CN118147101A

CN118147101A - Method for preparing moxifloxacin intermediate by enzyme catalysis

Info

Publication number: CN118147101A
Application number: CN202410016077.1A
Authority: CN
Inventors: 陶荣盛; 沈青; 朱傅赟; 郑云; 潘震华; 胡海亮; 沈正权; 孙梁栋; 沈剑强
Original assignee: Huzhou Yisheng Biotechnology Co ltd
Current assignee: Huzhou Yisheng Biotechnology Co ltd
Priority date: 2024-01-03
Filing date: 2024-01-03
Publication date: 2024-06-07

Abstract

The invention discloses a aminotransferase mutant SEQ ID NO 3 or SEQ ID NO 5, which can efficiently catalyze a substrate 3- (3-chloropropyl) -4-oxo-pyrrolidine-1-carboxylic acid ethyl ester to react to obtain a moxifloxacin intermediate compound (4 aS,7 aS) -octahydro-6H-pyrrolo [3,4-b ] pyridine-1-carboxylic acid ethyl ester with high optical purity, and has good industrial application prospect.

Description

Method for preparing moxifloxacin intermediate by enzyme catalysis

Technical Field

The invention belongs to the technical field of enzyme catalysis, and particularly relates to a transaminase mutant and application thereof in preparation of moxifloxacin intermediate (4 aS,7 aS) -octahydro-6H-pyrrolo [3,4-b ] pyridine-1-carboxylic acid ethyl ester.

Background

Moxifloxacin (moxifloxacin) is a third-generation quinolone spectrum antibacterial drug, and is marketed in 1999 until now and is widely applied to clinic for treating respiratory tract infections such as acquired pneumonia, acute episode of chronic bronchitis, acute bacterial sinusitis and the like.

Moxifloxacin is a chiral compound

(4 AS,7 aS) -octahydro-1H-pyrrolo [3,4-b ] pyridine (formula I) is a key chiral intermediate of moxifloxacin, the molecular structure of the intermediate has two framework structures of piperidine and pyrrolidine and two chiral centers, and the reported preparation methods of the intermediate mainly comprise two main types of chemical synthesis methods and biological catalysis methods:

The chemical synthesis method mainly comprises a piperidine route, a pyrrolidine route, a technical route for preparing chiral amino compounds by the reductive amination reaction of chiral amine and carbonyl compounds, and the like, but the routes have the defects of high process cost and complex process flow in the existing synthesis technology no matter the routes adopt a resolution method or an asymmetric synthesis method to prepare the compound of the formula (I).

The inventor has disclosed a technical route of a biocatalysis method in patent document CN107686852 a: and (3) carrying out a transamination reaction on the compound (III) by adopting omega-transaminase and/or an immobilized form thereof under the action of an ammonia donor to prepare a compound (II), and then carrying out a deprotection reaction on the compound (II) to prepare the compound (I). The preparation method has low cost, few steps, simple operation and product ee value up to more than 99%.

However, the method has not been used for realizing industrialized elbow pulling mainly because the enzyme activity is not high, and a large amount of enzyme must be added to catalyze the reaction, so that the production cost is high, and the economical efficiency of industrial production is limited.

Disclosure of Invention

In order to overcome the defects of the enzyme catalysis method in the prior art, development of transaminase with high enzyme activity and high stereoselectivity is an important break-through for solving the technical problems.

The inventors have paid attention to Christopher K.Savile in literature (Chiral Amines from Ketones Applied to Sitagliptin Manufacture.Christopher K.Savile,et al.,SCIENCE.VOL 329,p305-309.16JULY 2010.) reported that mutant ATA-117 of Arthrobacter sp derived aminotransferase is an (R) -selective aminotransferase ((R) -SELECTIVE TRANSAMINASE, SEQ ID NO: 1) capable of catalyzing ketone synthesis of chiral amines of high optical purity for use in the preparation of sitagliptin. In the light of this document, an attempt was made to synthesize compound (II) by using ATA-117 for catalyzing the transamination reaction of compound (III) such as ethyl 3- (3-chloropropyl) -4-oxopyrrolidine-1-carboxylate, and compound (II), namely ethyl (4 aS,7 aS) -octahydro-6H-pyrrolo [3,4-b ] pyridine-1-carboxylate, was obtained with high optical purity. Next, in order to increase the enzyme activity of transaminase ATA-117 (referred to herein as ATA117 or moxidec transaminase), the inventors have made mutation attempts by error-prone PCR, which is most commonly used in enzyme mutation technology, screened for some mutant enzymes having significantly increased enzyme activity while maintaining high stereoselectivity, showing potential for industrial application. Based on these studies, the present invention includes the following technical solutions.

