Hetero-branched cyclodextrins and method of preparing them

Abstract: Novel hetero-branched cyclodextrins each having a glucosyl or maltosyl group as the side chain, in which a mannosyl group is α-bonded to the hydroxyl group of the glucosyl group of the side chain; and a method of preparing the same. In accordance with the present invention using the transglycosylation action of α-mannosyl transferases, novel hetero-branched CDs each having a glucosyl or maltosyl group as the side chain, in which a mannosyl group is α-bonded to the hydroxyl group of the glucosyl group of the side chain, may be obtained efficiently. The novel hetero-branched CDs of the present invention are expected to be utilized widely in various fields of drugs, foods and cosmetics.

Description: The present invention relates to novel hetero-branched cyclodextrins and a method of preparing them. More precisely, it relates to novel hetero-branched cyclodextrins each having a glucosyl or maltosyl group as the side chain and having a mannosyl group as α-bonded to the side chain, and to a method of preparing said novel hetero-branched cyclodextrins to be effected by transglycosylation. A cyclodextrin (hereinafter referred to as "CD") is a cyclic dextrin comprising plural glucose residues as bonded to each other by α-1,4-bonding. α-, β- and γ-CDs are well known, each comprising 6, 7 and 8 glucose residues, respectively. Recently, for the purpose of improving (or elevating) the solubility of CDs, branched CDs each having a glucosyl or maltosyl group as bonded thereto by α-1,6-bond have been prepared. Such CDs and branched CDs have a cavity in the molecule and the inside of the cavity is hydrophobic. Therefore, they have an including function and have a property of including various oily substances therein. Since CDs and branched CDs have such a property, they are widely used in various fields of food industry, cosmetic industry, drug industry etc. Recently, in the field of drug industry, saccharides have been noted to have specific cell recognizability, and for the purpose of reducing the influences of the side effects of drugs, a study of utilizing such saccharides as a sensor to the target cells for a drug carrier in a drug delivery system has been made greatly. Mannose is well known to have strong affinity to various parts in living bodies. Under the situation, the present inventors tried to synthesize hetero-branched CDs by transferring a mannosyl group to a branched CD, for the purpose of applying the including function of branched CDs and the characteristic of mannose to a drug delivery system. As a result, they have found that various commercial α-mannosidase are usable for producing hetero-branched glucosyl or maltosyl CDs in which a mannosyl group has been α-bonded by transfer action to the side chain of glucosyl- α, β and γCD (hereinafter referred to as G1-αCD, G1-βCD and G1-γCD, respectively) or maltosyl-α, β and γCD (hereinafter referred to as G2-αCD, G2-βCD and G2-γCD, respectively) from an α-mannosyl compound. They have further found that α-mannosidase derived from Jack beans (Canavalia ensiformi s) is usable for preferentially producing a hetero-branched CD in which one mannosyl group is transferred by α-1,6-bonding to the glucosyl group of the side chain of G1-βCD or to the non-reducing terminal glucosyl group of the maltosyl group of the side chain of C2-αCD. On the basis of the findings, they have completed the present invention. Specifically, the present invention provides novel hetero-branched CDs each having a glucosyl or maltosyl group as the side chain, in which a mannosyl group is α-bonded to the 6-positioned hydroxyl group of the glucosyl group of the side chain and also provides a method of preparing novel hetero-branched CDs each having a glucosyl or maltosyl group as the side chain and having a mannosyl group as α-bonded to the 6-positioned hydroxyl group of the glucosyl group of the side chain, in which a liquid containing a branched CD and an α-mannosyl compound is reacted with an α-mannosyl transfer enzyme. Fig. 1 shows structural formulae of novel hetero-branched CDs of the present invention. Fig. 2 shows high performance liquid chromatogram of the transfer product of Example 1. Fig. 3 shows high performance liquid chromatogram of the hydrolyzates from the transfer product of Example 1, as decomposed