Method for preparing chiral amide by adopting flow reaction system

Abstract

The invention discloses a method for efficiently preparing chiral amide by adopting a flowing reaction system. A fixed bed reactor is adopted, and immobilized enzyme / immobilized palladium synergistically catalyzes racemic amine to prepare the chiral amide with high yield and high enantioselectivity. According to the process, the chiral amide is efficiently prepared by chemical-enzymatic dynamic kinetic resolution, and the highest enantiomer purity and yield can reach 100%. According to the method, the problem of mutual inhibition of an enzyme resolution catalyst and a metal racemization catalyst is solved, the efficiency of dynamic kinetic resolution is remarkably improved, and the product chiral amide can be further converted into a chiral amine drug intermediate.

Description

Technical Field

[0001] The invention relates to constructing a continuous flow fixed bed reactor reaction system in which enzyme and palladium catalysts are spatially separated and do not affect each other, and using the system to prepare chiral amide, a pharmaceutical intermediate, belonging to the technical field of drug synthesis. Background Art

[0002] In recent years, the demand for chiral amines has been increasing, mainly used as important key intermediates in pharmaceuticals, fine chemicals and agrochemicals. Despite great achievements in catalytic asymmetric synthetic transformations, kinetic resolution (KR) of racemic substrates is still the most commonly used method to obtain enantiomerically pure amines in industry. Enzyme-catalyzed kinetic resolution is one of the most widely used methods in the synthesis of chiral amines. However, the maximum theoretical yield of kinetic resolution is 50%, resulting in a huge waste of substrates and poor atom economy. The combination of kinetic resolution and in situ racemization of the remaining enantiomers produces a dynamic kinetic resolution (DKR) process, which can break through the limitation of the maximum yield of kinetic resolution of 50%. This method increases the theoretical yield of preparing a single enantiomer from a racemic substrate to 100%.

[0003] In addition, one-pot dynamic kinetic resolution combines the racemization catalyst and the enzyme into one reaction vessel. In general, the racemization of amines is difficult to achieve and requires harsh reaction conditions, resulting in the racemization process becoming the rate-determining step in the one-pot dynamic kinetic resolution process. In order to ensure the optimal coordination between the racemization reaction and the enzyme-catalyzed kinetic resolution, a sufficiently high racemization rate of the racemization catalyst in the fixed-bed reactor is required. Continuous flow chemistry has emerged as a technology with great application potential in multi-catalytic processes because it allows reactions to be carried out continuously through a single reactor. For example, the use of fixed-bed reactors allows for catalyst partitioning, thereby avoiding compatibility issues, and extends the life of the catalyst by avoiding stirring and allowing its reuse, which can be critical when dealing with expensive catalysts. In addition, continuous flow processes have many advantages over batch processes, such as improved mass and heat transfer, better safety, easier operation, facilitated automation and scale-up, and precise control of temperature, pressure, and reaction time, thereby improving reproducibility. Despite the above advantages, there are only a few reports of continuous flow reactions for DKR, and the potential of continuous flow technology in this field remains underutilized.

[0004] One of the biggest bottlenecks facing the DKR system is the poor compatibility between the enzyme resolution catalyst and the metal racemization catalyst. The enzyme and the metal may interact with each other, inactivating the enzyme and inhibiting the metal catalyst. Over the years, researchers have conducted a lot of research to solve the compatibility problem between enzymes and metals.

[0005] Experimental studies have found that immobilized enzymes have an inhibitory effect on the racemization reaction of racemization catalysts. For example, the racemization reaction catalyzed by immobilized palladium is inhibited by the immobilized enzyme, which means that there is a compatibility problem between the enzyme and palladium. Therefore, how to solve the problem of enzyme inhibition of palladium reaction and the compatibility problem between enzyme and palladium is of great significance to DKR.

