Benzoxazole compounds or pharmaceutically acceptable salts, hydrates, N-oxides or solvates thereof and their applications

Abstract

The present invention belongs to the technical field of medicinal chemistry, and particularly relates to 4-alkoxy-2-substituted-7-arylbenzoxazole compounds represented by formula (I) or pharmaceutically acceptable salts thereof, and a preparation method and application thereof. The compounds represented by formula (I) exhibit PDE4 inhibitory activity and can be used to prepare drugs for treating inflammatory diseases, autoimmune diseases or neuropsychiatric diseases, especially for diseases related to Parkinson's disease, Parkinson's syndrome, stroke and ischemic dementia.

Description

Technical Field

[0001] The present invention belongs to the technical field of medicinal chemistry, and particularly relates to benzoxazole compounds or pharmaceutically acceptable salts, hydrates, N-oxides or solvates thereof, and preparation methods and applications thereof. Background Art

[0002] Cyclic nucleotide phosphodiesterases (PDEs) can specifically use cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) as substrates, and control their intracellular concentrations by catalyzing the hydrolysis of cAMP and / or cGMP to generate the corresponding AMP and / or GMP, thereby affecting various physiological processes and metabolic functions. The PDEs family contains a total of 11 subtypes (PDE1 - PDE11), which can be divided into three categories based on their substrates: cAMP-specific hydrolases (PDE4, PDE7, and PDE8), cGMP-specific hydrolases (PDE5, PDE6, and PDE9), and dual hydrolases (PDE1, PDE2, PDE3, PDE10, and PDE11). Among them, PDE4 and PDE9 can regulate many physiological and pathological activities, such as apoptosis, energy metabolism, learning and memory, inflammatory immune response, vision, olfaction, and the growth of various cell types, by regulating cAMP and cGMP respectively, and further activating the protein kinase A (PKA) and protein kinase G (PKG) pathways.

[0003] PDE4 has 4 subtypes, PDE4A - D. Except for PDE4C, the other three subtypes are highly expressed in the cerebral cortex, olfactory bulb, hippocampus, and brainstem. In addition, PDE4B is also highly expressed in the striatum, amygdala, hypothalamus, and thalamus of the brain. A large number of studies have confirmed that PDE4 is widely involved in various activities of the brain nerves. PDE4 inhibitors can inhibit PDE4 to up-regulate the cAMP concentration, activate the cAMP / PKA / CREB pathway to regulate the BDNF concentration, promote the growth of nerve cell synapses, increase synaptic plasticity and neuron survival, so as to achieve the purpose of improving cognitive function. In addition, the up-regulation of the cAMP concentration can inhibit the nuclear translocation of NF-κB, and then down-regulate the levels of intracellular inflammatory factors (such as TNF-α, IL-1, and IL-6, etc.), relieve neuroinflammation, and reduce inflammation-induced neuronal damage and apoptosis. PDE4 inhibitors have been used in the research of various diseases, such as asthma, chronic obstructive pulmonary disease (COPD), rheumatoid arthritis, atopic dermatitis, psoriasis, Alzheimer's disease, schizophrenia, depression, etc.

[0004] At present, only three PDE4 inhibitors, namely roflumilast, apremilast and Crisaborole, have been launched on the market. In actual clinical applications, the above three PDE4 inhibitors all have varying degrees of adverse reactions. It can be seen that the types of PDE4 inhibitors available for selection are very few at present. WO2018124060A and WO2020 / 004517A disclose active benzoxazole compounds with PDE4 inhibitory activity, but the substituents at the 2-position are relatively special. Therefore, it is necessary to broaden the research on the structures of benzoxazole compounds with similar activity. Summary of the Invention

[0005] The purpose of the present invention is to provide a novel compound having PDE4 inhibitory activity or a pharmaceutically acceptable salt, hydrate, N-oxide or solvate thereof. The benzoxazole compounds discovered by the present invention have not been reported in patents and literature and exhibit good PDE4 inhibitory activity.

[0006] Another purpose of the present invention is to provide a preparation method of the benzoxazole compound.

[0007] Another purpose of the present invention is to provide the application of the benzoxazole compound.

[0008] To achieve the above purposes, the present invention is realized through the following technical solutions:

[0009] A benzoxazole compound or a pharmaceutically acceptable salt, hydrate, N-oxide or solvate thereof, wherein the benzoxazole compound has the structure of formula (I):

[0010]

[0011] Wherein R 1 is selected from an alkyl group or an alkyl group substituted with one or more fluorine atoms;

[0012] R 2 is selected from an alkyl group having 1 to 5 carbon atoms, an ether group having 2 to 5 carbon atoms, a cycloalkyl group having 3 to 5 carbon atoms, a cyclic ether having 3 to 5 carbon atoms, and a furan ring;

[0013] R 3 is an aryl group, and R 3 is selected from

[0014] Preferably, R 1 The alkyl group is an alkyl group having 1 to 4 carbon atoms.

[0015] Preferably, when R 1 is an alkyl group; R 3 is selected from

[0016] Preferably, when R1 is an alkyl group; R 3 is selected from When; R 2 is selected from C1-C5 alkyl groups, C2-C5 ether groups, C3-C5 cyclic ethers, and furan rings.

[0017] Preferably, when R 1 is an alkyl group; R 3 is selected from R 2 is selected from C1-C5 alkyl groups, C2-C5 ether groups, and furan rings.

[0018] Preferably, R 1 is difluoromethyl.

[0019] Preferably, when R 1 is difluoromethyl, R 2 is selected from C2-C5 ether groups; R 3 is selected from

[0020] More specifically preferably, as the benzoxazole compounds that can be prepared by the invention, some are listed as follows:

[0021]

[0022] The "pharmaceutically acceptable salts" used in the present invention refer to the salts of the compounds of the present invention. More specifically, they refer to the salts prepared from the compounds with specific substituents discovered in the present invention and relatively non-toxic acids. When the compounds of the present invention contain relatively acidic functional groups, the base addition salts can be obtained by contacting the neutral form of such compounds with a sufficient amount of base in a pure solution or a suitable inert solvent.

