One-pot cascade synthesis method of flavonoids

Abstract

The application belongs to the technical field of organic compound preparation, and specifically discloses a one-pot cascade synthesis method of flavonoids. The one-pot cascade synthesis method is characterized in that, in the L-proline-formic acid-m-chloroperbenzoic acid mixed solution, the starting materials of o-hydroxyacetophenone compounds and aromatic aldehydes are continuously reacted to obtain the flavonoids. The preparation method has the advantages of fewer steps, easy operation, high yield, low time consumption, low requirement for raw materials, and universality, and the preparation of the flavonoids can be realized by using only the o-hydroxyacetophenone compounds and the aromatic aldehydes.

Description

Technical Field

[0001] This invention relates to the field of organic compound preparation technology, and in particular to a one-pot tandem synthesis method for flavonoids. Background Technology

[0002] Flavonoids are a class of natural products widely found in the plant kingdom. They possess a wide range of physiological activities, including anti-cardiovascular disease activity, anti-inflammatory activity, anti-hepatitis virus activity, and antibacterial activity, thus attracting widespread attention from chemists. Due to their structural diversity and broad pharmacological activities, the flavonoid skeleton has become an indispensable structural framework in medicinal chemistry and natural product research. Examples include apigenin, nobiletin, hesperidin, farnesin, and alfalfa extract. Finding simple and efficient methods for flavonoid synthesis is crucial for conducting in-depth activity studies.

[0003] Currently, various synthetic methods for constructing flavonoid skeletons have been reported in the literature. These methods can be classified into multi-step synthesis, one-step synthesis, and tandem reaction methods.

[0004] (a) Multi-step synthesis includes: the improved Baker-Venkataraman method and the synthesis of flavonoids using arylpropynic acid.

[0005] The improved Baker-Venkataraman method generally involves reacting 2-hydroxyacetophenone with aryl formaldehyde chloride in the presence of pyridine to form an ester. The resulting ester is then treated with a base to undergo an intramolecular Claisen condensation reaction, forming a β-propanedione compound. Finally, acid-catalyzed cyclization yields a flavonoid compound. Ares et al. reported that 2-hydroxy-6-methoxyacetophenone was first treated with 1.1 moles of potassium tert-butoxide to form a potassium salt of phenol, then esterified with benzoyl chloride. 1.1 moles of potassium tert-butoxide were then added directly to the reaction mixture, and after reflux overnight, the rearranged product β-propanedione was obtained. Finally, acid-catalyzed cyclization yielded a flavonoid. However, the overall yield was only 46%, and the reaction time required was over 12 hours (see: The Journal of Organic Chemistry, 1993, 58, 7903).

[0006]

[0007] Synthesis of flavonoids using arylpropynic acids: The carbonyl group of the synthesized flavonoid compounds comes from the arylpropynic acid component. The ester obtained by esterification of phenol with arylpropynic acid is rearranged to obtain a compound containing an alkyne group and an o-hydroxyacetophenone structure. This type of compound can form flavonoids through ring closure. Garcia et al. obtained aryl propynic acid esters by esterification of phenylpropynic acid with phenol, which underwent photochemical Fries rearrangement to obtain o-hydroxyarylethynyl ketones, which were then ring-closed to form flavonoids. However, the overall yield was low (10-25%). The desired phenolic propynic acid ester was obtained by esterification of phenylpropynic acid and phenolic compounds in polyphosphoric acid at 100°C (see: The Journal of Organic Chemistry, 1986, 51, 4432).

[0008]

[0009] (ii) One-step synthesis method: mainly based on the oxidative dehydrogenation method of dihydroflavonoids in continuous flow reaction.

[0010] Continuous flow reactions have attracted attention due to their advantages in heat and mass transfer, reaction safety, and other aspects. Chinese patent application CN112979603A discloses a process: using dihydroflavonoid hesperidin as a raw material and elemental iodine as an oxidant, iodine-mediated dehydrogenation is achieved in a continuous flow microchannel reactor. However, its starting material is dihydroflavonoids containing the basic flavonoid skeleton, and the reaction only completes the conversion of carbon-carbon single bonds to double bonds, without involving the construction of the basic flavonoid skeleton.

[0011]

[0012] (iii) Series reactions include: one-pot series synthesis.

[0013] In recent years, one-pot tandem reactions have attracted attention due to their ease of operation. Nadja et al. reported a method for the direct preparation of flavonoids from 2-hydroxyacetophenones and aromatic aldehydes via a tandem reaction in a pyrrolidine-iodine-dimethyl sulfoxide system (see: European Journal of Medicinal Chemistry, 2022, 238, 114332). Although this method achieves one-pot synthesis from simple starting materials, it has significant drawbacks: the reaction temperature is relatively high (requiring 150°C), and the yield of flavonoid products is generally low (only 19-52%), making it difficult to meet practical production needs.

