POLYSACCHARIDE DERIVATIVES AND SEPARATING AGENT

Abstract: New polysaccharide derivatives useful for the separation of optical isomers, prepared by substituting at least one atomic group of formula (1), (2) or (3) for part or the whole of hydrogen atoms of the hydroxyl or amino groups of the polysaccharide. In the formulae R is a group having 1 to 30 carbon atoms and at least one center of asymmetry.

Description: The present invention relates to a polysaccharide derivative which is extremely useful as a functional material for optical resolution. Particularly, the present invention relates to a polysaccharide derivative having an asymmetric carbon atom group, and a separating agent comprising said polysaccharide derivative. Further, the present invention relates to a process for the separation of β-lactam stereoisomers. Derivatives prepared by reacting polysaccharides with achiral compounds are known. These derivatives have a structure wherein an achiral group is bonded to a stereoregular polymer chain, so that they can discriminate asymmetry of various racemic modifications when used as column packings for liquid chromatography. However, they are apt to fail in discriminating asymmetry of some racemic modifications of compounds having complicated structures such as those having two asymmetric centers in the same molecule or those having various functional groups in their asymmetric centers. β-Lactams are important substances as raw materials for the preparation of various drugs including antibiotics. The separation of a β-lactam into respective stereoisomers is essential, because the action of such a drug on a living organism is, in many cases, different depending upon the kind of the stereoisomer used in the preparation thereof, like in the case of thalidomide [see G. Blaschke, Angew. Chem. Int. Ed. Engl., 19 , 13 (1980)]. Known processes for preparing a β-lactam stereoisomer include asymmetric synthesis, a diastereomer process and a chromatographic process. Among these processes, the chromatographic process has advantages in that a high-purity stereoisomer can be obtained and that even continuous operation is possible by employing the technique of Sarex techniques. However, none of the columns which have been used for the separation of β-lactam stereoisomers exhibits a sufficiently high separating power and therefore the separation of many β-lactams has been impossible as yet. FR-A-1472040 discloses the preparation of polymers bearing a chiral amino side group to be used for separating a racemic mixture of acids. JP-A-60-217201 discloses a polysaccharide derivative obtained by esterification of the optical active isomer of an organic acid by cellulose. JP-A-60-142930 and EP-A-0147804 disclose derivatives of cellulose bearing aromatic side groups which are bonded to the cellulose by means of ether, ester or urethane bonds. It is the object of the present invention to provide a polysaccharide and a separating agent having a high asymmetry discriminating power. Said object is achieved by a polysaccharide wherein at least a part of the hydrogen atoms of the hydroxyl and/or amino groups therein are replaced by at least one group represented by formula (1), (2) or (3) wherein R 1 is wherein R 2 is -R 3 wherein R 3 is wherein the symbol * represents an asymmetric center. Furthermore, a separating agent comprising said polysaccharide is provided. The degree of replacement with the above groups is at least 30%, preferably at least 50%, still preferably at least 85%. It has been found that β-lactams can be efficiently separated into respective stereoisomers by using a separating agent comprising the above polysaccharide derivative as the main component. The polysaccharide derivative of the present invention has a chiral side chain and can resolve a racemic mixture. The resolving power of the derivative can be exhibited not only by itself but also in a state supported on a carrier. The present invention also provides a process for separating a racemic mixture, particularly a compound represented by the following general formula (4), into respective stereoisomers by using a separating agent comprising the above polysaccharide derivative as the main component: wherein R 1 , R 2 , R 3 and R 4 are each a hydrogen atom or a substituent having 1 to 30 carbon atoms with the