One-step method for synthesizing amoxicillin from penicillin or salt thereof through enzyme catalysis

Abstract

A one-step method for synthesizing amoxicillin from penicillin or a salt thereof through an enzyme catalysis is provided. Conventional amoxicillin production requires sequential use of distinct penicillin acylases for hydrolysis and synthesis steps, necessitating isolation of the intermediate 6-aminopenicillanic acid (6-APA) and resulting in elevated manufacturing costs and suboptimal process efficiency. To address these limitations, the inventive method utilizes a mutant of penicillin acylase derived from Kluyvera citrophila as the exclusive biocatalyst in an aqueous reaction system. By reacting penicillin G potassium salt with D-p-hydroxyphenylglycine methyl ester, the process achieves direct amoxicillin synthesis in a single enzymatic step, attaining a product yield of 99%. This method exhibits advantages including fast catalytic rate, high product yield, environmentally friendly pure aqueous reaction system, low cost, and excellent economic benefits.

Claims

1. A one-step method for synthesizing amoxicillin from penicillin or a salt thereof through an enzyme catalysis, comprising using only one penicillin acylase mutant as a sole enzyme in a reaction system, using the penicillin or the salt thereof and D-p-hydroxyphenylglycine methyl ester as substrates, and carrying out a reaction in a reaction buffer system of pH 4-8; wherein the penicillin acylase mutant consists of an amino acid sequence identical to SEQ ID NO: 1 except for the following mutations: F146K, F24R, F71Y, N241K, and G385R.

2. The one-step method for synthesizing the amoxicillin from the penicillin or the salt thereof through the enzyme catalysis according to claim 1, comprising the following steps: S1: adding a buffer solution of pH 4-8 to a reaction flask as the reaction buffer system; S2: adding a penicillin potassium salt and the D-p-hydroxyphenylglycine methyl ester to the reaction buffer system, wherein a molar ratio of the penicillin potassium salt to the D-p-hydroxyphenylglycine methyl ester is 1:1-1:2, and stirring thoroughly; and S3: adding an immobilized penicillin acylase mutant to the reaction buffer system, and reacting at a reaction temperature controlled at 12-30 C.

3. The one-step method for synthesizing the amoxicillin from the penicillin or the salt thereof through the enzyme catalysis according to claim 2, wherein the buffer solution in the step S1 comprises any one of citric acid buffer, acetic acid buffer, phosphate buffered saline (PBS) buffer, sodium dihydrogen phosphate-citric acid buffer, sodium barbital-hydrochloric acid buffer, and pure water.

4. The one-step method for synthesizing the amoxicillin from the penicillin or the salt thereof through the enzyme catalysis according to claim 2, wherein in the step S2, a concentration of the penicillin potassium salt is 50-200 mmol/L, and a concentration of the D-p-hydroxyphenylglycine methyl ester is 50-400 mmol/L.

5. The one-step method for synthesizing the amoxicillin from the penicillin or the salt thereof through the enzyme catalysis according to claim 2, wherein in the step S3, an amount of immobilized penicillin acylase is 3000-30000 U/L, and a reaction time is 1-6 h.

6. The one-step method for synthesizing the amoxicillin from the penicillin or the salt thereof through the enzyme catalysis according to claim 2, wherein after the step S3, the one-step method further comprises a step of recovering the immobilized penicillin acylase mutant.

7. The one-step method for synthesizing the amoxicillin from the penicillin or the salt thereof through the enzyme catalysis according to claim 6, wherein the step of recovering the immobilized penicillin acylase mutant comprises: S4: filtering out immobilized penicillin acylase using a sieve; and S5: adding 20-30 mL of deionized water per 10 g of the immobilized penicillin acylase, stirring for 5-10 min, and draining and repeatedly washing until drained water is clear and transparent and an immobilized penicillin acylase sample has no odor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the amino acid sequence (SEQ ID NO: 1) of the wild-type penicillin acylase;

(2) FIG. 2 is a schematic diagram of the construction of the recombinant plasmid pET28a-kcPA;

(3) FIG. 3 displays the agarose gel electrophoresis analysis of the PCR-amplified recombinant plasmid;

(4) FIG. 4 presents the SDS-PAGE electrophoresis results of protein expression in E. coli BL21 (DE3)/pET28a-kcPA cells;

(5) FIG. 5 illustrates the HPLC chromatogram of amoxicillin synthesized in a one-step reaction catalyzed by KcPA from penicillin potassium salt in Embodiment 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(6) To provide a clear and comprehensive understanding of the objectives, technical solutions, and advantages of the present invention, the following detailed description is provided in conjunction with specific embodiments. Unless otherwise specified, all equipment and reagents used in the embodiments and experimental procedures are commercially available. The described embodiments are intended to illustrate but not limit the scope of the invention.

