A key intermediate of a small molecule glp-1 analogue and a method for synthesizing the same

Abstract

The application belongs to the field of pharmaceutical chemical synthesis, and discloses a key intermediate of a small molecule GLP-1 analogue and a synthesis method thereof. The key intermediate of the small molecule GLP-1 analogue is (S)-1-(4-fluoro-1-methyl-1H-indazol-5-yl)-3-(2-(4-fluoro-3,5-dimethylphenyl)-4-methyl-4,5,6,7-tetrahydro-2H-pyrazolo[4,3-c]pyridin-3-yl)-1,3-dihydro-2H-imidazole-2-thione, and a structural formula is as follows: The key intermediate containing an imidazole thione is prepared from (2S)-3-cyano-2-methyl-4-oxopiperidine-1-carboxylic acid tert-butyl ester as a raw material through seven steps of reactions. A plurality of series of small molecule GLP-1 analogues can be synthesized through the key intermediate, the small molecule GLP-1 analogues have the pharmacological activity of activating GLP-1 receptors like natural polypeptides, the synthesis method is simple to operate, raw materials are cheap and easy to obtain, and the synthesis method is suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of pharmaceutical chemical synthesis, and in particular relates to a key intermediate of a GLP-1 analog. Background Technology

[0002] Diabetes mellitus is a chronic disease that can lead to kidney failure, characterized by abnormally high blood glucose levels. The cause is the deficiency of insulin, which metabolizes blood sugar. Insulin, which lowers blood sugar, is secreted by pancreatic beta cells, and its secretion process is highly dependent on blood glucose levels. However, it has also been found that stimulation of the receptor proteins GLP-1R and GIP in the small intestinal mucosa can also produce large amounts of insulin.

[0003] Natural GLP-1 is an agonist of GLP-1R, promoting insulin secretion, but its half-life is extremely short (1-2 minutes). Exendin-4, a GLP-1 analog in the tarantula, has a half-life of several hours. Based on its structural modification, exenatide and lixisenatide were developed. However, Exendin-4 is a foreign protein, and long-term use can lead to antibody production, affecting efficacy. Novo Nordisk introduced a C16-18 fatty acid chain into the structure of human GLP-1, which promotes its binding to plasma albumin and improves stability, thus leading to liraglutide, a once-daily drug with a half-life of approximately 13 hours in humans. Further introduction of a PEG group targeting DPP-4 degradation into the liraglutide structure resulted in Novo Nordisk's blockbuster product semaglutide for the treatment of type 2 diabetes and obesity. Its application in non-alcoholic fatty liver disease and Alzheimer's disease has also entered phase III clinical trials. Science magazine named GLP-1 drugs the top scientific breakthrough of 2023.

[0004] Existing GLP-1 drugs are all large-molecule peptide compounds that require subcutaneous injection, which poses a challenge to patient compliance, leading to reduced absorption, adherence, and duration of action. In fact, due to their high cost and frequent injections, more than two-thirds of patients discontinue semaglutide after one year, and even after discontinuation, the blood sugar-lowering and weight-loss effects quickly rebound. Therefore, the development of small-molecule GLP-1 analogs with high bioavailability that can be taken orally is of great importance.

[0005] Orforglipron is a small-molecule GLP-1 analog currently in Phase 3 clinical trials. Phase 2 clinical trials have demonstrated its superior efficacy against dulaglutide in lowering blood sugar in type 2 diabetes; its potential in weight loss and anti-obesity is comparable to smegglutide. However, existing technologies, such as the method for preparing the GLP-1 receptor agonist Orforglipron disclosed in publication number CN 117964617A, may become the first marketed small-molecule GLP-1R agonist drug, but its low bioavailability is a major drawback. Therefore, proposing a novel structure for a key intermediate of a GLP-1 analog is of great significance for the synthesis and structural optimization of Orforglipron. Summary of the Invention

[0006] To address the aforementioned technical challenges and enhance the transmembrane absorption and metabolic stability of drug molecules, thereby improving drug bioavailability, this invention proposes a key intermediate for a small-molecule GLP-1 analog and its synthetic method.