In a first aspect, the invention provides a transaminase mutant having an amino acid sequence SEQ ID NO. 3 or SEQ ID NO. 5.

In a second aspect, the invention provides a gene encoding the above transaminase mutant.

Preferably, the nucleotide sequence of the gene encoding the amino acid sequence SEQ ID NO. 3 of the above transaminase mutant may be SEQ ID NO. 4; the nucleotide sequence of the gene encoding the amino acid sequence SEQ ID NO. 5 of the transaminase mutant may be SEQ ID NO. 6.

In another aspect, the invention provides a DNA molecule comprising a coding gene as described above.

Accordingly, another aspect of the present invention provides a plasmid comprising the above DNA molecule.

The plasmid vector may be selected from pET vectors (e.g., pET22b, pET24a, pET28 a), pSH plasmid, pRSFDuet plasmid or other vectors.

In another aspect, the present invention provides a microorganism engineering bacterium for expressing the above transaminase mutant, which has the above gene integrated into the host bacterium genome or has the above plasmid transformed into the host bacterium. Preferably, the microorganism engineering bacterium is a transformant transformed with the above plasmid.

The microbial host may be selected from the group consisting of Bacillus subtilis, pichia pastoris, saccharomyces cerevisiae or E.coli, preferably E.coli BL21 (DE 3).

In another aspect, the invention provides the use of the transaminase mutant or the microorganism engineering bacterium described above for the production of ethyl moxifloxacin intermediate (4 as,7 as) -octahydro-6H-pyrrolo [3,4-b ] pyridine-1-carboxylate.

As a specific application embodiment, 3- (3-chloropropyl) -4-oxo pyrrolidine-1-carboxylic acid ethyl ester is taken as a substrate, the transaminase mutant or the microorganism engineering bacteria are taken as biocatalysts, and the target product is obtained through enzyme catalytic reaction:

Preferably, the product (4 aS,7 aS) -octahydro-6H-pyrrolo [3,4-b ] pyridine-1-carboxylic acid ethyl ester has an optical purity ee value of more than 99%.

Preferably, pyridoxal phosphate (PLP) is added as a coenzyme to the reaction system. Pyridoxal phosphate (PLP) as a coenzyme can promote transaminase-catalyzed transamination reactions.

The pyridoxal phosphate may be added to the reaction system in an amount of 0.05 to 0.5g/L, preferably 0.1 to 0.4g/L, for example, about 0.2 g/L.

An ammonia donor such as methylbenzylamine, isopropylamine, triethanolamine, phthalic acid dimethylamine dihydrochloride, alanine, ammonium acetate, etc. is also added to the above reaction system.

Further, quaternary ammonium salt CTAB (cetyltrimethylammonium bromide) accounting for 0.05-0.5% of the weight of the substrate, for example, about 0.2% can be added into the reaction system as a phase transfer catalyst to assist dissolution so as to promote the reaction.

The above reaction may be carried out in a buffer solution such as a phosphate buffer or an acetate buffer, or isopropylamine hydrochloride as an ammonia donor may be directly used as a buffer, and the pH of the reaction system may be 7 to 10, preferably 7.5 to 9.5, more preferably 8 to 9, for example, about pH 8.5.

The terms "about," "approximately," or "about," when used herein in reference to a numerical feature, mean that the number represented may have an error range or float range of + -10%, + -9%, + -8%, + -7%, + -6%, or + -5%. In addition, unless otherwise defined, the scope of the terms presented herein includes the terms and any number within the scope.