[0014]

[0015] In summary, the currently reported methods for synthesizing flavonoids have the following problems: multi-step synthesis methods are lengthy and time-consuming (usually requiring more than 12 hours); continuous flow-based oxidative dehydrogenation methods are limited to using dihydroflavonoids as substrates and cannot construct the basic flavonoid framework; while one-pot methods using simple raw materials in series (such as Nadja's method) suffer from harsh reaction conditions and low yields.

[0016] Therefore, developing a new method to prepare flavonoids from simple raw materials in a short time (minutes) under mild conditions remains a pressing problem to be solved in this field. Summary of the Invention

[0017] In view of this, the present invention provides a one-pot tandem synthesis method for flavonoids to solve the problems of low yield, long time consumption and high requirements for raw materials in existing flavonoid synthesis methods.

[0018] To achieve the above objectives, the present invention adopts the following technical solution: A one-pot tandem synthesis method for flavonoids includes the following steps: Starting with o-hydroxyacetophenone compounds and aromatic aldehyde compounds, flavonoid compounds were obtained by a one-pot tandem synthesis method in a mixed solution of L-proline-formic acid-m-chloroperoxybenzoic acid. The structural formula of the o-hydroxyacetophenone compound is as follows: ; The structural formula of the aromatic aldehyde compound is: ; The structural formula of the flavonoid compound is: ; R 1 and R 3 Independently selected from hydrogen, methoxy, or hydroxyl; R 2 R 4 R 6 and R 8 Independently selected from hydrogen or methoxy; R 5 Selected from hydrogen, methyl, or cyclopropyl; R 7 It is selected from hydrogen, hydroxyl, methoxy, benzyloxy, aniline, pyridyl, pyrazinyl or cyclohexyl.

[0019] Preferably, the L-proline-formic acid-m-chloroperoxybenzoic acid mixed solution is obtained by mixing L-proline, formic acid and m-chloroperoxybenzoic acid; The molar ratio of L-proline to formic acid is 1:2~4; The mass of the m-chloroperoxybenzoic acid is 0.4 to 1% of the total mass of L-proline and formic acid.

[0020] Preferably, the reaction operation employing the continuous flow synthesis method includes: The o-hydroxyacetophenone compound was mixed with a portion of the L-proline-formic acid-m-chloroperoxybenzoic acid mixed solution as component A; the aromatic aldehyde compound was mixed with the remaining L-proline-formic acid-m-chloroperoxybenzoic acid mixed solution as component B; the components A and B were mixed to obtain a mixed solution, which was then fed into a continuous flow reactor for a one-pot series synthesis reaction.

[0021] Preferably, in the one-pot tandem synthesis reaction, the molar ratio of o-hydroxyacetophenone compounds to aromatic aldehyde compounds is 1:1 to 1.2.

[0022] Preferably, the molar volume ratio of the o-hydroxyacetophenone compound to a portion of the L-proline-formic acid-m-chloroperoxybenzoic acid mixed solution is 0.04~0.06 mol: 100 mL; The molar volume ratio of the aromatic aldehyde compound to the remaining L-proline-formic acid-m-chloroperoxybenzoic acid mixed solution is 0.04~0.06 mol: 100 mL.

[0023] Preferably, the residence time of the one-pot series synthesis reaction is 1.6~3.9 min, and the temperature is 90~100℃.

[0024] This invention provides a reaction system using a mixed solution of L-proline, formic acid, and m-chloroperoxybenzoic acid, namely the Pro-FA-CPBA reaction system. In the Pro-FA-CPBA reaction system, formic acid is used as the solvent, and L-proline is the building block, forming an intermolecular hydrogen bond network with formic acid. The system also contains m-chloroperoxybenzoic acid, which acts as a mild oxidant. Heating in a continuous flow reactor of a continuous flow synthesis method enables o-hydroxyacetophenone compounds and aromatic aldehyde compounds to undergo a tandem condensation-cyclization-dehydrogenation reaction, yielding flavonoid compounds in high yield and rapidly.

[0025] The continuous flow tandem reaction described in this invention proceeds as follows: First, under the catalysis of L-proline, o-hydroxyacetophenone compounds and aromatic aldehyde compounds undergo a condensation reaction to generate o-hydroxychalcone intermediates; subsequently, under acidic media provided by formic acid and heating conditions, the intermediates undergo intramolecular cyclization to form dihydroflavonoid intermediates; finally, m-chloroperoxybenzoic acid present in the system oxidizes and dehydrogenates the dihydroflavonoid intermediates, aromatizing them to obtain the final target flavonoid compound.

[0026] In this system, L-proline acts as a condensation catalyst, formic acid as an acidic medium and solvent to promote cyclization, and m-chloroperoxybenzoic acid as a terminal oxidant. These three components do not interfere with each other, achieving a highly efficient cascade reaction within the confined space of a continuous flow reactor. It is worth noting that although the reaction involves multiple steps, because this invention uses a continuous flow method, the reactants, once mixed, rapidly pass through each reaction stage sequentially. Intermediates do not require separation, and the residence time is extremely short (1.6~3.9 min), simplifying operation.

[0027] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: This invention uses readily available o-hydroxyacetophenone compounds and aromatic aldehyde compounds as starting materials to efficiently and rapidly synthesize flavonoid compounds via a continuous flow method.

