ENZYMATIC ASYMMETRIC REDUCTION PROCESS TO PRODUCE 4 H-THIENO(2,3-6)THIO PYRANE DERIVATIVES

Abstract: A compound of formula (I), in which X is hydrogen or a group of formula -SO2NH2 is reduced to the trans (4S, 6S) form of the corresponding alcohol by an enzyme reduction system.

Description: ENZYMATIC ASYMMETRIC REDUCTION PROCESS TO PRODUCE 4 H - THIENO (2 , 3-6) THIO PYRANE DERIVATIVES . THIS INVENTION relates to an asymmetric reduction process. The compound is a topically active carbonic anhydrase inhibitor which is proposed for treatment of glaucoma. The compound with a methyl substituent in the 6 position in which the orientation is trans with regard to the 4-substιtuent (the 4S,6S diastereoisomer) is of therapeutic interest, but it is difficult to produce in the absence of a preponderant amount of the cis isomer (the 4R.6S diastereoisomer). We have devised a process for producing a compound of formula in which X is hydrogen or a group of formula -SONH- which is a useful intermediate in the production of the desired trans (4S,6S) isomer III described above and derivatives thereof in an amount greater that that of the corresponding cis isomer from a compound of formula I X = -H or -SO;, NH 2 Background chemistry related to the synthesis of these materials is disclosed in Jones, et al, J.Org.Chem 1991 56 763-769, Shinkai, J. Heterocyclic Chem. (1992) 29 627-639 and US Patents 4,968,814 and 4,968,815, and, in a publication made subsequently to the priority of this patent application, by Blacklock et al J. Org Chem. 1993 58 1 672-1 679. The reduction of compound (I) using reducing agents such as borane- tetrahydrofuran complex results in the formation of the (4R,6S) diastereoisomer (IV) as the major product ( > 90%) with the desired (4S,6S) trans diastereoisomer (II) accounting for a minor proportion of the product. Jones et al, J Org. Chem. (1991 ), 5_6, 763-769 have disclosed a method for the enantioselective reduction of a close analogue, compound (V), using bakers yeast (Saccharomyces cerevisiae). This reaction yields the (R)- and (S)- alcohols in the ratio 1 1 :89. 1 1 % 89% V VI VII However, when a range of bakers' and brewers' yeasts were tested in the reduction of compound (I) the undesired cis diastereoisomer was the major product (60 to 85%). Examination of a wider range of microorganisms (bacteria, yeasts and fungi) demonstrated that most produced predominantly the undesired cis diastereoisomer. Surprisingly, however, we have found that it is in fact possible to produce the trans isomer in preponderant yield by enzyme reduction and have identified a range of microorganisms including bacteria, fungi and yeasts which are able to reduce compound (I) to the desired trans alcohol (ID. This invention comprises a process in which a compound of formula in which X is hydrogen or a group of formula S0 2 NH 2 s converted into a compound of formula by contacting it with an enzyme reduction system Suitable systems comprise a suitable oxido reductase enzyme and the reduced form of a co-factor for the enzyme. The enzyme reduction system may be provided as whole or broken cells of suitable microorganisms By "selectively" is meant that more of the trans (4S,6S) isomer is produced than of the cis (4R,6S) isomer. Preferably at least 60% and more preferably at least 80% for example at least 90% of the product is the trans isomer. The process is preferably carried out at a pH of at most 8 and more preferably at most 6. We have found that the stereospecificity of the process is improved by operation under acidic conditions and it is preferred that it be carried out at a pH of 2 to 5. Microorganisms containing the enzyme reduction systems are surprisingly resistant to such conditions. Suitable oxido reductases may be found by a process of screening. Examples of suitable reductases are those from Lactobacillus plantarum NCIMB 40027, Pichia haplophila CBS 2008, Candida utilis NCYC 322, Lactobacillus buchneπ NCIMB 881 8, Aspergiilus flavus oryzae IMI 51 983 or especially that from Neurospora crassa IMI 1 9419. In general, bakers' and brewers' yeasts give the undesired cis product. The co-factor may be for example, NADH, NADPH, FADH, FMNH and/or PQQ or any cofactor which occurs with the aforesaid enzyme in a microorganism. Preferably means to reduce the co-factor continuously are also present. Very suitably the enzyme and co-factor may be supplied as broken or preferably whole cells of suitable microorganisms, and the cells may be supplied with a suitable substrate, for example a carbohydrate especially a sugar substrate, for example glucose, fructose or sucrose or glycerol or lactic acid. Such cells in general comprise means to reduce the co-factor by utilising the substrate. The process is suitably carried out at temperatures of 20° C to 40°C preferably in aqueous media in which the pH may be pH2 to pH6 and preferably pH3 to pH5 and the concentrations of the reactant are suitably 5 g/litre to 1 0 g/litre. Substrate e g glucose is suitably present in concentrations of 5 g litre to 50 g/litre and other nutrients for example yeast extract may be present. EXAMPLE 1 Reduction of Ketone (I) (where X = H) using tetrahydrofuran- borane complex. To an oven dried 250 ml round bottom flask was added ketone (I) (500 mg) and the headspace flushed with dry nitrogen To the flask was added 25 ml of anhydrous tetrahydrofuran and the resulting solution was stirred on ice to bring the temperature down to 5 °C. Tetrahydrofuran-borane complex ( 1 .0 molar, 3ml) was added dropwise during 1 5 minutes whilst maintaining the temperature at 5 °C. After the final addition of tetrahydrofuran-borane complex the mixture was stirred for a further 30 minutes whilst allowing it to reach room temperature Residual tetrahydrofuran-borane was quenched with methanol (25 ml), stirred for 30 minutes then a further 50 ml of methanol added. The product was recovered by removing the solvent under reduced pressure. The product was analysed by high pressure liquid chromatography (HPLC) using a Nova-Pak C 1 β column (3.9mm internal diameter x 300 mm). Product and starting material were eluted using a solvent gradient consisting of 20 mM aqueous phosphoric acid and acetonitnle under the following conditions: time zero to 10 minutes aqueous phosphoric acid (20 mM), 92.5%: acetonitnle 7.5%; time 10 to 25 minutes the acetonitnle concentration was increased linearly to 27.5% whilst the aqueous phosphoric acid was decreased to 72.5%. The solvent flow rate was 1 .0 ml/minute. The alcohols were eluted at 16 minutes (cis) and 17 minutes (trans) whilst the ketone was eluted at 24 minutes. Analysis performed on the sample obtained as described above indicated a yield of combined alcohols of 89% with a cιs:trans ratio of 9.1 EXAMPLE 2 Reduction of Ketone (I) (where X = H) using whole cells of the bacterium Lactobacillus plantarum Cells of L plantarum NCIMB 40027 were grown in Oxoid MRS medium (obtained as a preformulated powder from Unipath Ltd., Basingstoke, England). Eight two litre conical flasks each containing 1 .5 litres of medium were inoculated with L plantarum NCIMB 40027 and incubated at 28° C for 24 hours on a rotary shaker. Cells were recovered by centπfugation and washed by resuspension in 100 mM sodium/potassium phosphate buffer pH 7.0. Following recentπfugation the cells were resuspended in 500ml of sodium/potassium phosphate buffer (100 mM, pH 7.0) to a concentration of 33g/litre and added to a 1 litre conical flask. Ketone (I), 1 .25g, was dissolved in acetone, 2.5ml, and added to the cell suspension along with 25g of glucose. The mixture was incubated at 28°C on a rotary shaker for 24 hours. Cells were removed by centrifugation and the supernatant extracted with 500 ml of dichloromethane. The aqueous phase was then saturated with sodium sulphate and re-extracted with 500 ml of dichloromethane. The combined dichloromethane extracts were