrial scale, primarily due to limited yields. Reduced water content should increase yields by limiting the unwanted hydrolytic side reaction. However, previous studies have shown that a reduction in water content surprisingly favors hydrolysis over transglycosylation. In addition, glycoside hydrolases normally require a high degree of hydration to function efficiently. This study compares six enzyme preparation methods to improve resilience and activity of two glycoside hydrolases from Thermotoga neapolitana (TnBgl3B and TnBgl1A) in micro-aqueous hexanol. Indeed, when adsorbed onto Accurel MP-1000 both enzymes increasingly favored transglycosylation over hydrolysis at low hydration, in contrast to freeze-dried or untreated enzyme. Additionally, they displayed 17–70× higher reaction rates compared to freeze-dried enzyme at low water activity, while displaying comparable or lower activity for fully hydrated systems. These results provide valuable information for use of enzymes under micro-aqueous conditions and build toward utilizing the full synthetic potential of glycoside hydrolases.

Protection-free Synthesis of Alkyl Glycosides under Hydrogenolytic Conditions

Abstract A convenient protection-free synthetic route for the preparation of alkyl glycosides has been developed. The alcoholysis of one-step preparable glycosyl donors, 4,6-dibenzyloxy-1,3,5-triazin-2-yl (DBT) glycosides, under hydrogenolytic conditions gave the corresponding glycosides in good yields without the addition of any acid promoters. The method could be successfully applied to the glycosylation of an acid-labile oligosaccharide.

Improved Transferase/Hydrolase Ratio through Rational Design of a Family 1 β-Glucosidase from Thermotoga neapolitana

Alkyl glycosides are attractive surfactants because of their high surface activity and good biodegradability and can be produced from renewable resources. Through enzymatic catalysis, one can obtain well-defined alkyl glycosides, something that is very difficult to do using conventional chemistry. However, there is a need for better enzymes to get a commercially feasible process. A thermostable β-glucosidase from the well-studied glycoside hydrolase family 1 from Thermotoga neapolitana, TnBgl1A, was mutated in an attempt to improve its value for synthesis of alkyl glycosides. This was done by rational design using prior knowledge from structural homologues together with a recently generated model of the enzyme in question. Three out of four studied mutations increased the hydrolytic reaction rate in an aqueous environment, while none displayed this property in the presence of an alcohol acceptor. This shows that even if the enzyme resides in a separate aqueous phase, the presence of an organic solvent has a great influence. We could also show that a single amino acid replacement in a less studied part of the aglycone subsite, N220F, improves the specificity for transglycosylation 7-fold and thereby increases the potential yield of alkyl glycoside from 17% to 58%.

β-Glycosidases: An alternative enzyme based method for synthesis of alkyl-glycosides

Alkyl-glycosides and -polyglycosides are environment friendly, non-ionic surfactants with favourable properties like biodegradability and chemical stability. These are extensively used in personal care products, pharmaceutical preparations and membrane protein research. Commercial production of these surfactants is carried out in multiple steps through Fischer glycosylation reactions under extreme conditions in the presence of toxic catalysts. β-glycosidases provide an alternative enzymatic method for their synthesis as these are easily available from microbial systems and exhibit broad substrate specificity and high stereo-selectivity. This review highlights the recent progress in glycosidase catalyzed synthesis of alkyl-glycosides. Several reaction parameters that affect the overall reaction kinetics, such as, water activity, nature of the glycosyl donor, pH of the reaction medium, reaction time, temperature and source of enzyme are discussed. Strategies available to enhance the yield, including two-phase solvent systems and immobilization are described. Current challenges and future prospects in the biological routes of synthesis are also reviewed.