[0028] Rapid: The reaction residence time is short, far superior to the traditional batch process; High yield: The yield is not less than 85%; The method has a wide range of substrates: it can construct flavonoid compounds from simple aromatic small molecule raw materials, and has a wide selection of substrates, and can synthesize flavonoids with different types of substituents. Detailed Implementation

[0029] This invention provides a one-pot tandem synthesis method for flavonoids, comprising the following steps: Starting with o-hydroxyacetophenone compounds and aromatic aldehyde compounds, flavonoid compounds were synthesized in a continuous flow synthesis method in a mixed solution of L-proline-formic acid-m-chloroperoxybenzoic acid to carry out a one-pot tandem synthesis reaction.

[0030] In this invention, the structural formula of the o-hydroxyacetophenone compound is: The structural formula of the aromatic aldehyde compound is: The structural formula of the flavonoid compound is: ; wherein, the R 1 and R 3 Independently selected from hydrogen, methoxy, or hydroxyl; R 2 R 4 R 6 and R 8 Independently selected from hydrogen or methoxy; R 5 Selected from hydrogen, methyl, or cyclopropyl; R 7 It is selected from hydrogen, hydroxyl, methoxy, benzyloxy, aniline, pyridyl, pyrazinyl or cyclohexyl.

[0031] In this invention, the structural formulas of flavonoid compounds 3a-3l are specifically as follows:

[0032] In this invention, the L-proline-formic acid-m-chloroperoxybenzoic acid mixed solution is obtained by mixing L-proline, formic acid and m-chloroperoxybenzoic acid.

[0033] In this invention, it is preferable to first stir L-proline and formic acid under heating until they are homogeneous and transparent, and then slowly add m-chloroperoxybenzoic acid while stirring after cooling to a certain temperature; the mixing temperature of L-proline and formic acid is preferably 90~100℃, specifically 92℃, 94℃, 95℃, 96℃, or 98℃; the temperature at which m-chloroperoxybenzoic acid is added is preferably 40~50℃, specifically 42℃, 44℃, 45℃, 46℃, or 48℃.

[0034] In this invention, the molar ratio of L-proline to formic acid is 1:2 to 4, preferably 1:2.5 to 3.5, and more preferably 1:3.

[0035] In this invention, the mass of the m-chloroperoxybenzoic acid is 0.4-1% of the total mass of L-proline and formic acid, specifically 0.5%, 0.6%, 0.7%, 0.8%, or 0.9%.

[0036] In this invention, the reaction operation employing the continuous flow synthesis method includes: The o-hydroxyacetophenone compound was mixed with a portion of the L-proline-formic acid-m-chloroperoxybenzoic acid mixed solution as component A; the aromatic aldehyde compound was mixed with the remaining L-proline-formic acid-m-chloroperoxybenzoic acid mixed solution as component B; the components A and B were mixed to obtain a mixed solution, which was then fed into a continuous flow reactor for a one-pot series synthesis reaction.

[0037] In this invention, in the one-pot tandem synthesis reaction, the molar ratio of o-hydroxyacetophenone compounds and aromatic aldehyde compounds is 1:1 to 1.2, preferably 1:1 to 1.1, and more preferably 1:1.08.

[0038] In this invention, the molar volume ratio of the o-hydroxyacetophenone compound to a portion of the L-proline-formic acid-m-chloroperoxybenzoic acid mixed solution is 0.04~0.06 mol:100 mL, preferably 0.05 mol:100 mL; the molar volume ratio of the aromatic aldehyde compound to the remaining L-proline-formic acid-m-chloroperoxybenzoic acid mixed solution is 0.04~0.06 mol:100 mL, preferably 0.054 mol:100 mL.

[0039] In this invention, the residence time of the one-pot series synthesis reaction is 1.6~3.9 min, specifically 1.6 min, 1.8 min, 2.0 min, 2.1 min, 2.5 min, 2.8 min, 3.0 min, 3.1 min, 3.4 min, 3.6 min, and 3.9 min; the temperature is 90~100℃, specifically 92℃, 94℃, 95℃, 96℃, and 98℃; corresponding to the residence time of 1.6~3.9 min used in the instrument of this embodiment, the corresponding infeed rate of component A or component B is 2~5 mL / min, specifically 2.0 mL / min, 2.2 mL / min, 2.3 mL / min, 2.5 mL / min, 2.6 mL / min, 2.8 mL / min, 3.1 mL / min, 3.7 mL / min, 3.9 mL / min, 4.4 mL / min, and 5.0 mL / min.

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Example 1

[0042] Taking product 3a as an example, flavonoids were prepared.

[0043] L-proline and formic acid were mixed in a molar ratio of 1:3 (45.5 g proline and 54.5 g formic acid) in a beaker and stirred at 90 °C until homogeneous and transparent. After cooling to 45 °C, 0.5 g of m-chloroperoxybenzoic acid was slowly added while stirring, and stirring was continued for 20 min to obtain the Pro-FA-CPBA reaction medium.