proviso that, R 1 and R 2 and/or R 3 and R 4 are different from each other. In the above general formula (4), R 1 , R 2 , R 3 and R 4 are each a group wherein all of the constituent carbon atoms are of sp 3 hybrid orbital (an atomic orbital of a carbon atom of a C-C single bond) or a group constituted of carbon atoms of two or three hybrid orbitals selected from sp 3 , sp 2 (an atomic orbital of a carbon atom of a C=C double bond) and sp (an atomic orbital of a carbon atom of a C≡C or C≡N triple bond) and may contain atoms other than oxygen, nitrogen and carbon. Geometrically, R 1 , R 2 , R 3 and R 4 may be linear or cyclic and straight-chain or branched. Particular examples thereof include the following: A) groups wherein the constituent carbon atoms are all sp 3 hybridized: (1) R 1 , R 2 , R 3 , and R 4 : -CH 3 , -CH 2 CH 3 , -CH 2 CH 2 CH 3 , B) groups comprising sp 3 hybridized carbon atom and sp 2 hybridized carbon atom: (1) R 1 , R 2 , R 3 , and R 4 : C) groups comprising sp 3 hybridized carbon atom and sp hybridized carbon atom: (1) R 1 , R 2 , R 3 , and R 4 : -CH 2 -C≡CH, -CH 2 -C≡N The β-lactams described above can be efficiently separated into stereoisomers by using a separating agent comprising the polysaccharide derivative. Although the polysaccharide according to the present invention may be any of synthetic, natural and modified natural ones, as far as it is optically active, it is preferable that the polysaccharide has a high regularity in the bonding mode. Examples thereof include α-1,4-glucan (such as amylose and amylopectin), α-1,6-glucan (such as dextran), β-1,6-glucan (such as pustulan), β-1,3-glucan (such as curdlan and schizophyllan), α-1,3-glucan, β-1,2-glucan (such as Crown Gall polysaccharide), β-1,4-galactan, β-1,4-mannan, α-1,6-mannan, β-1,2-fructan (such as inulin), β-2,6-fructan (such as levan), β-1,4-xylan, β-1,3-xylan, β-1,4-chitosan, β-1,4-N-acetylchitosan (such as chitin), pullulan, agarose, alginic acid and amylose-containing starches, among which amylose, β-1,4-chitosan, chitin, β-1,4-mannan, β-1,4-xylan, inulin and curdlan are particularly preferable, because high-purity polysaccharides can be easily obtained therefrom. From the standpoint of handleability, the number-average degree of polymerization of the polysaccharide (average number of pyranose or furanose rings contained in one molecule) is 5 or above, preferably 10 or above and the upper limit thereof is 2000, preferably 500. The atomic group to be introduced into the polysaccharide is one derived from a compound which reacts with a hydroxyl or amino group of the polysaccharide to form an ester, urethane (carbamate) or ether linkage represented by the formula (1), (2) or (3). The polysaccharide derivative of the present invention can be prepared by, for example, the following processes: 1) ester linkage The carbonyl group constituting the polysaccharide ester derivative according to the present invention is represented by the above general formula (1) and the carbonyl group forms ester linkages together with 30 to 100%, preferably at least 50%, still preferably at least 85% of the whole hydroxyl and/or amino groups of the polysaccharide. The ester derivative according to the present invention can be easily prepared by reacting the corresponding carboxylic acid with thionyl chloride, oxalyl chloride or the like to give an acid chloride and reacting the acid chloride with the corresponding polysaccharide in pyridine as a solvent. 2) carbamate linkage The carbamoyl group constituting the polysaccharide carbamate derivative according to the present invention is represented by the above general formula (2) and it forms urethane linkages together with 30 to 100%, preferably at least 50%, still preferably at least 85% of the whole hydroxyl and/or amino groups of the corresponding polysaccharide. The carbamate derivative according to the present invention can be prepared by a conventional process for preparing a urethane from an alcohol and an isocyanate. For example, the carbamate derivative can be prepared by reacting the corresponding isocyanate with the corresponding polysaccharide in a suitable solvent in the presence of a Lewis base such as a tertiary amine or a Lewis acid such as a tin compound as a catalyst. The isocyanate to be used above can be easily prepared by reacting the amino group of the corresponding aniline derivative with phosgene. 3) ether linkage The group constituting the polysaccharide ether derivative according to the present invention is represented by the above general formula (3) and it forms ether linkages together with 30 to 100%, preferably at least 50%, still preferably at least 85% of the whole hydroxyl and/or amino groups of the corresponding polysaccharide. The ether derivative according to the present invention can be prepared by reacting the corresponding halide with the corresponding polysaccharide in dioxane or pyridine in the presence of a base such as potassium hydroxide or potassium t-butoxide. In the use of the polysaccharide derivative according to the present invention as a separating agent for liquid chromatography, it is convenient to pack the derivative in a powdered state into a column. Therefor, the polysaccharide derivative is preferably pulverized or formed into a bead and the resulting particle is still preferably porous. Further, it is preferable to support the polysaccharide derivative on a carrier with the purpose of improving the pressure resistance of the separating agent, preventing the agent from swelling and shrinking due to solvent replacement and enhancing the theoretical plate number. Although the particle size of the powdered polysaccharide derivative and the size of the carrier vary depending upon the size of the column used, they range from 1 µm to 1 mm, preferably from 1 µm to 300 µm. The carrier is preferably a porous one and the mean pore size thereof ranges from 10 Å to 100 µm, preferably from 50 Å to 50000 Å. The amount of the polysaccharide derivative to be supported on a carrier is 1 to 100% by weight, preferably 5 to 50% by weight based on the carrier. The process for making the polysaccharide derivative supported on a carrier may be either a chemical one or a physical one. The physical process includes a process which comprises mixing a solution of the polysaccharide derivative in a solvent with a carrier and distilling the mixture with an air stream either under a reduced pressure or at an elevated temperature to remove the solvent, and a process which comprises mixing a solution of the derivative in a solvent with a carrier and diffusing the solvent with a non-solvent for the derivative. The separating agent thus prepared may be subjected to a suitable treatment such as heating, addition of a solvent or washing in order to improve the separating power thereof. The carrier to be used in the present invention includes porous organic carriers and porous inorganic carriers, among which the latter are preferable. Suitable examples of the porous organic carrier include polymers such as polystyrene, polyacrylamide and polyacrylate. Suitable examples of the porous inorganic carrier include silica, alumina, magnesia, glass, kaolin, titanium oxide and silicates. The surface of such a porous inorganic carrier may be treated in order to improve the affinity of the carrier with the carbamate derivative or the surface characteristics thereof. The surface treatment includes silylation with an organosilane compound and plasma polymerization. The developer to be used in the liquid chromatography using the polysaccharide derivative of the present invention is not particularly limited with the proviso that those in which the derivative is soluble and those which are reactive with the derivative are excluded. When the polysaccharide derivative is in a state chemically supported on a carrier or in a state insolubilized by crosslinking, the developer may be any one except those which are reactive with the derivative. The polysaccharide derivative of the present invention is extremely useful as a functional material, particularly as a packing for optical resolution, i.e., separating agent. Although the separation of a mixture of compounds or an optical isomer mixture with the polysaccharide derivative of the present invention is generally conducted by gas, liquid or thin layer chromatography using a column packed with the polysaccharide derivative, it may be conducted by the membrane separation technique using a membrane containing the polysaccharide derivative. In the application of the polysaccharide derivative to thin-layer chromatography, a layer comprising the derivative in