Ammonium chloride mediated synthesis of alkyl glycosides and evaluation of their immunomodulatory activity

Therapeutic immunoadjuvants have been derived through a straightforward glycosylation of various alcohols with unprotected and non-activated monosaccharides, under solvent free conditions using ammonium chloride as a catalyst. Sugar acids such as glucuronic acid can be glycosylated without esterification and after acetylation yielded a novel 3,6-anhydro derivative. All the synthesized sugar glycosides were screened for immunomodulatory activities to be classified as immunostimulator, immunosuppressor, or immunoadjuvant against the weak antigen oval albumin (OVA). Most of the compounds revealed immunosuppressive (↓) or immunostimulatory (↑) activity with reference to lymphocyte proliferation and possess potential as vaccine adjuvants.

Substrate complexation and aggregation influence the cyclodextrin glycosyltransferase (CGTase) catalyzed synthesis of alkyl glycosides

Bacillus macerans cyclodextrin glycosyltransferase (CGTase) was used to convert dodecyl-β-maltoside (DDM) to dodecyl-β-maltooctaoside (DDMO) using α-cyclodextrin (α-CD) or starch as glycosyl donors. At 300mM α-CD, varied DDM concentration and 60°C, the reaction obeyed Michaelis-Menten kinetics with a K(m) value of 18mM and a V(max) value of 100U/mg enzyme. However, at 25mM α-CD the reaction rate decreased with increasing DDM concentration (5-50mM), and when the α-CD concentration was varied at fixed DDM concentration an S shaped curve was obtained. The deviations from Michaelis-Menten kinetics were interpreted as being caused by formation of inclusion complexes between α-CD and DDM and by micellation of DDM. To achieve a high reaction rate, a high concentration of free α-CD is necessary, since α-CD in the form of a complex has low reactivity. When starch is used as glycosyl donor in the CGTase catalyzed alkyl glycoside elongation reaction, it is thus important to choose reaction conditions under which the cyclization of starch to α-CD is efficient.

Synthesis of alkyl glycosides from cyclodextrin using cyclodextrin glycosyltransferase from Paenibacillus sp. RB01

Alkyl glycosides have potential use as biodegradable detergents due to their high surface activity with low toxicity. Recent progress in the application of enzymes to the preparation of these surface-active compounds demonstrates the advantages to the chemical synthesis. In this work, alkyl glycosides were, for the first time, synthesized from cyclodextrin (CD) and various soluble alcohols by transglycosylation reaction using cyclodextrin glycosyltransferase (CGTase) from Paenibacillus sp. RB01. Several alcohols (methanol, ethanol, 1-propanol, 2-propanol, 1-butanol and 2-butanol) as glycosyl-acceptor substrates were evaluated. It was found that the reaction products which were analyzed by TLC were maximum for 30% methanol, 20–30% ethanol, 10–20% 1-propanol, 10% 2-propanol, 8% 1-butanol and 5–10% 2-butanol. In addition, the increase in the yield of alkyl glycoside formation was achieved by using methanol as an acceptor. Optimal reaction conditions for methyl glycoside synthesis from CD were to incubate 1.2% (w/v) β-CD and 240 U/mL of CGTase in a water/methanol system containing 30% (v/v) methanol, pH 6.0 and a temperature of 40 °C. At least three main methyl glycoside products were formed having 1–3 monosaccharide units attached to methanol which were in accordance with the results of MS analysis.

One-step syntheses of alkyl glycosides and alkyl-substituted DNA oligomers by chemoselective glycosidations using DNA bases

The simple and practical synthesis of alkyl glycosides by novel chemoselective glycosidations using natural resources, DNA and RNA nucleosides, was realized, and the one-step synthesis of chemoselectively modified DNA oligomers using the glycosidation method was also demonstrated.