[0044] Add 8.4 g (0.05 mol) of 2,4,6-trihydroxyacetophenone (CAS: 480-66-0) and 100 mL of Pro-FA-CPBA medium to conical flask 1, sonicate until the solid dissolves, and draw 50 mL with syringe A, place it in a syringe pump, and set the flow rate to 4 mL / min; add 7.4 g (0.054 mol) of p-methoxybenzaldehyde (CAS: 123-11-5) and 100 mL of Pro-FA-CPBA medium to conical flask 2, sonicate until the solid dissolves, and draw 50 mL with syringe B, place it in a syringe pump, and set the flow rate to 4 mL / min; mix the materials in A and B first through a PTFE tee, and then enter a metal coil continuous flow reactor (flow rate of 8 mL / min). The reactor is placed in a 95℃ constant temperature oil bath, and the residence time is 2.0 min.

[0045] After the reaction mixture effluent flows out, the effluent (about 100 mL) is collected, cooled to room temperature, and 4 times its volume of water (about 400 mL) is added. A pale yellow solid precipitates out. The solid is filtered, and the filter cake is washed with 5 mL of cold ethanol. The crude product is dissolved by heating with 30 mL of ethanol. Impurities are adsorbed onto silica gel. The mixture is filtered while hot, cooled to crystallize, and dried to give 6.2 g of white needle-like solid, with a yield of 87.3%.

[0046] 3a (farnesin) 1H NMR data: 1 ¹H NMR (400 MHz, DMSO-D6) δ 12.933 (s, 1H), 10.890 (s, 1H), 8.037 (d, J = 9.2 Hz, 2H), 7.111 (d, J = 8.8 Hz, 2H), 6.876 (s, 1H), 6.515 (d, J = 2 Hz, 1H), 6.212 (d, J = 2 Hz, 1H), 3.861 (s, 3H); Carbon NMR data (some carbon signals are not listed due to overlap): 13 C NMR (100 MHz, DMSO-D6) δ 181.8, 164.2, 163.3,162.3, 161.4, 157.3, 128.3, 122.8, 114.6, 103.7, 103.5, 98.9, 94.0, 55.5; ESI-MS: m / z calculated for C 16 H 12 O5 [MH] — : 283.06, found 283.04.