dried with anhydrous magnesium sulphate and the solvent removed by rotary evaporation to yield a mixture of alcohol and residual ketone (I). The alcohol was purified by flash chromatography on a commercially available silica gel (Merck Kieselgel 60) (70-230 mesh ASTM) by elution with ethyl acetate: hexane (87.5: 12.5 by volume) to yield 349mg of trans alcohol (II) and 41 mg of cis alcohol (IV) as determined by the method of Example 1 . EXAMPLE 3 Reduction of ketone (I) (where X = H) using mycelium of the fungus Neurospora crassa. Neurospora crassa IMI 19419 was grown in a mineral salts medium containing the following components (g/litre) glucose, 20; yeast extract, 2; dipotassium hydrogen phosphate, 1 .9; sodium dihydrogen phosphate, 1.56; ammonium sulphate, 1 .8; magnesium sulphate heptahydrate, 0.1 ; ferric chloride, 0.001 ; calcium carbonate. 0.002; zinc sulphate heptahydrate, 0.0001 ; manganese sulphate tetrahydrate, 0.0001 . Two litre conical flasks containing one litre of medium were inoculated with spores of Neurospora crassa and incubated for 48 hours at 28°C on an orbital shaker. The mycelium was recovered by filtration through a Whatman grade 1 13 filter paper and washed with water. Mycelium was resuspended to a concentration of 20g dry weight/litre in 9.37ml of sodium/potassium phosphate buffer (pH 7.0 or pH 8.0, 100 mM) and transferred to 15ml screw cap vials. To the vials was added glucose (0.5ml of a 50% solution) and a solution of ketone (I), 65 mg dissolved in acetone (0.13ml). The vials were sealed and incubated with shaking at 28 °C for 21 hours. Analysis of the cell free supernatants by HPLC (as described in Example 1 ) indicated quantitative conversion of ketone to alcohol at both pH 7.0 and pH 8.0. At pH 7.0 the ratio of trans alcohol (II): cis alcohol (IV) was 94:6 whilst at pH 8.0 it was 89:1 1 . EXAMPLE 4 Reduction of ketone (I) (where X = H) using whole cells of the yeast Pichia haolophila CBS 2008. Cells of Pichia haolophila CBS 2008 were grown in the mineral salts, glucose, yeast extract medium described in Example 3. Two litre baffled conical flasks containing 400 ml of medium were inoculated with yeast and incubated for 48 hours at 28°C on an orbital shaker. Cells were recovered from the culture by centrifugation and washed by resuspension in 100 mM citrate/phosphate buffer, pH 5.0. Cells were then resuspended to a final concentration of 6g dry weight/litre in the citrate/phosphate buffer pH 5.0 and 10 ml dispensed into a 20 ml screw capped vial. To the vial was added glucose (0.2ml of a 50% solution) and 14.5 mg of ketone (I) dissolved in 25μl of acetone. The mixture was incubated at 28°C for 22 hours on an orbital shaker, cells were removed by centrifugation and the supernatant analysed by HPLC as described in Example 1 . The recovered supernatant contained no residual ketone, 0.65mg cis alcohol (IV) and 12.13 mg of trans alcohol (II). EXAMPLE 5 Example 4 was repeated using each of the microorganisms shown in the following table except that the cells were suspended in Na/K phosphate buffer (pH 7) (100 mM). The cell concentrations were 10-30g dryweight/litre. The conversions of the ketone fed and the percentage of trans isomer in the total reduced products are shown in Table 1 . TABLE 1 Microorganism Neurospora crassa IMI 19419 Lactobacillus plantarum NCIMB 40027 Pichia haplophila CBS 2008 Candida diddensiae ATCC 20213 Candida utilis NCYC 322 Pseudomonas oleovorans ATCC 29347 Fusarium graminearum IMI 346762 Hansenula anomala CBS 2230 Torulospora hansenii ATCC 20220 Lactobacillus buchneri NCIMB 8818 Lactobacillus buchneri NCIMB 8037 Lactobacillus brevis NCIMB 1777 Lactobacillus fermentum NCIMB 6991 Streptomyces lividans Aspergillus flavus oryzae IMI 51983 Geotrichum candidum IMI 45619 Arthrobacter petroleophagus ATCC 21494 Candida lipolytica IFO 1437 Pichia farinosa CBS 2007 Pichia farinosa CBS 2006 Pseudomonas putida NCIMB 9427 Corynebacterium species ATCC 15529 