NL1005947C2 - Method for the esterification of carbohydrates. - Google Patents

Description

Method for the esterification of carbohydrates

The invention relates to a method for the enzymatic esterification of carbohydrates.

Fatty acid esters of carbohydrates, both of mono, di and oligosaccharides and of polysaccharides, have useful properties such as surfactant, emulsifying and in some cases medicinal properties. Traditionally, such esters have usually been prepared chemically, in particular base-catalyzed reaction with fatty acid derivatives.

However, the chemical esterification of carbohydrates is not very selective. Moreover, drastic conditions are required here, as a result of which the carbohydrate itself can be attacked. This creates numerous undefined and / or unwanted by-products. Furthermore, chemical treatments are less desirable for food applications.

Enzymes such as lipases also appear to catalyze the esterification of carbohydrates, with more selectivity, mainly only primary hydroxyl groups, and under milder conditions. When such an enzyme-catalyzed esterification of carbohydrates in a water medium is carried out, the equilibrium strongly depends on the hydrolysis, and the yields of esters are consequently low. However, various enzymes, such as lipases and proteases, have also been found to be active in organic solvents. Commonly used solvents for enzyme-catalyzed esterifications are pyridine, dimethylformamide, tetrahydrofuran, etc. Recently, the selective esterification of disaccharides with C4 / C12-acyl groups by Woudenberg et al. (Biotechn. Bioeng. 49, 328-333 (1996)) is due to lipase of Candida antarctica in tert-butyl alcohol. The esters of maltose and trehalose 25 are thereby obtained in good yield, but sucrose and lactose are hardly esterified under those conditions.

Thus, the known enzymatic esterifications do not always lead to the desired yield, an additional drawback of these processes is the use of organic solvents. The use of organic solvents usually involves waste problems and residues in the esterification product, which is certainly undesirable for food applications. Enzymatic esterification without solvent succeeds 1005947 2 NO 41257 only to some extent for sorbitol and fructose (Ducret et al. Biotechn. Bioeng. 48, 214-221 (1995); Guillardeau et al. Tenside Surf. Det. 49, 342-344 (1992)). Other carbohydrates, especially the larger ones, do not mix sufficiently with the fatty acid derivatives, especially when they have long chains, so that little or no results are obtained.

EP-A-268461 discloses a process for the preparation of fatty acid esters of epoxidized sugars, in which an enzymatically obtained epoxide adduct is chemically reacted with a fatty acid. In this method, di- and polysaccharides are split into monosaccharides, such as galactose from lactose. In addition, the epoxide group is always introduced at the anomeric center.

It has now been found that carbohydrates can be effectively esterified with long acyl groups, while retaining the chain length of the carbohydrate when the carbohydrate is chemically modified in advance by reaction with an epoxyalkane. With short-chain carbohydrates, with a DP (degree of polymerization) up to about 4-6, no organic solvent is required at all. This solventless process is suitable for the esterification of monosaccharides and especially di- and oligosaccharides, such as sucrose, lactose, maltose, isomaltose, lactulose, raffinose, stachyose, verbascose, short chain inulin, amylodextrins, etc., in particular sucrose and lactose. Sugar alcohols, in particular of disaccharides such as lactitol and maltitol, can also be esterified in this way.

The starting materials for the process may be natural carbohydrates, such as sucrose, lactose, raffinose, starch, inulin, cellulose, etc., or pre-processed natural carbohydrates. The optional pre-treatment can for example be a hydrolysis, in particular an enzymatic hydrolysis, such as a chain shortening of starch (amylase), cellulose (cellulase), hemicellulose (xylanase) and inulin (inulinase). 25 (semi) synthetic carbohydrates can also be used.

Esterification without a solvent means an esterification in which no appreciable amounts of an unreacting solvent - this to distinguish it from the fatty acid or its derivative - are used.

The previous reaction with an epoxyalkane results in a hydroxyalkyl derivative of the carbohydrate. This hydroxyalkylation can take place in a manner known per se, for example by reacting the carbohydrate with an excess of epoxyalkane, in the presence of a base, such as sodium hydroxide, sodium bicarbonate, potassium 100 5947 3 NO 41257 carbonate or triethylamine. This hydroxyalkylation essentially does not take place at any anomeric center present. As the epoxy alkane, a monofunctional epoxide such as ethylene oxide can be used, but the epoxide preferably has a second function, such as a hydroxy, epoxy, amino or thiol group, which can be acylated later. Examples are glycidol, epichlorohydrin and butane deep oxide.