with α-mannosidase from jack beans (Canavalia ensiformis) . Fig. 4 shows 13 C-NMR spectrum of the transfer product as isolated in (1) of Example 1. Fig. 5 shows high performance liquid chromatogram of the transfer product of Example 2. Fig. 6 shows 13 C-NMR spectrum of the transfer product as isolated in (1) of Example 2. Fig. 7 shows FAB-MS of the transfer product as isolated in (1) of Example 3. Fig. 8 shows 13 C-NMR spectrum of the transfer product as isolated in (1) of Example 4. The novel hetero-branched CDs of the present invention may be represented by structural formulae I to VIII as shown in Fig. 1. The novel hetero-branched CDs of the present invention can be obtained by reacting a liquid containing a branched CD having a glucosyl or maltosyl group as the side chain and an α-mannosyl compound with an α-mannosyl transfer enzyme. The branched CD having a glucosyl or maltosyl group as the side chain, as referred to herein, includes G1-αCD, G1-βCD, G1-γCD, G2-αCD, G2-βCD, G2-γCD, and mixtures of them. The α-mannosyl compound to be used in the present invention (hereinafter referred to as a "mannosyl donor") includes, for example, α-mannosyl residue-containing glycosides, oligosaccharides or polysaccharides, such as methyl α-mannoside, phenyl α-mannoside, para-nitrophenyl α-mannoside, α-mannooligosaccharides, as well as partial decomposed products of them and mixtures of them. The α-mannosyl transfer enzyme to be used in the present invention may be anyone which may decompose a mannosyl donor to thereby transfer the resulting α-mannosyl group to the side chain of the branched CD having a glucosyl or maltosyl group as the side chain to be α-bonded thereto to produce a hetero-branched CD when applied to a liquid containing an α-mannosyl compound and a branched CD having a glucosyl or maltosyl group as the side chain. α-mannosyl transfer enzymes usable in the present invention are widely distributed in the natural field. For instance, well known are enzymes derived from plants such as jack beans ( Canavalia ensiformis ) or almonds ( Prunus amygdalus ), enzymes derived from animals such as turban shells (Turbo cornutu s) or livers (bovine, rat, human) as well as enzymes derived from microorganisms such as Arthrobacter aurescenc e and Aspergillus nige r. In the reaction system of the present invention, the liquid (aqueous solution or suspension) containing a branched CD having a glucosyl or maltosyl group as the side chain and a mannosyl donor is desirable to contain the branched CD in a concentration of approximately from 1 to 100 % (W/W) and the mannosyl donor in a concentration of approximately from 1 to 50 % (W/W), and the proportion (by weight) of the mannosyl donor to the branched CD is suitably within the range of approximately from 0.1/1 to 50/1, preferably approximately from 0.3/1 to 2/1, though varying in accordance with the kind of the mannosyl donor used. The pH value of the reaction liquid may be from 3 to 10, preferably from 4 to 9; and the reaction temperature is suitably adjusted to the range of from 20 to 70° C, preferably from 30 to 60°C. The amount of the enzyme to be used has close relation to the reaction time. In general, it may be such that the reaction may finish within 5 to 100 hours, preferably 5 to 20 hours, but is not limited. The liquid as reacted by the manner mentioned above is then subjected to high performance liquid chromatography, whereupon the transfer product to the branched CD having a glucosyl or maltosyl group as the side chain is isolated. Then, the structure of the transfer product is determined by enzymatic degradation and by analysis of nuclear magnetic resonance (NMR). As a result, they were identified to be hetero-branched CDs having structural formulae I to VIII, respectively, as shown in Fig. 1. In accordance with the present invention using the transglycosylation of α-mannosidase, novel hetero-branched CDs each having a glucosyl or maltosyl group as the side chain, in which a mannosyl residue is α-bonded to the hydroxyl group of the glucosyl residue of the side chain, may be obtained efficiently. The novel hetero-branched CDs of the present invention are expected to be utilized widely in various fields of drugs, foods and cosmetics. The present invention will be explained in more detail by way of the following examples, which, however, are not