[0023] Pharmaceutically acceptable acid addition salts include inorganic acid salts, and the inorganic acids include, for example, hydrochloric acid, hydrobromic acid, nitric acid, carbonic acid, phosphoric acid, sulfuric acid, phosphorous acid, etc.; and organic acid salts, and the organic acids include, for example, acetic acid, propionic acid, isobutyric acid, maleic acid, malonic acid, benzoic acid, succinic acid, suberic acid, fumaric acid, lactic acid, mandelic acid, phthalic acid, benzenesulfonic acid, p-toluenesulfonic acid, citric acid, tartaric acid, etc.

[0024] The benzoxazole compounds or their pharmaceutically acceptable salts, hydrates, N-oxides or solvates, preferably, the solvent is dimethyl sulfoxide, ethanol, isopropanol, acetonitrile, tetrahydrofuran, acetone or propylene glycol, etc.

[0025] The preparation method of the benzoxazole compounds includes the following steps:

[0026] S1. Prepare the compound of formula (II);

[0027] S2. The compound of formula (II) reacts with R 3 -X through a coupling reaction to obtain the compound shown in formula (I); X is B(OH)2 or B(Pin)2.

[0028]

[0029] The preparation method of the benzoxazole compound may further include the following steps:

[0030] S1. Prepare the compound of formula (III);

[0031] S2. The compound of formula (III) reacts with R 2 -CHO through a condensation reaction to obtain the compound shown in formula (I).

[0032]

[0033] Another object of the present invention is to provide the use of the benzoxazole compound or its pharmaceutically acceptable salt, hydrate, N-oxide or solvate in the preparation of a therapeutic phosphodiesterase 4 inhibitor.

[0034] Furthermore, the phosphodiesterase 4-related diseases refer to allergic diseases, autoimmune diseases, central nervous system diseases or diseases caused by heart failure, shock and cerebrovascular diseases with local ischemic reperfusion.

[0035] In view of the fact that PDE4 inhibitors currently have good research for use in a variety of diseases, such as asthma, chronic obstructive pulmonary disease (COPD), rheumatoid arthritis, atopic dermatitis, psoriasis, Alzheimer's disease, schizophrenia, depression, etc. Therefore, the compounds with PDE4 inhibitory activity involved in the present invention can also be used in the preparation of drugs for treating inflammatory allergic diseases, autoimmune diseases, central nervous system diseases or organ diseases related to local ischemic reperfusion caused by heart failure, shock and cerebrovascular diseases and similar diseases.

[0036] The inflammatory allergic diseases are, for example, asthma, chronic obstructive pulmonary disease (COPD), allergic rhinitis or nephritis.

[0037] The autoimmune diseases are, for example, rheumatoid arthritis, multiple sclerosis, Crohn's disease or systemic lupus erythematosus.

[0038] The central nervous system diseases are, for example, depression, amnesia or dementia.

[0039] Another object of the present invention is to provide the use of the benzoxazole compound or its pharmaceutically acceptable salt, hydrate, N-oxide or solvate in the preparation of drugs for treating Parkinson's disease and Parkinson's syndrome.

[0040] Another object of the present invention is to provide the use of the benzoxazole compound or a pharmaceutically acceptable salt, hydrate, N-oxide or solvate thereof in the preparation of a medicament for treating stroke and diseases related to ischemic dementia.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The present invention provides that the benzoxazole compound or a pharmaceutically acceptable salt, hydrate, N-oxide or solvate thereof exhibits good inhibitory activity against PDE4. It can be used for the preparation of a medicament for treating inflammatory diseases, autoimmune diseases or neuropsychiatric diseases, especially for the preparation of a medicament for treating Parkinson's disease, Parkinson's syndrome, stroke and diseases related to ischemic dementia. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the inhibitory activity of compound F12 against PDE4 D7;

[0044] Figure 2 It is a schematic diagram of the inhibitory activity of compound F13 against PDE4 D7;

[0045] Figure 3 It is a schematic diagram of the cytotoxicity test results of compound F12.

[0046] Figure 4 It is a schematic diagram of the effect of compound F12 on the viability of HT-22 cells in the OGD model. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] The present invention will be further elaborated in detail below with reference to specific embodiments. The embodiments are only used to explain the present invention and are not intended to limit the scope of the present invention. The test methods used in the following embodiments are all conventional methods unless otherwise specified; the materials, reagents, etc. used are all reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0048] Synthesis routes of Examples 1 to 14:

[0049] Example 1 Synthesis of 1-(3-(2-cyclopropyl-4-methoxybenzo[d]oxazol-7-yl)phenyl)ethyl-1-one (F01)

[0050]

[0051] Step 1: Synthesis of 2-nitro-3-methoxyphenol

[0052] 2-Nitro-m-catechol (10 g, 1 mmol) was added to a 50 ml round-bottom flask, dissolved in DMF (20 mL), and cesium carbonate (1.1 eq) was added. The mixture was stirred at room temperature for 30 minutes, then methyl iodide (0.3 eq) was added dropwise at 0 °C, and the mixture was stirred overnight at room temperature. The reaction process was monitored by thin-layer chromatography (TLC). After the reaction, the pH was adjusted to 10 - 12, water and ethyl acetate were added for extraction of the aqueous phase, then the pH was adjusted to 3 - 4, and extraction, washing of the organic phase with brine, and drying over anhydrous sodium sulfate were carried out. Separation and purification by silica gel column chromatography (n-hexane:ethyl acetate = 20:1, v / v) gave a yellow solid powder (37%). The spectral data of the obtained product were as follows: 1 H NMR (400 MHz, CDCl3) δ 10.20 (s, 1H), 7.40 (t, J = 8.6 Hz, 1H), 6.71 (d, J = 8.4 Hz, 1H), 6.54 (d, J = 8.4 Hz, 1H), 3.94 (s, 3H).