By way of example, the following general procedure for the pre-reaction with an epoxyalkane can be given. 100 to 800 mmol of glycidol is added to 100 mmol (monosaccharide units) of carbohydrate in 100 ml of basic water (e.g. 0.01-1 M lye). After a few hours (usually 1 to 5 hours, depending on the temperature, usually between 40 and 100 ° C), the reaction is complete and the reaction mixture is neutralized. The mixture is evaporated and is ready for enzymatic esterification.

In the case of hydroxyalkyl carbohydrates, the final esterification can be carried out chemically or enzymatically. The chemical esterification takes place in the usual manner, by reaction of a reactive derivative of the fatty acid, such as the chloride, the anhydride or an alkyl ester, usually in excess, in the presence of a base and optionally a catalyst. Preferably, however, the esterification takes place enzymatically.

The enzymatic esterification is effected with a long fatty acid or derivative thereof, such as an ester. The ethyl ester is preferred because, unlike, for example, the methyl ester, it does not interfere with the esterification enzyme. In general, the method is suitable for introducing acyl groups, especially acyl groups with at least 6 carbon atoms, with acyl groups with at least 10 carbon atoms being preferred, up to about 24 carbon atoms. A product with useful properties is already obtained with an average of 0.2 long acyl groups per monosaccharide unit or with at least 1 long acyl group per molecule. In particular, a product is prepared with 0.5-1.0 C6-C20 acyl groups per monosaccharide unit. For example, the disaccharides preferably prepare a mono-C6-C20-acyl or a di-C6-C24-acyl derivative or a mixture thereof. The long acyl groups 30 are introduced primarily at the primary positions, in sucrose the first at the 6-position of the fructose unit. In the hydroxyalkyl carbohydrates, the acyl groups can also be introduced on the hydroxyalkyl group.

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In the enzymatic esterification, a suitable enzyme is used, in particular a lipase. An example of a useful lipase is that of Candida antarctica, which is commercially available under the name Novozym 435. Other enzymes, including certain proteases such as subtilisin, can also be used for the enzymatic esterification.

If a solvent is used for the enzymatic esterification, it can be a polar organic solvent, such as an alcohol, ether, ketone, amide, nitrile, chloride, sulfone, sulfoxide, nitrile or nitro compound. Preferably, a tertiary alcohol, such as t-butyl alcohol, or, for example, dichloromethane or dimethyl-10-formamide is used. Preferably little or no water is present.

The invention also relates to acylated, hydroxyalkylated carbohydrates, which contain 0.5-2.0 acyl groups and 0.5-4.0 hydroxyalkyl groups per monosaccharide unit. The acyl groups can be esterified both with hydroxyl groups of the carbohydrate itself and with hydroxyl groups of the hydroxyalkyl groups. Thus, the esters of the invention conform to the formula: (Acy1) n-pSach (Hyal) mp (HyalAcy1) p wherein Sach represents the carbohydrate residue, Acyl the acyl group and Hyal represents the hydroxyalkyl residue, m the total number of hydroxyalkyl groups linked to the carbohydrate, n represents the total number of acyl groups coupled to the carbohydrate and p represents the number of acyl groups coupled to the carbohydrate via a hydroxyalkyl group, wherein p can represent a number between 0 and the smallest of m and n. Also, two or more hydroalkyl groups may be linked together as in the case of 2,3-dihydroxy-propyl groups structureSach-O- (CH2-CHOH-CH20) - (CH2-CHOH-CH20) q-Acyl, where q gives 0-10 , in particular, is 0-2.

The acyl groups can be, for example, alkanoyl, alkenoyl, alkynoyl, alkapolyenyl, aroyl, arylalkanoyl or cycloalkylalkanoyl groups or substituted variants thereof, such as substituted groups with hydroxy, alkoxy, carboxy, amino, alkoxycarbonyl and the like. Examples are acetyl, propionyl, caproyl, decanoyl, lauroyl, palmitoyl, stearoyl, ricinoleoyl, acryloyl, propiolyl, oleoyl, linoleyl, benzoyl, phenylacetyl, p-30 methoxycinnamoyl, nicotinoyl, cyclohexylcarboxyl, mixtures thereof, camphoroyl -acyl groups. C6-C20-alkanoyl groups are preferred. The hydroxyalkyl groups may be hydroxyethyl, hydroxy propyl, 2,3-dihydroxy-1005947 NO 41257 propyl, 2,3,4-trihydroxybutyl and the like, especially 2,3-dihydroxypropyl, these groups being in addition to or instead of the hydroxyl groups of the carbohydrate itself may be acylated.