intended to restrict the scope of the present invention. Example 1 (1) Transfer Reaction: Three grams(3 g) of methyl α-mannoside and 3 g of G1-βCD were dissolved in 10 ml of 50 mM acetate buffer (pH 4.5), and 25 units of α-mannosidase from jack beans ( Canavalia ensiformis ) (product by Sigma Co.) was added thereto and reacted at 40°C for 40 hours. A part of the reaction mixture was analyzed by high performance liquid chromatography to give the result shown in Fig. 2. After the reaction, the enzyme used was inactivated under heat and the resulting reaction mixture was subjected to high performance liquid chromatography to isolate 80 mg of the transfer product. (2) Analysis of Structure: The transfer product as isolated in the previous (1) was completely hydrolyzed into the same molar amounts of mannose and G1-βCD with α-mannosidase from jack beans ( Canavalia ensiformis ). By 13 C-NMR analysis, the product was identified to be a compound in which a mannosyl residue was α-bonded to the 6-positioned hydroxyl group of the glucosyl residue of the side chain of G1-βCD (having structural formula IV in Fig. 1), as shown in Fig. 4. Example 2 (1) Transfer Reaction: Three grams of methyl α-mannoside and 3 g of G2-αCD were dissolved in 10 ml of 50 mM acetate buffer (pH 4.5), and 25 units of α-mannosidase from jack beans ( Canavalia ensiformis ) (product by Sigma Co.) was added thereto and reacted at 40°C for 40 hours. A part of the reaction mixture was analyzed by high performance liquid chromatography to give the result shown in Fig. 5. After the reaction, the enzyme used was inactivated under heat and the resulting reaction mixture was subjected to high performance liquid chromatography to isolate 57 mg of the transfer product. (2) Analysis of Structure: The transfer product as isolated in the previous (1) was completely hydrolyzed into the same molar amounts of mannose and G2-αCD with α-mannosidase from jack beans ( Canavalia ensiformis ). By 13 C-NMR analysis, the product was identified to be a compound in which a mannosyl group was α-bonded to the 6-positioned hydroxyl group of the non-reducing or reducing terminal glucosyl residue of the maltosyl group of the side chain of G2- αCD (having structural formula II in Fig. 1), as shown in Fig. 6. In the same reaction of using α-galactosidase in place of α-mannosidase, a compound having a galactosyl residue as α-bonded to the 6-positioned hydroxyl group of the non-reducing terminal glucosyl residue of the maltosyl group of the side chain of G2-αCD was obtained, which was identified by methylation analysis. Accordingly, also in the case, the galactosyl group may be considered to be α-bonded to the 6-positioned hydroxyl group of the non-reducing terminal glucosyl residue of the maltosyl group. Example 3: (1) Transfer Reaction: One g of phenyl α-mannoside and 2 g of G1-αCD were dissolved in 10 ml of 50 mM acetate buffer (pH 6.0), and 20 units of a α-mannosidase from almonds (Prunus amygdalus ) (product by Sigma Co.) was added thereto and reacted at 40°C for 1 hour. After the reaction, the enzyme used was inactivated under heat and the resulting reaction mixture was subjected to high performance liquid chromatography to isolate 15 mg of the transfer product. (2) Analysis of Structure: The transfer product as isolated in the previous (1) was completely hydrolyzed into the same molar amounts of mannose and G1-αCD with α-mannosidase from almonds (Prunus amygdalus ). Further, it was found , that, by FAB-MS analysis, a molecular weight of the transfer product was 1296 as shown in Fig. 7. This transfer product was also identified to be a compound in which a mannosyl group was bonded to the glucosyl group of the side chain of G1-αCD, since this product has a peak at 971 (see Carbohydrate Research, 215(1991)127-136). Therefore, the transfer product as isolated in the previous (1) was identified to be a compound in which a mannosyl residue was transferred and α-bonded to the hydroxyl group at any of C2-, C3-, C4- or C6-position of the glucosyl group of the side chain of G1-αCD (having structural formula I in Fig. 1). Example 4: (1) Transfer Reaction: One g of phenyl α-mannoside and 2 g of G2-βCD were dissolved in 10 ml of 50 mM acetate buffer (pH 6.0), and 20 units of α-mannosidase from almonds ( Prunus amygdalus ) (product by Sigma Co.) was added thereto and reacted at 