NOVEL SOPHOROLIPID DERIVATIVE

Abstract

There is provided a novel sophorolipid derivative having high water solubility and surface activity. A plurality of sophorolipid derivatives having a novel structure is isolated and purified from a cultured product of sophorolipid producing microorganism (Starmerella bombicola, etc.)

##STR00001##

(wherein, R.sup.1 to R.sup.3 are each independently hydrogen, a fatty acid ester having 2 to 22 carbon atoms, or the above SL group, provided that at least one of R.sup.1 to R.sup.3 is the SL group in which R are the same or different and each represent hydrogen or an acetyl group and R.sup.n is a linear or branched alkyl or alkenyl group having 13 to 21 carbon atoms).

Claims

1. A sophorolipid derivative represented by the following general formula (1): ##STR00010## (wherein, R.sup.1 to R.sup.3 are each independently hydrogen, a fatty acid ester having 2 to 22 carbon atoms, or the above SL group, provided that at least two of R.sup.1 to R.sup.3 are the SL group in which R are the same or different and each represent hydrogen or an acetyl group and R.sup.n is a linear or branched alkyl or alkenyl group having 13 to 21 carbon atoms).

2. A sophorolipid derivative which is any of compounds represented by the following chemical formula (2): ##STR00011## (wherein, the SL group has the same definition as in the above formula (1) and R′ is a fatty acid ester having 2 to 22 carbon atoms).

3. A composition, comprising the sophorolipid derivative as claimed in claim 1.

4. The composition according to claim 3, which is a surfactant, a detergent, or an emulsifier.

5. The composition according to claim 3, which is feedstuff, a fertilizer, food and drink, an agrichemical, a pharmaceutical, a quasi-drug, or a cosmetic, or an additive thereto.

6. A composition, comprising the sophorolipid derivative as claimed in claim 2.

7. The composition according to claim 6, which is a surfactant, a detergent, or an emulsifier.

8. The composition according to claim 6, which is feedstuff, a fertilizer, food and drink, an agrichemical, a pharmaceutical, a quasi-drug, or a cosmetic, or an additive thereto.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 shows the normal-phase TLC analysis results of a solid SL mixture obtained in Example 1;

[0032] FIG. 2 shows the reversed-phase TLC analysis results of the solid SL mixture obtained in Example 1;

[0033] FIG. 3 is a chromatogram showing the results of the reversed-phase column chromatography of the solid SL mixture obtained in Example 1;

[0034] FIG. 4 shows the LC/MS analysis results of Compound A separated in Example 4;

[0035] FIG. 5 shows the LC/MS analysis results of Compound B separated in Example 4;

[0036] FIG. 6 shows the LC/MS analysis results of Compound C separated in Example 4;

[0037] FIG. 7 shows the .sup.1H-NMR results of Compound B;

[0038] FIG. 8 shows the .sup.1H-NMR results (enlarged) of Compound B;

[0039] FIG. 9 shows the .sup.1H-NMR results of Compound A;

[0040] FIG. 10 shows the .sup.1H-NMR results of Compound C;

[0041] FIG. 11 is a photograph of 0.1 wt % aqueous solutions obtained by adding distilled water to Compounds A, B, and C, respectively;

[0042] FIG. 12 shows the surface tension reducing ability of each of Compounds A, B, and C, wherein A is indicated by pale ,B by , and C by ;

[0043] FIG. 13 shows the MALDI-TOF/MS analysis results of the solid SL mixture obtained in Example 1;

[0044] FIG. 14 shows the results of HPLC analysis before and after the acetylation reaction of compound B; and

[0045] FIG. 15 shows the results of LC/MS analysis before and after the acetylation reaction of compound B.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] The present invention relates to a novel sophorolipid derivative and a composition containing the derivative.

[0047] The sophorolipid derivative (which may hereinafter be called “SL derivative”) of the present invention is represented by the following general formula (1).

