REDUCTION OF KETONE GROUPS

Abstract: A compound of formula (III) is produced by selectively reducing a compound of formula (II) using a reductase possessing the properties of one produced by Beauveria, Candida, Kluyveromyces, Torulaspora or Pichia or a compound of formula (IV) is produced by selectively reducing a compound of formula (II) using a reductase possessing the properties of one produced by Candida pelliculosa, Neurospora crassa, Pichia trehalophila or preferably Hansenula anomola.

Description: REDUCTION OF KETONE GROUPS THIS INVENTION relates to the reduction of ketone groups. It is knovm from Brower et al. Tetrahedron letters 1992, pages 2279-2282 to synthesise a compound of formula by diastereoselective reduction of a compound of formula using the method of Chen et al, Tetrahedron Letters 1987 22.155 and Chem Lett 1987 1923 followed by protection as the acetonide. A cross Claisen approach to coinpound (1) was also reported. These routes involved the use of temperatures of -90°C, which renders them expensive and inconvenient. Compound (1) may be used as an intermediate in the synthesis of CI-981, an inhibitor of HMG CoA reductase which reduces total plasma and low density lipoprotein cholesterol in man. Its key structural feature may also be derived from a compound of formula OH OH 0 (HD NC \ ^ A 0 R In the above formula R is an alkyl group, preferably having 1 to 6 carbon atoms and is more preferably a t- butyl group. We have found that compound (III) may be produced by reduction of compound (II) with moderate to high selectivity and at convenient temperatures using a ketone reductase commonly found among species of the genera Beauveria, Pichia, Candida, Kluyveromyces, and Torulaspora but that in each genus exceptions may occur or possibly the enzyme will be accompanied by one of opposite stereospecificity. The invention therefore comprises producing a compound of formula (III) by selectively reducing a compound of formula (II) using a reductase possessing the properties of those produced by a microorganism selected from Beauveria preferably Beauveria bassiana, Pichia preferably Pichia pastoris, haplophila or membranefaciens, Candida preferably Candida humicola, solani, diddenssiae or friedrichii, Kluyveromyces preferably Kluyveromyces drosophilarum, or Torulaspora preferably Torulaspora hansenii and preferably Pichia angusta. The invention also comprises producing a compound of formula (III) by selectively reducing a compound of formula (II) using whole cells of or extracts from the said microorganisms preferably Beauveria bassiana, Pichia pastoris, Pichia haplophila, Pichia membranefaciens, Candida humicola, Candida solani, Candida diddensiae, Candida friedrichii, Kluyveromyces drosophilarum, Torulaspora hansenii or preferably Pichia angusta. The invention is preferably carried out using whole cells of the organism as this avoids the need to separate the desired enzyme and provides co-factors necessary for the reaction. Any of the above species may be used but in order to obtain high conversions and high selectivity it is preferred to use the enzyme or whole cells of Pichia haplophila, or more preferably Pichia angusta. In general a co-factor, normally NAD(P)H (nico¬ tinamide adenine dinucleotide or nicotinamide adenine dinucleotide phosphate) and a system for re-generating the co-factor, for example glucose and glucose dehydrogenase, are used with the enzyme to drive the reaction. As suitable co-factors and reduction mechanisms are present in the whole cells it is preferred to use the whole cells in a nutrient medium which preferably contains a suitable carbon source, which may include one or more of the following: a sugar, e.g. maltose, sucrose or preferably glucose, a polyol e.g. glycerol or sorbitol, citric acid, or a lower alcohol, for example methanol or ethanol. If whole cells are intended to grow during the reaction nitrogen and phosphorus sources and trace elements should be present in the medium. These may be those normally used in culturing the organism. The process may be carried out by adding a compound of formula II to a culture of the growing organism in a medium capable of supporting growth or to a suspension of the live cells in a medium which preferably contains a carbon source but which lacks one or more nutrients necessary for growth. Dead cells