[0006] The present invention adopts continuous flow technology to solve the compatibility problem between enzyme and palladium, separates the two catalysts in space, separates the reaction areas, does not produce mutual adverse effects, greatly improves the reaction rate, effectively solves the inhibition of enzyme on palladium, solves the compatibility problem, and is an efficient reaction system. Summary of the invention

[0007] The purpose of the present invention is to construct a continuous flow fixed bed reactor reaction system in which enzyme and palladium catalysts are spatially separated and do not affect each other, and to use the system to prepare chiral amides. The technical solutions adopted by the present invention to achieve the above purpose are as follows:

[0008] The flow reaction system is as follows (see Appendix Figure 1 ), composed of the following units: 1. A raw material liquid storage tank, used to store the raw material liquid, i.e., a 0.15 mol / L toluene solution of the substrate phenylethylamine and a 0.3 mol / L toluene solution of the acyl donor ethyl methoxyacetate. 2. A constant flow pump 1, used to pump the reaction liquid, such as the CFSP-1 / CU-1 constant flow pump of Duke Industrial Technology (Shanghai) Co., Ltd. 3. A three-way pipe joint, used to receive the circulating liquid. 4. A fixed bed reactor, used for DKR reaction. 5. A three-way pipe joint, used to separate the circulating liquid. 6. A product liquid storage tank, used for the product liquid, 7. A regulating valve, used to adjust the circulation volume. 8. A constant flow pump, the same as pump 1, used to pump the circulating liquid, which can be circulated according to the reaction conditions. This system also has a thermostat to provide a constant temperature environment for the reaction, which is not drawn in the figure.

[0010] Wherein fixed-bed reactor is the continuous flow chemical-enzyme reactor that immobilized lipase and immobilized palladium are housed.The size of this reactor is long 100cm, the stainless steel pipe of internal diameter 0.5cm, wherein alternately fills immobilized enzyme and immobilized palladium, separates with thin cotton cloth between enzyme layer and palladium layer, and the thickness of single-layer immobilized enzyme layer is 2.5cm, and the thickness of single-layer immobilized palladium is 2.5cm, and stainless steel pipe is bent into the circle of diameter 25-30cm, is placed in thermostat, constitutes continuous flow reactor.As required, can adopt multiple different lipase, the immobilized lipase used by the present invention is IM-100, is the product of Qingdao Weilan Biotechnology Co., Ltd., and this product catalytic activity is high, high temperature resistant, and has good enantioselectivity.

[0011] The connection of each part in the reaction system is that one end of the polytetrafluoroethylene conduit is inserted into the raw liquid storage tank, and the other end is connected to the inlet of the constant flow pump. The outlet of the constant flow pump is connected to one end of the polytetrafluoroethylene conduit, and the other end is connected to the inlet of the fixed bed reactor. The outlet of the fixed bed reactor is connected to the polytetrafluoroethylene conduit, and the other end of the conduit is inserted into the reaction product storage tank. Start the constant flow pump, the reaction liquid is pumped from the raw liquid storage tank into the fixed bed reactor, and the flow reaction is carried out in the reactor. It reaches the reactor outlet and enters the reaction product storage tank through the outlet conduit to complete a reaction. This reaction system is called a continuous flow reaction system, or a fixed bed reaction system. Depending on the reaction situation, the effluent can be circulated.

[0012] The present invention adopts the above continuous flow reaction system to carry out DKR to obtain a chiral product. Specifically, immobilized lipase IM-100 and immobilized palladium are used to catalyze racemic phenylethylamine to carry out DKR to prepare (R)-amide.

[0013] The reaction principle is as follows: the immobilized enzyme acts as a resolution catalyst, catalyzing the reaction of the (R)-amine in the racemic amine with the acyl donor to generate (R)-amide with absolute specificity; the immobilized palladium acts as a racemization catalyst, catalyzing the conversion of the remaining substrate (S)-amine into racemic amine. The newly generated (R)-amine can be catalyzed by the enzyme to generate (R)-amide, and this process is repeated. The theoretical yield of the final product (R)-amide can reach 100%, and the ee is 100%.