##STR00005##

[0048] In the formula, R.sup.1 to R.sup.3 each independently represent hydrogen, any of fatty acid esters having 2 to 22 carbon atoms, or the above SL group, provided that at least two of R.sup.1 to R.sup.3 are the SL group.

[0049] Any of fatty acid esters having 2 to 22 carbon atoms is represented by —(O)C-hydrocarbon group and this hydrocarbon group has 1 to 21 carbon atoms.

[0050] R are the same or different and each represent hydrogen or an acetyl group.

[0051] R.sup.n is a linear or branched alkyl or alkenyl group having 13 to 21 carbon atoms.

[0052] The SL derivative of the present invention may be any one of the compounds represented by the following chemical formula (2):

##STR00006##

[0053] In the formula, the SL group has the same meaning as described in the formula (1) and R′ is a fatty acid ester having 2 to 22 carbon atoms and is represented by a —(O)C-hydrocarbon group. The number of carbon atoms of this hydrocarbon group is 1 to 21.

[0054] The SL derivative of the present invention can be obtained from a cultured product of an SL-producing microorganism, but can be chemically synthesized because it is a glyceride of an SL.

[0055] For example, it can be produced by carrying out esterification (ester exchange or reverse reaction of hydrolysis) of a SL and glycerin with an immobilized enzyme such as lipase as a catalyst in a non-alcoholic organic solvent (chloroform, toluene, acetone, or the like) or without a solvent; or by carrying out an ester exchange reaction using a plant oil (triglyceride) instead of the glycerin. In particular, when a lactonic form (LSL) having excellent reactivity is used, the SL derivative of the present invention can be produced by mixing it with glycerin or the like and heating and stirring the resulting mixture.

[0056] Furthermore, a hydroxyl group of a SL group can be acetylated by reacting it with acetic anhydride or the like even after it is obtained from the culture. By utilizing this reaction, it is possible to produce a SL derivative (for example, all Rs of the SL groups of chemical formula (1) are acetyl groups) with improved lipophilicity by introducing acetyl groups to all hydroxyl groups.

[0057] As a surfactant, an emulsifier, or a dispersant, depending on the surface activity of the SL derivative of the present invention, the composition of the present invention can be applied to feedstuff, fertilizers, food and drink, agrichemicals, pharmaceuticals, quasi drugs, or cosmetics, or additives thereto.

[0058] Although an amount of the SL derivative contained in the composition of the present invention is not particularly limited, it is 0.01 to 100 wt %, preferably 0.1 to 50 wt %, more preferably 1 to 30 wt %. When the amount of the SL derivative in the composition is as small as 1 wt % or less, the resulting composition has less water solubility, while the amount as large as 50 wt % or more may reduce the economic efficiency.

EXAMPLES

[0059] The present invention will hereinafter be described more specifically by Examples but the present invention will not be limited to or by the following Examples. In Examples, “%” means “wt %”.

Example 1

Production and Recovery of Sophorolipid

Culture of Starmerella bombicola ATCC A22214 Strain

(1) Seed Culture

[0060] A platinum loopful of the aforesaid Starmerella bombicola ATCC 22214 strain which had been kept in a preservation medium (10 g/L of a yeast extract, 20 g/L of peptone, 20 g/L of glucose, and 20 g/L of agar) was inoculated in a test tube containing 4 mL of a liquid medium composed of 10 g/L a yeast extract, 20 g/L of peptone, and 20 g/L of glucose and shake-cultured at 28° C. for one day.

(2) Main Culture

[0061] The microbial culture solution obtained in (1) was inoculated in an Erlenmeyer flask containing 30 mL of a liquid medium composed of 10 g/L of a yeast extract, 20 g/L of peptone, 100 g/L of glucose, and 100 g/L of a rapeseed oil and shake-cultured at 28° C. for 7 days.