[0053] Step 2: Synthesis of 6-bromo-2-nitro-3-methoxyphenol

[0054] 2-Nitro-3-methoxyphenol (1 g, 1 mmol) was added to a 50 mL round-bottom flask and stirred at -40 °C. After dissolution, trimethylchlorosilane (0.05 eq) was added, and then NBS (1.1 eq) was added slowly in portions. The reaction process was monitored by thin-layer chromatography (TLC). After the reaction was completed, the reaction solution was poured into 50 mL of ice water and allowed to stand. Extraction was carried out with dichloromethane, washing with brine, and drying over anhydrous sodium sulfate. Separation and purification by silica gel column chromatography (n-hexane:ethyl acetate = 25:1, v / v) gave a yellow solid powder (80%). The spectral data of the obtained product were as follows: 1 H NMR (400 MHz, CDCl3) δ 9.81 (s, 1H), 7.59 (t, J = 21.5 Hz, 1H), 6.50 (d, J = 9.1 Hz, 1H), 3.92 (s, 3H).

[0055] Step 3: Synthesis of 6-bromo-2-amino-3-methoxyphenol

[0056] 6-Bromo-2-nitro-3-methoxyphenol (1 g, 1 mmol) was dissolved in anhydrous ethanol:water (4:1) in a 50 mL round-bottom flask, and iron powder (4 eq) and ammonium chloride (4 eq) were added in sequence. The mixture was stirred at 80 °C for 4 h. The reaction process was monitored by thin-layer chromatography (TLC). Filtration was carried out, washing with ethyl acetate, concentration, addition of saturated aqueous sodium bicarbonate solution, separation of the organic layer, washing with brine, and drying over anhydrous sodium sulfate. It was directly used in the next step without purification.

[0057] Step 4: Synthesis of 6-bromo-3-methoxy-2-(1-cyclopropylcarboxamido)phenol

[0058] 6-Bromo-2-nitro-3-methoxyphenol (0.5 g) was added to a 50 mL round-bottom flask, and dichloromethane, 5% DMAP, cyclopropanecarbonyl chloride, and triethylamine were successively added at 0 °C, followed by stirring at room temperature for 4 h. The reaction process was monitored by thin-layer chromatography (TLC). After filtration, washing with dichloromethane, concentration, addition of saturated aqueous sodium bicarbonate solution, separation of the organic layer, washing with brine, and drying over anhydrous sodium sulfate, silica gel column chromatography (n-hexane:ethyl acetate = 10:1, v / v) was used for separation and purification to obtain a yellow solid powder (56%). The spectral data of the obtained product are as follows: 1 H NMR (400 MHz, CDCl3) δ 10.88 (s, 1H), 8.03 (s, 1H), 7.29 (d, J = 8.8 Hz, 1H), 6.34 (d, J = 8.8 Hz, 1H), 1.76 - 1.64 (m, 1H), 1.21 - 1.08 (m, 2H), 1.01 - 0.92 (m, 2H). 13 C NMR (100 MHz, CDCl3) δ 174.29, 149.60, 146.46, 128.98, 116.57, 105.59, 102.53, 56.12, 15.61, 9.00.

[0059] Step 5: Synthesis of compound 7-bromo-2-cyclopropyl-4-methoxybenz[d]oxazole

[0060] 6-Bromo-3-methoxy-2-(1-cyclopropylcarboxamido)phenol (1 g, 1 mmol) and triphenylphosphine (4 eq) were successively added to a 10 mL Schlenk reaction tube, and the gas was replaced with argon. Acetonitrile was added, stirred and dissolved, and then carbon tetrachloride was added dropwise, followed by stirring at 60 °C for 2 h. The reaction process was monitored by thin-layer chromatography (TLC). After filtration, washing with dichloromethane, concentration, addition of saturated aqueous sodium bicarbonate solution, separation of the organic layer, washing with brine, and drying over anhydrous sodium sulfate, silica gel column chromatography (n-hexane:ethyl acetate = 10:1, v / v) was used for separation and purification to obtain a yellow solid powder (67%). The spectral data of the obtained product are as follows: 1 H NMR (400 MHz, CDCl3) δ 7.29 (d, J = 8.6 Hz, 1H), 6.66 (d, J = 8.7 Hz, 1H), 4.00 (d, J = 9.1 Hz, 3H), 2.28 - 2.16 (m, 1H), 1.36 - 1.31 (m, 2H), 1.22 - 1.12 (m, 2H). 13 C NMR (100 MHz, CDCl3) δ 167.75, 150.11, 149.40, 131.53, 127.04, 107.27, 93.00, 56.25, 9.47, 9.12.

[0061] Step 6: Synthesis of 1-(3-(2-cyclopropyl-4-methoxybenzo[d]oxazol-7-yl)phenyl)ethyl-1-one (F01)

[0062] 7-Bromo-2-cyclopropyl-4-methoxybenzoxazole (0.05 g, 1 eq), 3-acetylphenylboronic acid (2 eq), potassium carbonate (2 eq), and 5% Pd(dppf)Cl2 were placed in a 10 mL Schlenk reaction tube. After sealing, the oxygen was displaced with argon, and dioxane / water was used as the solvent for injection to participate in the reaction. The reaction was carried out at 80 °C for 2 hours. The reaction process was monitored by thin-layer chromatography (TLC). After the reaction was complete, it was extracted with ethyl acetate and water. The upper organic layer was taken, washed with brine, dried over anhydrous sodium sulfate, and rotary evaporated. It was separated and purified by silica gel column chromatography (n-hexane:ethyl acetate = 5:1, v / v) to obtain a white solid powder (67%). The spectral data of the obtained product are as follows: 1 HNMR(400MHz,CDCl3)δ8.38(s,1H),7.98(d,J=7.7Hz,1H),7.94(d,J=7.7Hz,1H),7.58(t,J=7.8Hz,1H),7.44(d,J=8.5Hz,1H),6.86(d,J=8.5Hz,1H),4.05(s,3H),2.68(s,3H),2.28-2.20(m,1H),1.35-1.31(m,2H),1.20-1.25(m,2H). 13 CNMR(100MHz,CDCl3)δ198.07,167.78,150.53,149.11,137.56,136.26,132.10,131.41,129.01,127.44,127.06,123.60,116.52,106.33,99.95,56.17,26.74,9.42,9.26.