[0014] The specific reaction steps are as follows: when the thermostat temperature reaches the set temperature of 60°C, turn on the constant flow pump, pump the racemic substrate amine and acyl donor solution in the raw material bottle into the fixed bed reactor at a flow rate of 0.2-3ml / min, and perform chemical-enzymatic DKR on the substrate racemic amine until it flows out of the reactor. After the reaction is stable for 30 minutes, collect the reaction solution into the product bottle, and after 30 minutes, turn off the pump to end the DKR reaction. The product is sampled for HPLC analysis. The solvent in the reaction solution is evaporated with a rotary evaporator. The concentrated product solution is separated and purified by preparative chromatography, and the eluent is isopropanol / hexane 10 / 90 to obtain a (R)-amide solution, and the solvent is evaporated under reduced pressure. The product (R)-amide is a white or off-white solid.

[0015] Flow rate (space time) is an important operating parameter of the continuous flow reactor. In order to evaluate the effect of flow rate on the DKR of the continuous flow packed bed, DKR experiments were carried out at different flow rates of 0.5, 1, 1.5, 2.5 and 3 ml / min, corresponding to space times of 39.23, 19.63, 13.09, 7.85 and 6.54 minutes, respectively. The results show that within the flow rate range of 0.5 to 1 ml / min, the yield of the product (R)-amide reaches more than 99%, indicating that the immobilized enzyme and immobilized palladium contained in the reactor can completely convert the substrate at a flow rate of 1 ml / min. As the flow rate increases, the conversion rate decreases, which means that the substrate load at this time has exceeded the catalytic capacity of the catalyst. After the reaction solution flows out of the reactor, the unreacted substrate, product, etc. flow out of the fixed bed reactor and are directly separated from the enzyme and palladium catalyst. This is the characteristic and advantage of the fixed bed reactor.

[0016] The palladium is a self-made immobilized palladium, specifically 0.75-0.8g of palladium acetate is added to a small amount of acetonitrile to dissolve, and then 160ml of water is slowly added and stirred until it is evenly mixed. Take 6g of ethanol-swollen macroporous adsorption resin and add 30mL of palladium acetate solution. Adsorb 4-5.5h in a gas bath constant temperature oscillator at room temperature, and filter dry after adsorption. Weigh 0.155g of potassium borohydride and add 50ml of water to dissolve. Under ultrasonic conditions, potassium borohydride solution is added dropwise to the above resin for palladium reduction. After all the potassium borohydride solution is dripped in, it is placed in a gas bath constant temperature oscillator and oscillated for 4h to fully react. The reduced resin is washed with water 3 times, filtered and placed in a 45°C oven, and dried to a constant weight of the resin mass. The palladium content is determined to be 0.0095-0.011g palladium / g dry resin using EDTA complexometric titration.

[0017] Liquid phase detection conditions: Shimadzu liquid chromatograph LC-16, mobile phase: n-hexane: isopropanol: diethylamine = 90:10:0.1, Daicel chiral column IB N-3, 3μm×5mm×250mm, product retention time 9.6min. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 It is a schematic diagram of a flow reaction system. The flow reaction system is mainly composed of a raw material liquid storage tank, a constant flow pump, a three-way pipe joint, a fixed bed reactor, a product liquid storage tank, and a regulating valve. DETAILED DESCRIPTION

[0018] Example 1

[0019] (1) Preparation of immobilized palladium:

