RESOLUTION OF CHIRAL AMINES

Abstract: Chiral amines are resolved by selectively reacting an enantiomer of the amine with an alkyl ester in the presence of an enantioselective lipase enzyme to produce an amide of that enantiomer and separating it from the unreacted enantiomer, the alkyl group of the ester being an isoalkyl group. Isobutyl and especially isopropyl groups are preferred.

Description: RESOLUTION OF CHIRAL AMINES THIS INVENTION relates to the resolution of chiral amines. It is known for example from WO95/08636, Kitaguchi et al (J.Am. Chem. Soc, 1989, 111, 3094-3095), Gotor et al (J.Chem. Soc. Perkin Trans. 1 , 1993, 2453-2456), Ohrner et al (Enzyme and Microbial Technology, 1996, 19, 328-331) and Sanchez et al (Tetrahedron Asymmetry, 1997, 8, 37-40) and Chiou et al, Bio-organic & Medicinal Chemistry Letters Vol. 7, No 4, pp 433-436 (1977) to resolve racemic amines by acylating one enantiomer by reaction with an alkyl ester in the presence of an enantioselective enzyme as catalyst. However, the results obtained have in many cases been disappointing. We have found that such reactions of attractive stereospecificity occur if the alkyl group of the ester is an isoalkyl group preferably an isopropyl group. The invention therefore comprises a process of resolution of chiral amines which comprises selectively reacting one enantiomer of the amine with an alkyl ester in the presence of a enantioselective lipase enzyme to produce an amide of one enantiomer and separating it from an unreacted enantiomer optionally after further reaction characterised in that the alkyl group of the ester is an isoalkyl group and preferably an isopropyl group. A lipase is an enzyme capable of catalysing the esterification of aliphatic acids with glycerol and the hydrolysis of esters of glycerol and aliphatic acids. Either or both enantiomers may be recovered. The untreated enantiomer may be recovered as such. The reacted enantiomer may be converted to the original amine enantiomer suitably by hydrolysis. It may of course be utilised as the amide if desired. Suitably such hydrolysis may be carried out using as catalyst an amidase of the same stereospecificity and/or hydrolysing any unwanted stereoisomer present using an amidase of opposite stereospecificity, separating the unwanted amide and hydrolysing that, thus providing a second stage of resolution and enhancing the enantiomeric excess of the product, but if the first stage provides sufficient specificity a non selective hydrolysis may be employed. The acid component of the ester may have 1 to 10 for example 1 to 5 carbon atoms. It is preferably of formula RCOOH in which R is a hydrocarbyl group, for example an aryl group such as a phenyl, naphthyl or benzyl group, an alkyl or cycloalkyi group or a chloro or bromo substituted derivative thereof, the substitution being preferably on a carbonation adjacent to the C=O group or one next to it. It may suitably be an unsubstituted alkyl group suitably having 1 to 4 carbon atoms as these are often of moderate cost tend not to be involved in unwanted side reactions and tend not to be aggressive to metal reaction vessels. The process is suitable for the resolution of primary and secondary amines for example amines of formula NHR 3 R 2 A " R 1 in which R 1 and R 2 are alkyl, cycloalkyi, alkenyl or alkynyl, or an aryl group or such a group, which is substituted with for example NO 2 , SO 3 H, COOR 4 , Cl, Br, F, I, OH, SO, SO 2 , CN, alkoxy and in the case of aryl substitution NH 2 in which R 1 and R 2 are different and R 3 is H, alkyl, cycloalkyi, alkenyl, alkynyl, or an aryl group or such a group which is substituted with for example, NO 2 , SO 3 H, COOH, Cl, Br, F, I, OH, SO, SO 2 , CN and R 4 is alkyl, cycloalkyi, alkenyl, alkynyl or an aryl group optionally substituted as described above. The process is suitable for the resolution of amino acids and their esters. The amine preferably has the formula R D in which R 4 is an alkyl group having for