[0007] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0008] A key intermediate for a small-molecule GLP-1 analog is named (S)-1-(4-fluoro-1-methyl-1H-indazol-5-yl)-3-(2-(4-fluoro-3,5-dimethylphenyl)-4-methyl-4,5,6,7-tetrahydro-2H-pyrazolo[4,3-c]pyridin-3-yl)-1,3-dihydro-2H-imidazol-2-thione, and its structural formula is as follows:

[0009]

[0010] A thiourea derivative was synthesized through the design and optimization of the intermediate structure. From a theoretical perspective, the introduction of sulfur atoms can enhance molecular stability, alter drug targeting and selectivity, improve pharmacokinetic properties, increase biological activity, and potentially reduce side effects. Sulfur atoms are generally more stable than oxygen atoms in certain environments, especially under acidic or reducing conditions, which helps improve drug stability in vivo and reduce metabolic degradation. Sulfur atoms can also withstand higher reducing pressures, further enhancing drug tolerance to oxidative environments. Furthermore, sulfur atoms penetrate cell membranes more easily than oxygen atoms; replacing oxygen with sulfur can sometimes increase drug permeability, especially for molecules that need to enter the lipid bilayer. Finally, some drugs are converted into inactive forms through oxidation reactions during metabolism in vivo. Replacing oxygen with sulfur may alter the metabolic pathway of drug molecules in vivo, thereby slowing down drug metabolism and prolonging efficacy.

[0011] The synthesis method of the key intermediate of the above-mentioned small molecule GLP-1 analogue is as follows:

[0012] S1.(2S)-3-cyano-2-methyl-4-oxopiperidin-1-carboxylic acid tert-butyl ester (1) and 4-fluoro-3,5-dimethylphenylhydrazine hydrochloride (2) were condensed to give a polycyclic aromatic amine compound (3);

[0013] S2. In the presence of an alkaline catalyst, the polycyclic aromatic amine compound (3) obtained in step S1 is subjected to an amidation reaction with N-(2,2-dimethoxyethyl)-1H-imidazolium-1-carboxamide (4) to obtain a 1,3-disubstituted urea compound (5).

[0014] S3. The 1,3-disubstituted urea compound (5) obtained in step S2 was treated with acid to obtain the cyclized product (6);

[0015] S4. In the presence of an alkaline acid-binding agent, step S3 yields a cyclized product (6), which is protected with an acid-resistant protecting group R to obtain product (7).

[0016] S5. In the presence of a copper catalyst, ligand and base, the product (7) obtained in step S4 is subjected to a Buchward-Goldberg arylation reaction with 5-bromo-4-fluoro-1-methyl-1H-indazole (8) to obtain a polycyclic compound (9).

[0017] S6. The polycyclic compound (9) was reacted with the sulfiding agent under reflux in a solvent to obtain the imidazolium thione derivative (10);

[0018] S7. Step S6 yields the imidazolium thione derivative (10). The protecting group R of the piperidine secondary amine group is removed to obtain the key intermediate (Ⅰ) of the small molecule GLP-1 analog.

[0019] The synthetic route for the key intermediate of the above-mentioned small molecule GLP-1 analog, namely compound (Ⅰ), is shown below:

[0020]

[0021] The condensation reaction in step S1 above is carried out under acid catalysis and ethanol reflux conditions.

[0022] Furthermore, hydrochloric acid is preferred as the acid catalyst used.

[0023] In step S2 above, the alkaline catalyst is any one of triethylamine, tributylamine, N,N-diisopropylethylamine, N,N-dicyclohexylmethylamine, DBU, sodium acetate, sodium carbonate, potassium carbonate, cesium carbonate, sodium hydroxide, potassium hydroxide, and potassium tert-butoxide.

[0024] In step S3 above, the acid is any one of hydrochloric acid, trifluoroacetic acid, methylbenzenesulfonic acid, benzenesulfonic acid, chlorosulfonic acid, trifluoromethanesulfonic acid, formic acid, and methanesulfonic acid.

[0025] In step S4 above, the acid-resistant protecting group R is any one of acetyl, benzyloxycarbonyl protecting group Cbz, benzenesulfonyl, and 9-fluorenylmethoxycarbonyl protecting group Fmoc.