[0020] Weigh 6g of macroporous adsorption resin, add anhydrous ethanol and soak overnight, filter dry, and wash with water 3 times. Then soak the washed resin in water, oscillate in an air bath constant temperature oscillator for 30 minutes, filter dry and set aside. Weigh 0.75g of palladium acetate in a beaker, add 50mL of acetonitrile to dissolve, then slowly add 160ml of water and stir until it is evenly mixed. Add 30mL of the above palladium acetate solution to the resin and adsorb in an air bath constant temperature oscillator for 5.5h at room temperature. Filter dry after adsorption. Weigh 0.155g of potassium borohydride and add 50ml of water to dissolve. Add potassium borohydride solution dropwise to the above resin under ultrasonic conditions to reduce palladium. After all the potassium borohydride solution is dripped, put it in an air bath constant temperature oscillator and oscillate for 4h to fully react. Wash the reduced resin with water 3 times, filter dry and put it in a 45℃ electric constant temperature blast drying oven to dry until the resin mass is constant weight. The palladium content was determined to be 0.0104 g palladium / g dry resin using EDTA complexometric titration.

[0021] (2) Continuous flow reaction in fixed bed reactor, DKR preparation of chiral (R)-2-methoxy-N-(1-phenylethyl)acetamide:

[0022] The flow reaction system is composed of the following units: (1) a constant flow pump for pumping the reaction liquid, such as the CFSP-1 / CU-1 constant flow pump of Duke Industrial Technology (Shanghai) Co., Ltd. (2) a fixed bed reactor for DKR reaction (3) a raw material liquid storage tank for storing the raw material liquid, i.e., a 0.15 mol / L toluene solution of the substrate phenylethylamine and a 0.3 mol / L toluene solution of the acyl donor ethyl methoxyacetate (4) a reaction product storage tank for receiving the reaction liquid from the reactor outlet (5) a thermostat for providing a constant temperature environment for the reaction.

[0023] Adopting fixed bed of the present invention is the continuous flow chemical-enzyme reactor that immobilized lipase and immobilized palladium are housed.The size of this reactor is long 100cm, the stainless steel pipe of internal diameter 0.5cm, wherein alternately fills immobilized enzyme and immobilized palladium, separates with thin cotton cloth between enzyme layer and palladium layer, the thickness of single-layer immobilized enzyme layer is 2.5cm, the thickness of single-layer immobilized palladium is 2.5cm, stainless steel pipe is bent into the circle of diameter 25-30cm, is placed in thermostat, constitutes continuous flow reactor.As required, can adopt multiple different lipase, the used immobilized lipase of the present invention is IM-100, is the product of Qingdao Weilan Biotechnology Co., Ltd.

[0024] The reaction principle is as follows: the immobilized enzyme IM-100 acts as a resolution catalyst, and absolutely specifically catalyzes the reaction of (R)-phenylethylamine in racemic phenylethylamine with an acyl donor to generate (R)-amide; the immobilized palladium acts as a racemization catalyst, and catalyzes the conversion of the remaining substrate (S)-phenylethylamine into racemic phenylethylamine. The newly generated (R)-phenylethylamine can be specifically catalyzed by the enzyme to generate (R)-amide, and this process is repeated. The final product (R)-amide has a theoretical yield of 100% and an ee of 100%. The reaction route is as follows:

[0025]

[0026] The specific reaction steps are as follows: the solvent in the raw material bottle is 300 mL of a toluene solution containing 0.15 mol / L substrate racemic phenylethylamine and 0.3 mol / L acyl donor ethyl methoxyacetate. When the thermostat temperature reaches the set temperature of 60°C, turn on the constant flow pump, pump the solution in the raw material bottle into the fixed bed reactor at a flow rate of 1 ml / min, and perform chemical-enzyme DKR on the substrate phenylethylamine until it flows out of the reactor. After the reaction is stable for 30 minutes, the reaction solution is collected in the product bottle. After the reaction continues for 30 minutes, the pump is turned off to terminate the DKR reaction. The product is sampled for HPLC analysis, and the yield is 99%. Liquid phase detection shows that the reaction product is only (R)-amide, and no (S)-amide is detected, that is, the enantiomeric excess rate is 100%. It shows that under the present reaction conditions, the immobilized lipase IM-100 has absolute selectivity and excellent enantiomeric selectivity. It also shows that the ratio of the reaction immobilized enzyme to the immobilized palladium in the reaction system is appropriate.