[0047] Example 2

[0048] Preparation of flavonoid compounds 3b-3l

[0049] Based on products 3b~3l, select the corresponding sites (R) 1 ~R 8 Substrates containing the same groups as the products (o-hydroxyacetophenone compounds and aromatic aldehyde compounds) were prepared using the same preparation method as in Example 1, and 3b-3l were prepared. The characterization data and yields are shown below: 3b (Alfalfa extract): Starting materials: 2,4,6-trihydroxyacetophenone (CAS: 480-66-0) and 3,5-dimethoxy-4-hydroxybenzaldehyde (CAS: 134-96-3); Reaction residence time: 2.5 min; Yield: 87.5%; 1H NMR data: 1¹H NMR (400 MHz, DMSO-D6) δ 12.974 (s, 1H), 10.822 (s, 1H), 9.346 (s, 1H), 7.331 (s, 2H), 6.993 (s, 1H), 6.563 (d, J = 2.4 Hz, 1H), 6.208 (d, J = 2 Hz, 1H), 3.890 (s, 6H); Carbon NMR data (some carbon signals are not listed due to overlap): 13 C NMR (100 MHz, DMSO-D6) δ 181.8,164.1, 163.6, 161.4, 157.3, 148.2, 139.8, 120.4, 104.4, 103.7, 103.6, 98.8,94.2, 56.3; ESI-MS: m / z calculated for C 17 H 14 O7 [MH] — : 329.07, found 329.09. 3c (Chuan Chenpixin): 1-(2-hydroxy-3,4,5,6-tetramethoxyphenyl)ethyl-1-one (CAS: 3162-28-5) and 3,4-dimethoxybenzaldehyde (CAS: 120-14-9); reaction residence time: 3.0 min; yield: 86.2%; 1H NMR data: 1 ¹H NMR (400 MHz, CDCl₃) δ 7.581 (dd, J = 8.8 Hz, J = 2.4 Hz, 1H), 7.420 (d, J = 2 Hz, 1H), 7.001 (d, J = 8.4 Hz, 1H), 6.661 (s, 1H), 4.112 (s, 3H), 4.031 (s, 3H), 3.984–3.958 (m, 12H); Carbon NMR data: 13 C NMR (100 MHz, CDCl3) δ 177.4, 161.1,152.0, 151.4, 149.3, 148.5, 147.7, 144.1, 138.0, 124.1, 119.6, 114.9, 111.3,108.6, 106.9, 62.3, 62.0, 61.8, 61.7, 56.1, 56.0; ESI-MS: m / z calculated forC 21 H 22 O8 [M+Na] +: 425.12, found 425.03. 3d (Hesperidin): Starting materials: 1-(2-hydroxy-3,4,5,6-tetramethoxyphenyl)ethyl-1-one (CAS: 3162-28-5) and p-methoxybenzaldehyde (CAS: 123-11-5); Reaction residence time: 3.1 min; Yield: 88.6%; 1H NMR data: 1 ¹H NMR (400 MHz, CDCl₃) δ 7.89 (d, J = 12 Hz, 2H), 7.03 (d, J = 8 Hz, 2H), 6.64 (s, 1H), 4.11 (s, 3H), 4.03 (s, 3H), 3.95 (s, 6H), 3.89 (s, 3H); Carbon NMR data (some carbon signals are not listed due to overlap): 13 C NMR (100 MHz, CDCl3) δ 177.4, 162.3, 161.2,151.4, 148.4, 147.7, 144.1, 138.1, 127.7, 123.9, 114.9, 114.5, 106.7, 62.3,62.0, 61.8, 61.7, 55.5; ESI-MS: m / z calculated for C 20 H 20 O7 [M+Na] + : 395.11, found 395.07. 3e (apigenin): Starting materials: 2,4,6-trihydroxyacetophenone (CAS: 480-66-0) and p-hydroxybenzaldehyde (CAS: 123-08-0); Reaction residence time: 3.6 min; Yield: 87.9%; 1H NMR data: 1 ¹H NMR (400 MHz, DMSO-D6) δ 12.98 (s, 1H), 10.83 (s, 1H), 10.38 (s, 1H), 7.93 (d, J = 8 Hz, 2H), 6.94 (d, J = 8 Hz, 2H), 6.79 (s, 1H), 6.49 (s, 1H), 6.20 (s, 1H); Carbon NMR data (some carbon signals are not listed due to overlap): 13C NMR (100 MHz, DMSO-D6) δ 181.7, 164.1, 163.7, 161.4,161.2, 157.3, 128.5, 121.2, 115.9, 103.7, 102.8, 98.8, 93.9; ESI-MS: m / zcalculated for C 15 H 10 O5 [MH] — : 269.04, found 269.07. 3f: Starting materials: 2'-hydroxy-5'-methoxyacetophenone (CAS: 705-15-7) and benzaldehyde (CAS: 100-52-7); Reaction residence time: 2 min; Yield: 88.2%; 1H NMR data: 1 ¹H NMR (400 MHz, CDCl₃) δ 7.82–7.80 (m, 2H), 7.49 (d, J = 4 Hz, 1H), 7.42–7.39 (m, 4H), 7.20–7.16 (m, 1H), 6.71 (s, 1H), 3.80 (s, 3H); Carbon NMR data (some carbon signals are not listed due to overlap): 13 C NMR (100 MHz, CDCl3) δ 178.3, 163.1, 157.0, 151.1, 131.9, 131.5, 129.0, 126.2, 124.5,123.8, 119.5, 106.8, 104.8, 55.9; ESI-MS: m / z calculated for C 16 H 12 O3 [M+Na] + :275.07, found 275.03. 3g: Starting materials: 2'-hydroxyacetophenone (CAS: 118-93-4) and 4-(phenylamino)benzaldehyde (CAS: 100727-07-9); Reaction residence time: 2.7 min; Yield: 87.9%; 1H NMR data: 1¹H NMR (400 MHz, CDCl₃) δ 8.22 (d, J = 8 Hz, 1H), 7.80 (d, J = 12 Hz, 2H), 7.69–7.59 (m, 2H), 7.53 (d, J = 8 Hz, 1H), 7.41–7.33 (m, 3H), 7.20 (d, J = 8 Hz, 2H), 7.11–7.05 (m, 3H), 6.72 (s, 1H); Carbon NMR data (some carbon signals are not listed due to overlap): 13 C NMR (100 MHz, CDCl3) δ178.4, 163.6, 156.1, 147.2, 140.8, 138.4, 133.4, 129.5, 127.9, 125.6, 124.9,124.0, 123.1, 122.4, 121.6, 120.3, 117.9, 116.1, 115.5, 105.3; HRMS (ESI-): m / z calculated for C 21 H 15 NO2 [MH] — : 312.1025, found 312.1023. 