[0026] Furthermore, the acetyl group is a trifluoroacetyl group; the benzenesulfonyl group is any one of o-nitrobenzenesulfonyl Ns, p-nitrobenzenesulfonyl Nos, o-, p-dinitrobenzenesulfonyl DNs, and p-toluenesulfonyl Ts.

[0027] Furthermore, the acid-resistant protective agent can be any one of Cbz-Cl, p-toluenesulfonyl chloride, benzenesulfonyl chloride, o-nitrobenzenesulfonyl chloride Ns-Cl, p-nitrobenzenesulfonyl chloride Nos-Cl, o, p-dinitrobenzenesulfonyl chloride DNs-Cl, Fmoc-Cl, trifluoroacetic anhydride, and trifluoroacetyl chloride; the acid-binding agent can be an alkaline substance such as triethylamine, tributylamine, N,N-dimethylaminopyridine, imidazole, N-methylimidazolium, N,N-diisopropylethylamine, DBU, N,N-dicyclohexylmethylamine, sodium acetate, sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, cesium carbonate, sodium hydroxide, potassium hydroxide, and potassium tert-butoxide.

[0028] In step S5 above, the copper catalyst is any one of cuprous iodide, cuprous bromide, cuprous chloride, cuprous oxide, copper acetate, and Cu(acac)2; the ligand is trans-N,N'-dimethylcyclohexanediamine or N,N'-dimethylethylenediamine; the base is preferably potassium phosphate, sodium phosphate, sodium carbonate, potassium carbonate, cesium carbonate, or sodium hydroxide; and the reaction solvent is preferably NMP, DMF, THF, toluene, or dioxane.

[0029] In step S6 above, the sulfiding agent is Lawson's reagent or phosphorus pentasulfide, and the solvent is any one of toluene, THF, DMF, xylene, DMSO, 1,4-dioxane, and pyridine.

[0030] More preferably, the sulfiding agent is Lawson's reagent.

[0031] In step S7 above, for different protecting groups R, corresponding conventional methods can be selected to remove the protecting groups. The key point of the reliable protection scheme for piperidine imine provided by the present invention is that the protecting group must be acid-resistant, stable in the Lawson reagent sulfidation process, and can be efficiently removed in the structure of the subsequent intermediate compound (10).

[0032] Furthermore, when the protecting group in the intermediate (7) structure is a 9-fluorenylmethoxycarbonyl protecting group Fmoc, its structural formula is (7a): When the corresponding intermediate (10a) structure protecting group is removed, alkaline conditions are preferred, wherein the alkaline is diethylamine, piperidine, lithium hydroxide, sodium hydroxide or potassium hydroxide, etc.

[0033] When the protecting group in the intermediate (7) structure is a benzyloxycarbonyl protecting group Cbz, its structural formula is (7b): When the protecting group in the structure of the corresponding intermediate (10b) is removed, TMSCl, TMSBr, TMSI, boron trichloride or boron tribromide are preferred for removal.

[0034] In the structure of intermediate (7), the protecting group is selected from any one of o-nitrobenzenesulfonyl (Ns), p-nitrobenzenesulfonyl (Nos), o-, p-dinitrobenzenesulfonyl (DNs), and p-toluenesulfonyl (Ts). For example, when its protecting group is o-nitrobenzenesulfonyl (Ns), the corresponding intermediate (7c) structure is as follows: When the protecting group in the structure of the corresponding intermediate (10c) is removed, the protecting group is preferably removed by reduction in an alkaline medium using a mercapto-containing reagent such as thiophenol, mercaptoethanol, or mercaptoacetic acid.

[0035] The application of the key intermediates of the above-mentioned small molecule GLP-1 analogs in the preparation of small molecule GLP-1 analogs.