The invention obviously improves the enzyme activity of E42G/S54P mutant (SEQ ID NO: 3) and E42G/S54P/S124F mutant (SEQ ID NO: 5) obtained by carrying out genetic engineering mutation on aminotransferase ATA117 (SEQ ID NO:1, moxidec aminotransferase), simultaneously maintains high stereoselectivity, can effectively catalyze and synthesize moxifloxacin intermediate (4 aS,7 aS) -octahydro-6H-pyrrolo [3,4-b ] pyridine-1-carboxylic acid ethyl ester with the optical purity ee value of more than 99%, and promotes the application of industrial production.

Drawings

FIG. 1 is a schematic diagram of the structure of plasmid pET24a-ATA117 for expression of the starting aminotransferase ATA 117.

FIG. 2 is an HPLC chart of synthesis of moxifloxacin intermediate compounds by the transaminase ATA117 catalyzed substrate reaction. Wherein, the substrate peak time: 11.824min; product off-peak time: 11.178min.

Detailed Description

In view of the fact that the aminotransferase ATA117 (SEQ ID NO: 1) has (R) -selectivity, the inventors examined its catalytic substrate ethyl 3- (3-chloropropyl) -4-oxopyrrolidine-1-carboxylate for transammoniation and closing, and found that it is also capable of stereoselectively synthesizing ethyl (4 aS,7 aS) -octahydro-6H-pyrrolo [3,4-b ] pyridine-1-carboxylate with a chiral desired isomer ratio of less than 1%.

In order to increase the possibility of industrial application, it is necessary to modify the structure of the enzyme by mutation with ATA117 as the original enzyme, and it is expected to obtain mutant aminotransferase with improved enzyme activity and still maintain stereoselectivity, and several ideal mutant enzymes are fortunately obtained.

In this context, the terms "primary enzyme", "starter enzyme" and "starter enzyme" are used in the same sense and refer to the amino acid sequence of the aminotransferase ATA117 of SEQ ID NO.1 as reported in the literature (Christopher K.Savile, et al). Sometimes, for convenience of description, the starting enzyme ATA117 and its mutants may be referred to herein collectively as "transaminases".

Mutants with improved enzyme activity, including E42G/S54P mutant (SEQ ID NO: 3) and E42G/S54P/S124F mutant (SEQ ID NO: 5), were selected by several rounds of error-prone PCR random mutagenesis.

The amino acid sequence of the transaminase mutants of the present invention is clear, and thus the person skilled in the art can easily obtain the genes encoding them, expression cassettes and plasmids comprising these genes, and transformants comprising the plasmids.

In order to optimally express the aminotransferase ATA117 or a mutant thereof in escherichia coli, which is most commonly used in genetic engineering, the expressed genes of these enzymes may be codon-optimized.

Codon optimization is a technique that can be used to maximize protein expression in an organism by increasing the translational efficiency of a gene of interest. Different organisms often show a special preference for one of some codons encoding the same amino acid due to mutation propensity and natural selection. For example, in a fast-growing microorganism such as E.coli, the optimized codons reflect the composition of their respective genomic tRNA pool. Thus, in fast-growing microorganisms, the low frequency codons of an amino acid can be replaced with codons of the same amino acid but at a high frequency. Thus, the expression of the optimized DNA sequence is improved in fast growing microorganisms.

For example, for expressing aminotransferase in E.coli, the nucleotide sequence of the coding gene of the codon-optimized mutant SEQ ID NO. 3 may be SEQ ID NO. 4 and the coding gene of the mutant SEQ ID NO. 5 may be SEQ ID NO. 6.

These coding genes, expression cassettes, plasmids, transformants can be obtained by genetic engineering construction methods well known to those skilled in the art.

The transformant host can be any microorganism suitable for expressing the transaminase and/or the carbamoylase, including bacteria and fungi. Preferably the microorganism is bacillus subtilis, pichia pastoris, saccharomyces cerevisiae, or escherichia coli, preferably escherichia coli, more preferably escherichia coli BL21 (DE 3).

