Douglas B. Sarney

Application of enzymes to the synthesis of surfactants

Recent progress in the application of isolated enzymes to the preparation of surface-active compounds demonstrates the feasibility of an alternative to organosynthetic methods. Processes such as the syntheses of monoglycerides, sugar fatty acid esters, (lyso)phospholipids, anomerically pure alkyl glycosides and amino acid-based surfactants are discussed, highlighting some of the advantages of enzymatic methods over conventional organic syntheses and whole-cell systems.

Enzymic solvent-free synthesis of sugar acetal fatty acid esters

Abstract An enzymic solvent-free acylation of sugar acetals with a range of long-chain fatty acids (lauric, myristic, palmitic, stearic) and their methyl esters is described. The lipase-catalysed reaction was carried out at 1:1 and 2:1 molar ratios of fatty acid or methyl ester of fatty acid to sugar acetal to obtain mono- or diesters, respectively. A range of 6 monoesters of 1,2-O-isopropylidene- d -glucofuranose and 1,2:3,4-Di-O-isopropylidene- d -galactopyranose as well as 5-mono- and 3,5-diesters of 1,2-O-isopropylidene- d -xylofuranose were prepared. The synthesis was performed at 75°C in open vials or under vacuum, to provide an equilibrium shift towards the final products via evaporation of water or methanol produced in the course of the reaction. Typically yields of 50–90% were obtained under optimal conditions.

A novel approach to the recovery of biologically active oligosaccharides from milk using a combination of enzymatic treatment and nanofiltration

A new easily scalable approach to the recovery of biologically active oligosaccharides from milk has been developed which relies on the combination of enzymatic treatment of defatted milk using beta-galactosidase and nanofiltration. It was shown that enzymatic hydrolysis of lactose significantly improves the efficiency and selectivity of membrane-based separations. With the best membrane, as much as 6.7 g of oligosaccharides (containing very little contaminating lactose) could be obtained from one liter of defatted human milk in just four nanofiltration cycles. The human milk oligosaccharides recovered by this method were shown to inhibit binding of intimin, an adhesion molecule of enteropathogenic Escherichia coli, to epithelial cells in vitro. No significant difference in the oligosaccharide profile between samples prepared by this method and conventional gel-permeation chromatography was found. The developed approach is also suitable for the recovery of substantial quantities of tri- and tetra-saccharides from caprine milk.

Enzymatic synthesis of monosaccharide fatty acid esters and their comparison with conventional products

Abstract5-O-Acyl-1,2-O-isopropylidene-D-xylofuranose and 6-O-acyl1,2∶3,4-di-O-isopropylidene-D-galactopyranose were enzymatically prepared from the corresponding monosaccharide acetals and commercial (crude) fatty acid mixtures. Subsequent acid-catalyzed hydrolysis of the isopropylidene group(s) gave monosaccharide esters with overall yields of 59–88%, where the monoester content was at least 80% (galactose oleate) and typically 90% for the other preparations. In contrast to sugar fatty acid esters prepared by conventional, high-temperature (trans)esterification, the enzymatically obtained monosaccharide esters contained no appreciable quantities of undersirable side products, and the only contaminants were monosaccharides and fatty acids.

Application of lipases to the regioselective synthesis of sucrose fatty acid monoesters

A regioselective synthesis of 6′-O-acyl sucrose monoesters has been developed through the lipase-catalyzed esterification of sucrose acetals with fatty acids in both organic solvents and under solvent-free conditions. The products were obtained in overall yields of 20–27% after hydrolysis of the isopropylidene groups with aqueous acids. The strict selectivity of the enzymes used also enabled the preparation of a monoester fraction that was highly enriched in 6-O-acyl sucrose. This was accomplished by lipase-catalyzed transesterification of sucrose monoesters, prepared by conventional chemical methods, in propan-2-ol. After removal of the transesterification products (sucrose and fatty acid isopropyl esters) and column chromatography on silica gel, the obtained monoester product contained 80% of the single regioisomer, 6-O-acyl sucrose.