[0036] The beneficial effects of this invention are:

[0037] (1) This invention proposes a key intermediate for a small molecule GLP-1 analog: (S)-1-(4-fluoro-1-methyl-1H-indazol-5-yl)-3-(2-(4-fluoro-3,5-dimethylphenyl)-4-methyl-4,5,6,7-tetrahydro-2H-pyrazolo[4,3-c]pyridin-3-yl)-1,3-dihydro-2H-imidazol-2-thione (I). The introduction of a sulfur atom can enhance molecular stability, alter the drug's targeting and selectivity, improve pharmacokinetic properties, enhance biological activity, and potentially reduce side effects. Sulfur atoms are generally more stable than oxygen atoms in certain environments, especially under acidic or reducing conditions. This helps improve drug stability in vivo and reduce metabolic degradation. Sulfur atoms can also withstand higher reducing pressures, further enhancing drug tolerance to oxidative environments. Furthermore, sulfur atoms penetrate cell membranes more easily than oxygen atoms; replacing oxygen with sulfur can sometimes increase drug permeability, especially for molecules that need to enter the lipid bilayer. Finally, some drugs are converted into inactive forms through oxidation reactions during metabolism in vivo. Replacing oxygen with sulfur may alter the metabolic pathways of drug molecules in vivo, thereby slowing down drug metabolism and prolonging efficacy. This key intermediate can be used to synthesize several series of small-molecule GLP-1 analogs, possessing the pharmacological activity of natural peptides that activate GLP-1 receptors, potentially leading to the discovery of new oral small-molecule hypoglycemic and weight-loss drugs.

[0038] (2) This invention proposes a method to obtain the key intermediate (I) containing imidazolium thione in high yield through a seven-step reaction using (2S)-3-cyano-2-methyl-4-oxopiperidin-1-carboxylic acid tert-butyl ester as the starting material. Moreover, the synthetic method proposed in this invention is simple to operate, uses inexpensive and readily available raw materials, and does not require expensive resolution instruments and methods, making it suitable for large-scale production. Detailed Implementation

[0039] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1

[0041] The preparation method of the key intermediate of the small molecule GLP-1 analog in this embodiment is as follows:

[0042]

[0043]

[0044] The specific preparation steps are as follows:

[0045] S1. Preparation of Intermediate 3: (2S)-3-cyano-2-methyl-4-oxopiperidin-1-carboxylic acid tert-butyl ester 1 (1 g, 4.2 mmol) was dissolved in 10 mL of ethanol. Purchased (4-fluoro-3,5-dimethylphenyl)hydrazine hydrochloride 2 (1.2 g, 6.29 mmol) was eluted with 2 M sodium hydroxide to remove the free amine and then added to the system. Subsequently, 2 mL of HCl (2 M) solution was added, and the mixture was refluxed at 80 °C overnight. After the reaction was complete as monitored by TLC, saturated potassium carbonate solution was added to adjust the pH to 7. The mixture was extracted three times with ethyl acetate, backwashed once with saturated brine, dried over anhydrous sodium sulfate, filtered, and concentrated. The crude product was separated by silica gel column chromatography (PE:EA = 4:1) to obtain a white powder, namely intermediate 3 (polycyclic aromatic amine compound) (1.20 g, 76%); MS m / z: 375 [M+H]. + .

[0046] S2. Preparation of Intermediates 4 and 5: At 0°C, aminoacetaldehyde-O,O-dimethyl acetal (1.95 g, 18.51 mmol) was slowly added dropwise to a solution of CDI (3 g, 18.51 mmol) in 10 mL of ethyl acetate. After 10 minutes, the ice bath was removed, and the mixture was stirred overnight at room temperature. After the reaction was complete as monitored by TLC, distilled water was added to quench the reaction. The mixture was extracted three times with ethyl acetate, backwashed once with saturated brine, dried over anhydrous sodium sulfate, and concentrated under reduced pressure. The crude product was then separated by silica gel column chromatography (PE:EA = 1:2) to obtain colorless liquid 4 (900 mg, 24%); MS: m / z = 200 [M+H]. + .

[0047] Intermediate 4 (766 mg, 3.85 mmol) and potassium tert-butoxide (719 mg, 6.41 mmol) were added to a solution of intermediate 3 (1.20 g, 3.20 mmol) in N,N-dimethylacetamide (15 mL). The mixture was stirred at room temperature for 4 hours, then quenched with distilled water. The mixture was extracted three times with ethyl acetate, backwashed once with saturated brine, dried over anhydrous sodium sulfate, and concentrated under reduced pressure. The crude product was then separated by silica gel column chromatography (PE:EA = 2:1) to obtain intermediate 5, namely the 1,3-disubstituted urea compound (1.20 g, 74%); MS: m / z = 506 [M+1]. + .