(3) Recovery of Sophorolipid

[0062] By allowing the culture solution obtained in (2) to stand for one hour, an SL phase appeared in the lower layer. The resulting SL phase was recovered, neutralized with an aqueous solution of sodium hydroxide, and washed with water to recover the SL mixture in the form of an aqueous solution. In order to perform a test later on the resulting aqueous solution of the SL mixture, a solid SL mixture was recovered by adding hexane to the aqueous solution, stirring and centrifuging the resulting mixture to extract and remove the remaining oil or fat, or fatty acid in the hexane phase, and freeze drying the aqueous phase.

(4) Purification of Lactonic Sophorolipid and Acidic Sophorolipid Specimens

[0063] To use the resulting mixture solid as a specimen in the subsequent experiment, a lactonic SL (LSL) and an acidic SL (ASL) were separated from each other by a known purification technique. Described specifically, the solid SL mixture was dissolved in acetone and the resulting solution was placed on a silica gel column obtained by filling a glass column tube with silica gel (Wakogel C-200) and purified by column chromatography using a chloroform-acetone mixture as a developing solvent. The separation and recovery of LSL were performed at a chloroform:acetone ratio of 8:2, followed by those of acidic SL at 2:8. The fractions thus recovered were confirmed to be intended LSL specimen and ASL specimen, respectively, by thin-layer chromatographic analysis which will be described later.

Example 2

Thin-Layer Chromatographic Analysis of Sophorolipid

[0064] The solid SL mixture obtained in Example 1 was dissolved in methanol and the resulting solution was subjected to thin-layer chromatographic (TLC) analysis.

[0065] First, conventional normal-phase TLC analysis using a chloroform/methanol/aqueous ammonia=80/20/2 mixed solvent as a developing solvent was performed on a silica gel TLC glass plate (Silica gel 60F254 glass plate, product of Merck). When the component is detected using an anthrone-sulfuric acid indicator, a compound containing a sugar skeleton is detected as a bluish green color. As a result, non-polarity LSL was developed in the upper phase, while a high-polarity ASL was developed in the lower phase (FIG. 1).

[0066] Next, reversed-phase analysis using a methanol/water=95/5 mixed solvent as a developing solvent was performed on a reversed-phase modified silica gel TLC plate (TLC silica gel 60RP-18F254S glass plate, product of Merck). As expected, contrary to the aforesaid result in the normal phase, high-polarity ASL was developed in the upper phase. Further, non-polarity LSL was developed in the intermediate phase and a spot presumed to be derived from a structurally unknown glycolipid not detected by the conventional method was detected in the lower phase (FIG. 2).

[0067] The results have revealed that the SL mixture obtained in Example 1 contains a glycolipid different from the conventionally known LSL and ASL.

Example 3

High-Performance Liquid Chromatographic Analysis of Sophorolipid

[0068] The solid SL mixture obtained in Example 1 was dissolved in methanol and the resulting solution was subjected to high-performance liquid chromatographic (HPLC) analysis. Component analysis was performed using HPLC (Thermo Scientific Ultimate 3000 HPLC, product of Thermo Fisher Scientific) equipped with a corona charged aerosol detector (CAD) (Corona™ Veo™, product of Thermo Fisher Scientific); using a reversed-phase ODS column (InertSustain™ VC18, product of GL Science) as an analysis column; at a column temperature of 40° C.; using a (5 mM ammonium formate methanol)/(5 mM aqueous ammonium formate) mixed solvent system as an eluting solution; according to the following gradient program: 70% methanol (step: 0 min to 3 min), 70% to 100% (gradient: 3 min to 18 min), 100% (step: 18 min to 25 min), and 70% (step: 25 min to 35 min); and at a flow rate of 0.3 mL/min. The chromatogram thus obtained is shown in FIG. 3.

[0069] As a result of the analysis, ASL and LSL were detected after the retention time of 3 to 10 minutes and 12 to 16 minutes, respectively, and then, three unknown component peaks (A, B, and C) were detected after around 18 minutes, around 20 minutes, and around 22 minutes, respectively. The results were consistent with those of the reversed-phase TLC analysis in Example 2 showing the detection of an unknown glycolipid after that of ASL and LSL.

