WO2019038366A1

WO2019038366A1 - Oligosaccharide synthesis by high-frequency ultrasounds

Info

Publication number: WO2019038366A1
Application number: PCT/EP2018/072748
Authority: WO
Inventors: François JEROME; Prince Nana AMANIAMPONG; Karine De Oliveira Vigier
Original assignee: Centre National De La Recherche Scientifique; Universite De Poitiers
Priority date: 2017-08-24
Filing date: 2018-08-23
Publication date: 2019-02-28
Also published as: FR3070391B1; FR3070391A1

Abstract

The present invention relates to a method for preparing at least one oligosaccharide, comprising a step of ultrasound irradiation, at a frequency higher than 100 kHz, of an alcohol composition comprising at least one saccharide monomer and at least one monoalcohol ROH, R being an alkyl chain comprising 1 to 24 carbon atoms.

Description

HIGH FREQUENCY ULTRASONIC OLIGOSACCHARIDE SYNTHESIS

The subject of the present invention is a process for the synthesis of oligosaccharides by the implementation of a high frequency ultrasound irradiation step. It also relates to a composition comprising an oligosaccharide as obtained by said process.

To date, the preparation of polysaccharides, functionalized or not, is essentially according to two technologies, namely: acid catalyzed polymerizations or enzymatic processes. However, these processes have many disadvantages such as obtaining secondary products such as furan compounds and humins, which requires the implementation of purification steps. In addition, the enzymatic processes are carried out in water and require an effluent treatment step. In addition, the implementation of these processes in highly diluted media is detrimental to their productivity.

In addition, such methods only allow the production of alkylpolyglycosides with about 1 alkyl chain for 1, 1 - 1, 5 monosaccharide units.

However, increasing the degree of polymerization monosaccharide is an important issue especially in the field of surfactants.

Also, there is a need for a method to avoid the aforementioned drawbacks, and in particular to overcome purification steps after the polymerization.

However, to date, there is no method for obtaining macromolecules with a high degree of polymerization and not requiring the implementation of a catalyst.

The present invention therefore aims to provide a method for obtaining oligosaccharides of high degree of polymerization, without the implementation of a (bio) catalyst, and to overcome any purification steps .

The present invention also aims to provide a method having a high productivity and a very high selectivity. Thus, the present invention relates to a method for preparing at least one oligosaccharide, comprising a step of ultrasonic irradiation at high frequency, that is to say greater than 100 kHz, of an alcoholic composition comprising at least one monomer saccharide and at least one ROH monoalcohol, R representing an alkyl chain comprising from 1 to 24 carbon atoms.

The process according to the invention thus makes it possible to oligomerize monosaccharides without catalyst intervention and by initiation by the radicals generated during the ultrasonic irradiation.

More particularly, as described below, this irradiation step allows oligomerization of the monomers and possibly glycosylation.

The present invention thus relates to the use of high frequency ultrasound for the oligomerization of monosaccharides of renewable origin. In the presence of an alkyl alcohol, there occurs an oligomerization reaction of the monosaccharides and glycosylation of the reducing ends by an alkyl chain thus making it possible to obtain alkylpolyglycosides. Typically, the reaction is carried out by ultrasonic irradiation of a monosaccharide solution in an alcohol.

According to the invention, the term "oligosaccharide" designates an oligomer formed of monosaccharides (or monosaccharide units) by alpha or beta glycosidic linkage. Preferably, an oligosaccharide according to the invention comprises from 2 to 10 monosaccharide units, optionally functionalized.

Preferably, the oligosaccharides obtained according to the process of the invention have molecular weights ranging from 300 g / mol to 2000 g / mol.

The method of the invention comprises subjecting an alcoholic composition as defined above to ultrasonic irradiation. The alcoholic composition according to the invention may be a composition in which the saccharide monomer (or sugar) is dissolved or in which the sugar is suspended in the alcohol.

According to the invention, the alcoholic composition may be an alcoholic solution comprising at least one saccharide monomer or may be an alcoholic suspension of at least one saccharide monomer. According to one embodiment, the alcoholic composition as defined above contains a single saccharide monomer or a mixture of different saccharide monomers.

The ultrasonic irradiation step according to the invention is a step of high frequency ultrasonic irradiation, that is to say at a frequency greater than or equal to 100 kHz.

According to one embodiment, the ultrasound frequency is between 530 kHz and 550 kHz.