α-Amylase-catalysed synthesis of alkyl glycosides

Alkyl glycosides were synthesised from starch and alcohols using Aspergillus oryzae α-amylase as catalyst. In the degradation of starch by α-amylase, the alcohols competed with water as glycosyl acceptors. In the reaction with methanol, methyl maltoside and methyl maltotrioside were the main alcoholysis products. Conversion of 45 g/l starch in 30% methanol resulted in a product mixture containing 26 mM maltooligosaccharides and 3.6 mM methyl glycosides. With ethanol, propanol and butanol, alkyl maltosides and alkyl maltotetraosides were detected, and with benzyl alcohol, benzyl glycosides having two, three or five glucose units were formed. No alcoholysis reaction occurred with hexanol or octanol. In conclusion, α-amylase is promising for the one-step synthesis of alkyl glycosides having more than one monosaccharide unit, which are difficult to synthesise in other ways.

Fungus β-glycosidases: immobilization and use in alkyl-β-glycoside synthesis

Production of β-glycosidases: β-xylosidase and β-glucosidase by the fungus Sclerotinia sclerotiorum was optimized in the presence of different carbon sources. Immobilization supports with different physico-chemical characteristics were evaluated for use in continuous reactors. Immobilization and activity yields were calculated. Among the adsorption on Duolite, Amberlite, Celite and DEAE-sepharose, and entrapment in polyacrylamide gel or reticulation using glutaraldehyde, highest yields were obtained when β-xylosidase was adsorbed on Duolite A 7 and when β-glucosidase was adsorbed on DEAE-sepharose.Enzyme preparations from S. sclerotiorum cultures were used in a biphasic (alcohol/aqueous) medium for the synthesis of alkyl-glycosides by trans-glycosylation of sugars and long-chain alcohols. The synthesis was studied under different conditions with primary and secondary alcohols as substrates, in the presence of free or immobilized enzyme. Xylan and cellobiose were used for the synthesis of alkyl-xylosides and alkyl-glucosides, respectively. The majority of the immobilized preparations were unable to catalyze the synthesis of alkyl-glycosides.Highest yields were obtained when using xylan and C4–C6-alcohols. The reaction produced alkyl-β-xyloside and alkyl-β-xylobioside, as confirmed by MS/MS. Up to 22mM iso-amyl-xyloside and 14mM iso-amyl-xylobioside were produced from iso-amyl alcohol and xylan.

ChemInform Abstract: Microwave‐Assisted Synthesis of Alkyl Glycosides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis of Alkyl Glycosides Catalyzed by β-Glycosidases in a System of Reverse Micelles

A basic possibility of enzymic synthesis of alkyl glycosides in a system of the Aerosol-OT (AOT) reverse micelles was studied. Octyl β-D-galactopyranoside and octyl β-D-glucopyranoside were synthesized from the corresponding sugars (lactose or glucose) and octyl alcohol under catalysis with glycolytic enzymes, β-galactosidase and β-glucosidase, respectively. The transglycosylation/hydrolysis ratio was shifted toward transglycosylation by using octyl alcohol, one of the substrates, as an organic solvent. The alkyl glycosides were thus obtained in one step from a hydrophilic mono- or disaccharide and a hydrophobic aliphatic alcohol. The direction of the reaction was shown to depend on the pH of aqueous solution solubilized in reverse micelles. The maximum yields were 45% and 40% for octyl galactoside and octyl glucoside, respectively; they markedly exceeded the yields of enzymic syntheses in a two-phase system reported previously.

Synthesis of alkyl glycosides through β-glucosidase-catalyzed condensation in an aqueous–organic biphasic system and estimation of the equilibrium constants for their formation

Hexyl, heptyl and octyl glucosides, galactosides and fucosides were separately synthesized through the β-glucosidase-catalyzed condensation of glucose, galactose and fucose with the corresponding alcohols in an aqueous–organic biphasic system, where one of the substrates, alcohol, was the organic phase, at various volume ratios. An equation for predicting the equilibrium yield of an alkyl glycoside was proposed, and the parameters involved in the equation were experimentally determined. The equilibrium constant K for the alkyl glycoside formation was then evaluated. Although the K value slightly depended on both the saccharide moiety and the alkyl chain length, it was approximately 2.