example 1 to 12 and preferably 1 to 6 carbon atoms and R 5 is an aryl preferably a naphthyl group, an alkyl group or cycloalkyi group in each case optionally substituted by one or more alkoxy, hydroxy, halogen and/or -CN group or in the case of aryl groups, amine groups, groups which preferably have at most 12 and more preferably at most 6 carbon atoms in total in all of the said substituents. The amount of lipase present is preferably 10 to 50% by weight of the amine. The lipase is preferably supported on a solid support to enable it to be removed mechanically, for example by filtration or centrifugation, after reaction. Separation of the amide of the reacted amine from unreacted amine may be accomplished by known methods, for example, distillation or crystallisation. The reaction may be carried out in the presence of a solvent which may be the ester, an ether (for example methyl tert butyl ether, dimethoxy ethane or tetrahydrofuran) or a hydrocarbon, for example toluene or an alkane or cycloalkane having 5 to 10 carbon atoms or a halogenated hydrocarbon solvent. It is preferably free from -OH and NH 2 groups. The reaction may be carried out at 20-60°C for example at 20-40°C. At least one mole of the ester should be provided per two moles of the amine so as to permit stoichiometric reaction of an enantiomer, but it is preferred that an excess be provided. The excess should normally be sufficient to provide preferably at least 90% and more preferably at least 95% for example 99% reaction of the most reactive enantiomer. In judging the appropriate excess, conditions should not be such as to cause unacceptable conversion of the less reactive enantiomer, and if a very high selectivity for the more reactive enantiomer is needed it may be preferred to convert only part thereof, thus requiring little or no excess; indeed operation with less than the stoichiometric amount may be desirable in some cases. The step of converting the amine to the amide is preferably carried out in the substantial absence of water and other hydroxy compounds. Example 1 2-Amino-3, 3-dimethylbutane (125mg) was added to 3ml of acyl donor (e.g. ethyl acetate or isopropyl acetate) and incubated at 28°C in the presence of 60mg of immobilised lipase from Candida antarctica (NOVO SP 435). The extent of reaction was followed by quantitative gas chromatography on a Perkin Elmer 8500 system fitted with a J&W 30m x 0.32mm fused silica capillary GC column. The gas chromatograph was operated with helium carrier gas at 8 psi using a temperature gradient starting at 80°C and rising to 200°C at a rate of 20° min "1 followed by 6 minutes held at 200°C. Under such conditions 2-amino-3, 3-dimethyIbutane was eluted with a retention time of 3.0 minutes and the corresponding acetamide at 6.1 minutes. The enantiomeric purity of unreacted 2-amino- 3, dimethylbutane (derivatised as the N-butyramide) and the acetamide product of the aminolysis reaction was determined by chiral phase gas chromatography using a 25m x 0.32mm Chrompack CP-Chirasil-Dex CB column. The gas chromatograph was operated with a helium carrier gas at 8 psi and at 120°C. Under such conditions the two enantiomers of the acetamide derivative of 2-amino-3, 3-dimethylbutane were eluted with retention times of 4.78 minutes (S) and 4.95 minutes (R) and the two enantiomers of the butyramide derivative 8.38 minutes (S) and 8.51 minutes (R). The results are summarised in Table 1. Table 1. Effect of structural changes to the alcohol component of the acyl donor on the enantioselectivity of the resolution of 2-amino-3, 3-dimethylbutane by Candida antarctica lipase. Example 2 1-(1-Naphthyl) ethylamine (100mg) was added to 5ml of acyl donor e.g. ethyl acetate or isopropyl acetate) and incubated at 28°C in the presence of 50mg of immobilised Candida antarctica lipase (NOVO SP 435). The extent of conversion was determined from measurements of the enantiomeric excess of the unreacted amine (derivatised as its butyramide) and product