Example 4

Separation/Purification of Structurally-Unknown Glycolipid

[0070] To isolate the three peak components newly detected in Example 3, the components were separated from each other by silica gel column chromatography. First, almost all the amount of the LSL fraction was eluted with a chloroform/acetone=50/50 solvent by the normal-phase column method using a chloroform/acetone mixed solvent similar to that used in Example 1 (4) and then, a remaining component containing a mixture of ASL and the intended unknown glycolipids was recovered with a solvent composed of 100% acetone or 100% methanol. Next, by the reversed-phase column chromatography with a methanol/water mixed solvent as a developing solvent on a column filled with octadecyl-modified silica gel (Wakogel 100C18), the unknown glycolipids were separated/recovered using a two-step column purification method for separating ASL from the unknown glycolipids. Each of the components thus obtained by separation was confirmed to be almost a single-spot component and a single-peak component by the reversed-phase TLC analysis and the reversed-phase HPLC analysis, respectively.

[0071] The components will hereinafter be called “Compound A”, “Compound B”, and “Compound C” in the order in which they were eluted from the reversed-phase column. Compound A was a clear and viscous solid, B was a clear solid harder than A, and C was a waxy white solid.

Example 5

Mass Spectrum Analysis of Structurally Unknown Glycolipids

[0072] Compounds A, B, and C separated from each other in Example 4 were subjected to liquid chromatography/mass spectrum (LC/MS) analysis. FIGS. 4 to 6 show the respective results of the LC/MS analysis conducted under separation conditions similar to those of Example 3 by using the HPLC described in Example 3 to which an electrospray ionization mass spectrometer (ESI-MS) (Exactive Plus, product of Thermo Fisher Scientific) was connected.

[0073] Compounds A, B, and C had, as a main component thereof, m/z=1468, m/z=2157, and m/z=1731 (each, detection in negative mode) and contained components (1426, 2115, and 1689) obtained by subtracting 42 from the main components, respectively. Such a pattern was frequently observed from glycolipid type biosurfactants and the component other than the main component was presumed to have one acetyl group removed therefrom. Further, they contained components (1582, 2271, and 1845) obtained by adding 114 to the main components or components obtained by subtracting 42 therefrom, respectively. The components were all presumed to be obtained by partially modifying the functional group of the main component. Compounds A to C are presumed to contain components having the same basic structure but different in fatty acid composition.

Example 6

Structural Analysis of Structurally-Unknown Glycolipids

[0074] The chemical structure of Compounds A, B, and C separated from each other in Example 4 was identified by the nuclear magnetic resonance spectrum (NMR) analysis. It has been confirmed that as a result of the .sup.1H-NMR analysis of Compound B showing the largest content among the three components by NMR (AV-400), product of Bruker, the spectrum is almost the same as that of the structurally known ASL (FIG. 7).

[0075] On the other hand, the spectrum of the sugar skeleton portion was enlarged and compared. As a result, it has been confirmed that a new peak different from that of ASL appeared near 5.3 ppm and a peak near 4.1 to 4.4 ppm had a peak area ratio obviously larger than that of the peak at the 1 position of sophorose as the referential peak. To specifically analyze these peaks further, .sup.1H-.sup.1HCOSY analysis was performed to find that a new peak different from a peak which might originally appear near 4.1 to 4.4 ppm and was derived from the 6 position of sophorose appeared and they overlapped in position, showing the correlation with the new peak near 5.3 ppm (FIG. 8).

[0076] The NMR data of Compound B are shown in Table 1.