(7) Based on the information disclosed herein, those skilled in the art may make various modifications to the precise embodiments of the invention without departing from the spirit and scope of the appended claims. It is understood that the scope of the invention is not limited to the specific processes, properties, or components described, as these embodiments and other descriptions are provided merely to exemplify particular aspects of the invention. In practice, any modifications to the disclosed embodiments that are obvious to those skilled in the art or related fields shall fall within the scope of the appended claims.

(8) For clarity and to avoid limiting the scope of the invention, all numerical values expressing quantities, percentages, or other parameters in this application shall be interpreted as being modified by the term about. Unless explicitly stated otherwise, all numerical parameters in the specification and claims are approximations that may vary depending on the desired properties sought to be achieved. These numerical parameters should be interpreted in light of the reported significant digits and conventional rounding techniques. As used herein, about means within +10% of a stated value or range, preferably within +5%.

(9) Ambient temperature: Unless otherwise specified, experiments are conducted under ambient conditions (natural room temperature without additional cooling/heating), typically defined as 10 to 30 C., preferably 15 to 25 C.

(10) Abbreviations: min (minute), s (second), U (enzyme activity unit), mM (millimolar per liter), M (molar per liter), rpm (revolutions per minute), mol (mole), g (microgram), mg (milligram), g (gram), L (microliter), mL (milliliter), bp (base pair), LB medium (Luria-Bertani medium), Kan50 (medium containing 50 g/mL kanamycin).

(11) Unless specified, methods follow standard laboratory practices as described in Molecular Cloning: A Laboratory Manual (4th Edition, J. Sambrook and M. R. Green, translated by He Fuchu, Science Press, Beijing, 2017) and New England Biolabs (NEB) reagent kit instructions.

(12) The present invention discloses one-step method for synthesizing amoxicillin from penicillin or a salt thereof through an enzyme catalysis. The method employs a mutant form of penicillin acylase (PA) derived from Kluyvera citrophila to catalyze the direct conversion of penicillin potassium salt to amoxicillin in a single reaction step. This technical solution provided by the present invention eliminates the need for intermediate separation, substantially simplifies the production process, enhances the yield of reaction products, significantly reduces production costs, and thereby introduces a revolutionary transformation to the amoxicillin synthesis industry. Below, the technical solution of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention.

Embodiment 1

(13) Construction of the prokaryotic expression for the mutant of penicillin acylase from Kluyvera citrophila, and its functional characterization

(14) 1. Construction of wild-type PA expression vector pET 28a-kcPA

(15) The wild-type penicillin acylase used in this Embodiment originates from Kluyvera citrophila ATCC 21285. Its amino acid sequence (SEQ ID NO: 1) comprises four domains, the sequence from the N-terminus to the C-terminus of the protein is as follows: Signal peptide: Positions 1-26. -subunit: Positions 27-235 (209 amino acids). Linker peptide: Positions 236-289 (54 amino acids). -subunit: Positions 290-846 (557 amino acids). Refer to FIG. 1 for domain annotations (single underline: -subunit; wavy line: linker; double underline: -subunit). The nucleotide sequence is provided as SEQ ID NO: 2.

(16) The recombinant plasmid pET 28a-kcPA was constructed as illustrated in FIG. 2. Using genomic DNA from K. citrophila ATCC 21285 as a template, primers were designed based on the nucleotide sequence of PA (SEQ ID NO: 2): Forward primer (SEQ ID NO: 3): 5-CGG/AATTCATGAAAAACCGCAATCGCAT-3.

