Method for preparing squalamine key intermediate

Abstract

A method for preparing a squalamine key intermediate of formula (I), wherein R is as defined in the description. In the method, 5α-chenodeoxycholic acid is used as a raw material, and is reacted with a Weinreb reagent to obtain a Weinreb amide; then, the Weinreb amide is sequentially subjected to an oxidation reaction, a ketalization reaction with ethylene glycol, and a nucleophilic reaction with an organometallic reagent, and is finally subjected to a reductase-catalyzed asymmetric carbonyl reduction reaction to obtain the compound of formula I. The method has the advantages of simple steps, high overall yield, high product purity, etc., and is suitable for industrial production.

Description

Preparation method of a squalamine key intermediate TECHNICAL FIELD

[0001] The present application belongs to the field of drug synthesis, and particularly relates to a preparation method of a squalamine key intermediate. BACKGROUND

[0002] Squalamine is an aminosteroid compound, which is initially isolated from shark tissues. Squalamine has multiple biological activities, in addition to broad-spectrum antibacterial and antiviral effects, it also has certain therapeutic effects on Parkinson's disease, malaria, obesity, asthma, and can inhibit abnormal angiogenesis occurring in the processes of age-related macular degeneration, diabetic retinopathy and cancer occurrence. The chemical name of squalamine is (3β, 5α, 7α)-3-[[3-((4-aminobutyl) amino) propyl] amino] cholestane-7, 24-diol 24-hydrogen sulfate, and its structural formula is as shown below:

[0003] The natural source of squalamine is limited, so chemical or biological synthesis of squalamine becomes an important source of squalamine. At present, the preparation methods of related squalamine key intermediates reported include:

[0004] Literature Org. Lett., Vol. 2, No. 19, 2000, 2921-2922 reports a preparation method of a squalamine key intermediate (Scheme 1). The method selects compound 1 as a raw material, obtains compound 2 through enzyme catalytic oxidation, obtains compound 3 through lithium and ammonia reduction, then obtains compounds 4 to 6 through protection, oxidation and Wittig reaction in turn, and then obtains chiral alcohol compound 7 through CBS reduction, and finally obtains squalamine key intermediate compound 8 through double bond reduction.

[0005] The route has seven reaction steps, and uses platinum carbon, chiral CBS reagent, lithium ammonia, TEMPO, borane and other reagents, which are expensive and have high operation risk coefficient, and are not conducive to scale-up production.

[0006] Another method for preparing the key intermediate of squalamine is reported in J. Org. Chem., Vol. 63, No. 11, 1998, 3786-3789 (Scheme 2). In this method, stigmasterol of formula 1' is used as the starting material. First, propenyl oxidation is carried out at the C-7 position using N-hydroxyphthalimide to obtain compound 2'; compound 2' is subjected to conjugate reduction with lithium / ammonia to obtain compound 3'; the ketone is reduced to a hydroxyl group under K-selectride conditions to obtain compound 4'; compound 4' is selectively oxidized in the presence of silver carbonate to obtain compound 5'; then the hydroxyl group is protected by benzoyl chloride and the carbonyl functional group is protected by 1,3-dioxolane to obtain compound 7'; compound 7' is subjected to ozonization to obtain compound 8'; compound 8' is subjected to Wittig addition reaction with (3-methyl-2-oxobutyl) diethyl phosphonate and sodium hydride to obtain compound 9'; compound 9' is subjected to reduction reaction with (R)-2-methyl-CBS-oxazaborolidine in a borane system to obtain compound 10'; finally, compound 10' is subjected to palladium reduction reaction to obtain the key intermediate of squalamine of formula I.

[0007] Many steps in the above route have harsh reaction conditions, for example, ozone has a risk of fire and explosion, sodium hydride is explosive, it is difficult to use in industrial scale-up, there are multi-step reflux reactions, etc.; the reagents used involve expensive reagents, such as chiral CBS reducing agent, silver carbonate, palladium reagent, etc.; and the entire route has 10 steps of reactions, which is complicated and is not conducive to commercialization. SUMMARY

[0008] In order to overcome the deficiencies in the prior art, the present application provides an improved method for preparing the key intermediate of squalamine of formula I

[0009] wherein R is a hydroxyl protecting group. The method of the present application has readily available raw materials, simple operation, high yield and high purity, and is conducive to industrial production.