TABLE-US-00001 TABLE 1 .sup.13C-NMR .sup.1H-NMR δ (ppm) δ (ppm) Sugar skeleton C-1′ 101 2 H-1′ 4.45 d C-2′ 82.4 H-2′ 3.36 m C-3′ 76.4 H-3′ 3.30-3.60 m C-4′ 70 0 H-4′ 3.30-3.60 m C-5′ 73 5 H-5′ 3.30-3.60 m C-6′ 63 5 H-6′a 4.19 m H-6′b 4.36 m C-1″ 104.3 H-1″ 4.55 d C-2″ 74.7 H-2″ 3.25 m C-3″ 76 1 H-3″ 3.30-3 60 m C-4″ 70 0 H-4″ 3.30-3.60 m C-5″ 74.2 H-5″ 3.30-3.60 m C-6″ 63 5 H-6″a 4.19 m H-6″b 4.36 m Acetyl group —C═O (C-6′,6″) 171.3 —CH.sub.3 (C-6′,6″) 19.4, 19.6 2.05, 2.06 s Glycerin skeleton —CH.sub.2O— 61 9 4 17, 4.35 m —CHO— 70.0 5 28 m Fatty acid chain —C═O 173.4 —CO—CH — 33 5 2.33 m —CO—CH CH — 24 9 1 60 b —(CH.sub.2).sub.n— 24.5-29 6 1 25-1 46 b —CH═CH—CH — 26 8 2 00-2 10 b —CH═CH— 129 5 5.35 m —OCH(CH.sub.2)—CH — 36 5 1 60 b —OCH(CH.sub.2)— 77 2 3 74 m —CH.sub.2 20.5 1 20 d indicates data missing or illegible when filed

[0077] It has been found from the aforesaid results that Compound B is an SL derivative having, in addition to the structure of ASL, a chemical structure showing those two kinds of peaks. Examples of a typical compound exhibiting peaks near 5.3 ppm and near 4.1 to 4.4 ppm include the glycerin skeleton of an oil or fat (fatty acid triglyceride). Based on the aforesaid finding, Compound B is presumed to be represented by the chemical formula (6) in which ASL is ester-linked to three hydroxyl groups of glycerin.

[0078] The main component of Compound B confirmed in Example 5 was m/z=2157, which was completely consistent with the molecular weight of a compound having a triglyceride structure in which two ASLs having a C18:1 fatty acid site and one ASL having a C18:2 fatty acid site were ester linked to glycerin. Based on the above findings, Compound B is identified as the compound of the chemical formula (6).

##STR00007##

[0079] Compounds A and C were subjected to similar analysis. The results of the .sup.1H-NMR analysis of Compounds A and C are shown in FIGS. 9 and 10. The NMR data of Compound A or C are shown in Table 2 or 3.

TABLE-US-00002 TABLE 2 .sup.13C-NMR .sup.1H-NMR δ (ppm) δ (ppm) Sugar skeleton C-1′ 101 2 H-1′ 4.45 d C-2′ 82 4 H-2′ 3.36 m C-3′ 76 4 H-3′ 3.30-3.60 m C-4′ 70 0 H-4′ 3 30-3.60 m C-5′ 73 5 H-5′ 3.30-3.60 m C-6′ 63 5 H-6′a 4.19 m H-6′b 4.36 m C-1″ 104 3 H-1″ 4.55 d C-2″ 74 7 H-2″ 3.25 m C-3″ 76 1 H-3″ 3.30-3.60 m C-4″ 70 0 H-4″ 3.30-3.60 m C-5″ 74 2 H-5″ 3.30-3.60 m C-6″ 63 5 H-6″a 4.19 m H-6″b 4.36 m Acetyl group —C═O (C-6′,6″) 171.3 —CH  (C-6′,6″) 19.4, 19.6 2.05, 2.06 s Glycerin skeleton —CH.sub.2O— 64.6 4.11 m —CHO— 67.0 4.02 m Fatty acid chain —C═O 173.8 —CO—CH — 33.5 2.35 m —CO—CH CH — 24 9 1.60 b —(CH.sub.2).sub.n— 24.5-29.6 1 25-1.46 b —CH═CH—CH — 26 8 2 00-2 10 b —CH═CH— 129.5 5.35 m —OCH(CH )—CH — 36 5 1 60 b —OCH(CH )— 77 2 3.74 m —CH  (SL) 20.5 1.20 d indicates data missing or illegible when filed