the form of a particle having a size of 0.1 µm to 0.1 mm and, if necessary, a small amount of a binder and having a thickness of 0.1 to 100 mm is formed on a support. In the application of the polysaccharide derivative to membrane separation, the derivative is used in the form of a hollow yarn or a film. The present invention will now be described in more detail by referring to the following examples. Further, the separation effect of the polysaccharide derivative will be also illustrated in application examples. Example 1 [synthesis of cellulose tris(1-phenylethylcarbamate)] 0.80 g of cellulose (Avicel, a product of Merck) was stirred in a mixture comprising 1.2 g of LiCl and 12 ml of N,N-dimethylacetamide at 80°C for 6 hours. 6 ml of pyridine and 3.5 ml of (-)-1-phenylethyl isocyanate were added thereto to carry out a reaction at 100°C for 26 hours. The reaction mixture was poured into methanol to precipitate a product. This product was recovered by filtration through a glass filter and dried in a vacuum at 60°C. amount of the product: 2.21 g, yield: 74.2% The (-)-1-phenylethyl isocyanate used above was one prepared by reacting (-)-1-phenylethylamine with phosgene. (-)-1-phenylethyl isocyanate: b.p.: 69 to 71°C/ 6 mmHg The results of the elemental analysis of the obtained cellulose tricarbamate derivative (hereinafter referred to as "(-)-isomer") are as follows: C% H% N% found: 64.42 6.08 6.78 calculated: 65.66 6.18 6.96 Application Example 1 One part (by weight, the same applies hereinbelow) of the polysaccharide derivative prepared in Example 1 was dissolved in 8 parts of acetone to give a solution. This solution was mixed with 4 parts of diphenylsilane-treated silica gel (a product of Merck, Lichrospher Si-1000). The acetone was removed from the resulting mixture by vacuum distillation to give a separating agent, which was packed into a stainless steel column having an inner diameter of 0.46 cm and a length of 25 cm by a slurry method using methanol. Various racemic mixtures were separated by using the resulting packed column. The results are given in Table 1. The capacity ratio (k'), separation factor (α) and resolution (Rs) given in the Table are those defined by the following equations, respectively: capacity ratio (k') = retention time of separated compound - dead time dead time separation factor (α) = capacity ratio of more strongly adsorbed compound capacity ratio of more weakly adsorbed compound (A resolution of 1 or above means complete separation) Example 2 [synthesis of xylan bis((+)-1-phenylethylcarbamate) and xylan bis((-)-1-phenylethylcarbamate)] 1) synthesis of (+) and (-)-1-phenylethyl isocyanates The synthesis was carried out according to a conventional process. -(+)-1-phenylethyl isocyanate 66.2 to 67.8°C/5 mmHg yield: 69.4% [α] 25 / D: +10.4° (Aldrich [α] 19 : +9.2° (neat)) (-)-1-phenylethyl isocyanate 66.3 to 66.8°C/5 mmHg yield: 71.1% 2) synthesis of xylan bis(1-phenylethylcarbamate) A reflux condenser was set on a 50-ml two-necked flask. 0.80 g of xylan (a product of Seikagaku Kogyo K.K.) and 0.85 g of LiCl were fed into the flask in a nitrogen atmosphere, followed by the addition of 6 ml of dry dimethylacetamide (on molecular sieved). The obtainer mixture was stirred at 90°C for 2 hours to give a homogeneous system having a considerably high viscosity. 15 ml of dry pyridine (on KOH) was added to the flask, followed by the addition of 2.5 ml (molar amount of OH group of the xylan x 1.5) of 1-phenylethyl isocyanate. After 24 hours, no isocyanate was present in the reaction mixture (as analyzed by IR) and the reaction had proceeded only a little. Therefor, 1.1 ml of 1-phenylethyl isocyanate was further added to the flask. After 92 hours from the initiation of the reaction, the reaction mixture was poured into methanol to give a precipitate. This precipitate was recovered by centrifuging. Just before the recovery, the isocyanate remained in the reaction system (as analyzed by IR). The steps subsequent to the above addition of the pyridine were conducted in a state wherein a calcium chloride tube was set on the flask. The obtained xylan bis((+)-1-phenylethylcarbamate) (hereinafter referred to as "(+)-isomer") and xylan bis((-)-1-phenylethylcarbamate) (hereinafter referred to as "(-)-isomer") have each a structure represented by the following