[0010] Specifically, the present application provides a method for preparing a compound of formula I,

[0011] The method comprises the following steps:

[0012] Step 1: compound of formula VII is reacted with Weinreb reagent under the action of a base and a condensing agent to obtain compound of formula VI;

[0013] Step 2: compound of formula VI is oxidized under the action of an oxidizing agent to obtain compound of formula V;

[0014] Step 3: condensation of the compound of formula V with ethylene glycol to obtain a compound of formula IV;

[0015] Step 4: reaction of the compound of formula IV with an isopropyl metal organic reagent to obtain a compound of formula III;

[0016] Step 5: reaction of the compound of formula III with a compound of formula RX to obtain a compound of formula II;

[0017] Step 6: chiral asymmetric carbonyl reduction of the compound of formula II under the action of a ketoreductase to obtain a compound of formula I;

[0018] wherein R is a hydroxyl protecting group, for example, R is selected from benzoyl, C1-C6 alkyl substituted benzoyl, halogen substituted benzoyl such as m-chlorobenzoyl, halogenated C1-C6 alkyl substituted benzoyl, C1-C6 alkanoyl such as acetyl and diphenylacetyl;

[0019] X is halogen, for example, chlorine or bromine.

[0020] In one embodiment, in step 1, the compound of formula VII is reacted with a Weinreb reagent in the presence of a base and a condensing agent in an organic solvent to obtain a compound of formula VI;

[0021] The compound of formula VII as described in step 1 is 5a-chenodeoxycholic acid, which can be prepared by methods known in the art or obtained by commercially available routes.

[0022] The base as described in step 1 is an organic base selected from one or more of trimethylamine, ethylenediamine, tetramethylethylenediamine, triethylamine, N,N- diisopropylethylamine, pyridine, piperidine, piperazine.

[0023] The condensing agent as described in step 1 is selected from one or more of O-benzotriazol- N,N,N',N'-tetramethyluronium tetrafluoroborate, N,N'-dicyclohexylcarbodiimide- 1- hydroxybenzotriazole, N,N'-carbonyldiimidazole, benzotriazol-N,N,N',N'-tetramethyluronium hexafluorophosphate, l-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, O-(7-azabenzotriazol-l-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, O-[(ethoxycarbonyl) cyanomethylamino]-N,N,N',N'-tetramethylthiou- ronium hexafluorophosphate, lH-benzotriazole-l-yloxytrispyrrolidinophosphonium hexafluorophosphate, Carter's condensing agent, 2-succinimidyl-l, l,3,3-tetramethyluronium tetrafluoroborate.

[0024] The Weinreb reagent as described in step 1 is selected from N,O-diethylhydroxylamine hydrochloride or N,O-di-tert-butylhydroxylamine hydrochloride.

[0025] The reaction of step 1 is carried out at a temperature of -10 to 55 °C, for example at 0 to 10 °C; the reaction time is 2 to 15 h.

[0026] The solvent for the reaction of step 1 is selected from one or more of tetrahydrofuran, methyltetrahydrofuran, dichloromethane, ethyl acetate, isopropyl acetate, diisopropyl ether, methyl tert-butyl ether.

[0027] In one embodiment, the oxidizing agent in step 2 is selected from one or more of 2,2,6,6-tetramethylpiperidine oxide-sodium hypochlorite, peroxoacetic acid, manganese dioxide, m-chloroperbenzoic acid. Preferred are manganese dioxide and 2,2,6,6-tetramethylpiperidine oxide-sodium hypochlorite.

[0028] After completion of the reaction of step 2, it is quenched with a quenching agent selected from one or more of alcohols such as isopropanol, ethanol or methanol, sodium thiosulfate, sodium sulfite, sodium bisulfite, potassium sulfite, potassium bisulfite. Preferred is isopropanol as the quenching agent.

[0029] In one embodiment, step 3 is carried out in a solvent selected from one or more of toluene, chlorobenzene, dichloromethane, tetrahydrofuran, methyltetrahydrofuran, diisopropyl ether, methyl tert-butyl ether.

[0030] The reaction of step 3 is carried out at a temperature of 10 to 70 °C, preferably 40 to 60 °C.

[0031] The reaction time of step 3 is 2 to 8 hours.

[0032] In one embodiment, in step 4, the isopropyl metal organic reagent is selected from one or more of isopropyl lithium, isopropyl magnesium chloride, isopropyl magnesium bromide.

[0033] The molar ratio of the compound of formula IV to the isopropyl metal organic reagent is 1 :2 to 1 :6, preferably 1 :2.1 to 1 :3.