3h: Starting materials: 2'-hydroxyacetophenone (CAS: 118-93-4) and 4-(2-pyrazinyl)benzaldehyde (CAS: 127406-08-0); Reaction residence time: 2.9 min; Yield: 88.2%; 1H NMR data: 1 ¹H NMR (400 MHz, CDCl₃) δ 9.124 (s, 1H), 8.698 (t, J = 2 Hz, 1H), 8.587 (d, J = 2.8 Hz, 1H), 8.250 (dd, J = 8 Hz, J = 1.6 Hz, 1H), 8.210 (d, J = 8.4 Hz, 2H), 8.087 (d, J = 8.8 Hz, 2H), 7.754–7.711 (m, 1H), 7.616 (d, J = 8.4 Hz, 1H), 7.447 (t, J = 8 Hz, 1H), 6.915 (s, 1H); Carbon NMR data (some carbon signals are not listed due to overlap): 13C NMR (100 MHz, CDCl3) δ178.3, 162.5, 156.3, 151.4, 144.4, 143.7, 142.3, 139.2, 133.9, 133.1, 127.5,126.9, 125.8, 125.4, 124.0, 118.1, 108.1; HRMS (ESI+): m / z calculated forC 19 H 12 N₂O₂ [M+Na] + : 323.0796, found 323.0793. 3i: Starting materials: 2'-hydroxyacetophenone (CAS: 118-93-4) and 2-cyclopropylbenzaldehyde (CAS: 20034-51-9); Reaction residence time: 2.4 min; Yield: 86.4%; 1H NMR data: 1 ¹H NMR (400 MHz, CDCl₃) δ 8.28 (d, J = 8 Hz, 1H), 7.70 (t, J = 8 Hz, 1H), 7.53–7.43 (m, 4H), 7.30 (t, J = 8 Hz, 1H), 7.12 (d, J = 8 Hz, 1H), 6.62 (s, 1H), 2.16–2.10 (m, 1H), 0.95 (d, J = 8 Hz, 2H), 0.74 (d, J = 4 Hz, 2H); Carbon NMR data (some carbon signals are not listed due to overlap): 13 C NMR(100 MHz, CDCl3) δ 178.3, 166.0, 156.6, 142.1, 133.7, 133.5, 130.8, 129.0,126.1, 125.9, 125.8, 125.2, 123.8, 118.1, 112.4, 13.9, 8.6; HRMS (ESI+): m / zcalculated for C 18 H 14 O2 [M+Na] + : 285.0891, found 285.0889. 3j: Starting materials: 2'-hydroxyacetophenone (CAS: 118-93-4) and 4-cyclohexylbenzaldehyde (CAS: 27634-89-5); Reaction residence time: 2.6 min; Yield: 86.3%; 1H NMR data: 1¹H NMR (400 MHz, CDCl₃) δ 8.231 (dd, J = 8 Hz, J = 1.6 Hz, 1H), 7.852 (d, J = 8.4 Hz, 2H), 7.709–7.666 (m, 1H), 7.561 (d, J = 8.8 Hz, 1H), 7.430–7.349 (m, 3H), 6.806 (s, 1H), 2.615–2.550 (m, 1H), 1.923–1.762 (m, 5H), 1.506–1.260 (m, 5H); Carbon spectrum data (some carbon signals are not listed due to overlap): 13 C NMR (100 MHz, CDCl3) δ 178.4, 163.7, 156.2, 152.2, 133.6,129.3, 127.5, 126.3, 125.7, 125.1, 124.0, 118.0, 107.0, 44.5, 34.1, 26.7,26.0; HRMS (ESI+): m / z calculated for C 21 H 20 O2 [M+Na] + : 327.1361, found327.1359. 3k: Starting materials: 2'-hydroxyacetophenone (CAS: 118-93-4) and 4-(pyridin-3-yl)benzaldehyde (CAS: 127406-55-7); Reaction residence time: 3.5 min; Yield: 88.7%; 1H NMR data: 1 ¹H NMR (400 MHz, CDCl₃) δ 8.921 (s, 1H), 8.661 (d, J = 6.4 Hz, 1H), 8.246 (dd, J = 8 Hz, J = 1.6 Hz, 1H), 8.050 (d, J = 8.4 Hz, 2H), 7.945 (dt, J = 8 Hz, J = 2 Hz, 1H), 7.764–7.703 (m, 3H), 7.601 (d, J = 7.2 Hz, 1H), 7.457–7.410 (m, 2H), 6.883 (s, 1H); Carbon NMR data (some carbon signals are not listed due to overlap): 13C NMR (100 MHz, CDCl3) δ 178.3, 162.7,156.2, 149.3, 148.2, 140.9, 135.3, 134.3, 133.8, 131.4, 127.7, 127.0, 125.7,125.3, 124.0, 123.7, 118.1, 107.7; HRMS (ESI+): m / z calculated for C 20 H 13 NO2 [M+H] + : 300.1025, found 300.1021. 3l: Starting materials: 2'-hydroxyacetophenone (CAS: 118-93-4) and 4-(benzyloxy)-2-methylbenzaldehyde (CAS: 101093-56-5); Reaction residence time: 3.2 min; Yield: 88.1%; 1H NMR data: 1 ¹H NMR (400 MHz, CDCl₃) δ 8.252 (dd, J = 8 Hz, J = 1.6 Hz, 1H), 7.698–7.655 (m, 1H), 7.508–7.346 (m, 8H), 6.932–6.895 (m, 2H), 6.466 (s, 1H), 5.121 (s, 2H), 2.487 (s, 3H); Carbon NMR data (some carbon signals are not listed due to overlap): 13 C NMR (100 MHz, CDCl3) δ 178.3, 165.9,160.5, 156.4, 138.9, 136.4, 133.6, 130.9, 128.6, 128.1, 127.4, 125.7, 125.4,125.1, 123.8, 118.0, 117.7, 112.3, 111.4, 70.0, 21.0; HRMS (ESI+): m / zcalculated for C 23 H 18 O3 [M+Na] + 365.1154 was found, and 365.1152 was found. Example 3 The difference between this embodiment and Example 1 lies only in adjusting the flow rate of syringe A to 1 mL / min, 2 mL / min, 3 mL / min, 4 mL / min, 5 mL / min, and 6 mL / min (while controlling the flow rate of syringe B to be equal to that of syringe A). The corresponding residence times for the continuous flow synthesis method are 7.9 min, 3.9 min, 2.6 min, 2.0 min, 1.6 min, and 1.3 min, respectively. The yield was tested and calculated, and the results are shown in Table 1.