may also be used providing the necessary enzymes and co-factors are present; if necessary they may be added to the dead cells. If desired the cells may be immobilised on a support which is contacted with compound of formula II preferably in the presence of a suitable carbon source as previously described. The pH is suitably 3.5 to 9, for example 4 to 9, preferably at most 6.5 and more preferably at most 5.5. Very suitably a pH of 4 to 5 is used. The process may suitably be carried out at a temperature of 10 to 50°C, preferably 20 to 40°C and more preferably 25 to 35°C. It is preferred to operate under aerobic conditions if live whole cells of the aforesaid organisms are present. An aeration rate equivalent to 0.01 to 1.0 volumes of oxygen measured at standard temperature and pressure per volume of the culture medium per minute is suitably employed at the aforesaid conditions of pH and temperature but it will be appreciated that considerable variation is possible. The oxygen may be supplied as air. Similar pH temperature and aeration conditions may be used during growth of the organisms if this is carried out separately from the process. Purified enzymes may be isolated by known means suitably by centrifuging a suspension of disintegrated cells and separating a clear solution from debris, separating the desired enzyme from the solution for example by ion exchange chromatography suitably with elution from the column with liquid of increasing ionic strength and/or by selective precipitation by the addition of an ionic material, for example ammonium sulphate. Such operations may be repeated if desired to enhance purity. EXAMPLE 1 Preparation of the Can-pound of formula (III). Microorganisms were maintained on YM (Oxoid Company) agar plates prepared by dissolving 41g of yeast and mold agar in IL of distilled water and sterilizing in an autoclave. For growth in liquid medium a loopful of microbial cells was aseptically transferred from an agar plate to a IL baffled flask containing 200 ml of mineral salts medium of composition (per litre) K 2 HP0 4 (1.9g), NaH 2 P0 4 .2H 2 0 (2.02g) (NH 4 ) 2 S0 4 (1.8g), MgS0 4 7H 2 0 (0.2g), FeCl 3 (0.97 mg) and trace elements solution (lml). Trace elements solution consisted of (per litre) CuS0 4 .5H 2 0 (0.02g), MnS0 4 .4H 2 0 (O.lg), ZnS0 4 .7H 2 0 (O.lg) and CaC0 3 (1.8g) . The minimal medium was supplemented with 0.2% (w/v) yeast extract and 2.25% (w/v) glucose. Microorganisms were grown at 28°C on an orbital shaker at 150 rpm for 24-48 hours. Microbial cells were harvested by centrifuging at 7000 rpm for 20 minutes at 10°C. The cell pellet was resuspended in 100 ml of 50 mM sodium phosphate buffer, pH 6.4 and the cells washed by centrifuging as above. The cell pellet was finally resuspended in 50 ml of the above buffer. To the 50 ml of cell suspension in a 250 ml baffled flask was added glucose (10 g per litre) and the compound of formula II (2 g per litre) . The cells were incubated at 28°C on a rotary shaker at 150 rpm for 18-24 hours. The entire reaction broth was extracted with 2 x 1 volume of ethyl acetate. In many cases an emulsion was formed which was broken by centrifuging at 10,000 rpm for 5 minutes at 28°C. The pooled ethyl acetate extracts were dried over anhydrous sodium sulphate and the solvent removed by vacuum distillation to afford a golden oil. The extent of conversion of the compound of formula II to the compound of formula III and the enantiomeric composition of the compound of formula III was determined by HPLC (high pressure liquid chromatography) . The conditions for HPLC are described below: HPLC : Waters 590 programmable pump. Column : "Chiralcel" OJ (250mm x 4.6mm) (Chiracel is a trade mark of Diacel Chemical Industries Ltd) with a Guard Column 50mm x 4.6mm of lOμm Particle size. Solvent Hexane; Ethanol (95:5) Flow Rate 1 ml min' 1 Temperature Ambient Detection Refractive Index Waters differential refractometer R401 The retention times of the compounds of formula II, III and the diastereoisomer of III, IV were 43 minutes, 27 minutes and 21 minutes respectively. The results obtained are summarised in Table 1. TABUS 1 Microorganism Conversion Ratio of (%) Compound III : IV Beauveria bassiana ATCC 7159 34 17:1 Candida humicola CBS 1897 8 > 20:1* Candida diddensiae ATCC 20213 2 > 20:1* Candida frieddrichii ATCC 22970 3 > 