[0048] S3. Preparation of Intermediate 7a: Trifluoromethanesulfonic acid (356 mg, 2.37 mmol) was added to a tetrahydrofuran (15 mL) solution of intermediate 5 (1.20 g, 2.37 mmol), and the mixture was heated to 60 °C for 2 hours. After the reaction was completed by TLC monitoring, the mixture was concentrated under vacuum. Crude product 6 was dissolved in an acetone-water mixture (1:1, 20 mL), and Fmoc-Cl (1.33 g, 2.84 mmol) and K2CO3 (820 mg, 5.9 mmol) were added. The mixture was stirred overnight at room temperature. Acetone was removed by rotary evaporation under reduced pressure. The mixture was acidified with 1N HCl aqueous solution (50 mL) and extracted with EtOAc (50 mL × 3). The combined organic phases were backwashed with brine, dried, filtered, and concentrated. The residue was purified by silica gel column chromatography (PE:EA = 2:1) to give a white solid product, intermediate 7a (1.07 g, 80%); MS: m / z = 564 [M+1]. + .

[0049] S4. Preparation of Intermediate 9a: Intermediate 7a (1070 mg, 1.90 mmol) was dissolved in 10 mL of N-methylpyrrolidone, and 5-bromo-4-fluoro-1-methyl-1H-indazole 8 (872 mg, 3.81 mmol), trans-N,N'-dimethylcyclohexanediamine (135 mg, 0.95 mmol), potassium carbonate (789 mg, 5.71 mmol), and cuprous iodide (181 mg, 0.95 mmol) were added. The mixture was reacted at 135 °C for 6 hours. After the reaction was completed by TLC monitoring, distilled water was added to quench the reaction, and the mixture was extracted three times with ethyl acetate, backwashed once with saturated brine, dried over anhydrous sodium sulfate, and concentrated under reduced pressure. The crude product was then separated by silica gel column chromatography (PE:EA = 2:1) to obtain a white solid, namely intermediate 9a (770 mg, 57%); MS: m / z = 712 [M+1]. + .

[0050] S5. Preparation of Intermediate 10a: Intermediate 9a (240 mg, 0.34 mmol), Lawson's reagent (300 mg, 0.74 mmol), and 1,4-dioxane (4 mL) were added to a microwave-controlled reaction tube. The tube was sealed and placed in a microwave reactor at 155 °C for 2 hours. After the reaction was complete, the solvent was removed under reduced pressure. The residue was separated by silica gel column chromatography (PE:EA = 3:1) to obtain a pale yellow solid product, namely intermediate 10a (96 mg, 39%); MS: m / z = 728 [M+1]. + .

[0051] S6. Preparation of compound (Ⅰ): Intermediate 10a (60 mg, 0.091 mmol) and 4-methylpiperidine (44 μL, 0.373 mmol) were dissolved in DCM (2 mL) and stirred at room temperature for 3 hours. After the reaction was completed by TLC monitoring, DCM (10 mL) was added for dilution, and the mixture was backwashed with 1 N HCl solution and saturated brine. The mixture was dried over anhydrous sodium sulfate and concentrated under reduced pressure. The crude product was separated by alumina column chromatography (DCM:MeOH = 20:1) to obtain a brownish-yellow solid product (I) (446 mg, 84%). 1 H NMR(400MHz, Methanol-d4)δ8.14(d,J=10.3Hz,1H),7.44(dd,J=40.8,7.5Hz,2H),7.33-7.15(m,2H),6.95(s,1H),4.31- 4.18(m,1H),4.07(d,J=8.4Hz,3H),3.42(d,J=9.2Hz,1H),3.09(s,1H),2.85(d,J=15.6Hz,2H),2.22(s,6H),1.24(s,3H). 19F NMR(376MHz,Methanol-d4)δ-122.91,-126.79.HRMS(ESI)Calcd for C 26 H 25 F2N7S[M+H] + :506.1938,found 506.1935.