[0027] Liquid phase detection conditions: Shimadzu liquid chromatograph LC-16, mobile phase: n-hexane: isopropanol: diethylamine = 90:10:0.1, Daicel chiral column IB N-3, 3μm×5mm×250mm, product retention time 9.6min.

[0028] The solvent in the reaction solution was evaporated by a rotary evaporator, and the concentrated product solution was separated and purified by preparative chromatography, with the eluent being isopropanol / hexane 10 / 90, to obtain a solution of (R)-2-methoxy-N-(1-phenylethyl)acetamide. The solvent was evaporated under reduced pressure, and the product (R)-2-methoxy-N-(1-phenylethyl)acetamide was obtained as a white or off-white solid. 1HNMR(500MHz,Chloroform-d)δ7.29,7.29,7.29,7.28,7.28,7.28,7.28,7.27,7.27,7.27,7.26,7.26,7.26,7. 25,6.15,6.13,5.13,5.11,5.11,5.10,5.10,5.10,5.09,5.09,5.07,4.40,4.37,4.15,4.12,3.36,1.52,1.50. 13 C NMR (125MHz, Common NMR Solvents) δ170.28,144.79,128.16,126.65,125.84,70.35,62.64,50.14,22.58.

[0029] Example 2

[0030] The preparation of immobilized palladium was the same as in Example 1, and the prepared palladium content was 0.0098 g palladium / g dry resin.

[0031] The reaction system, reaction conditions, separation and purification conditions and NMR data were the same as those in Example 1, except that the feed flow rate was changed from 1 ml / min to 0.5 ml / min. In the reaction, the yield was 100% and the enantiomeric excess ee was 100%. It can be seen that when the feed flow rate is reduced, the yield is increased because the reaction time is extended.

[0032] Example 3

[0033] The immobilized palladium prepared in Example 2 was used.

[0034] The reaction system, reaction conditions, separation and purification conditions, NMR data, etc. were the same as those in Example 1, except that the feed flow rate was changed from 1 ml / min to 3 ml / min. In this reaction, the yield was 66.4% and the enantiomeric excess ee was 100%. It can be seen that when the flow rate is increased, the yield is reduced because the reaction time is reduced.

[0035] Example 4

[0036] The immobilized palladium prepared in Example 1 was used.

[0037] The reaction system, reaction conditions, separation and purification conditions, NMR data, etc. were the same as those in Example 1, except that the feed flow rate was changed from 1 ml / min to 2 ml / min. In this reaction, the yield was 82.1% and the enantiomeric excess ee was 100%. It can be seen that when the flow rate is increased, the yield is reduced because the reaction time is reduced.

[0038] Comparative Example 1

[0039] The immobilized palladium prepared in Example 1 was used.

[0040] The reaction system, reaction conditions, separation and purification conditions, NMR data, etc. were the same as those in Example 1, except that the fixed bed reactor was made differently. The dimensions of the stainless steel tube were the same as those in Example 1, and only the filling methods of the immobilized enzyme and immobilized palladium were changed.

[0041] The fixed bed reactor was prepared as follows: the immobilized enzyme and the immobilized palladium were mixed evenly and then filled into a stainless steel tube.

[0042] It can be seen that the difference between Comparative Example 1 and Example 1 is that the catalyst filling method of the fixed bed reactor is changed, and the others are the same. However, in this reaction, the yield obtained is 68.2%. It can be seen that after changing the catalyst filling method, the yield is greatly reduced. The reason is that the enzyme and palladium are mixed and filled, and they affect each other, which inhibits the catalytic activity of the enzyme and palladium, so that the yield decreases. In Example 1, since the enzyme and palladium are separately filled, the area is separated, and there is no direct contact, they no longer affect each other, inhibit each other, and the catalytic reaction activity is not affected, so a high yield is obtained, and the yield is as high as 99%, which is much higher than the comparative example.