acetamide using the mathematical expression described by Chen et. al. (J. Am. Chem. Soc, 1982, Vol 104, pp 7294-7299). Enantiomeric excess measurements were made by chiral phase HPLC on a Hewlett Packard HP 1050 system fitted with a 250mm x 4.6mm Daicel Chiralcel OD column. The column was eluted isocratically with a mixture of 92.5% hexane and 7.5% ethanol in 1ml min "1 . Compounds were detected by UV absorbance at 254mm. The retention times of the unreacted amine (derivatised as its butyramide) were 7.65 minutes (R)and 15.2 minutes (S) and the product acetamide 8.9 minutes (R) and 17.9 minutes (S). The results are summarised in Table 2. Table 2. Effect of structural changes to the alcohol component of the acyl donor on the enantioselectivity of the resolution of 1-(1 -naphthyl) ethylamine by Candida antarctica lipase. Example 3 Racemic 1-(1-naphthyl)ethylamine (100mg) was added to 5ml of acyl donor (see Table 3) and incubated at ambient temperature in the presence of 20mg of Chirazyme l_2 (immobilised Candida antarctica lipase). At intervals 0.5ml samples were removed and diluted to 1ml with a solution of hexane/ethanol (92.5:7.5). The unreacted amine was converted to its corresponding butyramide by the addition of 10μl of butyric anhydride. Each sample was analysed by chiral phase HPLC on a Hewlett Packard HP1050 system using a Daicel Chiralcel OD analytical column (250mm x 4.6mm) eluted with hexane/ethanol (92.5:7.5) at a flow rate of 1 ml min '1 . Compounds were detected by UV absorbance at 254nm. The retention times of the two enantiomers of the unreacted amine (derivatised as its butyramide) were 7.9 minutes (R) and 15.0 minutes (S) and the product acetamide 9.3 minutes (R) and 17.9 minutes (S). The extent of conversion and enantiomeric ratio was determined from measurements of the enantiomeric excess of unreacted amine and product acetamide using the mathematical expression described by Chen et. al. (J. Am. Chem. Soc, 1982, Vol 104, pp 7294-7299). The results are summarised in Table 3. Table 3. Effect of structural changes to the alcohol component of the acyl donor on the enantiospecificity of the resolution of 1-(1-naphthyl)ethylamine by Chirazyme L2 lipase. Example 4 Racemic 1,2,3,4-tetrahydro-1-naphthylamine (100mg) was added to 5ml of acyl donor (see Table 4) and incubated at ambient temperature in the presence of 20mg of Chirazyme L2 (immobilised Candida antarctica lipase). At intervals 0.5ml samples were removed and diluted to 1ml with dichloromethane. The unreacted amine was converted to its corresponding butyramide by the addition of 10μl of butyric anhydride. Each sample was analysed by chiral phase GC on a Perkin Elmer 8700 system using a Chrompack CP-Chirasil-Dex CB column (25m x 0.32mm). The gas chromatograph was operated isothermally at 175°C with helium carrier gas at 8 psi. Compounds were detected by flame ionisation. The retention times of the two enantiomers of the unreacted amine (derivatised as its butyramide) were 23.8 minutes (S) and 25.8 minutes (R) and the product acetamide 14.4 minutes (S) and 15.9 minutes (R). The extent of conversion and enantiomeric ratio was determined from measurements of the enantiomeric excess of unreacted amine and product acetamide using the mathematical expression described by Chen et. al. (J. Am. Chem. Soc, 1982, Vol 104, pp 7294-7299). The results are summarised in Table 4. Table 4. Effect of structural changes to the alcohol component of the acyl donor on the enantiospecificity of the resolution of 1,2,3,4-tetrahydro-1-naphthylamine by Chirazyme L2 lipase. Example 5 Racemic 2-amino-3,3-dimethylbutane (100mg) was added to 5ml of acyl donor (see Table 5) and incubated at ambient temperature in the presence of 40mg of Chirazyme L2 (immobilised Candida antarctica lipase). At intervals 0.5ml samples were removed and diluted to 1ml with dichloromethane. The unreacted amine was converted to its corresponding butyramide by the addition of 10μl of butyric anhydride. Each sample