[0052] Example 2

[0053] The preparation method of the key intermediate of the small molecule GLP-1 analog in this embodiment, part of the synthetic route is as follows:

[0054]

[0055] The specific steps are as follows:

[0056] The preparation methods for steps S1 and S2 are the same as in Example 1.

[0057] S3. Preparation of Intermediate 7b: Trifluoromethanesulfonic acid (356 mg, 2.37 mmol) was added to a tetrahydrofuran (15 mL) solution of intermediate 5 (1.20 g, 2.37 mmol), and the mixture was heated to 60 °C for 2 hours. After the reaction was completed by TLC monitoring, the mixture was concentrated under vacuum. Crude product 6 was dissolved in an acetone-water mixture (1:1, 20 mL), and Cbz-Cl (2.84 mmol) and K2CO3 (820 mg, 5.9 mmol) were added. The mixture was stirred overnight at room temperature. Acetone was removed by rotary evaporation under reduced pressure. The mixture was acidified with 1N HCl aqueous solution (50 mL) and extracted with EtOAc (50 mL × 3). The combined organic phases were backwashed with brine, dried, filtered, and concentrated. The residue was purified by silica gel column chromatography (PE:EA = 2:1) to give a white solid product, intermediate 7b (830 mg, 74%); MS: m / z = 476 [M+1]. + .

[0058] S4. Preparation of Intermediate 9b: Starting material 7b (475 mg, 1 mmol) was dissolved in 10 mL of N-methylpyrrolidone. 5-Bromo-4-fluoro-1-methyl-1H-indazole (460 mg, 2 mmol), trans-N,N'-dimethylcyclohexanediamine (70 mg, 0.5 mmol), potassium carbonate (415 mg, 3 mmol), and cuprous iodide (95 mg, 0.5 mmol) were added, and the mixture was reacted at 135 °C for 5 hours. After the reaction was complete as monitored by TLC, distilled water was added to quench the reaction mixture. The mixture was extracted three times with ethyl acetate, backwashed once with saturated brine, dried over anhydrous sodium sulfate, and concentrated under reduced pressure. The crude product was then separated by silica gel column chromatography (PE:EA = 2:1) to obtain a white solid, intermediate 9b (305 mg, 49%); MS: m / z = 624 [M+1].+ .

[0059] S5. Preparation of Intermediate 10b: Intermediate 9b (305 mg, 0.49 mmol), Lawson's reagent (476 mg, 1.17 mmol), and 1,4-dioxane (5 mL) were added to a microwave-controlled reaction tube. The tube was sealed and placed in a microwave reactor at 155 °C for 2 hours. After the reaction was complete, the solvent was removed under reduced pressure. The residue was separated by silica gel column chromatography (PE:EA = 3:1) to obtain a pale yellow solid product, namely intermediate 10b (106 mg, 34%); MS: m / z = 640 [M+1]. + .

[0060] S6. Preparation of Compound (I): Boron tribromide (1M, 0.8mL, 0.8mmol) was added dropwise to a DCM (10mL) solution of intermediate 10b (106mg, 0.16mmol) at -20℃, and the reaction mixture was stirred for 3 hours. After the reaction was completed as monitored by TLC, the reaction mixture was poured into a 10% potassium carbonate aqueous solution and extracted with DCM. The organic layer was separated, dried over MgSO4, filtered, and the solvent was evaporated to dryness. The residue was separated by alumina column chromatography (DCM:MeOH = 20:1) to give a brownish-yellow solid product, namely compound (I) (65mg, 81%).

[0061] Example 3

[0062] The preparation method of the key intermediate of the small molecule GLP-1 analog in this embodiment, part of the synthetic route is as follows:

[0063]

[0064] The specific steps are as follows:

[0065] The preparation methods for steps S1 and S2 are the same as in Example 1.