[0063] Example 2 Synthesis of 1-(3-(2-cyclopentyl-4-methoxybenzo[d]oxazol-7-yl)phenyl)ethyl-1-one (F02)

[0064]

[0065] Step 1: Synthesis of 1-(3-amino-2-hydroxy-4-methoxy-[1-biphenyl]-3-yl)ethyl-1-one

[0066] 6-Bromo-2-amino-3-methoxyphenol (1 g, 1 mmol), 3-acetylphenylboronic acid (2 eq), 5% Pd(dppf)2Cl, and K2CO3 (2 eq) were placed in a 10 mL Schlenk reaction tube, dissolved in 1,4-Dioxane / H2O (4:1, 5 mL), protected by argon, and stirred at 80 °C for 2 h. The reaction process was monitored by thin-layer chromatography (TLC). After dilution with water, the mixture was extracted with ethyl acetate. The organic phase was washed with saturated brine, dried over anhydrous sodium sulfate, and the solvent was removed under reduced pressure to obtain the crude product. The crude product was directly used in the next reaction without purification.

[0067] Step 2: Synthesis of 1-(3-(2-cyclopentyl-4-methoxybenzo[d]oxazol-7-yl)phenyl)ethan-1-one

[0068] F02-1 from Step 1, cyclopentanecarbaldehyde, and xylene were added and stirred to dissolve at 120 °C under oxygen protection. After 0.5 h, 4-methoxy-TEMPO (0.05 mmol) was added and stirred for 5 h. The reaction process was monitored by thin-layer chromatography (TLC). After dilution with water, the mixture was extracted with ethyl acetate. The organic phase was washed with saturated brine, dried over anhydrous sodium sulfate, and the solvent was removed under reduced pressure to obtain the crude product. The crude product was purified by flash silica gel chromatography using ethyl acetate / petroleum ether = 1:8 (V / V) as the eluent to obtain a white solid (yield 80%). This was compound F02. The spectral data of the obtained product were as follows: 1 H NMR (400 MHz, CDCl3) δ 8.10 (s, 1H), 7.92 (d, J = 7.5 Hz, 1H), 7.73 (d, J = 7.2 Hz, 1H), 7.51 (t, J = 7.5 Hz, 1H), 7.24–7.17 (m, 2H), 4.25 (s, 3H), 3.45–3.31 (m, 1H), 2.64 (s, 3H), 2.20–2.10 (m, 2H), 2.08–2.04 (m, 2H), 1.92 - 1.82 (m, 2H), 1.78–1.65 (m, 2H). 13 C NMR (100 MHz, CDCl3) δ 198.23, 170.69, 154.10, 149.40, 139.18, 137.07, 134.49, 132.25, 129.68, 128.24, 126.66, 126.63, 103.97, 77.21, 60.88, 38.89, 31.43, 29.69, 26.71, 25.72.

[0069] Example 3: Synthesis of 1-(3-(2-isopropyl-4-methoxybenzo[d]oxazol-7-yl)phenyl)ethan-1-one (F03)

[0070]

[0071] According to the above method, replace cyclopentanecarbaldehyde in step 2 of Example 2 with isopropylformaldehyde to prepare compound F03. The spectral data of the obtained product are as follows: 1 H NMR(400MHz,CDCl3)δ8.43(s,1H),8.02(d,J=7.6Hz,2H),7.95(d,J=7.3Hz,1H),7.59(t,J=8.1Hz,1H),7.49(d,J=8.4Hz,1H),6.88(d,J=8.2Hz,1H),4.07(s,3H),3.33–3.26(m,1H),2.68(s,3H),1.50(s,3H),1.50(s,3H). 13 CNMR(100MHz,CDCl3)δ198.07,170.22,151.00,137.57,136.26,132.04,131.61,131.21,129.03,127.49,127.03,124.02,116.64,106.11,56.12,29.67,28.93,26.72,20.43.

[0072] Example 4: Synthesis of 1-(3-(2-furan-4-methoxybenzo[d]oxazol-7-yl)phenyl)ethyl-1-one (F04)

[0073]

[0074] According to the above method, replace cyclopentanecarbaldehyde in step 2 of Example 2 with furan-2-carbaldehyde to prepare compound F04. The spectral data of the obtained product are as follows: 1 H NMR(400MHz,CDCl3)δ8.43(s,1H),8.02(d,J=7.1Hz,1H),7.93(d,J=7.5Hz,1H),7.63(s,1H),7.60–7.55(m,1H),7.51–7.48(m,1H),7.31(d,J=5.7Hz,1H),6.89(dd,J=8.4,3.9Hz,1H),6.59(d,J=1.2Hz,1H),4.07(s,3H),2.68(s,3H). 1313C NMR (101 MHz, CDCl3) δ 198.00, 154.27, 151.26, 148.64, 145.54, 142.35, 137.51, 135.80, 131.98, 131.71, 129.03, 127.39, 127.11, 124.74, 116.71, 114.33, 112.22, 106.96, 56.27, 26.70.