Corynebacterium paurometabolum ATCC 15530 Pseudomonas aeruginosa ATCC 15525 Beauveria bassiana ATCC 7159 Beauveria bassiana NRRL 3352 Proteus vulgaris NCIMB 67 Xanthomonas campestris ATCC 13951 Proteus mirabilis NCIMB 8268 Beauveria brongniartii CBS 722.71 Streptococcus faecium NCIMB 30013 Saccharomyces cerevisiae NCYC 240 Candida oleophilia ATCC 20177 Pichia pastoris BPCC 420 Table 1 Continued Microorganism Zygosaccharomyces rouxii NCYC 564 Pichia capsulata CBS 837 Geotrichum candidum IMI 96825 Candida chalmersi NRRL Y 1260 Pichia trehalophilia CBS 5361 EXAMPLE 6 Dependence on pH of racemisation of ketone (I) (Where X = H). A 50% w/w solution of ketone (I) in acetone was made up (the enantiomeric excess of the (6S) ketone was 98.0%). Into separate vials was dispensed 2ml of the following aqueous buffers (each supplemented with 50mg of glucose to mimic biotransformation conditions) - sodium acetate (0.1 M), pH 4.3; sodium citrate (0.1 M), pH 5.0; potassium phosphate (0.1 M), pH 6.5; sodium borate (0.05M); pH 9.0. To the buffer solutions was added 10mg of ketone I (as a solution in acetone), the vials were capped and maintained with shaking at 28°C. At intervals vials were extracted with ethyl acetate (1 ml twice), the organic layer separated, dried with anhydrous sodium sulphate and the ketone recovered by removal of solvent under a stream of dry nitrogen. The optical purity of the recovered ketone was determining by high pressure liquid chromatography (HPLC) using a Chiralcel O.D. column (0.46mm internal diameter x 250mm) with hexane:ethanoi (9:1 ) as eluant, eluant flow rate 1 ml/minute and detection by UV absorbtion at 240nm. The (R)-enantiomer eluted at 22.5 minutes whilst the (S)- enantiomer eluted at 24.2 minutes. Separate vials were extracted for each time point. The results are shown in Table 2. TABLE 2 - pH- DEPENDENCE OF RACEMISATION OF KETONE (I) Enantiomeric Excess of (6S) - Ketone n.d. - not determined EXAMPLE 7 Reduction of Ketone (I) (Where X = H) using mycelium of the fungus Neurospora crassa maintained at pH 4. Neurospora crassa IMI 19419 was grown in a Braun Biostat ED fermenter (15 litre working volume). The medium contained the following components (g/litre) glucose, 40; yeast extract, 2; magnesium sulphate heptahydrate, 1 .2; dipotassium sulphate, 0.21 ; potassium dihydrogen phosphate, 0.69; phosphoric acid, 1 .7; ferric chloride, 0.05; calcium carbonate, 0.07; zinc sulphate heptahydrate, 0.0035; manganese sulphate tetrahydrate, 0.0035; polypropylene glycol antifoam, 2. Ammonium hydroxide was used to bring the solution to pH 6.5 prior to inoculation. The fermenter was inoculated with 400ml of culture previously grown for 24 hours using the medium and growth conditions described in Example 3. During fermentation the following parameters were controlled at the stated values, temperature 28°C; pH, 6.5; air flow, 7.5 litres/minute; stirrer speed, 400 rpm. The culture was grown under these conditions for 30 hours at which point the mycelial concentration had reached 8.2g dry weight/litre. At this point the temperature was increased to 34°C, the stirrer speed was automatically controlled to maintain a dissolved oxygen tension of 40% saturation and 2 molar hydrochloric acid was added to the fermenter to bring the culture to pH 4.0. Ketone (I), 107g, was dissolved in 300ml of acetone. The acetone solution of ketone was added to the fermenter in small aliquots (15-30ml) over a period of 13 hours. The rate of addition of ketone was adjusted such that the steady state concentration of ketone remained below 0.2g litre. This was monitored using the HPLC method described in Example 1 . When the ketone had been completely transformed the culture broth was removed from the fermenter and filtered through a Whatman 1 13 filter paper. The aqueous filtrate was extracted twice with 0.5 volume of ethyl acetate. The solvent was dried using anhydrous sodium sulphate and then removed by vacuum