Chemo-enzymatic synthesis of disaccharide fatty acid esters

A novel enzymatic method for the synthesis of disaccharide fatty acid esters was developed with immobilizedMucor miehei lipase (Lipozyme IM-60; Novo Nordisk, Bagsvaerd, Denmark) as a catalyst. A range of lactose and maltose monoesters was prepared in overall yields of 48–77% from the corresponding sugar acetals and fatty acids.

Lipase-Catalyzed Synthesis of Lysophospholipids in a Continuous Bioreactor

A novel enzymatic method of lysolecithin synthesis was developed with immobilized lipase as a catalyst. The enzymatic transesterification was carried out in a number of alcohols, and the reaction was optimized with regard to the water content and temperature of the medium. Similar kinetics of transesterification were observed with several individual phospholipids. The reaction was also performed continuously in a packed-column bioreactor, which was operated for 1180 h. The lipase displayed strict regio-selectivity towardsn-1 fatty acid in the phospholipid molecule, thus yielding exclusivelysn-1 lysolecithins as the final product.sn-2 Lysophospholipids were subsequently obtained by acyl migration catalyzed by ammonia vapor. Advantages associated with the use of lipases as opposed to conventional, phospholipase-A2 catalyzed hydrolysis are briefly discussed.

Enhancement of subtilisin-catalysed interesterification in organic solvents by ultrasound irradiation

The effect of ultrasound irradiation on subtilisin-catalysed interesterification of N-acetyl-phenylalanine ethyl ester in various alcohols has been studied. The pretreatment of subtilisin suspension by ultrasound led to a substantial increase of enzyme activity. The effect appeared to be dependent on the amplitude of sonication and the water content of the reaction medium; it was more pronounced in long-chain alcohols. An enhancement of reaction rate was observed with continuously sonicated preparations of the enzyme compared to those pretreated with ultrasound. Subtilisin was found to be much more resistant to inactivation by ultrasound irradiation in organic solvents than in water.

A novel approach to biotransformations in aqueous-organic two-phase systems : Enzymatic synthesis of alkyl β-[D]-glucosides using microencapsulated β-glucosidase

A novel approach to enzymatic biotransformations in aqueous-organic two-phase systems was developed where the aqueous phase was contained within permeable polymeric capsules suspended in organic solvent. Microencapsulated β-glucosidase, used as a model enzyme, was shown to retain its catalytic activity for a considerable time and was repeatedly used in batch experiments after recharging the microcapsules with solid glucose. The reaction conditions for the synthesis of hexyl β-[D]-glucopyranoside were optimized with regard to the polymer composition of the microcapsules, pH, and the volume ratio of aqueous to organic phases. The potential for further improvement in the efficiency of the system was demonstrated by designing a bioreactor which incorporated units for product recovery and recycling of the organic solvent. Other advantages of the proposed methodology include facile control over the size and composition of the microcapsules, and mild reaction conditions during their preparation.

Facile Chemo-Enzymatic Synthesis of Monosaccharide Fatty Acid Esters

A range of monosaccharide fatty acid esters was prepared by enzymatic esterification of sugar acetals to provide a series of esters for detailed investigation of their surfactant properties. 6-O-acyl-D-galactopyranoses 2, 6-O-acyl-D-glucopyranoses 4 and 5-O-acyl-D-xylofuranoses 6 were prepared by Mucor miehei lipase catalysed esterification of 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose 1a, 1,2-O-isopropylidene-α-D-glucofuranose 3a and 1,2-O-isopropylidene-α-D-xylofuranose 5a with decanoic, dodecanoic, tetradecanoic, hexadecanoic and octadecanoic acids respectively followed by cleavage of the isopropylidene group(s) of the monosaccharide acetal estes 1b-f, 3b-f and 5b-f.