[0075] Example 5: Synthesis of (R)-1-(3-(2-Tetrahydrofuran-4-methoxybenzo[d]oxazol-7-yl)phenyl)ethyl-1-one (F05)

[0076]

[0077] According to the above method, cyclopentanecarbaldehyde in Step 2 of Example 2 was replaced with (R)-tetrahydrofuran carbaldehyde to prepare compound F05. The spectral data of the obtained product are as follows: 1 1H NMR (400 MHz, CDCl3) δ 8.40 (s, 1H), 8.01 (d, J = 7.8 Hz, 1H), 7.93 (d, J = 7.7 Hz, 1H), 7.58 (t, J = 7.8 Hz, 1H), 7.53 (d, J = 8.5 Hz, 1H), 6.89 (d, J = 8.5 Hz, 1H), 5.25 (dd, J = 7.7, 5.6 Hz, 1H), 4.14–4.09 (m, 1H), 4.07 (s, 3H), 4.04–3.98 (m, 1H), 2.67 (s, 3H), 2.53–2.35 (m, 2H), 2.28–2.03 (m, 2H). 13 13C NMR (100 MHz, CDCl3) δ 198.19, 165.39, 151.26, 149.71, 137.84, 136.23, 132.12, 130.84, 129.05, 127.41, 127.16, 124.81, 116.96, 106.53, 73.75, 69.34, 56.28, 30.67, 26.72, 25.94.

[0078] Example 6: Synthesis of (S)-1-(3-(2-Tetrahydrofuran-4-methoxybenzo[d]oxazol-7-yl)phenyl)ethyl-1-one (F06)

[0079]

[0080] According to the above method, cyclopentanecarbaldehyde in Step 2 of Example 2 was replaced with (S)-tetrahydrofuran carbaldehyde to prepare compound F06. The spectral data of the obtained product are as follows: 11H NMR (400 MHz, CDCl3) δ 8.40 (s, 1H), 8.01 (d, J = 7.8 Hz, 1H), 7.93 (d, J = 7.7 Hz, 1H), 7.58 (t, J = 7.8 Hz, 1H), 7.53 (d, J = 8.5 Hz, 1H), 6.89 (d, J = 8.5 Hz, 1H), 5.25 (t, J = 6.4 Hz, 1H), 4.14–4.09 (m, 1H), 4.07 (s, 3H), 4.04–3.98 (m, 1H), 2.67 (s, 3H), 2.53–2.35 (m, 2H), 2.28–2.03 (m, 2H). 13 13C NMR (100 MHz, CDCl3) δ 198.02, 165.26, 151.36, 149.61, 137.57, 136.01, 132.11, 130.85, 129.04, 127.41, 127.15, 124.81, 116.96, 106.53, 73.75, 69.34, 56.28, 30.67, 26.71, 25.94.

[0081] Example 7: Synthesis of 1-(3-(2-Methoxymethyl-4-methoxybenzo[d]oxazol-7-yl)phenyl)ethyl-1-one (F07)

[0082]

[0083] According to the above method, cyclopentanecarbaldehyde in Step 2 of Example 2 was replaced with methoxyacetaldehyde to prepare compound F07. The spectral data of the obtained product are as follows: 1 1H NMR (400 MHz, CDCl3) δ 8.37 (t, J = 1.6 Hz, 1H), 8.05–8.00 (m, 1H), 7.94 (d, J = 7.8 Hz, 1H), 7.58 (t, J = 7.8 Hz, 1H), 7.54 (d, J = 8.5 Hz, 1H), 6.91 (d, J = 8.5 Hz, 1H), 4.74 (s, 2H), 4.08 (s, 3H), 3.51 (s, 3H), 2.67 (s, 3H). 13 13C NMR (100 MHz, CDCl3) δ 198.05, 161.49, 151.42, 149.74, 137.60, 135.94, 132.30, 130.85, 129.08, 127.36, 127.26, 125.18, 117.09, 106.67, 66.75, 59.13, 56.33, 26.74.

[0084] Example 8: Synthesis of 1-(3-(2-ethyl-4-methoxybenzo[d]oxazol-7-yl)phenyl)ethan-1-one (F08)

[0085]

[0086] According to the above method, cyclopentanecarbaldehyde in step 2 of Example 2 was replaced with propionaldehyde to prepare compound F08. The spectral data of the obtained product are as follows: 1 H NMR (400 MHz, CDCl3) δ 8.38 (s, 1H), 7.99 (d, J = 7.7 Hz, 1H), 7.92 (d, J = 7.8 Hz, 1H), 7.56 (t, J = 7.8 Hz, 1H), 7.46 (d, J = 8.5 Hz, 1H), 6.86 (d, J = 8.5 Hz, 1H), 4.05 (s, 3H), 3.00 (q, J = 7.4 Hz, 2H), 2.66 (s, 3H), 1.47 (t, J = 7.6 Hz, 3H). 13 C NMR (100 MHz, CDCl3) δ 198.05, 167.10, 150.89, 149.46, 137.53, 136.22, 132.14, 131.24, 128.98, 127.38, 127.07, 124.06, 116.63, 106.20, 56.13, 26.72, 22.14, 11.04.

[0087] Example 9: Synthesis of 1-(3-(2-propyl-4-methoxybenzo[d]oxazol-7-yl)phenyl)ethan-1-one (F09)

[0088]

[0089] According to the above method, cyclopentanecarbaldehyde in step 2 of Example 2 was replaced with butyraldehyde to prepare compound F09. The spectral data of the obtained product are as follows: 1 H NMR (400 MHz, CDCl3) δ 8.38 (s, 1H), 7.99 (d, J = 7.7 Hz, 1H), 7.92 (d, J = 7.7 Hz, 1H), 7.56 (t, J = 7.8 Hz, 1H), 7.46 (d, J = 8.5 Hz, 1H), 6.85 (d, J = 8.5 Hz, 1H), 4.04 (s, 3H), 2.94 (t, J = 7.5 Hz, 2H), 2.66 (s, 3H), 1.98–1.89 (m, 2H), 1.05 (t, J = 7.4 Hz, 3H). 1313C NMR (100 MHz, CDCl3) δ 197.90, 166.00, 150.97, 149.35, 137.18, 136.84, 133.12, 131.57, 128.44, 127.14, 126.88, 123.70, 117.17, 105.58, 56.39, 30.40, 26.42, 20.43, 13.56.