[0050] Table 1. Correspondence between Flow Rate and Yield

[0051] Table 1 shows that excessive flow rate leads to shorter residence time and decreased yield. Conversely, insufficient flow rate results in longer residence time, which may cause the target flavonoid to undergo ring-opening or excessive oxidation side reactions during prolonged high-temperature retention in the oxidizing Pro-FA-CPBA medium, also leading to a decrease in yield.

[0052] Example 4

[0053] Determination of the inhibitory activity of compound 3g-3l against xanthine oxidase (disclosed for the first time)

[0054] Experimental materials and solution preparation: Phosphate-buffered saline (PBS, pH 7.4) was prepared according to standard methods. Xanthine oxidase (Sigma X4875) was diluted with PBS to the appropriate activity. Xanthine substrate was prepared into a 280 µmol / L solution with PBS. The test compound and the positive control allopurinol were prepared into stock solutions with DMSO, and diluted to the target concentration with PBS containing an equal proportion of DMSO before use (final DMSO concentration ≤ 0.1%).

[0055] Sample addition and reaction system (96-well plate, total volume 200 µL): The experiment was divided into four groups. Enzyme activity control group: 20 µL PBS containing DMSO + 80 µL enzyme solution; Sample group: 20 µL working solution of the test compound + 80 µL enzyme solution; Sample background group: 20 µL working solution of the test compound + 80 µL PBS (as a substitute for enzyme); Substrate background group: 20 µL PBS containing DMSO + 80 µL PBS (as a substitute for enzyme). After mixing all the above wells, incubate at 37°C for 5 min, then add 100 µL of xanthine substrate solution to each well to start the reaction.

[0056] Detection and Data Processing: Place the sample in an ELISA reader and monitor continuously at 295 nm for 5 min, recording the absorbance value every 30 s. Calculate the slope (V) of each well within the linear reaction interval. Subtract the substrate background slope from the slope of each group (i.e., subtract the measured slope of the substrate background slope from the measured slope of each group), and calculate the inhibition rate using the following formula: Inhibition rate (%) = [1 - (V 样品 -V 样品背景 ) / V 酶活性对照 ]×100% Experimental results: The inhibition rates of compound 3g~3l on xanthine oxidase at a concentration of 100 µmol / L are shown in Table 2.

[0057] Table 2. Inhibition rate of compounds on xanthine oxidase

[0058] As shown in Table 2, the compound 3g-3l described in this invention exhibits significant inhibitory effects on xanthine oxidase at a concentration of 100 µmol / L, with inhibition rates all exceeding 60%. These results indicate that this class of novel compounds can lower uric acid levels by inhibiting xanthine oxidase activity and blocking the uric acid production pathway, thus possessing potential application value as a drug for treating hyperuricemia or gout.

[0059] Comparative Example 1

[0060] The only difference between this comparative example and Example 1 is that the continuous flow synthesis method is replaced with a traditional batch reactor.

[0061] 2,4,6-Trihydroxyacetophenone (4.2 g, 0.025 mol), p-methoxybenzaldehyde (3.7 g, 0.027 mol), and Pro-FA-CPBA reaction medium (100 mL) were added together into a 500 mL three-necked flask equipped with a reflux condenser. The mixture was stirred continuously in a 95°C oil bath for 2 min. TLC analysis showed no formation of the target flavonoid compounds, and the raw materials in the reaction system were recovered.

[0062] Comparative Example 2

[0063] The only difference between this comparative example and Example 1 is that the continuous flow synthesis method is replaced with a traditional batch reactor, and the reaction time is adjusted.

[0064] 2,4,6-Trihydroxyacetophenone (4.2 g, 0.025 mol), p-methoxybenzaldehyde (3.7 g, 0.027 mol), and Pro-FA-CPBA reaction medium (100 mL) were added together into a 500 mL three-necked flask equipped with a reflux condenser and stirred continuously in a 95°C oil bath. After 12 hours of reaction, TLC analysis showed that the product was mainly 3a. After the same post-processing as in Example 1, the final yield was 63.1%.

[0065] Comparative Example 3

[0066] The only difference between this comparative example and Example 1 is that the continuous flow synthesis method is replaced with a traditional batch reactor, and the reaction time is adjusted.