The invention further relates to new intermediates in the form of hydroxyalkylated di- or polysaccharides, which contain 0.5-4.0 2,3-dihydroxyalkyl groups or other 0.5-4.0 polyhydroxyalkyl groups per monosaccharide unit. or only at positions other than any anomeric position that may be present. In particular, the di- or polysaccharides are sucrose, lactose, maltose, isomaltose, cellobiose, and higher homologues such as maltotriose and raffinose.

The invention provides surfactant and emulsifying compounds which are obtained on the one hand from renewable raw materials, namely sugars, glycerol and fatty acids, and which are on the other hand biodegradable. As a result, they are environmentally friendly in terms of both production and final processing. In addition, the fabrics are suitable for use in foodstuffs.

15 Examples Example 1

Etherification of sucrose with glycidol 10 g of sucrose are dissolved in 0.15 M sodium hydroxide solution and 3 equivalents of glycidol (relative to sucrose) are added dropwise at 80-85 ° C. After 2 hours, the reaction mixture is cooled and neutralized with dilute hydrochloric acid. The reaction mixture is then evaporated. Under these conditions, 51% glyceryl sucrose and 19% of a disubstituted product are formed on a molar basis by GC analysis. The remainder is unreacted sucrose.

If less glycidol is used, for example 1 or 2 equivalents, the amount of glyceryl sucrose drops to 31% and 42% respectively, while with a larger amount of glycidol, for example 4 or 5 equivalents, the disubstituted product becomes the main product by 45% and 48 respectively %. If the reaction is carried out with 1.5 M sodium hydroxide, the main reaction is the formation of glycerol.

In all the reactions described above, glycerol is a by-product. Since this will give glycerol esters as a by-product in the esterification step, the glycerol is removed by column chromatography on a column of Norit ROX 0.8.

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Glycerol is eluted with water, which is followed by a gradient of acetone in water (up to 10%) sucrose and coupling products of glycidol and sucrose are eluted.

Example 2

Enzymatic esterification of glyceryl sucrose with ethyl palmitate. Glyceryl sucrose (2 g) synthesized with 3 equivalents of glycidol and purified from glycerol (see Example 1) is suspended in 10 ml of tert-butyl alcohol and 4 g of ethyl palmitate. After 1 g of zeolite 5A is added thereto to remove water and ethanol, the reaction mixture is heated to reflux and stirred. The reaction is initiated with 100 mg of immobilized Candida antarctica lipase. After 24 hours, the conversion is approximately 30% with the monoesters of glyceryl sucrose as the main product.

1005947

Claims (10)

1. Acylated, hydroxyalkylated carbohydrate, containing 0.5-4.0 hydroxyalkyl groups in non-anomeric positions and 0.5-2.0 acyl groups per monosaccharide unit. The acylated hydroxyalkylated carbohydrate of claim 1, wherein the 5 acyl groups are C 6 -C 6 q alkanoyl groups. The acylated hydroxyalkylated carbohydrate of claim 1 or 2, wherein the hydroxyalkyl groups are optionally acylated 2,3-dihydroxyalkyl groups. 4. Hydroxyalkylated mono-, di- or polysaccharide, which contains 0.5-4.0 2,3-dihydroxyalkyl groups at non-anomeric positions per monosaccharide unit. Process for the esterification of carbohydrates with a fatty acid or active derivative thereof, characterized in that the carbohydrate is alkylated before the esterification with an epoxyalkane. 6. Process according to claim 5, wherein 0.2-4.0 hydroxyalkyl groups, in particular 2,3-dihydroxypropyl groups per monosaccharide unit, are introduced in the hydroxyalkylation. Process according to claim 5 or 6, in which 0.5-1.0 C6-C20 acyl groups per monosaccharide unit are introduced during the esterification. Process according to any one of claims 5-7, wherein the esterification is carried out enzymatically, preferably with an ethyl ester of the fatty acid. A method according to any one of claims 5-8, wherein the carbohydrate is a mono-, di- or oligosaccharide, in particular is sucrose or lactose. A process according to any one of claims 5-9, wherein the esterification is carried out without a solvent or with a tertiary alcohol as a solvent. 1005947