When used as biocatalysts, the aminotransferase and/or carbamoyl hydrolase of the present invention may take the form of an enzyme or a bacterial form. The enzyme forms include free enzyme, immobilized enzyme, including purified enzyme, crude enzyme, fermentation broth, carrier immobilized enzyme, etc.; the forms of the bacterial cells include viable bacterial cells, dead bacterial cells, immobilized bacterial cells, and the like.

In order to allow the reaction to proceed rapidly when the E42G/S54P mutant enzyme, the E42G/S54P/S124F mutant enzyme or the expressed microorganism thereof catalyzes the synthesis to produce moxifloxacin intermediate, a phase transfer catalyst such as a quaternary ammonium salt may be added to the reaction system, and when the quaternary ammonium salt is CTAB (cetyltrimethylammonium bromide), the amount of addition may be about 0.05 to 0.5% by weight of the substrate, for example, about 0.2%. Alternatively, an organic solvent which is miscible with water but has little damage to enzymes, such as acetonitrile, DMSO, etc. can be added into the reaction system to promote the dissolution of the substrate, thereby achieving the purpose of assisting the dissolution.

Pyridoxal phosphate (PLP) is preferably also added as a coenzyme to the reaction system of the present invention. Pyridoxal phosphate acts as a coenzyme in many enzymatic processes, and the actions include decarboxylation, deamination, transamination, racemization, etc., and mainly plays a role in promoting transamination in the present invention.

The present invention will be described in further detail with reference to specific examples. It should be understood that the following examples are illustrative of the present invention and are not intended to limit the scope of the present invention.

Examples

The amounts, amounts and concentrations of various substances are referred to herein, wherein the percentages refer to percentages by mass unless otherwise specified.

In the examples herein, if no specific explanation is made for the reaction temperature or the operating temperature, this temperature is usually referred to as room temperature (10-40 ℃).

Materials and methods

The whole gene synthesis, primer synthesis and sequencing were completed by the division of the Committee Biotechnology (Shanghai) Co., ltd.

The molecular biology experiments in the examples include plasmid construction, enzyme digestion, ligation, competent cell preparation, transformation, medium preparation and the like, and are mainly performed by referring to the third edition of molecular cloning experiment guidelines (J. Sam Broker, D.W. Lassel, huang Peitang et al, scientific Press, beijing, 2002). The specific experimental conditions can be determined by simple experiments, if necessary.

The PCR amplification experiments were performed according to the reaction conditions or kit instructions provided by the plasmid or DNA template suppliers. Can be adjusted if necessary by simple tests.

LB medium: 10g/L tryptone, 5g/L yeast extract, 10g/L sodium chloride, pH7.2. (LB solid Medium additionally 20g/L agar powder.)

TB medium: 24g/L yeast extract, 12g/L tryptone, 16.43g/L K ₂HPO₄.3H₂O、2.31g/L KH₂PO₄ g/L glycerol, pH7.0-7.5. (TB solid medium additionally added with 20g/L agar powder.

It should be noted that, for convenience of description, in the embodiment, the strain number, the plasmid number, the enzyme number, and the enzyme coding gene number may be used together by one number, which is easily understood by those skilled in the art, that is, the same number may refer to different biological forms in different environments.

Example 1: construction of engineering strain of colibacillus for expressing aminotransferase ATA117

According to the amino acid sequence SEQ ID NO:1 of aminotransferase ATA117 reported in literature (Christopher K.Savile, et al.), preferred codon optimization of Escherichia coli is carried out, the nucleotide sequence of the coding gene is SEQ ID NO:2, the whole gene synthesis is carried out by entrusted biological engineering (Shanghai) stock Co., ltd, restriction enzyme sites NdeI and BamHI are designed at both ends of the gene, and subcloning is carried out to corresponding sites of vector pET24a (Novagen), thus obtaining recombinant plasmid pET24a-ATA117, the structure of which is shown as 1.

The recombinant plasmid pET24a-ATA117 is transformed into competent cells of expression host escherichia coli BL21 (DE 3) by an electrotransformation method to obtain recombinant escherichia coli BL21 (DE 3)/pET 24a-ATA117 expressing aminotransferase ATA117.