[0067] 2,4,6-Trihydroxyacetophenone (4.2 g, 0.025 mol), p-methoxybenzaldehyde (3.7 g, 0.027 mol), and Pro-FA-CPBA reaction medium (100 mL) were added together into a 500 mL three-necked flask equipped with a reflux condenser and stirred continuously in a 95°C oil bath. After 18 hours of reaction, a sample was taken for TLC analysis, which showed a significant increase in impurities compared to Comparative Example 2. After the same post-processing as in Example 1, the final purification yield was 33.1%.

[0068] The experimental results of Comparative Examples 1, 2, and 3 show that, under the same Pro-FA-CPBA system and temperature, the mass and heat transfer efficiency of the batch reactor is low. Under the same residence time of 2 minutes as in Example 1, the condensation-cyclization-dehydrogenation reaction cannot be completed, resulting in the failure to synthesize flavonoids. Even with the reaction time extended to 12 hours, the yield (63.1%) is still significantly lower than the 87.3% achieved in a continuous flow process after 2 minutes. Further extending the reaction time to 18 hours, the yield decreases to 33.1%, indicating that the target product underwent excessive oxidation or decomposition in a prolonged high-temperature oxidizing medium. This demonstrates that the high efficiency of the Pro-FA-CPBA system can only be fully realized under continuous flow process conditions, and there is a significant synergistic effect between the two.

[0069] Comparative Example 4

[0070] The only difference between this comparative example and Example 1 is that the temperature of the constant-temperature oil bath in the continuous flow reactor was replaced with 60°C, while the residence time remained at 2 min; all other conditions were unchanged. TLC analysis revealed no formation of the target flavonoids, and the raw materials in the reaction system were recovered.

[0071] Experimental results show that under the same continuous flow reaction conditions, lowering the temperature to 60℃ will result in insufficient activation energy provided by the reaction system for the entire series reaction, thus preventing the synthesis of the target flavonoid.

[0072] Comparative Example 5

[0073] The only difference between this comparative example and Example 1 is that the Pro-FA-CPBA reaction medium was replaced with the Pro-FA reaction medium (only without the addition of CPBA m-chloroperoxybenzoic acid). After the reaction was completed, TLC detection showed that no target flavonoid compounds were generated, and the raw materials in the reaction system were recovered.

[0074] Experimental results show that the absence of m-chloroperoxybenzoic acid makes the reaction system required for the conversion of raw materials into the target product incomplete, resulting in the inability to synthesize the target flavonoid.

[0075] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0076] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A one-pot tandem synthesis method for flavonoids, characterized in that, Includes the following steps: Starting with o-hydroxyacetophenone compounds and aromatic aldehyde compounds, flavonoid compounds were obtained by a one-pot tandem synthesis method in a mixed solution of L-proline-formic acid-m-chloroperoxybenzoic acid. The structural formula of the o-hydroxyacetophenone compound is as follows: ; The structural formula of the aromatic aldehyde compound is: ; The structural formula of the flavonoid compound is: ; R 1 and R 3 Independently selected from hydrogen, methoxy, or hydroxyl; R 2 R 4 R 6 and R 8 Independently selected from hydrogen or methoxy; R 5 Selected from hydrogen, methyl, or cyclopropyl; R 7 It is selected from hydrogen, hydroxyl, methoxy, benzyloxy, aniline, pyridyl, pyrazinyl or cyclohexyl.

2. The one-pot tandem synthesis method for flavonoids according to claim 1, characterized in that, The L-proline-formic acid-m-chloroperoxybenzoic acid mixed solution is obtained by mixing L-proline, formic acid and m-chloroperoxybenzoic acid; The molar ratio of L-proline to formic acid is 1:2~4; The mass of the m-chloroperoxybenzoic acid is 0.4 to 1% of the total mass of L-proline and formic acid.

3. A one-pot tandem synthesis method for flavonoids according to claim 1 or 2, characterized in that, The reaction operation employing the continuous flow synthesis method includes: The o-hydroxyacetophenone compound was mixed with a portion of the L-proline-formic acid-m-chloroperoxybenzoic acid mixed solution as component A; the aromatic aldehyde compound was mixed with the remaining L-proline-formic acid-m-chloroperoxybenzoic acid mixed solution as component B; the components A and B were mixed to obtain a mixed solution, which was then fed into a continuous flow reactor for a one-pot series synthesis reaction.

4. The one-pot tandem synthesis method for flavonoids according to claim 3, characterized in that, In the one-pot tandem synthesis reaction, the molar ratio of o-hydroxyacetophenone compounds to aromatic aldehyde compounds is 1:1 to 1.

2.

5. The one-pot tandem synthesis method for flavonoids according to claim 4, characterized in that, The molar volume ratio of the o-hydroxyacetophenone compound to a portion of the L-proline-formic acid-m-chloroperoxybenzoic acid mixed solution is 0.04~0.06 mol: 100 mL; The molar volume ratio of the aromatic aldehyde compound to the remaining L-proline-formic acid-m-chloroperoxybenzoic acid mixed solution is 0.04~0.06 mol: 100 mL.

6. The one-pot tandem synthesis method for flavonoids according to claim 5, characterized in that, The residence time of the one-pot series synthesis reaction is 1.6~3.9 min, and the temperature is 90~100℃.

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