Novel branched cyclodextrins and methods of preparing them

Abstract: Disclosed are (1) a novel galactosyl-cyclodextrin having a galactosyl group as bonded to the hydroxyl group of the glucosyl group of a cyclodextrin via an α-bond and a method of producing said galactosyl-cyclodextrin ; (2) a novel galactosyl-cyclodextrin having a galactosyl group as bonded to the hydroxyl group of the glucosyl group of a cyclodextrin via a β-bond and a method of producing said galactosyl-cyclodextrin ; and (3) a novel mannosyl-cyclodextrin having a mannosyl group as bonded to the hydroxyl group of the glucosyl group of a cyclodextrin via an α-bond and a method of producing said mannosyl-cyclodextrin. The new branched cyclodextrins are expected to be widely useful in various fields of drug industry, food industry and cosmetic industry.

Description: The present invention relates to novel branched cyclodextrins and methods of preparing them and, more precisely, to a novel galactosyl-cyclodextrin having a galactosyl group as bonded to the glucosyl group of a cyclodextrin by an α - on β -bond and a method of preparing the novel galactosyl-cyclodextrin using the transgalactosylation activity of an enzyme, A cyclodextrin (hereinafter referred to as "CD") is a cyclic dextrin composed of glucoses as bonded to each other by α-1,4 bond therebetween, and α-, β- and γ-CDs each comprising 6, 7 and 8 glucoses, respectively, are well known. Recently, in order to elevate the solubility of CDs, branched CDs each having a glucosyl group or maltosyl group as bonded to CD via α-1,6 bonds have been produced. US-A-4 931 389 and GB-A-2 165 549 disclose glucosyl branched cyclodextrins produced in a multi-step-process. Such CDs and branched CDs have cavities in the inside of the molecule and the inside of the cavities is lipophilic. Therefore, these have an including capacity for forming inclusion (clathrate) conpounds, taking various oily substances thereinto. As CDs and branched CDs have such properties, they are widely used in various fields of food industry, cosmetic industry and drug industry. Recently, in the field of drug industry, in order to reduce the harmful side effect of drugs, a cell recognizing property of saccharides has been noticed and a study of utilizing them as a sensor to marker cells for a drug carrier in a drug delivery system has been effected successfully. In particular, it is well known that galactose has a strong affinity with liver tissues and mannose with liver parenchymatous cells, liver non-parenchymatous cells and macrophages. The development of a galactosyl-branched CD and a mannosyl-branched CD in which a galactosyl group or a mannosyl group, respectively, is bonded to the glucosyl group of the side chain of a branched cyclodextrin was already successful. Under this situation, one object of the present application was the production of a galactosyl-CD in which a galactosyl group, is directly bonded to the CD ring by transglycosylation, for the purpose of applying both the including capacity of CDs and the above-mentioned characteristics of galactose to a drug delivery system. As a solution of the above object it was found that a commercial α - galactosidase can be used for producing a galactosyl-CD in which a galactosyl group is bonded to the glucosyl group of an α-, β- or γ-CD via an α-bond by transgalactosylation from an α-galactosyl compound, that a commercial β -galactosidase can be used for producing a galactosyl-CD in which a galactosyl group is bonded to the glucosyl group of an α-, β- or γ-CD via a β-bond by transgalactosylation from a β-galactosyl compound. In particular, it was found that an α-galactosidase derived from green coffee beans can be used for efficiently producing a galactosyl-CD in which one or two galactosyl groups are bonded to the glucosyl group of an α-, β- or γ-CD via an α-1,6 bond by transgalactosylation. Specifically, the present invention provides a novel galactosyl-CD having a galactosyl group as bonded to the 6-hydroxyl group of the glucosyl group of a CD via an α- or β-bond; and also provides a method of producing a novel galactosyl-CD having a galactosyl group as bonded to the 6-hydroxyl group of the glucosyl group of a CD via an α-bond, in which a liquid containing a CD and an α-galactosyl compound is treated with an α-galactosyl transfer enzyme, as well as a method of producing a novel galactosyl-CD having a galactosyl group as bonded to the 6-hydroxyl group of the glucosyl group of a CD via a β-bond, in which a liquid containing a CD and a β-galactosyl compound is treated with a β -galactosyl transfer enzyme. Fig. 1 shows structures of branched CDs to be obtained by the present invention. Fig. 2 shows a high performance liquid chromatogram of the reaction