formula: (+)-isocyanate (-)-isocyanate Yield (%) 42.6 59.4 Elemental analysis C% 64.28 (64.79) 64.49 H% 6.20 (6.10) 6.23 N% 6.60 (6.57) 7.02 Note) figures in parentheses are calculated values Application Example 2 0.75 g of the xylan bis(1-phenylethylcarbamate) prepared in Example 2 was dissolved in 7 ml of dimethylacetamide to give a solution. This solution was mixed in two or three portions with 3 g of silica gel (4000-7, treated with 3-aminopropyltriethyoxysilane) to make the xylan bis(1-phenylethylcarbamate) supported on the silica gel. The separating agent thus obtained was packed into a column (25 x 0.46 (i.d.) cm) in a state dispersed in a hexane/liquid paraffin (2 : 1) mixture. pressure : 330 kg/cm 2 Various racemic mixtures were separated by using the resulting packed column. The results are given in Tables 2, 3 and 4. Example 3 [synthesis of amylose tris((-)-1-phenylethylcarbamate)] A reflux condenser was set on a 50-ml two-necked flask. 0.80 g of amylose (Nakarai Chemicals) and 0.80 g of LiCl were fed into the flask in a nitrogen atmosphere, followed by the addition of 5 ml of dry dimethylacetamide (on molecular sieve). The contents were stirred under heating at 90°C for 2 hours to give a heterogeneous system. 7 ml of dry pyridine (on KOH) was added to the flask, followed by the addition of (-)-1-phenylethyl isocyanate. The obtained mixture was kept at 90°C for 50 hours to carry out a reaction. The resulting reaction system had a considerably high viscosity. When the reaction mixture was poured into methanol, the formed polymer precipitated in the form of a thread, not a powder. amount of the product: 1.33 g, yield: 44.7% The polymer was subjected to solvent fractionation with THF. solubles; 0.77 g (61.1%) insolubles; 0.49 g (38.9%) .....unreacted OH groups were recognized The amount of the obtained amylose tris((-)-1-phenyl-ethylcarbamate) was 0.77 g and the yield thereof was 25.9%. elemental analysis C% H% N% found: 63.93 6.05 6.72 calculated: 65.72 6.14 6.97 Application Example 3 0.72 g of the polymer prepared in Example 3 was dissolved in 15 ml of THF and supported on 2.90 g of silica gel (treated with 3-aminopropyltriethoxysilane). The separating agent thus obtained was packed into a column in a state dispersed in a hexane/liquid paraffin (2 : 1) mixture and pressed at 32362 kPa (330 kg/cm 2 ). Various racemic mixtures were optically resolved by using the resulting packed column. The results are given in Table 5. Example 4 [synthesis of amylose tris((+)-1-phenylethylcarbamate)] A reflux condenser was set on a 50-ml two-necked flask. 0.80 g of amylose (Nakarai Chemicals) and 0.80 g of LiCl were fed into the flask, followed by the addition of 7 ml of dry dimethylacetamide (on molecular sieve). The contents were stirred under heating at 90°C for 5 hours to give a heterogeneous system. 10 ml of dry pyridine (on KOH) was added to the flask, followed by the addition of 3.6 g of (+)-1-phenylethyl isocyanate. The contents were kept at 90°C for 70 hours to carry out a reaction. The resulting reaction mixture had a considerably high viscosity. When the reaction mixture was poured into methanol, the formed polymer precipitated in the form of a thread, not a powder. The polymer was subjected to solvent fractionation with THF. solubles: 0.72 g (61.1%) The amount of the obtained amylose tris((+)-1-phenylethylcarbamate) was 0.72 g and the yield thereof was 22.6%. elemental analysis C% H% N% found: 64.85 6.11 6.87 calculated: 65.72 6.14 6.97 Application Example 4 0.72 g of the polymer prepared in Example 4 was dissolved in 15 ml of THF and supported on 2.90 g of silica gel (treated with 3-aminopropyltriethoxysilane). The obtained separating agent was packed into a column in a state dispersed in a hexane/liquid paraffin (2 : 1) mixture and pressed at 32362 kPa (330 kg/cm 2 ). Various racemic mixtures were optically resolved by using the packed column. The results are given in Table 5. Example 5 [synthesis of cellulose tris((+)-1-phenylethylcarbamate)] A reflux condenser was set on a 50-ml two-necked flask. 0.80 g of cellulose (Merck) and 0.90 g of LiCl were fed into the flask in a nitrogen atmosphere, followed by the addition of 7 ml of dry dimethylacetamide (on molecular sieve). The contents were stirred under heating at 90°C for 4 hours to give a heterogeneous system. 