Example 2: construction of error-prone PCR and random mutation library and high throughput screening

1. Coding gene of the enzyme ATA117 or plasmid pET24a-ATA117 is used as a template, and error-prone PCR and large primer PCR technology are applied to construct a random mutant library. The primers were designed as follows:

Forward primer err-F:5'-GTTTAACTTTAAGAAGGAGATATAC-3';

reverse primer err-R:5'-CTTGTCGACGGAGCTCGAAT-3'.

The 100. Mu.L error-prone PCR reaction system comprises: 50ng of plasmid template, 0.2. Mu.M each of a pair of primers err-F and err-R,1X Taq buffer,0.2mM dGTP,0.2mM dATP,1mM dCTP,1mM dTTP,7mM MgCl₂,(0.2mM、0.3mM、0.4mM)MnCl₂,1U Taq.

The PCR reaction conditions were: 95 ℃ for 5min;94℃30s,55℃30s,72℃1min,40 cycles; 7min at 72 ℃. The 1kb random mutant fragment was recovered as a large primer using KOD FX neo DNA polymerase MEGAPRIMER PCR:94 ℃,2min,68 ℃ for 10min;98 ℃ for 10s,55 ℃ for 30s,68 ℃ for 3min,25 cycles; and at 68℃for 10min.

Adding DpnI into PCR product, digesting at 37deg.C to remove plasmid template, purifying and recovering, electrically transforming E.coli BL21 (DE 3), adding 1mL LB culture medium, resuscitating at 37deg.C for 1 hr, coating Kan plate, culturing at 37deg.C overnight to obtain random mutation of more than 10 ⁴ clones

2. High throughput screening method for mutant library

Preparing a reaction solution: 50 μl of 2.5M isopropyl amine hydrochloride at pH8.5, 2 μl of 10mM PLP, and 100 μl of double distilled water (containing CTAB).

Preparing a substrate solution: 0.02g of the substrate ethyl 3- (3-chloropropyl) -4-oxopyrrolidine-1-carboxylate was weighed out and dissolved in 650. Mu.l DMSO.

Preparing a color-developing agent: 0.1g of phenol red was dissolved in 60% ethanol.

Strains in the mutant library were picked up to 200. Mu.l LB 96-well plates containing kan resistance, incubated at 37℃for 6h, 200. Mu.l LB containing the inducer IPTG and kan resistance was added, and incubated overnight at 28 ℃. The next morning 50. Mu.L of the culture was transferred to a 96-well deep-well culture plate, centrifuged at 3500rpm for 3min, the supernatant was discarded, 50. Mu.L of double distilled water was added for resuspension, frozen at-70℃for 2h, thawed at 37℃for 30min, and repeated three times. 150. Mu.L of the reaction solution and 30. Mu.L of the substrate solution were added, the reaction was carried out at 50℃for 2 hours, 15. Mu.L of the color-developing agent was added, and the mutant strain having a high enzyme activity, which turned yellow from red, was observed.

3. Comparison of catalytic Capacity of mutant strains to substrates

Shaking flask fermentation of strains: preparing TB liquid culture medium (pH 7.0-7.5), subpackaging in 1000mL triangular shake flask, filling 200mL liquid, and sterilizing in autoclave at 121deg.C for 20min. The strain LB plate is inoculated with a loop of fungus body by inoculating loop, 100 mug/mL kanamycin is added into TB culture medium before inoculation, shake cultivation is carried out at 37 ℃ and 220rpm until OD ₆₀₀ = 5-6, 0.2mM IPTG is added, and induction is carried out at 28 ℃ for about 24 hours.

Preparation of crude enzyme solution: 50mL of fermentation liquor is taken and placed in a centrifuge tube; obtaining thalli by centrifugation, adding purified water according to the ratio of 200g/L for resuspension, and then carrying out ultrasonic disruption: the suspended cells were cooled in an ice bath and subjected to ultrasonic disruption (voltage 400W, ultrasonic time 3s, interval time 5s, number of works 80).