[0034] The solvent used in step 4 is selected from one or more of tetrahydrofuran, diethyl ether, 1,4-dioxane, methyltetrahydrofuran.

[0035] The reaction of step 4 is carried out at a temperature of -80 °C to -20 °C.

[0036] The reaction time of step 4 is 4 to 24 hours.

[0037] In one embodiment, the compound of formula RX in step 5 is selected from benzoyl chloride, benzoyl bromide, Ci-C6alkyl substituted benzoyl chloride, Ci-C6alkyl substituted benzoyl bromide, halogen substituted benzoyl chloride, halogen substituted benzoyl bromide, halogenated Ci-C6alkyl substituted benzoyl chloride, halogenated Ci-C6alkyl substituted benzoyl bromide, Ci-C6alkanoyl chloride, Ci-C6alkanoyl bromide, diphenylacyl chloride and diphenylacyl bromide, for example benzoyl chloride, benzoyl bromide, m-chlorobenzoyl chloride, acetyl chloride, acetyl bromide, diphenylacyl chloride and diphenylacyl bromide.

[0038] The solvent used for the reaction of step 5 is selected from one or more of tetrahydrofuran, methyltetrahydrofuran, dichloromethane, ethyl acetate, isopropyl acetate, isopropyl ether, methyl tert-butyl ether.

[0039] The reaction time for step 5 is 1.0 to 3.0 hours.

[0040] In the work-up of step 5, the organic phase is washed with an aqueous solution selected from one or more of a 10% aqueous solution of disodium hydrogen phosphate, a 10% aqueous solution of dipotassium hydrogen phosphate.

[0041] In one embodiment, the ketoreductase enzyme used in step 6 is KRED-101 or KRED-171 and the reaction temperature is 10-40°C, for example room temperature, for example 25°C; and the reaction time is 3 to 20 hours.

[0042] In one embodiment, R in the compound of formula I produced is selected from benzoyl and acetyl.

[0043] Definitions:

[0044] For the purposes of interpreting this specification, the following definitions will apply and whenever appropriate, terms used in the singular will also include the plural; and vice versa. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting.

[0045] The term "halogen" as used herein means F, CI, Br or I. Furthermore, the term "halogen substituted" group is intended to include mono- or poly-halogenated groups wherein one or more hydrogens in one or more of the same or different halogen substituents are replaced with a halogen.

[0046] "Alkyl" refers to a straight or branched chain, saturated hydrocarbon group consisting of carbon and hydrogen atoms. The term "Ci-C6alkyl" as used herein refers to a straight or branched chain, saturated hydrocarbon group having from 1 to 6 carbon atoms, examples of which are methyl, ethyl, propyl (including n-propyl and isopropyl), butyl (including n-butyl, isobutyl, sec-butyl, or t-butyl), pentyl (including n-pentyl, isopentyl, neopentyl), n-hexyl, 2-methylpentyl, and the like.

[0047] As used herein, the term "haloCi-C6alkyl" refers to a Ci-C6alkyl group as defined above wherein one or more (e.g. 1, 2, 3, 4, or 5) hydrogen atoms have been replaced with a halogen. It will be appreciated by those skilled in the art that when there is more than one halogen substituent, the halogens can be the same or different and can be located on the same or different C atoms. Examples of "haloCi-C6alkyl" groups include, for example, -CH2F, -CHF2, -CF3, -CC13, -C2F5, -C2C15, -CH2CF3, -CH2C1, -CH2CH2CF3, -CF(CF3)2, and the like.

[0048] As used herein, the term "Ci-C6alkanoyl" refers to a group of formula Ci-C6alkyl-C(=0)- wherein Ci-C6alkyl is as defined above. Examples of Ci-C6alkanoyl groups include formyl, acetyl, propionyl, butyryl, and the like.

[0049] As used herein, the term "Ci-C6alkyl substituted benzoyl" refers to a benzoyl group substituted on the phenyl ring with one or more "Ci-C6alkyl" groups as defined above.

[0050] As used herein, the term "halo substituted benzoyl" refers to a benzoyl group substituted on the phenyl ring with one or more "halogen" groups as defined above.

[0051] As used herein, the term "haloCi-C6alkyl substituted benzoyl" refers to a benzoyl group substituted on the phenyl ring with one or more "haloCi-C6alkyl" groups as defined above. DETAILED DESCRIPTION

[0052] The method of the present application is further illustrated by the following examples. It is to be understood that the following examples are provided by way of illustration and nothing therein should be taken as a limitation on the overall scope of the present application.