20:1* Candida solani CBS 1908 7 12:1 Hansenula nonfermentans CBS5764 75 1.8:1 Kluyveromyces drosophilarum CBS 5 6:1 2105 Pichia angusta NCYC 495 100 110:1 Pichia angusta NCYC R320 + 98 >100:1* Pichia angusta NCYC R322 * 98 >100:1* Pichia haplophila CBS 2028 97 33:1 Pichia membranefaciens DSM 4 >20:1* 70366 Pichia pastoris BPCC 260 20 >20:1* Pichia pastoris BPCC 443 17 >20:1* Pichia pastoris NCYC R321 * 20 >20:1* Torulaspora hansenii ATCC 20220 17 >20:1* * Compound IV not detected. Results based on detection limit for compound IV. + Deposited under the provisions of the Budapest Treaty on 18 May 1995. EXAMPLE 2 Preparation of the compound IV, the diastereoisomer of compound of formula XII Microorganisms were maintained and grown as described in Example 1. The biotransformation and analysis was also performed exactly as described in Example 1. The results are summarised in Table 2. TABLE 2 Microorganism Conversion Ratio of (%) Compound V : III Candida pelliculosa ATCC 2149 98 9:1 Hansenula anomola CBS 2230 85 37:1 Neurospora crassa ATCC 9277 58 10:1 Pichia trehalophila CBS 5361 65 3:1 It will be seen from the above results that certain members of each genus Candida and Pichia produce both diastereoisomers. The specificity of for example Pichia angusta on the one hand and Hansenula anomola on the other for different diastereoisomers indicates the existence of two enzymes of opposite stereospecificity and both and/or a further enzyme of lesser stereo- specificity may be present in some species . EXAMPLE 3 Growth of Pichia angusta NCYC R320 in fermenters and in altu preparation of the compound of formula (III) (R-t- butyl) Pichia angusta NCYC R320 was grown in both batch and fed-batch culture in a Braun Biostat ED/ER5 5L fermenter. Growth in batch culture was performed in 5L of medium of composition (per litre) glucose, 40g; MgS0 4 7H 2 0, 1.2g; K 2 S0 4 , 0.21g; KH 2 P0 4 , 0.69g; H 3 P0 4 (17M) , lml; yeast autolysate, 2g; FeS0 4 7H 2 0, 0.05g; polypropylene glycol antifoam, 0.3ml; trace element solution, 2ml. The trace element solution comprises (per litre) ZnS0 4 7H 2 0, lOg; MnS0 4 4H 2 0, lOg; CuS0 4 5H 2 0, lg and H 3 P0 4 (11.6M), lml. The medium was prepared in tap water. The medium was adjusted and controlled at the desired pH by addition of 7M NH 4 OH. Growth in fed-batch culture was performed as described for batch culture except that when the glucose concentration had decreased to <10g/L, IL of the fermentation broth was aseptically removed and IL of medium of composition (per litre) glucose, 240g; yeast autolysate, 7g; FeS0 4 7H 2 0, 0.175g, polypropylene glycol antifoam, lml and trace element solution, 7ml, was fed in at a rate sufficient to maintain the glucose concentration in the range 2 to 5g/L. Fermentations performed under both batch and fed- batch culture were initiated by the addition of an inoculum of Pichia angusta NCYC R320. The inoculum was prepared in 200ml of the mineral salts medium described in Example 1 and was grown at 28°C on an orbital shaker at 150 rpm for 18-20 hours. Prior to inoculation of the fermenter the inoculum was diluted 10-fold in sterile medium of the same composition. Fermentations were performed under the following conditions of pH, temperature, aeration and agitation until a dry cell weight in the range 10 to 15g/L was obtained: Temperature: 28, 34, 40°C pH: 4.5, 5.5, 6.5 Aeration: 0.1, 1.0 wm (volume air per volume of medium per minute) Agitation: 600 rpm The preparation of the compound of formula (III) (R=t-butyl) was initiated by the addition of the compound of formula II (R=t-butyl) as a crude oil of approximately 65% w/w concentration the balance being substantially t- butyl aceto acetate. The compoimd of formula (II) (R=t- butyl) was added as a continuous feed at a rate sufficient to maintain its concentration at typically 1 to 5g/L, preferably at 2g/L. Solid glucose was added to the fermentation broth as cosubstrate to maintain a concentration of 1 to 5g/L. In each experiment the preparation of the compound of formula (III) (R=t-butyl) was performed under the same conditions of temperature, pH, aeration and agitation as for the growth stage of the microorganism. The concentration of the compounds of formula (II) (R=t-butyl) and (III) (R=t-butyl) in the fermentation broth were measured by reverse phase HPLC. The conditions for HPLC are