According to one embodiment, the alcoholic composition according to the invention is an alcoholic solution comprising at least one monoalcohol comprising from 1 to 5 carbon atoms. Such an alcoholic composition is particularly advantageous in that it makes it possible to obtain alkylpolyglycosides.

Thus, when the alcoholic composition according to the invention is an alcoholic solution comprising at least one monoalcohol comprising 1 to 5 carbon atoms, the process of the invention further comprises a step of functionalization of the oligosaccharide by the alkyl chain R .

According to this embodiment, the process of the invention also makes it possible to obtain functionalized oligosaccharides, namely alkylpolyglycosides.

Preferably, according to the invention, the above-mentioned irradiation step is carried out at a temperature of between 10 ° C. and 80 ° C., preferably between 40 ° C. and 60 ° C.

In particular, advantageously, for short-chain monohydric alcohols, in particular comprising from 1 to 5 carbon atoms, in particular for methanol or butanol, the irradiation step is carried out at 40 ° C., and for the fatty alcohols (comprising more than 5 carbon atoms), the irradiation step is carried out at 80 ° C.

According to one embodiment, the alcoholic composition used in the process of the invention comprises from 10% to 80%, preferably from 20% to 80%, by weight of saccharide monomer relative to the total weight of said alcoholic composition. . According to one embodiment, the irradiation step is carried out for a period of between 10 minutes and 6 hours.

Preferably, during this irradiation step, the power delivered is between 65 W and 75 W.

According to the invention, the saccharide monomer may be a monosaccharide or a disaccharide.

According to a preferred embodiment, the saccharide monomer is a monosaccharide, preferably chosen from mannose, glucose or xylose.

Preferably, the oligosaccharide obtained according to the process of the invention has an average degree of polymerization greater than or equal to 2, preferably of between 2 and 12, and preferably of between 3 and 7.

According to the invention, the degree of polymerization (or DP) is determined by mass spectrometry (infusion) and steric exclusion chromatography.

According to one embodiment, the method of the invention further comprises a preliminary step of preparing the alcoholic composition as defined above, for example by bringing together the saccharic monomer and the monoalcohol as defined above.

According to one embodiment, the method of the invention further comprises a final step of removing the monoalcohol, comprising removing said monoalcohol from the composition comprising at least one oligosaccharide according to the invention. This step then makes it possible to isolate the oligosaccharide according to the invention.

This removal step may for example consist of a distillation step or a step of washing on a silica column of the composition obtained after the irradiation.

In particular, the conversion to monosaccharide is greater than 80-90% after 3 hours of irradiation and leads to 100% oligosaccharides with degrees of polymerization in a range 1 -12, 1 -5 and 1 -7 respectively for the mannose, glucose and xylose. At the end of the handling, the monoalcohol is removed by distillation and the products obtained are in solid form. The oligosaccharides obtained were analyzed using various analytical techniques such as gas chromatography, mass spectrometry or steric exclusion chromatography. Type 1, 6 links are the links majorities between the saccharide units and the oligosaccharides obtained are very soluble in water. The oligosaccharides are selectively obtained, i.e., only the glycosylation reactions take place. These oligosaccharides present original structures that are not accessible by conventional pathways involving biotechnologies and catalysis. These macromolecules therefore have a high potential for application in the field of materials (self-assembly properties, amphiphilic properties, etc.) and preferentially in the field of surfactants.

The present invention also relates to a composition comprising at least one oligosaccharide obtainable by the process as defined above, said oligosaccharide having an average degree of polymerization greater than or equal to 2.

As indicated above, the process of the invention makes it possible, unlike the processes of the state of the art, to access oligosaccharides of average degree of polymerization of at least 2.

The present invention also relates to a composition comprising mixtures of oligosaccharides that can be obtained according to the process as defined above, said oligosaccharides having an average degree of polymerization greater than or equal to 2.

Preferably, the composition according to the invention comprises at least one oligosaccharide of the following formula:

in which :

n is an integer from 1 to 12; and

m is 0 or is from 1 to 23, preferably 0, 1, 2, 3, 4 or 5. The compositions of the invention preferably comprise at least one compound of formula (I

that is to say at least one oligosaccharide functionalized with a monohydric alcohol of formula ROH, R corresponding to the - (CH ₂ ) _m -CH ₃ chain as defined above.

The compositions of the invention are essentially in the form of mixtures of oligosaccharides with different degrees of polymerization and different glycosidic bonds.

The compositions of the invention may especially be used as surfactants in various fields of application, in particular in the cosmetics field.