[0053] Unless otherwise indicated, the following various solvents and reagents are commercially available. The starting materials used are either commercially available or are readily prepared by conventional reactions well known to those skilled in the art.

[0054] Example 1: Preparation of compound (VI)

[0055] To a solution of 14 g of compound (VII) and 4.2 g of N, O-dimethylhydroxylamine hydrochloride in 140 ml of dichloromethane in a three-necked flask, 12.6 ml of DIPEA (N, N-diisopropylethylamine) was added, and the mixture was stirred for 30 min. The reaction system was cooled to 0-10 °C, and 5.22 g of EDCI (1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride) and 7.28 g of HOBT (1-hydroxybenzotriazole) were added, and the reaction was allowed to proceed for 5 h. TLC (EA: Hex: AC = 2: 1: 6 d) showed that the reaction was completed. To the reaction mixture, 60 ml of saturated brine was added to quench the reaction, and the layers were separated. To the separated organic layer, 50 ml of 2N HCl was added, and a large amount of solid was precipitated. The mixture was filtered, and the filtrate was separated into layers. The separated organic layer was washed with 50 ml of saturated aqueous sodium bicarbonate solution, and then with 50 ml of saturated brine, and the organic layer was separated, and then the organic layer was concentrated under reduced pressure to dryness. The residue was crystallized with dichloromethane and hexane. The formed crystals were filtered, and dried at 50-55 °C to obtain 15 g of compound (VI) as a solid, with a yield of 95.1% and a purity of 99.0%.

[0056] Example 2: Preparation of compound (V)

[0057] To a solution of 14 g of compound (VII) and 4.2 g of N, O-dimethylhydroxylamine hydrochloride in 140 ml of dichloromethane in a three-necked flask, 12.6 ml of DIPEA (N, N-diisopropylethylamine) was added, and the mixture was stirred for 30 min. The reaction system was cooled to 0-10 °C, and 5.22 g of EDCI (1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride) and 7.28 g of HOBT (1-hydroxybenzotriazole) were added, and the reaction was allowed to proceed for 5 h. TLC (EA: Hex: AC = 2: 1: 6 d) showed that the reaction was completed. To the reaction mixture, 60 ml of saturated brine was added to quench the reaction, and the layers were separated. To the separated organic layer, 50 ml of 2N HCl was added, and a large amount of solid was precipitated. The mixture was filtered, and the filtrate was separated into layers. The separated organic layer was washed with 50 ml of saturated aqueous sodium bicarbonate solution, and then with 50 ml of saturated brine, and the organic layer was separated, and then the organic layer was concentrated under reduced pressure to dryness. The residue was crystallized with dichloromethane and hexane. The formed crystals were filtered, and dried at 50-55 °C to obtain 15 g of compound (VI) as a solid, with a yield of 95.1% and a purity of 99.0%.

[0058] Example 3: Preparation of compound (IV)

[0059] To a 250 mL four-necked flask, fitted with a water separator, was added 12 g of compound (V) and 120 mL of toluene. The reaction mixture was heated to 60 °C. A mixture of 0.24 g of p-toluenesulfonic acid and 8.0 g of ethylene glycol was added and the reaction mixture was heated to 85-90 °C to form a clear solution. The reaction mixture was heated to reflux (external temperature 120 °C) for 4-6 h. At this time, TLC (acetone:hexane = 3:7) showed that the reaction was complete. The heating was turned off and the reaction mixture was allowed to cool to room temperature. The reaction was quenched by the addition of 80 mL of 10% potassium carbonate solution and the layers were separated. To the organic layer was added 100 mL of 5% brine and 0.8 g of potassium bicarbonate and the layers were separated. The combined aqueous layers were back extracted with 60 mL of toluene. The layers were separated and the combined organic layers were concentrated to dryness under reduced pressure. To the residue was added 100 mL of acetonitrile and 0.04 mL of triethylamine. The mixture was slurried at 55 °C for 1 h, cooled to 0-5 °C and stirred for 1 h. The mixture was filtered. The filter cake was slurried in 100 mL of acetonitrile at 55 °C for 1 h, cooled to 0-5 °C and stirred for 1 h. The mixture was filtered and the filter cake was dried under reduced pressure to give compound (IV) in 99.0% yield and 99.1% purity.