(17) Reverse primer (SEQ ID NO: 4): 5-CCA/AGCTTTTAGCGCTGCACCTGCAGC-3. EcoRI and HindiIl restriction enzyme sites were introduced into the primer sequences (the underlined bases indicate the restriction enzyme recognition sites), and the target fragment of the wild-type PA was then amplified by PCR.

(18) TABLE-US-00001 PCR Reaction mixture Component Volume Sterile ddH.sub.2O 10 L template 0.5 L Forward primer (10 M) 1 L Reverse primer (10 M) 1 L 2 Taq Polymerase 12.5 L Total reaction volume 25 L

(19) PCR Thermal Cycling as following:

(20) TABLE-US-00002 {circle around (1)}. 95 C. 5 min {circle around (2)}. 95 C. 45 s {circle around (3)}. 60 C. 50 s {circle around (4)}. 72 C. 90 s {circle around (5)}. Go to {circle around (2)} 30 cycles {circle around (6)}. 72 C. 10 min {circle around (7)}. 4 C. forever

(21) The empty plasmid pET28a and PCR-amplified PA DNA fragment were subjected to double restriction enzyme digestion using EcoRI and HindIII restriction enzymes.

(22) TABLE-US-00003 Double enzyme digestion system: Component Volume/Amount 10 Buffer 5 L EcoRI 1.5 L HindIII 1.5 L Empty vector or PCR product 42 L Total 50 L

(23) The double restriction enzyme digestion was carried out at 37 C. for 1 hour, followed by enzyme inactivation at 80 C. for 20 minutes. The digested products were purified and quantified via agarose gel electrophoresis, yielding approximate concentrations of 50 ng/L for the pET28a vector and 140 ng/L for the kcPA insert.

(24) The purified fragments were ligated using T4 DNA ligase in a 16 C. metal bath overnight to generate the recombinant plasmid pET28a-kcPA. The recombinant plasmid was introduced into competent E. coli DH5a cells via heat shock transformation.

(25) Connection reaction system of the target fragment and the linearized vector:

(26) TABLE-US-00004 Component Volume 10 Buffer 1 L T4 DNA ligase 1 L Linearized vector 4 L Insert fragment 4 L Total 10 L

(27) To verify successful plasmid transformation, single colonies were picked from Kan50-LB agar plates and inoculated into Kan50-LB liquid medium. On the following day, plasmids were extracted using a plasmid extraction kit and subjected to PCR verification. A garose gel electrophoresis confirmed the presence of a 2500-bp target band (see FIG. 3). The validated expression vector pET28a-kcPA was then transformed into E. coli BL21 (DE3) to generate the recombinant strain E. coli BL21 (DE3)/pET 28a-kcPA for wild-type PA expression.

(28) 2. Generation of Mutant Expression Vectors

(29) In this embodiment, a total of 18 mutants were obtained through site-directed mutagenesis, as shown in the table below. The notation F146aK indicates that the amino acid at position 146 on the a subunit was changed from F (Phenylalanine) to K (Lysine). The explanation for other mutation sites follows the same logic.

(30) TABLE-US-00005 TABLE 1 Mutants and Corresponding Mutation Sites Mutant ID Mutation Sites KcPA Wild-type KcPA 01-06 Single-point mutants: F146K, F24R, F71Y, N241K, G385Y, G385R KcPA 07-11 Double-point mutants: F146K combined with one of F24R, F71Y, N241K, G385Y, or G385R KcPA 12 Triple-point mutant: F146K & F24R & F71Y KcPA 13 Triple-point mutant: F146K & N241K & G385Y KcPA 14 Triple-point mutant: F146K & N241K & G385R KcPA 15 Triple-point mutant: F146K & F71Y & N241K KcPA 16 Quadruple-point mutant: F146K & F71Y & N241K & G385Y KcPA 17 Quintuple-point mutant: F146K & F24R & F71Y & N241K & G385Y KcPA 18 Quintuple-point mutant: F146K & F24R & F71Y & N241K & G385R

(31) First, primers corresponding to each mutation site were designed. Then, Using the wild-type PA target fragment as the initial template, site-directed mutagenesis was performed with the NEB Q5 Site-Directed Mutagenesis Kit (Q5 SDM Kit). The primers for each mutation site are listed below (lowercase letters indicate mutated nucleotides):