mixture of Example 1. Fig. 3 shows a high performance liquid chromatogram of the transfer product A of Example 1. Fig. 4 shows a high performance liquid chromatogram of hydrolyzates of the transfer product A of Example 1. Fig. 5 shows a 13 C-NMR analysis spectrum of the transfer product A of Example 1. Fig. 6 shows a high performance liquid chromatogram of the reaction mixture of Example 2. Fig. 7 shows a high performance liquid chromatogram of the transfer product C of Example 2. Fig. 8 shows a high performance liquid chromatogram of hydrolyzates of the transfer product C of Example 2. Fig. 9 shows a 13 C-NMR analysis spectrum of the transfer product C of Example 2. Fig. 10 shows a high performance liquid chromatogram of the reaction mixture of Example 3. Fig. 11 shows a high performance liquid chromatogram of the transfer product E of Example 3. Fig. 12 shows a high performance liquid chromatogram of hydrolyzates of the transfer product E of Example 3. Fig. 13 shows a 13 C-NMR analysis spectrum of the transfer product E of Example 3. Fig. 14 shows a high performance liquid chromatogram of the reaction mixture (reaction time: 0 minute) of Example 4. Fig. 15 shows a high performance liquid chromatogram of the reaction mixture (lactose only) of Example 4. Fig. 16 shows a high performance liquid chromatogram of the reaction mixture (reaction time: 4 hours) of Example 4. Fig. 17 shows a high performance liquid chromatogram of the transfer product of Example 4. Fig. 18 shows a high performance liquid chromatogram of hydrolyzates of the transfer product of Example 4. New branched CDs of the present invention are represented by structural formulae I to VI shown in Fig. 1. New branched CDs of the present invention can be obtained by treating a liquid containing a CD and an α-galactosyl compound with an α-galactosyl transfer enzyme, or by treating a liquid containing a CD and a β-galactosyl compound with a β-galactosyl transfer enzyme. In the present invention, CD may be any of α-, β- and γ-CDs or branched CDs each having a glucosyl group or maltosyl group or may also be a mixture of them. As the α-galactosyl compound for use in the present invention (hereinafter referred to as "glycosyl donor 1"), there are mentioned for example, α-galactosyl residue containing glycosides, oligosaccharides and polysaccharides, such as melibiose, phenyl α-galactoside, paranitrophenyl α-galactoside and α-galactooligosaccharides, as well as partially decomposed products of them and mixtures of them. The β-galactosyl compound for use in the present invention (hereinafter referred to as "glycosyl donor 2") includes, for example, β-galactosyl residue-containing glycosides, oligosaccharides and polysaccharides, such as lactose, phenyl β-galactoside, paranitrophenyl β-galactoside and β-galactooligosaccharides, as well as partially decomposed products of them and mixtures of them. As the α-galactosyl transfer enzyme for the present invention, any one may be used which reacts with a liquid containing an α-galactosyl compound and a CD to decompose the glycosyl donor 1 to thereby transfer the α-galactosyl group to the CD by an α-bond to give an α-galactosyl-CD. In the same manner, as the β-galactosyl transfer enzyme for the present invention, anyone may be used which reacts with a liquid containing a β-galactosyl compound and a CD to decompose the glycosyl donor 2 to thereby transfer the β-galactosyl group to the CD by a β-bond to give a β-galactosyl-CD. The α-galactosyl transfer enzyme to be used in the present invention is selected from those which are widely distributed in the natural field. For instance, well known are enzymes derived from plants such as green coffee beans and enzymes derived from microorganisms such as Aspergillus niger , Escherichia coli and Mortiellera vinasce. The β-galactosyl transfer enzyme for use in the present invention may be also selected from those which are widely distributed in the natural field. For instance, well known are those derived from microorganisms such as Aspergillus niger Aspergillus oryzae and Penicillium multicolor. In the reaction system of the present invention, the liquid (aqueous solution or suspension) containing a CD and a glycosyl donor is desired to have a CD concentration of approximately from 1 to 50 % (w/w) and a glycosyl donor concentration of approximately from 1 to 90 % (w/w). The proportion (by weight) of glycosyl donor to CD is, though varying in accordance with the kind of the glycosyl donor to be used, suitably within the range of from 0.1/1 to 50/1, preferably from 0.3/1 to 2/1. In carrying out the reaction of the present invention, the pH value of the reaction mixture may be from 3 to 10, preferably from 4 to 9; and the temperature thereof may be from 