8 ml of dry pyridine was added to the flask, followed by the addition of (+)-1-phenylethyl isocyanate. The contents were kept at 90°C for 27 hours to carry out a reaction. Since the resulting reaction mixture was heterogeneous, 0.80 g of (+)-1-phenylethyl isocyanate was additionally added to the flask 2 hours before the termination. The formed polymer was precipitated in methanol and recovered with a glass filter. amount of the obtained polymer: 2.10 g, yield: 70.6% The polymer was subjected to solvent fractionation with THF. solubles: 1.96 g (91.6%) insolubles: 0.18 g (8.4%) .....unreacted OH groups were recognized The amount of the obtained cellulose tris((+)-1-phenylethylcarbamate) was 1.96 g and the yield thereof was 65.9%. elemental analysis C% H% N% found: 65.44 6.19 6.96 calculated: 65.72 6.14 6.97 Application Example 5 0.74 g of the polymer prepared in Example 5 was dissolved in 12 ml of THF and supported on 3.00 g of silica gel (tread with 3-aminopropyltriethoxysilane). The separating agent thus obtained was packed into a column in a state dispersed in a hexane/liquid paraffin (2 : 1) mixture and pressed at 32362 kPa (330 kg/cm 2 ). Various racemic mixtures were optically resolved by using the above separating agent (hereinafter abbreviated to "(+)-isomer". The results are given in Table 6. Example 6 [synthesis of cellulose tris(1-phenylethylcarbamate)] 0.80 g of cellulose (Avicel, a product of Merck) was stirred in a mixture comprising 1.2 g of LiCl and 12 ml of N,N-dimethylacetamide at 80°C for 6 hours, followed by the addition of 6 ml of pyridine and 3.5 ml of 1-pienylethyl isocyanate. The obtained mixture was kept at 100°C for 26 hours to carry out a reaction. The reaction mixture was poured into methanol to precipitate a product, which was recovered with a glass filter and dried in a vacuum at 60°C. amount of the obtained product: 2.21 g (yield: 74.2%) The 1-phenylethyl isocyanate used above is one prepared by reacting 1-phenylethylamine with phosgene. 1-phenylethyl isocyanate: b.p.: 69 to 71°C/0.8 kPa (6 mmHg) The results of the elemental analysis of the obtained cellulose tricarbamate derivative are as follows: C% H% N% found: 64.42 6.08 6.78 calculated: 65.66 6.18 6.96 Application Example 6 One part (by weight, hereinafter the same applies) of the polysaccharide derivative prepared in Example 6 was dissolved in 8 parts of acetone to give a solution. This solution was mixed with 4 parts of diphenylsilane-treated silica gel (a product of Merck, Lichrospher Si-1000). The acetone was removed from the resulting mixture by vacuum distillation to give a separating agent. This agent was packed into a stainless steel column having an inner diameter of 0.46 cm and a length of 25 cm by a slurry method using methanol. Various racemic mixtures were separated by using the packed column. The results are given in Table 7. Example 7 [synthesis of cellulose tris(1-(p-tolyl)ethyl carbamate)] 0.560 g of cellulose (Avicel, a product of Merck) and 0.75 g of lithium chloride were stirred in 7.5 ml of N,N-dimethylacetamide (DMA) at 80°C for 12 hours. 4.0 ml of dry pyridine and 3.5 g of 1-(p-tolyl)ethyl isocyanate were successively added thereto to carry out a reaction at 80°C for 48 hours. The progress of the reaction was ascertained by the presence of an absorption peak assignable to a carbamate group in the IR spectrum. The reaction mixture was poured into methanol to give a precipitate, which was recovered by filtration through a glass filter and dried. A part of the precipitate was subjected to solvent fractionation with CHCL 3 to give an objective product as a soluble part. amount of the product: 0.86 g (38.6%) The 1-(p-tolyl)ethyl isocyanate used above is one prepared by reacting the corresponding amine with phospgene (yield: 86%, b.p.: 83.0°C/0.9 kPa (6.5 mmHg)). Further, the corresponding amine is one prepared by reacting the corresponding ketone with ammonium formate (yield: 60%, b.p.: 81.0°C/1.7 kPa (13 mmHg)). The results of the elemental analysis of the obtained cellulose tricarbamate derivative are as follows: C% H% N% found: 65.26 6.63 6.39 calculated: 66.96 6.71 6.51 Application Example 7 A packed column was prepared by using the polymer obtained in Example 6 in a similar manner to that of Application Example 6. Various racemic mixtures were