(32) TABLE-US-00006 F146K, Forward(F): SEQIDNO:5 5-GGCGAACCGTaaaTCTGACAGCACCAG-3; Reverse(R): SEQIDNO:6 5-ATGGTGCCGACAAAAATCATCGCCA-3; F24R, Forward(F): SEQIDNO:7 5-TGGGCCGCAGcgcGGTTGGTATGCG-3; Reverse(R): SEQIDNO:8 5-TTGACCATAATGGCCTTCGCATCCT-3; F71Y, Forward(F): SEQIDNO:9 5-CACCGCCGGTtatGGTGATGATG-3; Reverse(R): SEQIDNO:10 5-GATCCCCATGAAATGGTGCCGTTGT-3; N241K, Forward(F): SEQIDNO:11 5-CGCCAACTGGaaaAACTCGCCGC-3; Reverse(R): SEQIDNO:12 5-ATATAGCCCGACTGCGGGTTATACAC-3; G385Y, Forward(F): SEQIDNO:13 5-CGGGCCAACCtatTCGCTGAACATCAGCGTG-3; Reverse(R): SEQIDNO:14 5-TCCTGGGTGGTTTCATAGCCACTGG-3; G385R, Forward(F): SEQIDNO:15 5-CGGGCCAACCcgcTCGCTGAACATC-3; Reverse(R): SEQIDNO:16 5-TCCTGGGTGGTTTCATAGCCACTGG-3;

(33) The primers were synthesized by a nucleic acid synthesis company, then dissolved in sterile water before proceeding with the protocol according to the kit instructions. As following:

(34) Step 1: Site-Directed Mutagenesis Via PCR

(35) PCR Reaction mixture:

(36) TABLE-US-00007 Component Volume Q5 Hot Start High-Fidelity 2X Master Mix 12.5 L 10 M Forward Primer 1.25 L 10 M Reverse Primer 1.25 L Template DNA (1-25 ng/L) 1 L Nuclease-Free Water 9.0 L Total Volume 25 L
Thermal Cycling Program:

(37) TABLE-US-00008 Step Temperature Time Initial 98 C. 30 s Denaturation 98 C. 10 s 25 Cycles 68 C. 10-30 s 72 C. 62 s Final Extension 72 C. 2 min Hold 4-10 C.

(38) For mutants with 2 mutation sites, the PCR product from the prior mutation step was used as the template for subsequent rounds of site-directed mutagenesis.

(39) Step 2: Kinase, Ligase & Dpnl (KLD) Treatment

(40) Reaction Mixture:

(41) TABLE-US-00009 Component Volume Final Concentration PCR Product 1 L 2 KLD Reaction Buffer 5 L 1 10 KLD Enzyme Mix 1 L 1 Nuclease-Free Water 3 L

(42) Incubate at room temperature for 5 minutes.

(43) Step 3: Heat Shock Transformation

(44) Add 5 L of the KLD reaction mixture to 50 L of chemically competent E. coli BL21 (DE3) cells. Incubate on ice for 30 minutes, apply a 42 C. heat shock for 30 seconds, and return to ice for 5 minutes. Subsequently, add 950 L of SOC sterile liquid medium and incubate at 37 C. with gentle shakingfor 1 hour. Spread 40-100 L of the bacterial suspension onto Kan50-LB agar plates and incubate overnight at 37 C. The resulting single colonies represent the mutant expression strains, designated as E. coli BL21 (DE3)/pET28a-kcPA0118.

(45) Step 4: Mutant Verification

(46) Inoculate the obtained mutant expression strains into 25 mL of LB liquid medium containing Kan50. Incubate at 37 C. overnight. Use a plasmid extraction kit to isolate the plasmid. Send the plasmid to a third-party biotech company for sequencing to confirm that the product is the intended point-mutated target product.