[0060] Example 4: Preparation of compound (III)

[0061] To a 250 mL four-necked flask, fitted with a water separator, was added 12 g of compound (V) and 120 mL of toluene. The reaction mixture was heated to 60 °C. A mixture of 0.24 g of p-toluenesulfonic acid and 8.0 g of ethylene glycol was added and the reaction mixture was heated to 85-90 °C to form a clear solution. The reaction mixture was heated to reflux (external temperature 120 °C) for 4-6 h. At this time, TLC (acetone:hexane = 3:7) showed that the reaction was complete. The heating was turned off and the reaction mixture was allowed to cool to room temperature. The reaction was quenched by the addition of 80 mL of 10% potassium carbonate solution and the layers were separated. To the organic layer was added 100 mL of 5% brine and 0.8 g of potassium bicarbonate and the layers were separated. The combined aqueous layers were back extracted with 60 mL of toluene. The layers were separated and the combined organic layers were concentrated to dryness under reduced pressure. To the residue was added 100 mL of acetonitrile and 0.04 mL of triethylamine. The mixture was slurried at 55 °C for 1 h, cooled to 0-5 °C and stirred for 1 h. The mixture was filtered. The filter cake was slurried in 100 mL of acetonitrile at 55 °C for 1 h, cooled to 0-5 °C and stirred for 1 h. The mixture was filtered and the filter cake was dried under reduced pressure to give compound (IV) in 99.0% yield and 99.1% purity.

[0062] Example 5: Preparation of compound (II) (where R = benzoyl)

[0063] To a reaction flask was added 3 g of compound (III), 3.2 g of DMAP (4-dimethylamino pyridine) and 30 mL of dichloromethane and stirred for 10 min. The reaction flask was cooled in an ice bath and 2.75 g of benzoyl chloride was added dropwise. After the addition was complete, the reaction was allowed to proceed for 1-2 h. At this time, TLC (ethyl acetate: hexane = 1 : 1) showed that the reaction was complete. The reaction was quenched by the addition of 50 mL of 10% potassium bicarbonate solution. The layers were separated and the aqueous layer was re-extracted with 20 mL of dichloromethane. The organic layers were combined and washed with 50 mL of 10% sodium phosphate dibasic solution, followed by 50 mL of 10% brine, 50 mL of water, and the organic layer was separated. The organic layer was then filtered and concentrated under reduced pressure to dryness. The residue was crystallized from ethyl acetate / heptane, the resulting crystals were filtered and dried at 50-55 °C to give compound (II) (where R = benzoyl) in 99.0% yield and 99.4% purity.

[0064] Example 6: Preparation of compound (I) (where R = benzoyl)

[0065] To a reaction flask was added 2.0 g of compound (II) (where R = benzoyl), 42 mg of KRED-101, 42 mM of glucose, 42 mM of NADPH, 42 mM of NADP + and 42 mg / mL of GDH. The reaction was carried out at 25 °C with 220 rpm for 12 h. At the end of the reaction, an equal volume of ethyl acetate was added to the reaction mixture and the extraction was repeated three times. The organic phases were combined and concentrated under reduced pressure to dryness. The residue was crystallized from acetonitrile, the resulting crystals were filtered and dried at 50-55 °C to give compound (I) (where R = benzoyl) in 97.5% yield, 99.7% purity, and 99.8% ee.

[0066] Example 7: Preparation of compound (II) (where R = acetyl)

[0067] To a reaction flask was added 4 g of compound (III), 4.3 g of DMAP (4-dimethylamino pyridine) and 40 mL of dichloromethane and stirred for 10 min. The reaction flask was cooled in an ice bath and 3.7 g of acetyl chloride was added dropwise. After the addition was complete, the reaction was allowed to proceed for 1-2 h. At this time, TLC (ethyl acetate: hexane = 1 : 1) showed that the reaction was complete. The reaction was quenched by the addition of 50 mL of 10% potassium bicarbonate solution. The layers were separated and the aqueous layer was re-extracted with 20 mL of dichloromethane. The organic layers were combined and washed with 50 mL of 10% potassium phosphate dibasic solution, followed by 50 mL of 10% brine, 50 mL of water, and the organic layer was separated. The organic layer was then filtered and concentrated under reduced pressure to dryness. The residue was crystallized from ethyl acetate / heptane, the resulting crystals were filtered and dried at 50-55 °C to give compound (II) (where R = acetyl) in 98.9% yield and 99.5% purity.