[0066] S3. Preparation of Intermediate 7c: Trifluoromethanesulfonic acid (356 mg, 2.37 mmol) was added to a tetrahydrofuran (15 mL) solution of intermediate 5 (1.20 g, 2.37 mmol), and the mixture was heated to 60 °C for 2 hours. After the reaction was completed by TLC monitoring, the mixture was concentrated under vacuum. Crude product 6 was dissolved in an acetone-water mixture (1:1, 20 mL), and o-nitrobenzenesulfonyl chloride Ns-Cl (2.84 mmol) and K2CO3 (820 mg, 5.9 mmol) were added. The mixture was stirred overnight at room temperature. Acetone was removed by rotary evaporation under reduced pressure. The mixture was acidified with 1N HCl aqueous solution (50 mL) and extracted with EtOAc (50 mL × 3). The combined organic phases were backwashed with brine, dried, filtered, and concentrated. The residue was purified by silica gel column chromatography (PE:EA = 2:1) to give a white solid product, intermediate 7c (1.11 g, 89%); MS: m / z = 527 [M+1]. + .

[0067] S4. Preparation of Intermediate 9c: Intermediate 7c (840 mg, 1.6 mmol) was dissolved in 15 mL of N-methylpyrrolidone, and 5-bromo-4-fluoro-1-methyl-1H-indazole (736 mg, 3.2 mmol), trans-N,N'-dimethylcyclohexanediamine (110 mg, 0.8 mmol), potassium carbonate (664 mg, 4.8 mmol), and cuprous iodide (152 mg, 0.8 mmol) were added. The mixture was reacted at 135 °C for 6 hours. After the reaction was completed by TLC monitoring, distilled water was added to quench the reaction mixture. The mixture was extracted three times with ethyl acetate, backwashed once with saturated brine, dried over anhydrous sodium sulfate, and concentrated under reduced pressure. The crude product was separated by silica gel column chromatography (PE:EA = 2:1) to obtain a white solid, namely intermediate 9c (658 mg, 61%); MS: m / z = 675 [M+1]. + .

[0068] S5. Preparation of intermediate 10c: In a microwave-safe reaction tube, reactant 9c (606 mg, 0.9 mmol), Lawson's reagent (810 mg, 2.0 mmol), and 1,4-dioxane (10 mL) were added. The tube was sealed and placed in a microwave reactor at 155 °C for 2 hours. After the reaction was complete, the solvent was removed under reduced pressure. The residue was separated by silica gel column chromatography (PE:EA = 2:1) to give a pale yellow solid product, intermediate 10c (267 mg, 43%); MS: m / z = 691 [M+1]. + .

[0069] S6. Preparation of Compound (I): At room temperature, thiophenol (0.065 mL, 0.64 mmol) was added dropwise to a mixture of sulfonamide compound 10c (145 mg, 0.21 mmol) and K2CO3 (90 mg, 0.64 mmol) in MeCN (5 mL), and the mixture was stirred for 5 hours. After the reaction was completed by TLC monitoring, the reaction mixture was diluted with EtOAc (20 mL), and 1M KOH aqueous solution (10 mL) was added to separate the layers. The aqueous phase was extracted twice with EtOAc, the combined organic layers were backwashed with brine, dried with MgSO4, filtered, concentrated, and the residue was separated by alumina column chromatography (DCM:MeOH = 20:1) to give a brownish-yellow solid product (I) (115 mg, 87%).

[0070] In summary, this invention provides a key intermediate (I) for small molecule GLP-1 analogs and its synthetic method, specifically involving the synthesis of (S)-1-(4-fluoro-1-methyl-1H-indazol-5-yl)-3-(2-(4-fluoro-3,5-dimethylphenyl)-4-methyl-4,5,6,7-tetrahydro-2H-pyrazolo[4,3-c]pyridin-3-yl)-1,3-dihydro-2H-imidazol-2-thione. Using (2S)-3-cyano-2-methyl-4-oxopiperidin-1-carboxylic acid tert-butyl ester (1) as the starting material, a polycyclic aromatic amine compound (3) was obtained by condensation reaction with 4-fluoro-3,5-dimethylphenylhydrazine (2); then, it was amidated with N-(2,2-dimethoxyethyl)-1H-imidazolium-1-carboxamide (4) and cyclized with acid catalysis; it is crucial to protect the obtained cyclized product (6) with an acid-resistant protecting group R, which helps to convert the 1,3-imidazolium-2-one heterocycle into an imidazolium thione derivative (10) using Lawson's reagent; finally, the target product (I) containing the imidazolium thione module was obtained by removing the protecting group R.