described below: HPLC: Hewlett Packard HP 1050 Column: Waters Nova-Pak R C18 column 3.9 x 300mm dimension and 4μm particle size. Nova¬ Pak is a registerd trademark of Millipore Corporation. Solvent: 0.02M phosphoric acid in water:acetonitrile (60:40) Flow rate: lml/min Detector: Hewlett Packard HP 1047A refractive index detector Temperature: Ambient The retention times of the compounds of formula (II) (R=t-butyl) and (III) (R=t-butyl) were 4.0 minutes and 3.1 minutes respectively. On completion of the bioreduction stage the fermentation broth was centrifuged at 5000 rpm for 20 minutes at 20-22°C. The compound of formula (III) (R=t-butyl) was isolated from the supernatant by extraction with a suitable organic solvent such as toluene, isoamyl acetate, 2-pentanone, ethyl acetate or 4-methyl-2-pentanone, preferably ethyl acetate or 2-pentanone. The solvent extract was dried over anhydrous sodium sulphate and the solvent removed by vacuum distillation to afford the crude product of formula III (R=t-butyl) as a golden oil. The ratio of the compound of formula (III) (R=t-butyl) to its diastereoisomer (IV) (R= -butyl) was either measured by HPLC of the crude product following the procedure described in Example 1 or by HPLC measurement of the ratio of the corresponding iso- propylidene derivatives (I) and its diastereoisomer(V) under the following conditions: HPLC: Hewlett Packard HP 1050 Column: YMC ODS AQ303 4.6 x 250mm dimension and 5μm particle size. Available from Hichro Limited. Solvent: Methanol:water (50:50) Flow rate: lml/min Detector: Hewlett Packard HP 1047A refractive index detector Temperature: Ambient The retention times of the compounds of formula (I) and (V) were 31.0 minutes and 35.5 minutes respectively. EXAMPLE 4 Preparation of the isopropylidene derivative (I) and its diastereoisomer (V) Samples of the compound of formula (III) (R=t- butyl) , (IV) (R=t-butyl) and the crude product from bioreduction of the compound of formula (II) (R=t-butyl) were converted to the corresponding isopropylidene derivative by reaction with 2,2-dimethoxypropane in dry acetone in the presence of catalytic methanesulphonic acid. In a typical reaction 3g of the crude bioreduction product was reacted with 2,2-dimethoxypropane (7ml) in dry acetone (5ml) containing methanesulphonic acid (5μl) for 2 hours at ambient temperature. The solution was then poured into 15ml of 2% w/v aqueous sodium bicarbonate and stirred for a further 5 minutes. The resulting mixture was extracted with 30ml ethyl acetate. The ethyl acetate extract was separated, combined with 15ml n-hexane and the combined organic extract washed with 30ml distilled water. The organic phase was dried over anhydrous sodium sulphate and the solvent removed by vacuum distillation to afford a deep orange oil which solidified on cooling. EXAMPLES 5-13 Preparation of the compound of formula (III) (R= -butyl) under varying conditions of pH, temperature, aeration and fermentation regime Examples 5-13 inclusive serve to illustrate operation of the process using Pichia angusta NCYC R320 in each case at an initial dry cell weight in the range 10 to 15g/L for preparing the compound of formula (III) (R=t-butyl) from the compound of formula (II) (R=t- butyl) . The process was carried out as described in Example 3 except when indicated in Table 3. The results from operation of the process under the conditions specified in Table 3 are summarised in Table 4. The reaction profile obtained by operation of the process under the conditions specified in Example 13 is shown in Figure 1. The initial dry cell weight in this case was 12.67 g/L. TABLE 3 Example PH Temperature Aeration Fed-batch/batch (°C) (wm) culture 5 5.5 28 1 Batch 6 5.5 34 1 Batch 7 5.5 40 1 Batch 8 5.5 28 0.1 Batch 9 6.5 28 1 Batch 10 4.5 28 1 Batch 11 4.5 34 1 Batch 12 5.5 28 1 Fed-batch 13 4.5 28 1 Fed-batch WM means volume of air (measured at standard temperature and pressure) per volume of culture medium per minute. TABLE 4 10 Compound (V) was not detected in any of the samples prepared. Results were calculated 15 based on the detection limit for compound (V) using the HPLC conditions described in Example 3. ND Not determined EXAMPLE 14 Characterisation of the compound of Formula (III) (R»t-butyl) The crude product (III) (R=t-butyl) obtained by operation of the process as described in Example 