(47) 3. Expression of Wild-Type and Mutant KcPA

(48) The recombinant strains E. coli BL21 (DE3)/pET28a-kcPA and E. coli BL21 (DE3)/pET28a-kcPA0118 were inoculated onto Kan50 LB agar plates and incubated in a 37 C. incubator for 12-16 hours. Single colonies were picked and inoculated into 25 mL of LB liquid medium containing Kan50. These cultures were grown overnight at 37 C. with shaking at 300 rpm. Next, 500 L of the bacterial suspension was transferred to 50 mL of Kan50 LB liquid medium and incubated at 37 C. with shaking at 280 rpm. The OD600 was monitored, and when it reached 0.6-0.8, IPTG was added to a final concentration of 0.3 mM to induce protein expression. The cultures were induced for 10 hours at 25 C. with shaking at 220 rpm. The cells were harvested by centrifugation, and the cell pellets were resuspended in pre-chilled PBS buffer (pH 7.5) and kept on ice for 10 minutes. The resuspended cells were then centrifuged at 4 C., 12,000 rpm for 6 minutes to collect the cell pellets. The cell pellets were further resuspended in 50 mM PBS buffer (pH 7.5), and after another round of centrifugation at 4 C., 12,000 rpm for 6 minutes, the supernatant was discarded, and the final cell pellets were resuspended at a concentration of 0.01 g/mL. The cells were lysed using a sonicator under the following conditions: ice-water bath, 400 W power, with cycles of 3 seconds on and 5 seconds off for a total of 80 cycles. After lysis, the mixture was centrifuged at 4 C., 12,000 rpm for 15 minutes, and the supernatant was collected as the crude enzyme extract. SDS-PAGE was then used to analyze the expressed proteins.

(49) FIG. 4 shows the SDS-PAGE analysis of the protein expressed by the mutant strain E. coli BL21 (DE3)/pET28a-kcPA 18. The lanes are labeled as follows: M: Protein marker. Lane 1: Supernatant of E. coli BL21 (DE3)/pET28a. Lane 2: Supernatant of E. coli BL21 (DE3)/pET28a-kcPA without induction. Lane 3: Supernatant of E. coli BL21 (DE3)/pET 28a-kcPA 18 without induction. Lane 4: Supernatant of IPTG-induced E. coli BL21 (DE3)/pET28a-kcPA 18.

Embodiment 2

(50) 1. Measurement of KcPGA Hydrolytic Activity

(51) Principle of Measurement: Penicillin G Potassium Salt (PGK) is hydrolyzed under the action of KcPA to produce 6-Aminopenicillanic Acid (6-APA) and phenylacetic acid. Under acidic conditions, 6-APA reacts with p-Dimethylaminobenzaldehyde (PDAB) to form a yellow-green substance that has a maximum absorption peak at 415 nm. The enzyme activity is defined as: in 0.1 M PBS buffer at 28 C., the amount of penicillin acylase required to catalyze the conversion of 20 mg/mL PGK into 1 mol of 6-A PA per minute is defined as KcPA enzyme activity one unit (U).

(52) Weigh 0.5 g of PGK and dissolve it in the aforementioned buffer solution, then adjust the volume to 25 mL. Pipette 2 mL of PGK solution into a centrifuge tube and add 0.1 mL of KcPA enzyme solution. Set up a control without adding KcPA while keeping all other conditions identical.

(53) Place the reaction system in a water bath shaker at 28 C. and 200 rpm for 10 minutes. After the reaction, deactivate the enzyme by placing it in a 90 C. water bath for 2 minutes. Then, take 200 L of the post-reaction solution and add it to 3 mL of 0.1 M citrate buffer at pH 3.0, followed by the addition of 1 mL of coloring reagent (0.5% PDAB). Allow it to stand at room temperature for 3 minutes before measuring the absorbance at 415 nm. Use the 6-APA standard curve to determine the concentration of 6-APA in the sample, and calculate the enzyme activity, i.e. the hydrolytic activity, using the formula provided.

(54) Calculation Formula: Hydrolytic activity of penicillin acylase per mL:

(55) $U=\frac{C_{6-\mathrm{APA}}V}{t{V}_E}$

(56) Where, C.sub.6-APA: Concentration of 6-APA in the sample, mol/L; V: Volume of the reaction system, mL; VE: Volume of penicillin acylase added, mL; t: Reaction time, 10 min.

(57) 2. Measurement of KcPA Synthesis Activity

(58) 6-Aminopenicillanic Acid (6-APA) and D-p-Hydroxyphenylglycine methyl ester (D-HPGM) are catalyzed by KcPA to synthesize Amoxicillin. The amount of Amoxicillin can be measured using High-Performance Liquid Chromatography (HPLC), thereby calculating the synthesis activity of Penicillin Acylase (PA). The enzyme activity is defined as: under certain conditions, the amount of enzyme required to catalyze the production of 1 mol of Amoxicillin per minute is considered one unit of synthesis activity, denoted as U.