distillation to yield 90.9g of alcohol. The relative concentrations of the four disastereoisomers of the product alcohol were determined using two separate HPLC methods. The first method used a chiral stationary phase, Chiralcel O.D. (4.6mm internal diameter x 250mm); eluant, hexane: ethanol (9:1 ); eluant flow rate, 1 .Oml/minute; detection by UV absorption at 250mm. The retention times were: (4S,6S) and (4R,6R) trans alcohols coeluted at 16.0 minutes; (4R,6S) cis alcohol, 16.8 minutes and (4S,6R) cis alcohol, 19.0 minutes. In the second method derivatives were made by reacting the alcohols with (S)-σ-methoxy-σ- (trifluoromethyl) phenylacetyl chloride according to the method of Dale, Dull and Mosher, J. Org. Chem. 2 , (9), 2543-2549 (1969). The derivatives were separated using a Zorbax silica column (4.6mm internal diameter x 250mm); eluant, hexane: ethyl acetate (9:1 ); eluant flow rate, 2.0ml/minute: detection by UV absorption at 260nm. The retention times were: (4R 6R) trans alcohol, 20.1 minutes; (4S, 6S) trans alcohol and (4S, 6R) cis alcohol coeluted, 22.5 minutes; (4R, 6S) cis alcohol, 23.7 minutes. The results of chromatographic analysis are shown in Table 3. TABLE 3 - RATIO OF DIASTEREOISOMERS OF ALCOHOL (II) 1 ) Direct analysis on Chiralcel O.D. diastereoisomer percentage of total alcohol (4R, 6S) 0.8% (4S, 6R) 0.3% (4S, 6S) plus (4R, 6R) 98.9% 2) MTPA derivative analysis diastereoisomer percentage of total alcohol (4R, 6S) 0.7% (4R, 6R) 0.1 % (4S, 6S) plus (4S, 6R) 99.2% IMI - International Mycological Institute, Ferry Lane, Kew, Surrey United Kingdom TW9 3QR NCIMB - National Collection of Industrial and Marine Bacteria Ltd 23 St Machar Drive, Aberdeen United Kingdom AB2 1 RY ATCC - American Type Culture Collection, 1 2301 Parklawn Drive Rockville, Maryland 20852 United States of America CBS - Centraal Bureau voor Schimmelcultures, Oosterstraat 1 3470 A G Baarn, Netherlands IFO - Institute for Fermentation, 17-85 Juso-honmachi 2-chome Yodogawa-ku, Osaka 532, Japan NRRL - Agricultural Research Service Culture Collection 1815 North University Street, Peoria, Illinois 61604 USA NCYC - National Collection of Yeast Cultures, The Food Research Institute, Colney Lane, Norwich, United Kingdom NR4 7UA 93TJL13S/MS - 20 Sep 1 993

Claims: CLAIMS 1 A process in which a compound of formula 0 . Me 0 0 in which X is hydrogen or a group of formula SO, NH, is converted into a compound of formula by contacting it with an enzymic reduction system. 2 A process as claimed in Claim 1 in which the enzymic reduction system is provided as whole or broken cells of a suitable microorganism. 3 A process as claimed in Claim 1 or 2 in which at least 90% of the product is the 4S, 6S isomer. 4 A process as claimed in any preceding claim in which the pH is 2 to 5. 5 A process as claimed in any preceding claim in which the reductase is from Lactobacillus plantarum, Pichia haplophila, Candida utilis, Lactobacillus buchneri, Aspergillus flavus oryzae or especially that from Neurospora crassa. 6 A process as claimed in any preceding claim in which the enzyme system is supplied as whole cells of a suitable microorganism and a substrate is provided the utilisation of which permits the reduction of a co-factor for the enzyme in the enzymic reduction system. 7 A process as claimed in Claim 6 in which the substrate is glucose, fructose, sucrose, glycerol or lactic acid. 8 A process as claimed in any preceding claim in which the temperature is 20°C to 40°C. 9 A process as claimed in any preceeding claim in which the concentration of the reactant is 5 to 50g/litre. 10 A process as claimed in any preceding claim in which 5 to l Og per litre of glucose is present.

Inventors: HOLT ROBERT ANTONY, RIGBY STUART RICHARD, HOLT, ROBERT, ANTONY, RIGBY, STUART, RICHARD
Applicants: HOLT ROBERT ANTONY, RIGBY STUART RICHARD, ZENECA LTD, ZENECA LIMITED
Application year: 1993
Main classification: C12P41
IPC codes: C07D495, C12P17, C12P41, C12R1