TABLE-US-00003 TABLE 3 .sup.13C-NMR .sup.1H-NMR δ (ppm) δ (ppm) Sugar skeleton C-1′ 101 2 H-1′ 4.45 d C-2′ 82 4 H-2′ 3.36 m C-3′ 76 4 H-3′ 3.30-3.60 m C-4′ 70.0 H-4′ 3.30-3.60 m C-5′ 73 5 H-5′ 3.30-3.60 m C-6′ 63 5 H-6′a 4.19 m H-6′b 4.36 m C-1″ 104 3 H-1″ 4.55 d C-2″ 74.7 H-2″ 3.25 m C-3″ 76 1 H-3″ 3.30-3.60 m C-4″ 70 0 H-4″ 3.30-3.60 m C-5″ 74 2 H-5″ 3.30-3.60 m C-6″ 63 5 H-6″a 4.19 m H-6″b 4.36 m Acetyl group —C═O (C-6′,6″) 171 3 —CH  (C-6′,6″) 19.4, 19.6 2 05, 2.06 s Glycerin skeleton 61.9 4 17, 4.35 m —CH.sub.2O— 70 0 5 28 m —CHO— Fatty acid chain —C═O 173 4 —CO—CH — 33 5 2.33 m —CO—CH CH — 24 9 1 60 b —(CH.sub.2).sub.n— 24.5-29 6 1 25-1 46 b —CH═CH—CH — 26 8 2 00-2 10 b —CH═CH— 129.5 5.35 m —OCH(CH )—CH — 36 5 1 60 b —OCH(CH )— 77 2 3.74 m —CH  (SL) 20 5 1 20 d —CH  (fatty acid) 13 2 0.91 m indicates data missing or illegible when filed

[0080] Based on the NMR measurement results, as a most likely compound having a representative structure, Compound A is presumed to be a compound of the chemical formula (5) in which two ASLs are linked to glycerin and Compound C is presumed to be a compound of the chemical formula (7) in which two ASLs and one long-chain fatty acid are ester-linked to glycerin. Their molecular weight is consistent with that of the main component of each compound confirmed in Example 5, supporting the results of this structural analysis.

[0081] Derivatives contained in the cultured product of a producing microorganism are not limited to them.

##STR00008##

Example 7

Aqueous Solutions of Novel Sophorolipid Derivatives A to C

[0082] Compounds A, B, and C separated from each other in Example 4 were weighed (each, 10 mg) in measuring flasks, respectively, and diluted with distilled water to prepare 1 mg/mL (0.1 wt. %) aqueous solutions (FIG. 11).

[0083] Clear aqueous solutions were obtained by completely dissolving Compound A and Compound B, but the aqueous solution of Compound C became clouded. Further, 10 mg/mL (1 wt %) aqueous solutions of Compounds A and B were prepared respectively in a similar manner. The aqueous solution of A became clouded and Compound B was dissolved completely. The clouded aqueous solutions of Compounds A and C were allowed to stand in a refrigerator and then, they were both dissolved completely to be a clear aqueous solution.

[0084] The phase change of the aqueous solutions depending on the temperature is a reversible phenomenon, showing that it has a cloud point at room temperature (25° C.) or less. This supports that Compounds A and C are a nonionic surfactant as structurally determined in Example 6. Further, the above results show that compared to Compound C having a long-chain fatty acid bonded thereto, Compound A not having it shows higher water solubility and Compound B is anionic surfactant having markedly high water solubility, though having a higher molecular weight than the other two.

Example 8

Surface Tension Reducing Ability of Novel SL Derivatives A to C

[0085] Aqueous solutions of Compounds A, B, and C separated from each other in Example 4 and having various concentrations were prepared and the surface tension of them was determined by the pendant drop method (Young Laplace method) using a contact angle meter (DMo-500, product of Kyowa Interface Science). FIG. 12 shows a logarithmically plotted graph of the concentration and the surface tension of the aqueous solutions.