[0043] Comparative Example 2

[0044] The reaction system, reaction conditions, separation and purification conditions, NMR data, etc. are the same as those in Example 4. The difference is that the fixed bed reactor uses the reactor of Comparative Example 1.

[0045] It can be seen that the difference between Comparative Example 4 and Example 4 is that the catalyst filling method of the fixed bed reactor is changed, and the others are the same. However, in this reaction, the yield obtained is 42.2%. It can be seen that after changing the catalyst filling method, the yield is greatly reduced. The reason is that the enzyme and palladium are mixed and filled, and they affect each other, which inhibits the catalytic activity of the enzyme and palladium, so that the yield decreases. In Example 4, since the enzyme and palladium are separately filled, the area is separated, and there is no direct contact, they no longer affect each other, inhibit each other, and the catalytic reaction activity is not affected, so a higher yield is obtained, and the yield is as high as 82.1%, which is much higher than the comparative example.

Claims

1. A method for preparing chiral amides using a flow reaction system, characterized in that: The method comprises the following steps: The substrate racemic amine and the acyl donor are dissolved in an organic solvent to prepare a raw material liquid, and the raw material liquid is pumped into a fixed bed reactor at a certain feed flow rate through a constant flow pump, and dynamic kinetic resolution (DKR) is performed at 50-70° C. The reaction liquid is concentrated under reduced pressure, separated and purified by preparative chromatography, and concentrated to obtain chiral amide; the flow reaction system is mainly composed of the following units: (1) a constant flow pump, (2) a fixed bed reactor, (3) a raw material liquid storage tank, (4) a reaction product storage tank, and (5) a thermostat; the fixed bed reactor is alternately filled with immobilized enzyme and immobilized palladium, and the enzyme layer and the palladium layer are separated by thin cotton cloth; the method adopts chemical-enzyme dynamic kinetic resolution to prepare chiral amide.

2. The method for preparing chiral amide using a flow reaction system according to claim 1, characterized in that: The preparation process of the immobilized palladium is as follows: the pretreated macroporous adsorption resin is soaked in anhydrous ethanol for one night, filtered and washed with water until there is no ethanol smell. Then the washed resin is soaked in water, shaken at room temperature for 30 minutes, and filtered for use; palladium acetate is weighed in a beaker, acetonitrile is added to dissolve, and then water is slowly added and stirred to mix evenly to obtain a palladium acetate solution; the above palladium acetate is dissolved in the pretreated macroporous adsorption resin, shaken and adsorbed at room temperature for 5.5 hours, and after the adsorption is completed, the macroporous adsorption resin adsorbed with palladium acetate is obtained by filtering; potassium borohydride is weighed, and potassium borohydride is added to water to dissolve to obtain a potassium borohydride solution; potassium borohydride solution is added dropwise to the macroporous adsorption resin adsorbed with palladium acetate under ultrasonic conditions. After the addition is completed, the macroporous adsorption resin is shaken at room temperature for 4 hours, and the macroporous adsorption resin is filtered out, washed with water 3 times, filtered and dried at 45°C to constant weight to obtain immobilized palladium, and the palladium content is determined by EDTA complexometric titration to be 0.0095-0.011g palladium / g dry resin.

3. The method for preparing chiral amide using a flow reaction system according to claim 1, characterized in that: The specific operation steps are: when the temperature of the thermostat reaches the set temperature, turn on the constant flow pump, pump the racemic substrate amine and acyl donor solution in the raw material storage tank into the fixed bed reactor, perform chemical-enzymatic DKR on the substrate racemic amine, collect the reaction solution into the product storage tank, and after the DKR reaction is completed, separate and purify to obtain the chiral amide product, and the enantiomeric purity and yield can reach 100%.

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