40 °C for 1 hour. After the reaction, the enzyme used was inactivated under heat and the resulting reaction mixture was subjected to high performance liquid chromatography (HPLC) to isolate 20 mg of the transfer product. (2) Analysis of Structure: The transfer product as isolated in the previous (1) was completely hydrolyzed into the same molar amounts of mannose and G2-βCD with α-mannosidase from almonds (Prunus amygdalu s). From 13 C-NMR analysis, this product was identified to be a compound in which a mannosyl group was α-bonded to the 6-positioned hydroxyl group of the non-reducing terminal glucosyl residue of the maltosyl group of the side chain of G2- βCD (having structural formula VI in Fig. 1), as shown in Fig. 8. Example 5: (1) Transfer Reaction: Five hundred mg of p-nitrophenyl α-mannoside and 1 g of G1-γCD were dissolved in 10 ml of 50 mM acetate buffer (pH 4.0), and 20 units of α-mannosidase from turban shells (Turbo cornutu s) (product by Sigma Co.) was added thereto and reacted at 40 °C for 1 hour. After the reaction, the enzyme used was inactivated under heat and the resulting reaction mixture was subjected to high performance liquid chromatography to isolate 15 mg of the transfer product. (2) Analysis of Structure: The transfer product as isolated in the previous (1) was completely hydrolyzed into the same molar amounts of mannose and G1-γCD with α-mannosidase from turban shells (Turbo cornutu s). Further, it was found, that, by FAB-MS analysis, a molecular weight of the transfer product was 1620. This transfer product was also identified to be a compound in which a mannosyl group was bonded to the glucosyl group of the side chain of G1-γCD, since this product has a peak at 1295 (see Carbohydrate Research, 215(1991)127-136). Therefore, the transfer product as isolated in the previous (1) was identified to be a compound in which a mannosyl group was transferred and α-bonded to the hydroxyl group at any of C2-, C3-, C4- or C6-position of the glucosyl group of the side chain of G1-γCD (having structural formula VII in Fig. 1). Example 6: (1) Transfer Reaction: Five hundred mg of p-nitrophenyl α-mannoside and 1 g of G2-γCD were dissolved in 10 ml of 50 mM acetate buffer (pH 4.0), and 20 units of α-mannosidase from turban shells (Turbo cornutu s) (product by Sigma Co.) was added thereto and reacted at 40°C for 1 hour. After the reaction, the enzyme used was inactivated under heat and the resulting reaction mixture was subjected to high performance liquid chromatography to isolate 18 mg of the transfer product. (2) Analysis of Structure: The transfer product as isolated in the previous (1) was completely hydrolyzed into the same molar amounts of mannose and G2-γCD with α-mannosidase from turban shells (Turbo cornutu s). Further, it was found, that, by FAB-MS analysis, a molecular weight of the transfer product was 1782. This transfer product was also identified to be a compound in which a mannosyl group was bonded to the mannosyl group of the side chain of G2-γCD, since this product has a peak at 1295 (see Carbohydrate Research, 215(1991)127-136). Therefore, the transfer product as isolated in the previous (1) was identified to be a compound in which a mannosyl group was transferred and α-bonded to the hydroxyl group at any of C2-, C3-, C4- or C6-position of the glucosyl group of the side chain of G2-γCD (having structural formula VIII in Fig. 1).

Claims: Hetero-branched cyclodextrins each having a glucosyl or maltosyl group as the side chain, in which a mannosyl group is α-bonded to the hydroxyl group of the glucosyl group of the side chain. A method of preparing hetero-branched cyclodextrins each having a glucosyl or maltosyl group as the side chain and having a mannosyl group as α-bonded to the hydroxyl group of the glucosyl group of the side chain, in which a liquid containing a branched cyclodextrin having a glucosyl or maltosyl group as the side chain and an α-mannosyl compound is reacted with an α-mannosyl 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 REF. CO.,LTD., HARA, KOJI C/O ENSUIKO SUGAR REF. CO.,LTD., KUWAHARA, NOBUHIRO C/O ENSUIKO SUGAR REF. CO.,LTD.
Applicants: ENSUIKO SUGAR REFINING, KOIZUMI KYOKO, OSAKA SHI, ENSUIKO SUGAR REFINING COMPANY, LIMITED, KOIZUMI, KYOKO, OSAKA-SHI
Application year: 1992
Main classification: C08B37
IPC codes: A61K47, C08B37, C12P19