20 to 70 °C, preferably from 30 to 60 °C. The amount of the enzyme to be used in the reaction and the reaction time are closely related to each other. In general, the former may be such that the reaction may be finished in 5 to 100 hours, preferably in 5 to 20 hours. The reaction mixture as obtained by the reaction method mentioned above is subjected to high performance liquid chromatography (HPLC), whereupon the transfer product of CD is fractionated and isolated. Next, the structure of the product thus obtained is analyzed by enzymatic decomposition, molecular weight measurement by FAB-MS and nuclear magnetic resonance (NMR). As a result, the product has been identified to be a branched CD as represented by any one of formulae I to VI of Fig. 1. The present invention will be explained in more detail by way of the following examples. EXAMPLE 1 (1) Transfer Reaction: Six hundred mg of melibiose and 600 mg of α-CD were dissolved in 1.5 ml of 50 mM acetate acid buffer (pH 6.5), and 9 units of green coffee beans α-galactosidase (produced by Sigma Co.) were added thereto and reacted at 40 °C for 17 hours. A part of the reaction mixture was analyzed by high performance liquid chromatography, and the analysis result is shown in Fig. 2. After the reaction, the reaction mixture in which the enzyme used was inactivated under heat was subjected to high performance liquid chromatography to isolate 85 mg of a transfer product A. (2) Analysis of Structure: The transfer product A (Fig. 3) as isolated in the above-mentioned step (1) was identified to have a molecular weight of 1134 by FAB-MS analysis. As shown in Fig. 4, it was completely hydrolyzed into galactose and α-CD of the same molar amounts by green coffee beans α-galactosidase. By 13 C-NMR analysis, the product was identified to be a compound having a galactosyl group as bonded to the 6-hydroxyl group of the glucosyl group of α-CD via an α-bond (structural formula I of Fig. 1), as shown in Fig. 5. In the same manner, the transfer product B as isolated in the above-mentioned step (1) was completely hydrolyzed by green coffee beans α-galactosidase to form α-CD and two molar times of galactose. From this, the transfer product B was presumed to be a compound having two molecules of galactosyl group as bonded to the 6-hydroxyl group of the glucosyl group of α-CD via an α-bond. EXAMPLE 2 (1) Transfer Reaction: Six hundred mg of melibiose and 300 mg of β-CD were dissolved in 1.5 ml of 50 mM acetate acid buffer (pH 6.5), and 9 units of green coffee beans α-galactosidase transferase (produced by Sigma Co.) were added thereto and reacted at 40 °C for 17 hours. A part of the reaction mixture was analyzed by high performance liquid chromatography, and the analysis result is shown in Fig. 6. After the reaction, the reaction liquid in which the enzyme used was inactivated under heat was subjected to high performance liquid chromatography to isolate 66 mg of a transfer product C. (2) Analysis of Structure: The transfer product C (Fig. 7) as isolated in the above-mentioned step (1) was identified to have a molecular weight of 1296 by FAB-MS analysis. As shown in Fig. 8, it was completely hydrolyzed into galactose and β-CD of the same molar amounts by green coffee beans α-galactosidase. Further, 13 C-NMR analysis of the transfer product C is shown in Fig. 9. From these results, the transfer product was identified to be a compound having a galactosyl group as bonded to the 6-hydroxyl group of the glucosyl group of β-CD via an α-bond (structural formula II of Fig. 1). In the same manner, the transfer product D as isolated in the above-mentioned step (1) was completely hydrolyzed by green coffee beans α-galactosidase to form β-CD and two molar times of galactose. From this, the transfer product D was presumed to be a compound having two molecules of galactosyl group as bonded to the 6-hydroxyl group of the glucosyl group of β-CD via an α-bond. EXAMPLE 3 (1) Transfer Reaction: Six hundred mg of melibiose and 600 mg of γ-CD were dissolved in 1.5 ml of 50 mM acetate buffer (pH 6.5), and 9 units of green coffee beans α-galactosidase transferase (produced by Sigma Co.) were added thereto and reacted at 40 °C for 17 hours. A part of the reaction mixture was analyzed by high performance liquid chromatography, and the analysis result is shown in Fig. 10. After the reaction, the reaction liquid in which the enzyme used was inactivated under heat was subjected to high performance liquid chromatography to isolate 93 mg of a transfer product E. (2) Analysis of Structure: The transfer product E (Fig. 11) as isolated in the above-mentioned step (1) was identified to have a molecular weight of 1458 by FAB-MS analysis. As shown in Fig. 12, it was completely hydrolyzed into