3G of substrate was weighed into 25ml of water, 5.29ml of 2.5M isopropylamine hydrochloride having a pH of 8.5 was added under stirring, the reaction pH was adjusted to about 8.5, and then crude enzyme solution and 0.02g pyridoxal phosphate were added, wherein two thousandths of CTAB was added as a cosolvent, the total system was 50ml,50℃was used for the reaction, pH8.5 was controlled with 50% isopropylamine, 100. Mu.l of the conversion solution was added into 900. Mu.l of methanol at the time of 3 hours for the reaction to measure the gas phase, and the enzyme catalytic ability was evaluated.

The detection method of the gas phase comprises the following steps:

chromatographic column: HP-5

Sample inlet: 250 DEG C

Split ratio: 50:1

Column constant flow mode, flow: 1.5ml/min

Detector temperature: 270 DEG C

Hydrogen gas: 30ml/min

Nitrogen gas: 25ml/min

Air: 400ml/min

Sample injection amount: 1 μl

Solvent: ethanol

Column temperature:

The starting temperature was 75℃and was constant for 2 minutes. The temperature was raised to 240℃at 15℃per minute and kept constant for 10 minutes.

By this screening method, mutant strains having increased enzyme activity are selected from a library of mutants having the gene encoding the aminotransferase SEQ ID NO. 1 as a template. For the strains with obviously improved enzyme activity, extracting plasmids, entrusting a biological engineering company to carry out nucleic acid sequencing, comparing transaminase related fragments in a genome with SEQ ID NO. 1, determining amino acid mutation sites, and taking the strains with highest activity improvement as starting strains for the next round of random mutant library construction. And reconstructing a site-directed saturated mutant library by taking the transaminase mutant coding gene as a template, and finally obtaining the mutant with greatly improved enzyme activity by applying the same screening method.

Further, for mutants with improved enzyme activity, the optical purity of the product was determined by HPLC. HPLC conditions for detecting optical purity of chiral product:

Chromatographic column: CHIRALPAK IC 4.6.6X250 mm,5 μm

Mobile phase: methanol-ethanol-diethylamine = 500:500:1

Detection wavelength: 340nm

Sample injection amount: 10 μl of

Flow rate: 0.6ml/min

Column temperature: 35 DEG C

Run time: and 40min.

The mutant strains with significantly improved enzyme activity obtained by the first round of error-prone PCR and the corresponding mutation sites are listed in Table 1.

Table 1, comparison of the ability of randomly mutated mutants to catalyze substrate reactions (substrate: enzyme=3:2.5)

Strain	3H substrate conversion (%)	Product optical purity ee%
			ATA117	32.25	99.7
ATA117/E42G/G59F	58.53	99.0
			ATA117/F45I/P48H	76.06	99.1
ATA117/E42G/S54P	85.50	99.4
			ATA117/F122V/Y150I/V152T	59.30	99.0
ATA117/Y20W/P185G	48.59	99.5.
			ATA117/A35M/Y154D/A275L/L279N	63.87	98.7
ATA117/S54L/T66A/V69E	80.50	92.3
			ATA117/I21D/L272T	66.58	97.6
ATA117/D19N/T66D/N74K/G193D	54.96	99.3
			ATA117/E42I/G280A	75.96	98.2
ATA117/D103A/G193V	81.05	96.9

The mutant strain ATA117/E42G/S54P obtained by the first round of error-prone PCR not only has greatly improved enzyme activity, but also maintains high stereoselectivity. Sequencing to obtain the coding gene nucleotide sequence of E42G/S54P mutant as SEQ ID NO. 4 and the corresponding amino acid sequence as SEQ ID NO. 3.

Example 3: construction of second round error-prone PCR and random mutation library and high-throughput screening

1. Plasmid pET24a-ATA117/E42G/S54P was constructed to express E42G/S54P mutant in E.coli according to the method described in example 1.

2. A random mutant library was constructed using error-prone PCR and large primer PCR techniques using the coding gene of the E42G/S54P mutant SEQ ID NO. 4 or plasmid pET24a-ATA117/E42G/S54P as a template according to the method described in example 2.

The remaining conditions and operation steps were the same as in example 2.