[0086] Compound C showed almost no change in the surface tension of its aqueous solution regardless of the concentration, while Compounds A and B showed a significant reduction in surface tension with an increase in the concentration. In addition, both were confirmed to have two-step inflection points in the plot with an increase in the concentration. When a critical micelle concentration (CMC) was calculated from the latter inflection point from which the surface tension became constant, Compound A had CMC of 1.91 g/L (about 1.3×10.sup.−3 M) and had a surface tension (γCMC) of 40.4 mN/m at that concentration and Compound B had CMC of 2.99 g/L (about 1.4×10.sup.−3 M) and had γCMC of 41.4 mN/m. With respect to LSL and ASL, LSL has CMC of 1.4×.sup.−5 M and γCMC of 32.3 mN/m and ASL has CMC of 1.2×10.sup.−4 M and γCMC of 37.1 mN/m, according to the literature. Compared to the conventional compounds, the novel SL derivatives found this time have remarkably high water solubility and exhibit mild surface tension reducing ability, though they are a nonionic surfactant, in other words, they are a surfactant very suitable for use in an aqueous system.

Example 9

Matrix Assisted Laser Ionization Time-of-Flight Mass Spectrum (MALDI-TOF/MS) Analysis of Sophorolipid

[0087] MALDI-TOF/MS analysis of the solid SL mixture obtained in Example 1 was performed by JMS-3000 SpiralTOF-MS, product of JASCO Corporation, with 2′,4′,6′-trihydroxyacetophenone (THAP) as a matrix (FIG. 13).

[0088] A peak of a structurally-unidentified compound having a structure of m/z=803.4 and different from that of conventional LSL and ASL was detected. Based on the molecular weight calculated with reference to the structure of Compounds A to C in which SL is ester-linked to glycerin, it is presumed to be a compound (Na adduct) in which one ASL having a C18:1 fatty acid site is ester-linked to glycerin as shown in the chemical formula (8).

##STR00009##

Example 10

Acetylation of Sophorolipid Derivatives

[0089] The compound B obtained in Example 4 (20 mg) was dissolved in acetone (1 mL) in a vial bottle, and acetic anhydride (200 μL) and triethylamine (10 μL) were added, respectively. The reaction solution was allowed to stand overnight at room temperature. After the reaction, all solvents were removed by drying under reduced pressure, and the product was recovered.

[0090] Reversed-phase TLC analysis of the product detected a compound with a lower mobility due to the acetylation, that is more hydrophobic than the starting compound B. Therefore, the progress of the acetylation reaction was confirmed. Subsequently, HPLC and LC/MS analysis of the product was performed in the same method as in Examples 3 and 5. On the HPLC chart, the peak of the product shifted to the longer retention time side, that is, to the hydrophobic side (FIG. 14), as in the above reversed-phase TLC. In addition, the molecular ion peaks of the main component of the product were 2536, 2578, 2494, etc. These were confirmed to be acetylated products in which 9, 10, and 8 acetyl groups are bonded to the sugar moiety of the compound B, respectively (FIG. 15). .sup.1H NMR analysis of the product also supported that the acetyl group was additionally introduced into the compound B due to the increase of the peak derived from the acetyl group at around 2.0 ppm.

[0091] By using a similar method, it is possible to introduce any number of acetyl groups into the compounds A and C as well. From the above results, it was confirmed that the SL derivatives of the present invention can be converted into novel SL derivatives with any number of acetyl groups (Formula (1)) by an acetylation reaction.

Industrial Availability

[0092] The novel SL derivatives of the present invention are sophorolipid derivatives having excellent water solubility, surface tension reducing ability, and self-organization characteristics and derived from highly-safe natural products, so that they can be applied to a wide range of fields such as feedstuff, fertilizers, food and drink, agrichemicals, pharmaceuticals, quasi drugs, and cosmetics.