An Integrated Enzymatic Approach to Produce Pentyl Xylosides and Glucose/Xylose Laurate Esters From Wheat Bran

Alkyl glycosides and sugars esters are non-ionic surfactants of interest for various applications (cosmetics, food, detergency,…). In the present study, xylans and cellulose from wheat bran were enzymatically converted into pentyl xylosides and glucose and xylose laurate monoesters. Transglycosylation reaction catalyzed by the commercial enzymatic cocktail Cellic Ctec2 in the presence of pentanol led to the synthesis of pentyl β-D-xylosides from DP1 to 3 with an overall yield of 520 mg/g of xylans present in wheat bran. Enzymatic hydrolysis of wheat bran with Cellic Ctec2 and subsequent acylation of the recovered D-glucose and D-xylose catalyzed by the commercial lipase N435 in the presence of lauric acid or methyl laurate produced one D-glucose laurate monoester and one D-xylose laurate monoester. An integrated approach combining transglycosylation and (trans)esterification reactions was successfully developed to produce both pentyl xylosides and D-glucose and D-xylose laurate esters from the same batch of wheat bran.

Transformation of Pectins into Non-Ionic or Anionic Surfactants Using a One-Pot and Cascade Mode Process

The present article describes the one-pot synthesis of double- and single-tailed surfactants by a cascade process that involves the hydrolysis/butanolysis of pectins into butyl galacturonate monosaccharides followed by transesterification/transacetalisation processes with fatty alcohols, and subsequent aqueous basic and acid treatments. The cascade mode allows the depolymerisation to proceed more efficiently, and the purification conditions are optimised to make the production of single-tailed surfactants more manufacturable. These products in a pure form or as mixtures with alkyl glycosides resulting from butanolysis and transglycosylation of pectin-derived hexoses, exhibit attractive surface-tension properties, especially for the n-oleyl ᴅ-galactosiduronic acid products. In addition, a readily biodegradability and an absence of aquatic ecotoxicity are shown for the galacturonic acid derivatives possessing an oleyl alkyl chain at the anomeric position.

Chemoenzymatic Synthesis of New Aromatic Esters of Mono- and Oligosaccharides

An efficient and convenient chemoenzymatic route for the synthesis of novel phenolic mono-, di- and oligosaccharide esters is described. Acetal derivatives of glucose, sucrose, lactose and inulin were obtained by chemical synthesis. The fully characterized pure sugar acetals were subjected to enzymatic esterification with 3-(4-hydroxyphenyl) propionic acid (HPPA) in the presence of Novozyme 435 lipase as a biocatalyst. The aromatic esters of alkyl glycosides and glucose acetal were obtained with good esterification yields, characterized by mass spectrometry (MALDI-TOF MS), infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (1H NMR, 13C NMR). The synthesis of aromatic esters of disaccharide acetals was successful only for the enzymatic esterification of sucrose acetal. The new chemoenzymatic route allowed the synthesis of novel aromatic esters of inulin as the inulin monoacetal monoester and diester and the inulin diacetal monoester with a polymerization degree of two, as well as the inulin monoacetal monoester with a degree of polymerization of three, were obtained by enzymatic acylation of inulin acetals with HPPA. These compounds could represent a new class of sugar ester surfactants with enhanced bioactivity, antioxidative and antimicrobial properties and with potential application in drug delivery systems.

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.

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.

Green, Microwave-Assisted Synthesis of O-Perbutyrylated-Alkyl-Glycosides

Chemical synthesis of carbohydrates is a challenging task. Several protection and deprotection steps of hydroxyl groups are required to ensure regioselective formation of the glycosidic bond. Usually, it is achieved through acylation, where conventional heating is combined with addition of Lewis acids as catalysts. This traditional approach has two drawbacks; it is time consuming and often catalysts are hazardous to the environment. An alternative route relies on application of microwaves and/or other Lewis acids with less or no toxicity. Such combination would reduce reaction times and offer a benign synthetic strategy to obtain peracylated compounds. The current work describes an efficient and environmentally mild synthesis of peracylated glycosides with potential application in enzymatic preparation of carbohydrates. Model compound O-perbutyrylated-phenyl-galactose was synthesized using imidazole as catalyst in the microwave-assisted process. The acylation protocol was optimized, and the target sugar was obtained at 50% yield after 1 h. In conclusion, the combination of imidazole and microwaves provides an excellent alternative to swiftly synthesize peracylated glycosides in a benign way.