galactose and γ-CD of the same molar amounts by green coffee beans α-galactosidase. Further, 13 C-NMR analysis of the transfer product E is shown in Fig. 13. From these results, the transfer product was identified to be a compound having a galactosyl group as bonded to the 6-hydroxyl group of the glucosyl group of γ-CD via an α -bond (structural formula III of Fig. 1). In the same manner, the transfer product F as isolated in the above-mentioned step (1) was completely hydrolyzed by green coffee beans a α-galactosidase to form γ-CD and two molar times of galactose. From this, the transfer product F was presumed to be a compound having two molecules of galactosyl group as bonded to the 6-hydroxyl group of the glucosyl group of γ-CD via an α-bond. EXAMPLE 4 (1) Transfer Reaction: Two g of lactose and 2 g of α-CD were dissolved in 3 ml of 50 mM acetate buffer (pH 4.5), and 40 units of Penicillium multicolor β-galactosidase (produced by KI Chemicals Co., Japan) were added thereto and reacted at 40°C for 4 hours. For comparison, only lactose was treated with the same enzyme in the absence of CD. A part of the reaction mixture was analyzed by high performance liquid chromatography, and the analysis results are shown in Fig. 14 to Fig. 16. Fig. 14 indicates the result of reaction for 0 (zero) minute between enzyme and lactose along with α-CD. Fig. 15 indicates the result of reaction for 4 hours between enzyme and only lactose in the absence of α-CD. Fig. 16 indicates the result of reaction for 4 hours between enzyme and lactose along with α-CD. After the reaction, the reaction liquid in which the enzyme used was inactivated under heat was subjected to high performance' liquid chromatography to isolate 10 mg of a transfer product. (2) Analysis of Structure: The transfer product (Fig. 17) as isolated in the above-mentioned step (1) was identified to have a molecular weight of 1134 by FAB-MS analysis. As shown in Fig. 18, it was completely hydrolyzed into galactose and α-CD of the same molar amounts by Penicillium multicolor β-galactosidase. The galactosyl-transfer position to maltosyl- α-CD by the present enzyme was already reported to be the 6-hydroxyl group of the glucosyl group of the side chain (Japanese Patent Kokai 4-23802). From the above results, the transfer product was identified to be a compound having a galactosyl group as bonded to the 6-hydroxyl group of the glucosyl group of α-CD via a β-bond (structural formula IV of Fig.1). In accordance with the present invention, as has been explained in detail in the above, a novel branched CD having a galactosyl group as bonded to the hydroxyl group of the glucosyl group in the CD molecule via an α-1,6 bond is obtained efficiently by transgalactosylation of an α-galactosyl transfer enzyme. Also, a novel branched CD having a galactosyl group as bonded to the hydroxyl group of the glucosyl group in the CD molecule via a β-1,6 bond is obtained efficiently by transgalactosylation of a β-galactosyl transfer enzyme. The new branched CDs of the present invention are expected to be widely used in various fields of drug industry, food industry and cosmetic industry.

Claims: A galactosyl-cyclodextrin having a galactosyl group as bonded to the hydroxyl group of the glucosyl group of a cyclodextrin via an α-bond. A method of producing a galactosyl-cyclodextrin having at least one galactosyl group as bonded to the hydroxyl group of the glucosyl group of a cyclodextrin via an α-bond, which comprises treating a liquid containing a cyclodextrin and an α-galactosyl compound with an α-galactosyl transfer enzyme. The method as claimed in claim 2, wherein a green coffee beans α-galactosidase is applied to the liquid to obtain a novel galactosyl-CD having one or two galactosyl groups as bonded to the glucosyl group of an α-, β- or γ-CD via an α-1,6 bond. A galactosyl-cyclodextrin having a galactosyl group as bonded to the hydroxyl group of the glucosyl group of a cyclodextrin via a β-bond. A method of producing a galactosyl-cyclodextrin having a galactosyl group as bonded to the hydroxyl group of the glucosyl group of a cyclodextrin via a β-bond, which comprises treating a liquid containing a cyclodextrin and a β-galactosyl compound with a β-galactosyl transfer enzyme.

Inventors: FUJITA KOKI, HARA KOJI, KITAHATA SUMIO, KOIZUMI KYOKO, KUWAHARA NOBUHIRO, FUJITA, KOKI, HARA, KOJI, KITAHATA, SUMIO, KOIZUMI, KYOKO, KUWAHARA, NOBUHIRO, FUJITA, KOKI, C/O ENSUIKO SUGAR REFINING CO., LTD., HARA, KOJI, C/O ENSUIKO SUGAR REFINING CO., LTD., KUWAHARA, NOBUHIRO, C/O ENSUIKO SUGAR REF. CO.,LTD
Applicants: ENSUIKO SUGAR REFINING, KITAHATA SUMIO, ENSUIKO SUGAR REFINING COMPANY, LIMITED, KITAHATA, SUMIO
Application year: 1993
Main classification: C12P19
IPC codes: C08B37, C12P19