(59) Weigh 1 g of 6-APA and 1.25 g of D-HPGM and dissolve them in 50 ml of 0.1 M PBS buffer at pH 6.3. Adjust the pH to 6.3 and then make up to a total volume of 100 mL with the same buffer. Add 0.1 mL of KcPA enzyme solution to this mixture and incubate at 25 C. with shaking at 200 rpm for 30 minutes. Inactivate the enzyme by placing it in a 90 C. water bath for 2 minutes. Filter 0.5 mL of the reaction mixture through a 0.22 m aqueous filter membrane and dilute with phosphate buffer to 100 mL for HPLC analysis to determine the concentration of Amoxicillin. The formula for calculating enzyme activity is provided below:

(60) Calculation Formula: Synthesis activity of penicillin acylase per mL:

(61) $U=\frac{C_{\mathrm{sample}}V200}{V_{E}t}$

(62) Where, C.sub.sample: Concentration of Amoxicillin, mol/L; V: Volume of the reaction mixture, mL; 200: Dilution factor; VE: Volume of enzyme added, mL; t: Reaction time, min.

(63) HPLC Conditions: Agilent ZORBAX SB-C18 4.6250 mm column, column temperature 25 C. Injection volume 10 L. Mobile phase A (0.02 M NaH.sub.2PO.sub.4Na.sub.2HPO.sub.4 buffer at pH 4.7), mobile phase B (methanol). Start with 90% mobile phase A and 10% mobile phase B for 5 minutes, increase mobile phase B from 10% to 50% between 5 and 7 minutes, maintain 50% for 10 minutes, reduce mobile phase B from 50% to 10% between 17 and 19 minutes, and finally equilibrate with 90% mobile phase A and 10% mobile phase B for 5 minutes. Total flow rate is 1 mL/min.

(64) TABLE-US-00010 TABLE 2 Comparison of Activities Between Mutants and Wild Type Comparison Comparison of of hydrolysis Synthesis Mutant ID activity Activity KcPA 100 100 KcPA 01 580 1530 KcPA 02 245 950 KcPA 03 286 838 KcPA 04 290 818 KcPA 05 492 709 KcPA 06 462 1118 KcPA 07 745 2054 KcPA 08 786 3037 KcPA 09 664 2260 KcPA 10 858 3574 KcPA 11 920 4380 KcPA 12 730 3410 KcPA 13 953 8842 KcPA 14 1074 10568 KcPA 15 620 4875 KcPA 16 831 8640 KcPA 17 1270 12680 KcPA 18 1440 15620

(65) Note: The hydrolytic activity of recombinantly expressed wild-type KcPA is 15 U/mL (fermentation broth), and the synthesis activity is 80 U/mL. For ease of comparison, the enzyme activity of the wild-type K cPA is defined as 100 in Table 2, with each mutant's activity compared against this baseline.

(66) From the table, it is evident that single-site mutants exhibit significantly enhanced hydrolytic and synthesis activities compared to the wild type, particularly F146K on the a subunit and G385R on the subunit. Specifically, the single-point mutation F146K shows 5.8 times higher hydrolytic activity and 15.3 times higher synthesis activity than the wild type. The G385R mutant exhibits 4.6 times higher hydrolytic activity and approximately 11.2 times higher synthesis activity than the wild type. Comparing G385Y and G385R mutants, the former has higher hydrolytic activity but not superior synthesis activity. When multiple mutations are combined, the enzyme activity increases significantly over single mutations, especially for the five-point mutant F146K & F24R & F71Y & N241K & G385R, which shows high levels of both hydrolytic and synthesis activities.

Embodiment 3

(67) One-Step Synthesis of Amoxicillin Catalyzed by Wild-Type and Penicillin Acylase Mutants Using PGK

(68) In PBS buffer at pH 7.0, PGK was added to reach a concentration of 200 mM, along with D-p-Hydroxyphenylglycine Methyl Ester (D-HPGM) to achieve a final concentration of 300 mM. Enzyme was added at 30 U/ml (based on synthetic activity). The reaction was carried out at 28 C. with constant stirring for 3 hours. After the reaction, HPLC analysis was performed to calculate the yield of Amoxicillin.