3. Comparison of catalytic Capacity of mutant strains to substrates

Increasing the feeding ratio of the substrate and the crude enzyme solution to the substrate: enzyme = 3:1.6, screening transaminase mutant strains with further improved enzyme activity and still maintaining stereoselectivity.

The mutant strains with significantly improved enzyme activity obtained by the second round of error-prone PCR and the corresponding mutation sites are listed in Table 2.

Table 2, comparison of the ability of randomly mutated mutants to catalyze substrate reactions (substrate: enzyme=3:1.6)

Strain	3H substrate conversion (%)	Product optical purity ee%
			ATA117/E42G/S54P	50.21	99.6
ATA117/E42G/S54P/H14N/A35D/V65K	84.1	89.9
			ATA117/E42G/S54P/T22I/G136L	69.87	99.0
ATA117/E42G/S54P/E117G/H203A/G222P	90.23	91.5
			ATA117/E42G/S54P/F88I	83.41	97.6
ATA117/E42G/S54P/S124F	91.40	99.3
			ATA117/E42G/S54P/N74W/I97V/W156C	79.84	99.4
ATA117/E42G/S54P/N32S	92.874	88.4
			ATA117/E42G/S54P/F45L/F78D/T250Q	89.12	87.9

The enzyme activity of the mutant strain ATA117/E42G/S54P/S124F obtained by the second round of error-prone PCR is further obviously improved, and high stereoselectivity is still maintained. Sequencing to obtain the coding gene nucleotide sequence of E42G/S54P/S124F mutant as SEQ ID NO. 6 and the corresponding amino acid sequence as SEQ ID NO. 5.

The experimental results show that the E42G/S54P mutant and the E42G/S54P/S124F mutant are used for catalyzing substrates to synthesize chiral compounds (4 aS,7 aS) -octahydro-6H-pyrrolo [3,4-b ] pyridine-1-carboxylic acid ethyl ester, and are beneficial to the preparation of moxifloxacin intermediates by a biocatalysis method.

The present invention is not limited to the above-mentioned embodiments, and any changes or substitutions that can be easily understood by those skilled in the art within the technical scope of the present invention are intended to be included in the scope of the present invention.

Claims

1. A transaminase mutant is characterized in that the amino acid sequence is SEQ ID NO. 3 or SEQ ID NO. 5.

2. A gene encoding the transaminase mutant of claim 1.

3. The gene according to claim 2, wherein the nucleotide sequence of the gene encoding the amino acid sequence SEQ ID NO. 3 of the transaminase mutant is SEQ ID NO. 4; the nucleotide sequence of the gene encoding the aminotransferase mutant amino acid sequence SEQ ID NO. 5 is SEQ ID NO. 6.

4. A DNA molecule comprising the gene of claim 3.

5. A plasmid comprising the DNA molecule of claim 7. The plasmid vector may be selected from the group consisting of pET vectors, such as pET22b, pET24a or pET28a, pSH plasmid, pRSFDuet plasmid.

6. A microorganism for expressing the transaminase mutant according to claim 1, characterized in that the gene according to claim 3 is integrated in the genome of the host bacterium or the plasmid according to claim 5 is transformed in the host bacterium. Preferably the microorganism is a transformant transformed with the plasmid according to claim 5.

7. Use of the transaminase mutant according to claim 1 or the microorganism according to claim 6 for the production of ethyl (4 as,7 as) -octahydro-6H-pyrrolo [3,4-b ] pyridine-1-carboxylate.

8. The use according to claim 7, wherein 3- (3-chloropropyl) -4-oxopyrrolidine-1-carboxylic acid ethyl ester is used as a substrate, and the transaminase mutant according to claim 1 or the microbial catalytic reaction according to claim 6 is used to obtain the target product:

9. the use according to claim 8, wherein pyridoxal phosphate is added to the reaction system.

10. The method according to claim 8, wherein an ammonia donor selected from the group consisting of methylbenzylamine, isopropylamine, triethanolamine, xylylenediamine dihydrochloride, alanine, and ammonium acetate is added to the reaction system.