EXAMPLES

Example 1 Preparation of an Oligosaccharide from Mannose

The starting monomer is mannose having the chemical composition according to Figure 1.

The mannose in a content between 20 and 50 g (20-80% by weight) is dissolved in 50 ml of methanol in air (or another gas as indicated below), at a temperature of 10-80 ° C and irradiated for 3 hours at a frequency of 530-550 kHz (power output: 65-75 W).

Figure 2 shows the chemical composition of the polysaccharide portion obtained at the end of the irradiation.

Table 1. Impact of experimental parameters

Temp. Mannose Gas Conv. Yield 3.6- Yield Yield Total Yield

(° C) Conc. (Mannose anhydromannose Me-Me- in

mass) (%) (%) Mannoside oligomannoside oligomannoside

(%) (DP> 2) (%) (%) (Me-

Mannoside + Me-

oligomannoside)

40 20 Air 81 2 37 42 79

40 80 Air 73 1 6 66 ^b 72

20 20 Air 58 1 26 31 57

0 0 Air 6 0 2 4 6

40 20 Ar 70 1 35 34 69

40 20 o ₂ 50 0 21 29 50

³ kHz ultrasonic irradiation at 550 for 3 h. For the sake of clarity, the sum of the forms a, b, pyranoside and furanoside is indicated; ^b mixture of methyl glycosyl oligomers and oligomannosides.

Example 2 Preparation of an Oligosaccharide from Other Sugars

The same protocol as that described in Example 1 was applied for the preparation of oligosaccharides from other monomers: glucose and xylose.

The results obtained are described in Table 2 below. Table 2. Composition of oligosaccharides according to the nature of the sugar used

Sugar Conv. DP glycoside binding (%)

(%)

1, 6 1, 4 1, 3 1, 2

1 mannose 81 1 -12 52 16 19 13

2 glucose 40 1 -5 53 16 21 10

3 xylose 65 1 -7 - 80 20

DP = degree of polymerization (measured by mass spectrometry and size exclusion chromatography)

Example 3 Effect of the monoalcohol used

The same protocol as that described in Example 1 was applied for the preparation of oligosaccharides from different monomers by varying the nature of the monoalcohol.

The ultrasonic irradiation is carried out at 550 kHz for 3 hours and the concentration of sugar in the alcoholic solution is 20% by weight.

The results obtained are described in Table 3 below.

Table 3. Effect of alcohol used

Sugar Alcohol Conv. DP

(%) way

1 Mannose ethanol 70 3

2 Mannose n-propanol 66 3

3 Mannose n-butanol 87 4

4 Mannose n-dodecanol 85 5

5 n-Dodecanol Glucose 71 3

Xylose n-dodecanol 54 4

Claims

A process for the preparation of at least one oligosaccharide, comprising a step of ultrasonic irradiation at a frequency greater than 100 kHz, of an alcoholic composition comprising at least one saccharide monomer and at least one ROH monoalcohol, R representing an alkyl chain comprising from 1 to 24 carbon atoms.

2. The method of claim 1, wherein the ultrasound frequency is between 530 kHz and 550 kHz.

3. Method according to any one of claims 1 or 2, wherein the alcoholic composition is an alcoholic solution comprising at least one monoalcohol comprising 1 to 5 carbon atoms.

4. Method according to claim 3, further comprising a step of functionalization of the oligosaccharide by the alkyl chain R.

5. Method according to any one of claims 1 to 4, wherein the irradiation step is carried out at a temperature between 10 ° C and 80 ° C, preferably between 40 ° C and 60 ° C.

6. Process according to any one of claims 1 to 5, wherein the alcoholic composition comprises from 10% to 80% by weight of saccharide monomer relative to the total weight of said alcoholic composition.

7. A process according to any one of claims 1 to 6, wherein the irradiating step is carried out for a period of between 10 minutes and 6 hours.

The process according to any one of claims 1 to 7, wherein the saccharide monomer is a monosaccharide, preferably selected from mannose, glucose or xylose.

9. Process according to any one of claims 1 to 8, wherein the oligosaccharide has an average degree of polymerization greater than or equal to 2, preferably between 2 and 12, and preferably between 3 and 7.

10. Composition comprising at least one oligosaccharide obtainable by the method according to any one of claims 1 to 9, said oligosaccharide having an average degree of polymerization greater than or equal to 2.

11. Composition according to claim 10, comprising at least one oligosaccharide of the following formula:

in which :

n is an integer from 1 to 12; and

m is 0 or is from 1 to 23, preferably 0, 1, 2, 3, 4 or 5.