(69) HPLC Conditions: Agilent ZORBAX SB-C18 4.6250 mm column, column temperature 25 C. Injection volume 10 L. Mobile phase A (0.02 M NaH.sub.2PO.sub.4-Na.sub.2H PO.sub.4 buffer at pH 4.7), mobile phase B (methanol). Start with 90% mobile phase A and 10% mobile phase B for 5 minutes, increase mobile phase B from 10% to 50% between 5 and 7 minutes, maintain 50% for 10 minutes, reduce mobile phase B from 50% to 10% between 17 and 19 minutes, and finally equilibrate with 90% mobile phase A and 10% mobile phase B for 5 minutes. Flow rate is 1 mL/min.

(70) The reaction scheme is as follows:

(71) ##STR00001##

(72) For mutant K cPA 18, the HPLC detection spectrum is shown in FIG. 5, where D-HPG represents D-p-Hydroxyphenylglycine, AMOX represents Amoxicillin, D-HPGM represents D-p-Hydroxyphenylglycine Methyl Ester, PAA represents Phenylacetic Acid, and PGK represents Penicillin Potassium Salt. As can be seen from the figure, the content of the intermediate 6-A PA is extremely low, almost negligible.

(73) TABLE-US-00011 TABLE 3 Yield of Amoxicillin Catalyzed by Various Mutants Amoxicillin Mutant ID Yield/% KcPA 8.5 KcPA 01 24.5 KcPA 02 16.3 KcPA 03 18.6 KcPA 04 17.2 KcPA 05 15.7 KcPA 06 20.1 KcPA 07 26.8 KcPA 08 28.5 KcPA 09 25.3 KcPA 10 29.2 KcPA 11 34.7 KcPA 12 28.9 KcPA 13 68.2 KcPA 14 85.6 KcPA 15 37.7 KcPA 16 67.9 KcPA 17 92.8 KcPA 18 99.0

(74) From the results in the table above, it is evident that all mutants are capable of catalyzing the reaction between potassium salt of penicillin and D-Hydroxyphenylglycine Methyl Ester in one step to synthesize Amoxicillin within a single reaction system. Moreover, the product yields are significantly higher compared to the wild type.

Embodiment 4

(75) Preparation of Immobilized Penicillin Acylase

(76) Penicillin acylase enzyme solution was prepared according to Embodiment 1. This enzyme solution was then added to epoxy resin (ER) activated with glutaraldehyde, and the cross-linking reaction was carried out at 15 C. for 1.5 hours. The cross-linking reaction system consisted of: 1200 U of enzyme solution, 0.25% glutaraldehyde, 5 g of ER, and 50 mL of phosphate buffer (KH 2PO 4-K2HPO.sub.4) at pH 7.5. After the completion of the cross-linking reaction, the immobilized enzyme was collected by filtration using a sieve. The immobilized enzyme was then washed with 100 ml of phosphate buffer (pH 7.5). The activity of the immobilized enzyme was measured to be 180 U/g, with an immobilized enzyme activity recovery rate reaching 75%.

(77) Embodiments 5-17 Optimization of Process Conditions for One-Step Synthesis of Amoxicillin Catalyzed by KcPGA 18 Using PGK

(78) The synthesis process includes the following steps:

(79) (1) Add a certain amount of PBS buffer or other buffers with a pH range of 4 to 8 into a reaction flask as the reaction buffer system.

(80) (2) Weigh a certain amount of Penicillin G Potassium Salt (PGK) and D-p-Hydroxyphenylglycine Methyl Ester (D-HPGM) and add them to the reaction buffer system. The molar ratio of PGK to D-HPGM is between 1:1 and 1:2, with PGK concentration ranging from 50 to 200 mmol/L and D-HPGM concentration ranging from 50 to 400 mmol/L. Stir thoroughly to ensure that PGK and D-HPGM substrates are uniformly dispersed in the solvent.

