Branched cyclodextrins and methods of preparing them

Abstract: Disclosed are 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 mannosyl-cyclodextrin having a mannosyl group as bonded to the glucosyl group of a cyclodextrin by an α-bond and a method of preparing the novel mannosyl-cyclodextrin by transmannosylation 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. 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) compounds, 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 actively. 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 mannosyl-CD in which a mannosyl 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 mannose to a drug delivery system. As a solution of the above object it was found that a commercial α-mannosidase can be used for producing a mannosyl-CD in which a mannosyl group is bonded to the glucosyl group of an α-, β- or γ-CD via an α-bond by transmannosylation, from an α-mannosyl compound. In particular, it was found that an α-mannosidase derived from jack beans can be used for efficiently producing a mannosyl-CD in which one mannosyl group is bonded to the glucosyl group of an α-, β- or γ-CD via an α-1,6 bond by transmannosylation. Specifically, the present invention provides a novel mannosyl-CD having a mannosyl group as bonded to the 6-hydroxyl group of the glucosyl group of a CD via an α-bond as well as a method of producing a novel mannosyl-CD having a mannosyl 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-mannosyl compound is treated with an α-mannosyl 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 the Example. Fig. 3 shows a high performance liquid chromatogram of the transfer product of the Example. Fig. 4 shows a high performance liquid chromatogram of hydrolyzates of the transfer product of the Example. New branched CDs of the present invention are represented by structural formulae I to III as shown in Fig. 1. New branched CDs of the present invention can be obtained by treating a liquid containing a CD and an α-mannosyl compound with an α-mannosyl 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. The α-mannosyl compound for use in the present invention (hereinafter referred to as "glycosyl donor ") includes, for example, α-mannosyl residue-containing glycosides, oligosaccharides and polysaccharides, such as methyl α-mannoside, phenyl α-mannoside, paranitrophenyl α-mannoside and α-mannooligosaccharides, as well as partially decomposed products of them and mixtures of them. As the α-mannosyl transfer enzyme for the present invention, any one may be used which reacts with a liquid containing an α-mannosyl compound and a CD to decompose the glycosyl donor to thereby transfer the α-mannosyl group to the CD by an α-bond to give an α-mannosyl-CD. The α-mannosyl transfer enzyme for use 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 jack beans or almond, enzymes derived from animals such as turbos or livers (bovine, rat, human), and enzymes derived from microorganisms such as Arthrobacter a urescens and A spergillus n iger. 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 III of Fig. 1. The present invention will be explained in more detail by way of the following example. EXAMPLE (1) Transfer Reaction: Three g of methyl α-mannoside and 3 g of α-CD were dissolved in 10 ml of 50 mM acetate buffer (pH 4.5), and 51 units of jack beans α-mannosidase (produced by Sigma Co.) were added thereto and reacted at 40 °C for 24 hours. A part of the reaction mixture was analyzed by high performance liquid chromatography, and the analyzed 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 73 mg of a transfer product. (2) Analysis of Structure: The transfer product (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 mannose and α-CD of the same molar amounts by jack beans α-mannosidase. The mannosyl-transfer position to glucosyl-α-CD by the present enzyme was already known to be the 6-hydroxyl group of the glucosyl group of the side chain (Japanese Patent Application No. 3-324021). Therefore, regarding the structure of the transfer product, it was identified to be a compound having a mannosyl 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). In accordance with the present invention, as has been explained in detail in the above, a novel branched CD having a mannosyl group as bonded to the hydroxyl group of the glucosyl group in the CD molecule via an α-1,6 bond is also obtained efficiently by transmannosylation of an α-mannosyl 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 mannosyl-cyclodextrin having a mannosyl group bonded to the hydroxyl group of the glucosyl group of a cyclodextrin via an α-bond. A method of producing the mannosyl-cyclodextrin of claim 1 which comprises treating a liquid containing a cyclodextrin and an α-mannosyl compound with an α-mannosyl transfer enzyme. The method as claimed in claim 2, wherein a beans α-mannosidase is applied to the liquid to obtain a novel mannosyl-cyclodextrin having one mannosyl group bonded to the glucosyl group of an α-, β- or γ-cyclodextrin via an α-1,6 bond.

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, Ensuiko Sugar Ref. Co., Ltd.
Applicants: ENSUIKO SUGAR, KITAHATA SUMIO, KITAHATA, SUMIO
Application year: 1993
Main classification: C12P19
IPC codes: C08B37, C12P19