[0071] The key intermediate designed in this invention can be used to prepare a variety of small molecule GLP-1 analogs, activate GLP-1 receptors distributed in multiple organs and tissues throughout the body, and thus produce pharmacological activities such as hypoglycemic and weight loss.

[0072] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A key intermediate for a small molecule GLP-1 analog, characterized in that, The structural formula of the key intermediate is as follows:

2. The method for synthesizing the key intermediate of the small molecule GLP-1 analogue according to claim 1, characterized in that, The steps are as follows: S1.(2S)-3-cyano-2-methyl-4-oxopiperidin-1-carboxylic acid tert-butyl ester and 4-fluoro-3,5-dimethylphenylhydrazine hydrochloride were condensed to give polycyclic aromatic amine compounds. S2. In the presence of an alkaline catalyst, the polycyclic aromatic amine compound obtained in step S1 is subjected to an amidation reaction with N-(2,2-dimethoxyethyl)-1H-imidazol-1-carboxamide to obtain a 1,3-disubstituted urea compound. S3. The 1,3-disubstituted urea compound obtained in step S2 is subjected to acid treatment to obtain the cyclized product; S4. In the presence of a basic acid-binding agent, the cyclized product obtained in step S3 is protected with an acid-resistant protecting group R to obtain the product; S5. In the presence of a copper catalyst, a ligand and a base, the product obtained in step S4 is subjected to an aromatic amidation reaction with 5-bromo-4-fluoro-1-methyl-1H-indazole to give a polycyclic compound. S6. The polycyclic compound from step S5 is refluxed with a sulfiding agent in a solvent to obtain an imidazolium thione derivative; S7. Step S6 yields the imidazolium thione derivative by removing the protecting group R of piperidine secondary amine group to obtain the key intermediate of the small molecule GLP-1 analog.

3. The method for synthesizing the key intermediate of the small molecule GLP-1 analog according to claim 2, characterized in that, The condensation reaction in step S1 is carried out under acid catalysis and ethanol reflux conditions.

4. The method for synthesizing the key intermediate of the small molecule GLP-1 analog according to claim 3, characterized in that, In step S2, the alkaline catalyst is any one of triethylamine, tributylamine, N,N-diisopropylethylamine, N,N-dicyclohexylmethylamine, DBU, sodium acetate, sodium carbonate, potassium carbonate, cesium carbonate, sodium hydroxide, potassium hydroxide, and potassium tert-butoxide.

5. The method for synthesizing the key intermediate of the small molecule GLP-1 analog according to claim 4, characterized in that, In step S3, the acid is any one of hydrochloric acid, trifluoroacetic acid, methylbenzenesulfonic acid, benzenesulfonic acid, chlorosulfonic acid, trifluoromethanesulfonic acid, formic acid, and methanesulfonic acid.

6. The method for synthesizing the key intermediate of the small molecule GLP-1 analog according to claim 5, characterized in that, In step S4, the acid-resistant protecting group R is any one of acetyl, benzyloxycarbonyl protecting group Cbz, benzenesulfonyl, and 9-fluorenylmethoxycarbonyl protecting group Fmoc.

7. The method for synthesizing the key intermediate of the small molecule GLP-1 analog according to claim 6, characterized in that, In step S5, the copper catalyst is any one of cuprous iodide, cuprous bromide, cuprous chloride, cuprous oxide, copper acetate, and Cu(acac)2.

8. The method for synthesizing the key intermediate of the small molecule GLP-1 analog according to claim 7, characterized in that, In step S5, the ligand is trans-N,N'-dimethylcyclohexanediamine or N,N'-dimethylethylenediamine.

9. The method for synthesizing the key intermediate of the small molecule GLP-1 analog according to claim 8, characterized in that, In step S6, the sulfiding agent is Lawson's reagent or phosphorus pentasulfide, and the solvent is any one of toluene, THF, DMF, xylene, DMSO, 1,4-dioxane, and pyridine.

10. The application of the key intermediate of the small molecule GLP-1 analog as described in claim 1 in the preparation of small molecule GLP-1 analogs.

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