separated by using the packed column. The results are given in Table 7. Example 8 [synthesis of cellulose tris(1-phenylpropylcarbamate)] The objective compound was prepared in the same manner as that of Example 7 except that 0.505 g of cellulose and 3.6 g of 1-phenylpropyl isocyanate were used, and that the solvent fractionation was conducted by using THF. yield: 1.69 g (84.1%) The 1-phenylpropyl isocyanate used above is one prepared by reacting the corresponding amine with phosgene (yield: 79%, b.p.: 63.0°C/0.4 kPa (3.0 mmHg)). The corresponding amine used is one prepared by reacting the corresponding ketone with ammonium formate (yield 60.9%, b.p.: 47.2°C/0.4 kPa (3.0 mmHg)). The results of the elemental analysis of the obtained cellulose tricarbamate derivative are as follows: C% H% N% found: 65.25 6.60 6.33 calculated: 66.96 6.71 6.51 Application Example 8 A packed column was prepared by using the polymer obtained in Example 8 in a similar manner to that of Application Example 6. Racemic mixtures were separated by using the packed column. The results are given in Table 7. Example 9 [synthesis of cellulose tris(1-(o-tolyl)ethylcarbamate] The objective compound was prepared in the same manner as that of Example 7 except that 0.510 of cellulose and 3.1 g of 1-(o-tolyl)ethyl isocyanate were used and that the solvent fractionation was carried out by using THF. yield: 1.20 g (59.1%) The 1-(o-tolyl)ethyl isocyanate used above is one prepared by reacting the corresponding amine with phosgene (yield: 90%, b.p.: 90.2°C/12 mmHg). The corresponding amine used is one prepared by reacting the corresponding ketone with ammonium formate (yield: 50%, b.p.: 59.9°C/4.5 mmHg). The results of the elemental analysis of the obtained cellulose tricarbamate derivative are as follows: C% H% N% found: 66.33 6.62 6.50 calculated: 66.96 6.71 6.51 Application Example 9 A packed column was prepared by using the polymer obtained in Example 9 in a similar manner to that of Application Example 6. Racemic mixtures were separated by using the packed column. The results are given in Table 7. Example 10 [synthesis of amylose tris(1-phenylethylcarbamate)] A reflux condenser was set on a 50-ml two-necked flask. 0.80 g of amylose (Nakarai Chemicals) and 0.80 g of LiCl were fed into the flask in a nitrogen atmosphere, followed by the addition of 7 ml of dry dimethyacetamide (on molecular sieve). The contents were stirred under heating at 90°C for 5 hours to give a heterogeneous system. 10 ml of dry pyridine (on KOH) and 3.6 g of 1-phenylethyl isocyanate were successively added to the flask. The contents were kept at 90°C for 70 hours to carry out a reaction. The resulting reaction mixture had a considerably high viscosity. When the mixture was poured into methanol, the polymer precipitated in the form of not a powder but a thread. The polymer was subjected to solvent fractionation with THF. solubles: 0.72 g (22.6 %) elemental analysis C% H% N% found: 64.39 6.08 6.80 calculated: 65.72 6.14 6.97 Application Example 10 0.72 g of the polymer prepared in Example 10 was dissolved in 15 ml of THF and supported on 2.90 g of silica gel (treated with 3-aminopropyltriethoxysilane). The separating agent thus prepared was packed into a column in a state dispersed in a hexane/liquid paraffin (2 : 1) mixture and pressed at 32362 kPa (330 kg/cm 2 ). Various racemic mixtures were optically resolved by using the packed column. The results are given in Table 8. Example 11 [synthesis of amylose tris(1-(p-tolyl)-ethylcarbamate)] 0.521 g of amylose and 0.75 g of LiCl were stirred in 7.5 ml of dry DMA at 90 C for 5 hours, followed by the addition of 4.0 ml of dry pyridine. 3.5 g of 1-(p-tolyl)ethyl isocyanate was added to the flask to carry out a reaction at 80°C for 24 hours. The IR spectrum revealed that unreacted OH groups remained though the isocyanate had been nearly completely consumed. Therefor, 1.2 g of 1-(p-tolyl)ethyl isocyanate was further added to continue the reaction for additional 24 hours. The solvent fractionation was carried out by using THF. yield: 0.86 g (47.7%) elemental analysis C% H% N% found: 65.26 6.63 6.39 calculated: 66.96 6.71 6.51 Application Example 11 A packed column was prepared by using the separating agent prepared in Example 11 in a similar manner to that of Application Example 