[0090] Example 10: Synthesis of 4-(4-(Difluoromethoxy)-2-(methoxymethyl)benzo[d]oxazol-7-yl)-2,3-dihydro-1H-inden-1-one (F10)

[0091]

[0092] Step 1: Synthesis of 7-Bromo-4-methoxy-2-(methoxymethyl)benzo[d]oxazole

[0093] Dissolve F1-4, methoxyacetaldehyde in xylene and stir at 120 °C for dissolution under oxygen protection. After 0.5 h, add 4-methoxy-TEMPO (0.05 mmol) and stir for 5 h. Monitor the reaction process by thin-layer chromatography (TLC). After dilution with water, extract with ethyl acetate. Wash the organic phase with saturated brine, dry over anhydrous sodium sulfate, and evaporate the solvent under reduced pressure to obtain the crude product. Purify the crude product by flash silica gel chromatography using ethyl acetate / petroleum ether = 1:8 (V / V) as the eluent to obtain a white solid (yield 80%). This is compound F10-1.

[0094] Step 2: Synthesis of 7-Bromo-2-(methoxymethyl)benzo[d]oxazol-4-ol

[0095] Dissolve F10-1 (100 mmol) in anhydrous dichloromethane (200 mL). Under argon protection, slowly add anhydrous aluminum trichloride (120 mmol, 1.2 eq) in batches. After stirring for 30 minutes, warm to room temperature and continue stirring for 1 hour. Then add acetic acid (10 mL), filter under reduced pressure through short diatomaceous earth, and wash with dichloromethane. Evaporate the solvent under reduced pressure to obtain the crude product. Recrystallize the crude product from ethyl acetate / absolute ethanol / petroleum ether (30 mL, volume ratio 2:1:2) to obtain a white solid F10-2 (yield 60%). 1 1H NMR (400 MHz, CDCl3) δ 7.36 (d, J = 8.7 Hz, 1H), 6.79 (d, J = 8.7 Hz, 1H), 4.72 (s, 2H), 3.54 (s, 3H).

[0096] Step 3: Synthesis of 7-Bromo-4-difluoromethoxy-2-(methoxymethyl)benzo[d]oxazole

[0097] Compound F10-2 (90 mmol, 1.0 eq) and sodium chlorodifluoroacetate (135 mmol, 1.5 eq) were dissolved in DMF (100 mL), and a saturated aqueous solution of potassium hydroxide (90 mmol, 1.0 eq) was added dropwise under argon protection. After stirring for 1 hour, the mixture was diluted with ethyl acetate, and the organic phase was washed with saturated brine, dried over anhydrous sodium sulfate, and the solvent was evaporated under reduced pressure to obtain a crude product. The crude product was purified by flash silica gel chromatography using ethyl acetate / petroleum ether = 1:10 (V / V) as the eluent to obtain white solid F10-3 (yield 95%). That is 1 1H NMR (400 MHz, CDCl3) δ 7.47 (d, J = 8.7 Hz, 1H), 7.19 (t, 2JFH = 73.8 Hz, 1H), 7.04 (d, J = 8.7 Hz, 1H), 4.73 (s, 2H), 3.54 (s, 3H).

[0098] Step 4: Synthesis of 4-(4-(difluoromethoxy)-2-(methoxymethyl)benzo[d]oxazol-7-yl)-2,3-dihydro-1H-indene-1-one

[0099] F10-3 (1 g, 1 mmol), 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,3-dihydro-1H-indene-1-one (2 eq), 5% Pd(dppf)2Cl, and K2CO3 (2 eq) were placed in a 10 mL Schlenk reaction tube, dissolved in 1,4-Dioxane / H2O (4:1, 5 mL), protected by argon, and stirred at 80 °C for 2 h. The reaction process was monitored by thin layer chromatography (TLC). After dilution with water, the mixture was extracted with ethyl acetate, the organic phase was washed with saturated brine, dried over anhydrous sodium sulfate, and the solvent was evaporated under reduced pressure to obtain a crude product. The crude product was purified by flash silica gel chromatography using ethyl acetate / petroleum ether = 1:10 (V / V) as the eluent to obtain white solid F10 (yield 75%). The spectral data of the obtained product are as follows: 1 1H NMR (400 MHz, CDCl3) δ 7.88 (d, J = 7.1 Hz, 2H), 7.79 (d, J = 8.0 Hz, 1H), 7.57 (d, J = 8.5 Hz, 1H), 7.29 (t, J = 74 Hz, 1H, -CHF2), 7.24 (d, J = 8.6 Hz, 1H), 4.74 (s, 2H), 3.53 (s, 3H), 3.25 (t, J = 5.6 Hz, 2H), 2.77 (t, J = 5.8 Hz, 2H). 13CNMR (100 MHz, CDCl3) δ 206.37, 162.87, 155.71, 149.89, 142.38, 140.89, 136.62, 132.27, 127.45, 126.13, 125.60, 124.22, 121.41, 115.63 (t, J = 264.5 Hz, CHF2), 115.50, 66.67, 59.36, 36.46, 25.93.

[0100] Example 11: Synthesis of 1-(4-(difluoromethoxy)-2-(methoxymethyl)benzo[d]oxazol-7-yl)ethan-1-one (F11)

[0101]

[0102] According to the above method, replace the 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,3-dihydro-1H-inden-1-one in step 4 of Example 10 with 3-acetylphenylboronic acid to prepare the compound F11. The spectral data of the obtained product are as follows: 1 H NMR (400 MHz, CDCl3) δ 8.36 (s, 1H), 7.99 (t, J = 5.1 Hz, 2H), 7.61 (t, J = 7.7 Hz, 1H), 7.56 (d, J = 8.4 Hz, 1H), 7.26 (t, J = 74 Hz, 1H, -CHF2), 7.23 (d, J = 8.4 Hz, 1H), 4.75 (s, 2H), 3.54 (s, 3H), 2.67 (s, 3H). 13 C NMR (100 MHz, CDCl3) δ 197.78, 162.87, 149.74, 141.89, 137.72, 135.16, 132.52, 132.26, 129.23, 128.01, 127.72, 125.15, 121.35, 115.67 (t, J = 261 Hz, CHF2), 115.51, 66.69, 59.38, 26.69.