[0068] Example 8: Preparation of compound (I) (wherein R = acetyl)

[0069] To a reaction flask was added 2.0 g of compound (II) (wherein R = acetyl), 1.0 mg of KRED-101, 98 mM of glucose, 1.0 mM of NADPH, 1.0 mM of NADP + and 1 mg of GDH in a reaction system of 200 mL, temperature controlled at 25 °C, 220 rpm for 12 hours. After the reaction was completed, an equal volume of ethyl acetate was used to extract the reaction solution, which was repeated three times. The organic phase was combined and concentrated to dryness under reduced pressure. The residue was crystallized with acetonitrile, and the formed crystals were filtered out and dried at 50-55 °C to obtain compound (I) (wherein R = acetyl) with a yield of 98.2%, a purity of 99.8%, and an ee value of 99.7%.

Claims

1. A process for the preparation of a compound of formula I ###000001### I The method comprises the following steps: Step 1: reacting a compound of formula VII with a Weinreb reagent in the presence of a base and a condensing agent to give a compound of formula VI; Step 2: oxidizing a compound of formula VI with an oxidizing agent to give a compound of formula V; Step 3: condensing a compound of formula V with ethylene glycol to give a compound of formula IV; Step 4: reacting a compound of formula IV with an isopropyl metal organic reagent to give a compound of formula III; Step 5: reacting a compound of formula III with a compound of formula RX to give a compound of formula II; Step 6: chiral asymmetric carbonyl reduction of a compound of formula II with a ketoreductase to give a compound of formula I; wherein R is a hydroxyl protecting group, for example, R is selected from the group consisting of benzoyl, C1-C6 alkyl substituted benzoyl, halogen substituted benzoyl such as m-chlorobenzoyl, halogenated C1-C6 alkyl substituted benzoyl, C1-C6 alkanoyl such as acetyl, and diphenylacetyl; X is halogen, for example, chlorine or bromine.

2. The process according to claim 1, wherein the base in step 1 is selected from one or more of trimethylamine, ethylenediamine, tetramethylethylenediamine, triethylamine, N,N-diisopropylethylamine, pyridine, piperidine, piperazine; the condensing agent is selected from one or more of O-benzotriazol-N,N,N',N'-tetramethyluronium tetrafluoroborate, N,N'-dicyclohexylcarbodiimide-1-hydroxybenzotriazole, N,N'-carbonyldiimidazole, benzotriazol-N,N,N',N'-tetramethyluronium hexafluorophosphate, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride; the Weinreb reagent is selected from N,O-diethylhydroxylamine hydrochloride or N,O-di-tert-butylhydroxylamine hydrochloride.

3. The process according to claim 1 or 2, wherein the oxidizing agent in step 2 is selected from one or more of 2,2,6,6-tetramethylpiperidine oxide-sodium hypochlorite, peroxyacetic acid, manganese dioxide, m-chloroperbenzoic acid, preferably manganese dioxide and 2,2,6,6-tetramethylpiperidine oxide-sodium hypochlorite.

4. The process according to any one of claims 1 to 3, wherein step 3 is carried out in a solvent selected from one or more of toluene, chlorobenzene, dichloromethane, tetrahydrofuran, methyltetrahydrofuran, diisopropyl ether, methyl tert-butyl ether.

5. The process according to any one of claims 1 to 4, wherein the isopropyl metal organic reagent in step 4 is selected from one or more of isopropyl lithium, isopropyl magnesium chloride, isopropyl magnesium bromide.

6. The process according to any one of claims 1 to 5, wherein the molar ratio of the compound of formula IV to the isopropyl metal organic reagent in step 4 is 1:2-1:6, preferably 1:2.1-1:

3.

7. The process according to any one of claims 1 to 6, wherein the compound of formula RX in step 5 is selected from benzoyl chloride, benzoyl bromide, Ci-C6alkyl substituted benzoyl chloride, Ci-C6alkyl substituted benzoyl bromide, halogen substituted benzoyl chloride, halogen substituted benzoyl bromide, halogenated Ci-C6alkyl substituted benzoyl chloride, halogenated Ci-C6alkyl substituted benzoyl bromide, Ci-C6alkanoyl chloride, Ci-C6alkanoyl bromide, diphenylacyl chloride and diphenylacyl bromide, such as benzoyl chloride, benzoyl bromide, m-chlorobenzoyl chloride, acetyl chloride, acetyl bromide, diphenylacyl chloride and diphenylacyl bromide.

8. The process according to any one of claims 1 to 7, wherein the ketoreductase in step 6 is KRED-101 or KRED-171.

9. The process according to any one of claims 1 to 8, wherein R in the compound of formula (I) is selected from benzoyl and acetyl.

Images