10. Various racemic mixtures were resolved by using the packed column. The results are given in Table 8. Example 12 [synthesis of amylose tris(1-phenylpropylcarbamate)] The objective compound was prepared in the same manner as that of Example 11 except that 0.499 g of amylose and 3.6 g of 1-phenylpropyl isocyanate were used and that the solvent fractionation was carried out by using THF. yield: 1.49 g (75.5%) elemental analysis C% H% N% found: 66.09 6.60 6.44 calculated: 66.96 6.71 6.51 Application Example 12 A packed column was prepared by using the polymer obtained in Example 12 in a similar manner to that of Application Example 10. Various racemic mixtures were resolved by using the packed column. The results are given in Table 8. Example 13 [synthesis of amylose tris(1-(o-tolyl)ethylcarbamate)] The objective compound was prepared in the same manner as that of Example 11 except that 0.502 g of amylose and 3.2 g of 1-(o-tolyl)ethyl isocyanate were used, that the stirring after the addition of dry DMA was conducted at 80°C for 5 hours, followed by the addition of dry pyridine and the isocyanate, and that the solvent fractionation was conducted by using THF. yield: 1.20 g (60.0%) elemental analysis C% H% N% found: 65.61 6.51 6.31 calculated: 66.96 6.71 6.51 Application Example 13 A packed column was prepared by using the polymer obtained in Example 13 in a similar manner to that of Application Example 10. Various racemic mixtures were resolved by using the packed column. The results are given in Table 8. Example 14 and Comparative Examples 1 and 2 The following objects of separation were separated by using the separating agent listed in Tables 9, 10 and 11 and the results are given in Tables 9, 10 and 11. <Object of separation> (wherein Ac represents an acetyl group, Me a methyl group, Et an ethyl group, Pr a propyl group, i-Pr an isopropyl group and Ph a phenyl group). The separatory column used in Example 14 is one prepared by dissolving amylose (S)-α-methylbenzylcarbamate in tetrahydrofuran to give a solution, mixing the solution with diphenylsilane-treated silica gel (a product of Merck, Lichrospher Si-1000), removing the tetrahydrofuran from the obtained mixture by vacuum distillation to give a separating agent and packing it into a stainless steel column having an inner diameter of 0.46 cm and a length of 25 cm by a slurry method with methanol. The separatory column used in Comparative Example 1 or 2 is one prepared in the same manner as that described above except that cellulose 3,5-dimethylphenylcarbamate or amylose 3,5-dimethylphenylcarbamate was used. The measurement was carried out by using a high-pressure pump TRI ROTAR-II mfd. by Japan Spectroscopic Co., Ltd. and an ultraviolet detector UV-100-III mfd. by the same company. The capacity ratio (k 1 '), separation factor (α) and resolution (Rs) given in Tables are those defined by the following equations, respectively: capacity ratio (k 1 ') = retention time of separated compound - dead time dead time separation factor (α) = capacity ratio of more strongly adsorbed compound capacity ratio of more weakly adsorbed compound (A resolution of 1 or above means complete separation)

Claims: A polysaccharide wherein at least a part of the hydrogen atoms of the hydroxyl and/or amino groups therein are replaced by at least one group represented by formula (1), (2) or (3) wherein R 1 is wherein R 2 is -R 3 wherein R 3 is wherein the symbol * represents an asymmetric center. The polysaccharide of claim 1, wherein the degree of replacement is 30% or more. A process for separating a racemic mixture by using a polysaccharide according to claim 1 or 2 as a separating agent. The process of claim 3, wherein said racemic mixture comprises a compound of formula (4): wherein R 1 , R 2 , R 3 and R 4 are each a hydrogen atom or a substituent having 1 to 30 carbon atoms, with the proviso that R 1 and R 2 and/or R 3 and R 4 are different from each other. A separating agent comprising a polysaccharide according to claim 1 or 2. The separating agent of claim 5 comprising a carrier.

Inventors: HATADA KOICHI, OKAMOTO YOSHIO, HATADA, KOICHI, OKAMOTO, YOSHIO
Applicants: DAICEL CHEM, DAICEL CHEMICAL INDUSTRIES, LTD.
Application year: 1990
Main classification: C08B3
IPC codes: C08B31, C07B57, C07D205, C07C45, B01J20, C08B37, C08B3, C08B15