[0103] Example 12: Synthesis of 6-(4-(difluoromethoxy)-2-(methoxymethyl)benzo[d]oxazol-7-yl)-2,3-dihydro-1H-inden-1-one (F12)

[0104]

[0105] According to the above method, replace 4-(4,4,5,5-tetramethyl-1,3,2-(pinacolboronate)-2-yl)-2,3-dihydro-1H-inden-1-one in step 4 of Example 10 with 6-(4,4,5,5-tetramethyl-1,3,2-(pinacolboronate)-2-yl)-2,3-dihydro-1H-inden-1-one to prepare compound F12. The spectral data of the obtained product are as follows: 1 H NMR(400MHz,CDCl3)δ7.86(d,J=7.6Hz,1H),7.70(d,J=7.4Hz,1H),7.53(t,J=7.4Hz,1H),7.38(d,J=8.3Hz,1H),7.30(t,J=74Hz,1H),7.25(d,J=9.8Hz,1H),4.70(s,2H),3.51(s,3H),3.09(t,J=5.2Hz,2H),2.72(t,J=5.2Hz,2H). 13 C NMR(100MHz,CDCl3)δ206.37,162.87,155.71,149.89,142.32,140.89,136.62,132.27,127.45,126.13,125.60,124.22,121.41,115.63(t,J=260.5Hz,CHF2),115.50,66.67,59.36,36.46,25.93.

[0106] Example 13: 6-(4-(Methoxy)-2-(methoxyethyl)benzo[d]oxazol-7-yl)-2,3-dihydro-1H-inden-1-one (F13)

[0107]

[0108] According to the above method, replace cyclopropanecarbonyl chloride in step 4 of Example 1 with methoxypropionyl chloride and 3-ethyl ketone phenylboronic acid in step 6 with 6-(4,4,5,5-tetramethyl-1,3,2-(pinacolboronate)-2-yl)-2,3-dihydro-1H-inden-1-one to prepare compound F13. The spectral data of the obtained product are as follows: 11H NMR (400 MHz, CDCl3) δ 8.15 (s, 1H), 8.05 (d, J = 7.9 Hz, 1H), 7.60 (d, J = 8.1 Hz, 1H), 7.47 (d, J = 8.5 Hz, 1H), 6.87 (d, J = 8.5 Hz, 1H), 4.06 (s, 3H), 3.94 (t, J = 6.7 Hz, 2H), 3.40 (s, 3H), 3.25 (t, J = 6.8 Hz, 2H), 3.20 (t, J = 5.8 Hz, 2H), 2.77 (t, J = 6.0 Hz, 2H). 13 13C NMR (100 MHz, CDCl3) δ 206.96, 163.52, 154.04, 150.90, 135.18, 134.18, 128.72, 126.99, 124.32, 123.75, 122.41, 116.71, 106.40, 100.27, 69.09, 58.76, 56.21, 36.61, 29.34, 25.64.

[0109] Example 14: 2-Cyclopropyl-4-methoxy-7-(pyridin-4-yl)benzoxazole (F14)

[0110]

[0111] According to the above method, 3-ethyl ketone phenylboronic acid in step 6 of Example 1 was replaced with 4-pyridineboronic acid to prepare compound F14. The spectral data of the obtained product are as follows: 1 1H NMR (400 MHz, CDCl3) δ 8.68 (d, J = 5.3 Hz, 2H), 7.72 (d, J = 5.8 Hz, 2H), 7.49 (d, J = 8.5 Hz, 1H), 6.85 (d, J = 8.6 Hz, 1H), 4.05 (s, 3H), 2.32–2.22 (m, 1H), 1.40–1.32 (m, 2H), 1.25–1.17 (m, 2H). 13 13C NMR (100 MHz, CDCl3) δ 167.94, 151.55, 150.20, 149.38, 143.12, 131.61, 123.58, 121.73, 114.38, 106.44, 56.22, 9.51, 9.20.

[0112] Example 15: PDE4 Assay

[0113] (1) Establish an in vitro screening method and model for inhibiting PDE4D7 enzyme activity. The time-resolved fluorescence resonance energy transfer method was used to detect the inhibitory activity of PDE4D7 kinase. Using Apremilast as a control drug, its half inhibitory concentration IC 50 value was measured. The results were similar to the IC 50 values reported in many literatures, indicating that the screening model was successfully constructed.

[0114] (2) Dissolve the compound in DMSO to prepare a 10 mM stock solution, and then continue to dilute it with DMSO in gradient and add it to the final reaction system to ensure that the concentration of DMSO should be lower than 1%. The enzyme reaction system of PDE4D7 consists of PDE4D7 enzyme, BSA (bovine serum albumin), PDE4D7-specific fluorescent substrate FAM-cAMP, reaction buffer, etc. After all components are mixed together, react at room temperature for 60 minutes. After the reaction is completed, add a specific phospho-binding antibody and incubate at room temperature for another 60 minutes. Then detect the fluorescence polarization signal on the SpectraMax M5 multi-functional microplate reader of MD Company, with the excitation wavelength of 485 nm and the emission wavelength of 528 nm. Substitute the values into the following formula to calculate the percentage of activity:

[0115] %activity = {(FP drug – FP background) / (FP enzyme – FP background)} × 100%

[0116] Test the IC50 value of the compound, and use Prism GraphPad software to fit the dose-effect curve of the inhibition rate of the compound at different concentrations on the enzyme by non-linear regression and normalization method.

[0117] Table 1 Inhibitory activity of 4-alkoxy-2-substituted-7-arylbenzoxazole compounds on PDE4D7 (IC 50 , nM) a

[0118]

[0119] a Note: All data are the averages of three independent experiments.

[0120] b Note: The inhibitory activity on PDE4D7 at a concentration of 1 μM, and all data are the averages of three independent experiments.