(81) (3) Accurately weigh a certain amount of immobilized penicillin acylase with synthetic catalytic activity and add it to the reaction flask at an enzyme dosage of 3000 to 30000 U/L (based on synthetic enzyme activity). Control the reaction temperature between 12 and 30 C. and the reaction time between 1 to 6 hours.

(82) (4) After the reaction ends, add 2 to 5 times the volume of deionized water to the reaction system, then slowly add 15% (w/v) phosphoric acid solution dropwise until the entire system becomes clear and transparent.

(83) (5) Filter out the immobilized penicillin acylase and rinse it 2-3 times with deionized water. Mix the collected washing solution thoroughly with the filtrate.

(84) (6) Soak the filtered immobilized penicillin acylase in deionized water for 15-20 minutes (during which 3-4 drops of phosphoric acid can be added to maintain weak acidity and enzyme activity), then rinse it 2-3 times with deionized water. Dry the surface moisture using blotting paper (or cold air drying) and store it in a refrigerator at 2-6 C. for reuse.

(85) HPLC Detection Conditions: Same as Embodiment 3.

(86) Experimental Results:

(87) TABLE-US-00012 Reaction Amoxi- PGK & Conditions cillin D-HPGM Enzyme (Temp, Yield Embodiment Reaction System (mmol/L) (U/L) Time) (%) Embodiment pH 4 citrate- 100, 200 3000 12 C., 75 5 sodium citrate 6 h buffer Embodiment pH 5 acetate 150, 300 20000 28 C., 80 6 buffer 1.5 h Embodiment pH 5 PBS buffer 100, 150 10000 14 C., 88 7 5 h Embodiment pH 6 PBS buffer 100, 150 20000 16 C., 90 8 2 h Embodiment pH 7 PBS buffer 150, 200 25000 16 C., 92 9 2 h Embodiment pH 7 PBS buffer 200, 400 25000 24 C., 85 10 1 h Embodiment pH 7 PBS buffer 200, 400 25000 26 C., 98 11 2 h Embodiment pH 7 PBS buffer 200, 300 25000 26 C., 98 12 3 h Embodiment pH 7 NaH2PO4- 150, 300 25000 24 C., 93 13 citrate buffer 2 h Embodiment pH 7 citrate- 150, 300 25000 22 C., 92 sodium citrate 1.5 h 14 buffer Embodiment pH 7.5 PBS 200, 300 30000 20 C., 94 15 buffer 2 h Embodiment pH 7 barbital 150, 300 25000 20 C., 95 16 sodium-HCl 2.5 h buffer Embodiment Deionized water 200, 300 20000 28 C., 97 17 4 h
Embodiment 18 Enzyme Recovery and Reuse

(88) The filtered immobilized penicillin acylase was soaked in deionized water for 20 minutes, with 20 to 30 mL of deionized water added per 10 g of immobilized enzyme. It was then stirred for 5 to 10 minutes, drained, and the washing process was repeated until the released water was clear and odorless. In the buffer used, a 0.5% o solution of hydroxybenzoate was added to cover the immobilized enzyme, which was then stored in a refrigerator at 4 C. for reuse.

(89) Recovered enzyme was used in a reaction system containing PBS at pH 7, with PGK concentration of 200 mmol/L, D-HPGM concentration of 300 mmol/L, and an enzyme amount of 25000 U/L. The reaction was carried out at 26 C. for 3 hours, achieving an Amoxicillin yield of 98%.

(90) Embodiment 19 Enzyme Recovery and Reuse

(91) Following the procedure described: The filtered immobilized penicillin acylase is soaked in deionized water for 20 minutes, with 20 to 30 mL of deionized water added per 10 g of immobilized enzyme. Stir for 5 to 10 minutes, drain, and repeat the cleaning process until the released water is clear and the enzyme sample is odorless, the enzyme was recovered and reused up to 20 times.

(92) For each cycle, the recovered enzyme was used in a reaction system containing PBS at pH 7, with PGK concentration of 200 mmol/L, D-HPGM concentration of 300 mmol/L, and an enzyme amount of 25000 U/L. The reaction was performed at 26 C. for 3 hours, resulting in an Amoxicillin yield of 92%.

(93) The above embodiments illustrate preferred embodiments of the invention and are not intended to limit it. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention shall fall within the scope of protection of this invention.