was analysed by chiral phase GC on a Perkin Elmer 8700 system using a Chrompack CP-Chirasil-Dex CB column (25m x 0.32mm). The gas chromatograph was operated isothermally at 120°C with helium carrier gas at 8 psi. Compounds were detected by flame ionisation. The retention times of the two enantiomers of the unreacted amine (derivatised as its butyramide) were 10.3 minutes (S) and 10.5 minutes (R) and the product acetamide 5.6 minutes (S) and 5.9 minutes (R). The extent of conversion and enantiomeric ratio was determined from measurements of the enantiomeric excess of unreacted amine and product acetamide using the mathematical expression described by Chen et. al. (J. Am. Chem. Soc, 1982, Vol 104, pp 7294-7299). The results are summarised in Table 5. Table 5. Effect of structural changes to the alcohol component of the acyl donor on the enantiospecificity of the resolution of 2-amino-3,3-dimethyibutane by Chirazyme L2 lipase. Example 6 Racemic 1-(1-naphthyl)ethylamine (100mg) was added to a solution of 4ml of dimethoxyethane and 1ml of acyl donor (see Table 6) and incubated at ambient temperature in the presence of 20mg of Chirazyme L2 (immobilised Candida antarctica lipase). At intervals 0.5ml samples were removed and diluted to 1ml with a solution of hexane/ethanol (92.5:7.5). The unreacted amine was converted to its corresponding butyramide by the addition of 10μl of butyric anhydride. Each sample was analysed by chiral phase HPLC as described in Example 3. The results are summarised in Table 6. Table 6. Effect of structural changes to the alcohol component of the acyl donor on the enantiospecificity of the resolution of 1-(1-naphthyl)ethylamine in dimethoxyethane by Chirazyme L2 lipase. Example 7 Racemic 1,2,3,4-tetrahydro-1-naphthylamine (100mg) was added to a solution of 4ml of dimethoxyethane and 1 ml of acyl donor (see Table 7) and incubated at ambient temperature in the presence of 20mg of Chirazyme L2 (immobilised Candida antarctica lipase). At intervals 0.5ml samples were removed and diluted to 1ml with dichloromethane. The unreacted amine was converted to its corresponding butyramide by the addition of 10μl of butyric anhydride. Each sample was analysed by chiral phase GC as described in Example 4. The results are summarised in Table 7. Table 7. Effect of structural changes to the alcohol component of the acyl donor on the enantiospecificity of the resolution of 1,2,3,4-tetrahydro-1-naphthylamine in dimethoxyethane by Chirazyme L2 lipase. Example 8 Racemic 2-amino-3,3-dimethylbutane (100mg) was added to a solution of 4ml of dimethoxyethane and 1 ml of acyl donor (see Table 8) and incubated at ambient temperature in the presence of 40mg of Chirazyme L2 (immobilised Candida antarctica lipase). At intervals 0.5ml samples were removed and diluted to 1ml with dichloromethane. The unreacted amine was converted to its corresponding butyramide by the addition of 10μl of butyric anhydride. Each sample was analysed by chiral phase GC as described in Example 5. The results are summarised in Table 8. Table 8. Effect of structural changes to the alcohol component of the acyl donor on the enantiospecificity of the resolution of 2-amino-3,3-dimethyibutane in dimethoxyethane by Chirazyme L2 lipase. Example 9 Racemic 1-(1-naphthyl)ethylamine (100mg) was added to 5ml of acyl donor (see Table 9) and incubated at ambient temperature in the presence of 50mg of Chirazyme L6 (Pseudomonas species lipase). At intervals 0.2ml samples were removed and diluted to 1ml with a solution of hexane/ethanol (92.5:7.5). The unreacted amine was converted to its corresponding butyramide by the addition of 4μl of butyric anhydride. Each sample was analysed by chiral phase HPLC as described in Example 3. The results are summarised in Table 9. Table 9. Effect of structural changes to the alcohol component of the acyl donor on the Enantiospecificity of the resolution of 1-(1-naphthyl)ethylamine by Chirazyme L6 lipase. Example 10 Racemic 1,2,3,4-tetrahydro-1-naphthylamine (100mg) was added to 5mi of acyl donor (see Table 10) and incubated at ambient temperature in the presence of 50mg of Chirazyme L6 (Pseudomonas species lipase). At intervals 0.2ml samples were removed and diluted to 1 μl with MTBE. The unreacted amine was converted to its corresponding butyramide by the addition of 6ml of butyric anhydride. Each sample was analysed by chiral phase GC as described in Example 4. The results are summarised in Table 10. Table 10. Effect of structural changes to the alcohol component of the acyl donor on the Enantiospecificity of the resolution of 1,2,3,4-tetrahydro-1-naphthylamine by Chirazyme L6 lipase. Chirazyme is a trade mark of Boehringer Mannheim GmbH Chiralcel is a trade mark of Daicel Chemical Industries Limited 97TJ L04S - MS - 04 December 1998

Claims: CLAIMS 1 A process of resolution of chiral amines which comprises selectively reacting an enantiomer of the amine with an alkyl ester in the presence of a enantioselective lipase enzyme to produce an amide of that enantiomer and separating it from an unreacted enantiomer optionally after further reaction characterised in that the alkyl group of the ester is an isoalkyl group. 2 A process as claimed in Claim 1 in which the isoalkyl group is an isobutyl or isopropyl group. 3 A process as claimed in Claim 1 or 2 in which the untreated enantiomer is recovered as such. 4 A process as claimed in Claim 1 or 2 in which the reacted enantiomer is separated in its reacted state. 5 A process as claimed in Claim 4 in which the reacted enantiomer is converted to the original amine enantiomer by hydrolysis. 6 A process as claimed in Claim 1 or 2 in which the reacted enantiomer is utilised in its amide form. 7 A process as claimed in any preceding claim in which the acid component of the ester has 1 to 10 carbon atoms and the parent acid is of formula RCOOH in which R is a hydrocarbyl group. 8 A process as claimed in Claim 7 in which the hydrocarbyl group is an unsubstituted alkyl group having 1 to 4 carbon atoms. 9 A process as claimed in any preceding claim in which the amine has the formula NHR J in which R 1 and R 2 are alkyl, cycloalkyi, alkenyl or alkynyl, or aryl groups or such a groups, substituted with for example NO 2 ,SO 3 H, COOR 4 , Cl, Br, F, I, OH, SO, SO 2 , CN, alkoxy and, in the case of aryl substitution, NH 2 in which R 1 and R 2 are different and R 3 is H, alkyl, cycloalkyi, alkenyl, alkynyl, or an aryl group or such a group which is substituted with for example, NO 2 , SO 3 H, COOH, Cl, Br, F, I, OH, SO, SO 2 , CN and R 4 is an alkyl, cycloalkyi, alkenyl, alkynyl or aryl group optionally substituted by one or more NO 2, SO 3 H, COOR 3 Cl, Br, F, I, OH, SO, SO 2 , CN or alkoxy groups. 10 A process as claimed in Claim 9 in which the amine has the formula in which R 4 is an alkyl group having for example 1 to 12 and preferably 1 to 6 carbon atoms and R 5 is an aryl preferably a naphthyl group, an alkyl group or cy oalkyl group Hi each case optionally substituted by one or more alkoxy, hydroxy, halogen and or -CN groups or in the case of naphthyl groups, amine groups, groups which preferably have at most 12 and more preferably at most β carbon atoms in total in all of the said substituents. 1 1 A process as claimed in any preceding claim in which 10 to 50% by weight of lipase is present based on the amine. 12 A process as claimed in any preceding claim in which the lipase is supported on a solid support 13 A process as claimed in any preceding daim which is carried out in the presence of a solvent which is an ester, ether or hydrocarbon or a halogenated hydrocarbon which is free from OH and NH 2 groups. u A process as claimed in any preceding daim which is earned out at a temperature σf 20 to 60*C.

Inventors: REEVE CHRISTOPHER DAVID, REEVE, CHRISTOPHER, DAVID
Applicants: REEVE CHRISTOPHER DAVID, ZENECA LTD, REEVE, CHRISTOPHER, DAVID, ZENECA LIMITED
Application year: 1998
Main classification: C12P41
IPC codes: C12P13, C12P41