[0121] It can be seen from Table 2 and Figure 1 and Figure 2 that most compounds (11 compounds) showed moderate to satisfactory inhibitory activity on PDE4D7 (10 nM < IC 50 < 50 nM). For example, compound F03 (IC50 = 19.6 nM), F04 (IC 50 = 20.8 nM), F05 (IC 50 = 23.1 nM), F06 (IC 50 = 24.6 nM), F07 (IC 50 = 12 nM), F08 (IC 50 = 17.2 nM), F09 (IC 50 = 18.9 nM), F10 (IC 50 = 15.9 nM), F12 (IC 50 = 16.6 nM), F13 (IC 50 = 12.3 nM). Among them, the inhibitory activity of F07 against PDE4 D7 is comparable to that of the positive control drug Apremilast (IC 50 = 10.1 nM). As can be seen from the table, the compounds of the present invention have good inhibitory activity against the PDE4D7 enzyme and can be used to treat related diseases mediated by abnormal expression of PDE4.

[0122] In addition, we found that the change of the group has a great influence on the activity of benzoxazole compounds; we also synthesized compounds F02, F11 and F15, and their activities decreased rapidly.

[0123]

[0124] Example 16: Cytotoxicity experiment of compound F12 (as Figure 3 shown):

[0125] Inoculate HT-22 cells into a 96-well cell culture plate (medium containing 1% FBS), and the cell density per well is 4×10 3Cells, with a total volume of 100 μL - 200 μL. Fill the area around the wells inoculated with cells with PBS to prevent the evaporation of the liquid in the outermost inoculated wells due to edge effects, reduce the reduction of the liquid, and increase experimental errors. Place the cells in a normal incubator for 12 - 24 h until the cells adhere and the cell density reaches 80% - 90% before treatment. First, perform serum deprivation treatment for 1 h. Gently aspirate and discard the original culture medium from top to bottom along the wall with a small pipette tip, add serum-free pure culture medium (the drug group adds the corresponding concentration of the drug after being prepared and mixed in advance), and place it in the incubator for 1 h. Subsequently, establish the cell oxygen-glucose deprivation model in the same manner as above. It should be noted that gentle operation is required when aspirating and adding the liquid to the microplate to avoid cell loss and increase experimental errors. After the model establishment is completed, take out the 96-well plate, add 10% of the total volume of CCK-8 reagent to each well (for example: if the culture medium is 180 μL, 20 μL of CCK-8 reagent needs to be added), keep it in the dark, and place it in a 37 °C incubator for 4 h. Finally, take out the 96-well plate and place it in a multi-functional microplate reader to detect the absorbance OD value (wavelength is 450 nm), and calculate the cell survival rate of each group. Cell survival rate = (experimental well - blank well) / (control well - blank well) × 100%.

[0126] As Figure 3 shown, compound F12 has no obvious toxicity to HT-22 cells.

[0127] Example 17: Effect of compound F12 on the viability of HT-22 cells in the OGD model (as Figure 4 shown):

[0128] Inoculate HT-22 cells into a 96-well cell culture plate (medium containing 1% FBS), with a cell density of 4 × 10 3Cells, with a total volume of 100 μL - 200 μL. Fill the area around the inoculated cell wells with PBS to prevent the evaporation of the liquid in the outermost inoculated cell wells due to edge effects, reduce the loss, and increase experimental errors. Place the cells in a normal incubator for 12 - 24 h until the cells adhere and the cell density reaches 80% - 90%, then they can be processed. First, perform serum deprivation for 1 h. Gently aspirate and discard the original culture medium from top to bottom along the wall with a small pipette tip, add serum-free pure culture medium (the drug group adds the corresponding concentration of the drug after pre-mixing in advance), and place it in the incubator for 1 h. Subsequently, establish the cell oxygen-glucose deprivation model in the same way as above. Note that gentle operation is required when aspirating and adding the liquid to the microplate to avoid cell loss and increase experimental errors. After the model establishment is completed, take out the 96-well plate, add 10% of the total volume of CCK-8 reagent to each well (for example, if the culture medium is 180 μL, 20 μL of CCK-8 reagent needs to be added), keep it in the dark, and place it in a 37 °C incubator for 4 h. Finally, take out the 96-well plate and place it in a multi-functional microplate reader to detect the absorbance OD value (wavelength is 450 nm), and calculate the cell survival rate of each group. Cell survival rate = (experimental well - blank well) / (control well - blank well) × 100%.

[0129] As Figure 3 shown, compound F12 showed no toxicity to cells at doses of 5 μmol / L to 20 μmol / L. As Figure 4 shown, compound F12 could reverse the decrease in the viability of HT-22 cells after OGD modeling at doses of 3 μmol / L to 10 μmol / L.

[0130] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limiting the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A benzoxazole compound or a pharmaceutically acceptable salt thereof, characterized in that, The benzoxazole compound has the following structure: 、 、 、 、 、 、 、 、 、 、 。 2. The preparation method of the benzoxazole compound or a pharmaceutically acceptable salt thereof according to claim 1, comprising the following steps: S1. Prepare the compound of formula (II); S2. The compound shown in claim 1 is obtained by a coupling reaction of the compound of formula (II) with R 3 -X; X is B(OH)2 or B(Pin)2; （Ⅱ） Or comprising the following steps: S1. Prepare the compound of formula (III); S2. The compound shown in claim 1 is obtained by the condensation reaction of the compound of formula (III) with R 2 -CHO （Ⅲ）。 3. The application of the benzoxazole compound or a pharmaceutically acceptable salt thereof according to claim 1 in the preparation of a phosphodiesterase 4 inhibitor.

4. The application of the benzoxazole compound or a pharmaceutically acceptable salt thereof according to claim 1 in the preparation of a drug for treating Parkinson's disease and Parkinson's syndrome.

5. The application of the benzoxazole compound or a pharmaceutically acceptable salt thereof according to claim 1 in the preparation of a drug for treating stroke and ischemic dementia-related diseases.

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