5 was converted to its isopropylidene derivative (I) following the procedure described below: The crude product (145g containing 65g of III, 0.28 mole) was placed in a IL roundbottom flask equipped with a magnetic stirrer. To the flask was added dry acetone (200ml), 2,2-dimethoxypropane (294ml, 2.39 moles) and methanesulphonic acid (1.5ml) . The pH of the solution was checked by spotting a small sample onto a piece of damp pH indicator paper to ensure it was acidic. The reaction mixture was stirred at ambient temperature and the disappearance of (III) monitored by HPLC using the procedure described in Example 3. The reaction was complete in 3 hours at which point 550ml of 2% w/v aqueous sodium bicarbonate was added. The pH was again checked as above to ensure it was in the range 7-9. The mixture was transferred to a separating funnel and extracted with 400ml of ethyl acetate. The ethyl acetate was removed and the aqueous re-extracted with a further 200 ml of ethyl acetate. The ethyl acetate extracts were combined and IL of n-hexane added. The combined ethyl acetate and hexane solution was washed with 3 x IL of distilled water and the organic phase separated and dried over anhydrous sodium sulphate. The solvent was removed by vacuum distillation to yield a red oil which solidified on cooling. The isopropylidene (I) was crystallised from n-hexane and recrystallised from n-heptane to afford a white crystalline product in 81% yield. The iso¬ propylidene (I) was found to be of 98.65% chemical purity, devoid of compounds (II), (III) and (V) (R=t-butyl) and indistinguishable by both infra-red spectroscopy and 250 MHz 1 H NMR spectrometry from an authentic sample of (I) . REFERENCES: ATCC American Type Culture Collection, 123031 Parklawn Drive, Rockville, Maryland 20852 USA. CBS Centraal Bureau Voor Schimmel Cultures, Oosterstraat 1, Postbus 273, NL-3740 AG Baarn, Netherlands. DSM Deutsche Sammlung Von Mikrooorganismen und Zellkulturen GmbH, Mascheroder Weg lb, D-330 Braunschweig, Germany NCYC National Collection of Yeast Cultures Institute of Food Research, Norwich Laboratory, Norwich Research Park, Colney, Norwich NR4 7UA BPCC ZENECA Limited, Bioproducts Culture Collection (Not publicly available) 95TJL03S - MS - 11 June 1996

Claims: CIAIMS 1 A process in which a compound of formula (III) is produced by selectively reducing a compound of formula (II) using a reductase possessing the properties of one produced by Beauveria, Candida, Kluyveromyces, Torulaspora or Pichia. A process according to claim 1 in which a compound of formula (III) is produced by selectively reducing a compound of formula (II) using a reductase possessing the properties of those produced by Beauveria bassiana, Pichia pastoris, Pichia haplophila, Pichia membranefaciens, Candida humicola, Candida solani, Candida diddensiae, Candida friedrichii, Kluyveromyces drosophilarum, Torulaspora hansenii or Pichia angusta. A process as claimed in claim 1 or 2 in which the reductase is obtained from Beauveria, Candida, Kluuveromyces or Torulaspora or Pichia. A process as claimed in claim 1, 2 or 3in which the reductase is provided by the presence of whole cells of Beauveria, Candida, Kluuveromyces, Torulaspora or Pichia during the selective reduction. A process as claimed in any preceding claim in which the reductase is one produced by Pichia. A process as claimed in claim 5 in which the reductase is that produced by Pichia haplophila or Pichia angusta. A process as claimed in any preceding claim which is carried out in the presence of whole cells of an organism producing the reductase in a nutrient medium which contains a carbon source for the organism. A process as claimed in claim 7 in which nitrogen and phosphorus sources and trace elements are present. A process as claimed in claim 7 or 8 which is carried out under aerobic conditions. A process in which a compound of formula is produced by selectively reducing a compound of formula III using a reductase possessing the properties of one produced by Candida pelliculosa, Neurospora crassa, Pichia trehalophila or preferably Hansenula anomola.

Inventors: REEVE CHRISTOPHER DAVID, REEVE, CHRISTOPHER, DAVID
Applicants: REEVE CHRISTOPHER DAVID, ZENECA LTD, REEVE, CHRISTOPHER, DAVID, ZENECA LIMITED
Application year: 1996
Main classification: C12P41
IPC codes: C12P7, C12P13, C12P41