CYCLOPENTYL ADENOSINE DERIVATIVE AND PHARMACEUTICAL USE THEREOF

Abstract

The present disclosure relates to a cyclopentyl adenosine derivative and a pharmaceutical use thereof. Specifically, the present disclosure provides a compound represented by formula (I) or a pharmaceutically acceptable salt thereof, wherein R.sup.1-R.sup.8 are as defined in the description.

##STR00001##

Claims

1. A compound represented by formula (I) or a pharmaceutically acceptable salt thereof, ##STR00061## wherein: R.sup.1, R.sup.2, and R.sup.3 are identical or different and are each independently selected from the group consisting of hydrogen, ##STR00062## (CO)C.sub.1-20 alkyl, (CO)C.sub.1-20 alkoxy, (CO)5-6 membered cycloalkyl, (CO)5-6 membered heterocyclyl, (CO)6-membered aryl, and (CO)5-6 membered heteroaryl, wherein the alkyl, alkoxy, cycloalkyl, heterocyclyl, aryl, or heteroaryl is optionally substituted with one or more substituents selected from the group consisting of halogen, hydroxy, oxo, amino, cyano, C.sub.1-6 alkyl, and C.sub.1-6 alkoxy; Y is selected from the group consisting of alkylene and heteroalkylene, wherein the alkylene or heteroalkylene is optionally substituted with one or more substituents selected from the group consisting of halogen, hydroxy, oxo, amino, cyano, C.sub.1-6 alkyl, and C.sub.1-6 alkoxy; R.sup.a, R.sup.b, and R.sup.c are identical or different and are each independently C.sub.1-6 alkyl, and R.sup.1, R.sup.2, and R.sup.3 cannot be hydrogen at the same time; R.sup.4 is selected from the group consisting of halogen, hydroxy, amino, cyano, C.sub.1-6 alkyl, and C.sub.1-6 alkoxy, wherein the alkyl or alkoxy is optionally substituted with one or more substituents selected from the group consisting of halogen, hydroxy, amino, cyano, C.sub.1-6 alkyl, and C.sub.1-6 alkoxy; R.sup.5, R.sup.6, R.sup.7, and R.sup.8 are identical or different and are each independently selected from the group consisting of hydrogen, halogen, hydroxy, amino, cyano, C.sub.1-6 alkyl, and C.sub.1-6 alkoxy, wherein the alkyl or alkoxy is optionally substituted with one or more substituents selected from the group consisting of halogen, hydroxy, amino, cyano, C.sub.1-6 alkyl, and C.sub.1-6 alkoxy; n is selected from the group consisting of 0, 1, 2, 3, 4, 5, 6, 7, and 8.

2. The compound or the pharmaceutically acceptable salt thereof according to claim 1, wherein both R.sup.2 and R.sup.3 are hydrogens.

3. The compound or the pharmaceutically acceptable salt thereof according to claim 1, wherein the compound represented by formula (I) or the pharmaceutically acceptable salt thereof is a compound represented by formula (1-1) or a pharmaceutically acceptable salt thereof, ##STR00063## wherein R.sup.1, R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8, and n are as defined in claim 1.

4. The compound or the pharmaceutically acceptable salt thereof according to claim 1, wherein R.sup.4 is halogen, preferably fluorine, chlorine, or bromine, and most preferably chlorine.

5. The compound or the pharmaceutically acceptable salt thereof according to claim 1, wherein the compound represented by formula (I) or the pharmaceutically acceptable salt thereof is a compound represented by formula (I-2) or a pharmaceutically acceptable salt thereof, ##STR00064## wherein R.sup.1, R.sup.5, R.sup.6, R.sup.7, R.sup.8, and n are as defined in claim 1.

6. The compound or the pharmaceutically acceptable salt thereof according to claim 1, wherein R.sup.5 is hydrogen.

7. The compound or the pharmaceutically acceptable salt thereof according to claim 1, wherein R.sup.6 is hydrogen.

8. The compound or the pharmaceutically acceptable salt thereof according to claim 1, wherein the compound represented by formula (I) or the pharmaceutically acceptable salt thereof is a compound represented by formula (I-3) or a pharmaceutically acceptable salt thereof, ##STR00065## wherein R.sup.1, R.sup.7, and R.sup.8 are as defined in claim 1.

9. The compound or the pharmaceutically acceptable salt thereof according to claim 1, wherein both R.sup.7 and R.sup.8 are hydrogens.

10. The compound or the pharmaceutically acceptable salt thereof according to claim 1, wherein the compound represented by formula (I) or the pharmaceutically acceptable salt thereof is a compound represented by formula (I-4) or a pharmaceutically acceptable salt thereof, ##STR00066## wherein R.sup.1 is as defined in claim 1.

11. The compound or the pharmaceutically acceptable salt thereof according to claim 1, wherein R.sup.1 is selected from the group consisting of (CO)C.sub.1-5 alkyl, (CO)C.sub.10-20 alkyl, (CO)5-6 membered cycloalkyl, (CO)5-6 membered heterocyclyl, (CO)phenyl, (CO)5-6 membered heteroaryl, and ##STR00067## Y is C.sub.1-6 alkylene; R.sup.a, R.sup.b, and R.sup.c are identical or different and are each independently C.sub.1-6 alkyl; the alkylene, alkyl, cycloalkyl, heterocyclyl, phenyl, or heteroaryl is optionally substituted with one or more substituents selected from the group consisting of halogen, hydroxy, amino, cyano, oxo, C.sub.1-6 alkyl, and C.sub.1-6 alkoxy, and the substituents are preferably fluorine, chlorine, bromine, hydroxy, amino, oxo, and methyl.

12. The compound or the pharmaceutically acceptable salt thereof according to claim 11, wherein R.sup.1 is selected from the group consisting of (CO)methyl, (CO)ethyl, (CO)propyl, (CO)butyl, (CO)pentyl, (CO)C.sub.14 alkyl, (CO)phenyl, (CO)cyclopropane, (CO)cyclobutane, (CO)cyclopentane, (CO)cyclohexane, (CO)pyrrolidine, (CO)piperidine, (CO)piperazine, (CO)morpholine, (CO)thiomorpholine, (CO)pyrrole, (CO)furan, (CO)thiophene, (CO)pyridine, (CO)thiazole, (CO)oxazole, (CO)imidazole, (CO)triazole, (CO)tetrazole, and ##STR00068## the R.sup.1 is optionally substituted with one or more substituents selected from the group consisting of halogen, hydroxy, amino, cyano, oxo, C.sub.1-6 alkyl, and C.sub.1-6 alkoxy, and the substituents are preferably fluorine, chlorine, bromine, hydroxy, amino, oxo, and methyl.

13. The compound or the pharmaceutically acceptable salt thereof according to claim 1, wherein the compound or the pharmaceutically acceptable salt thereof is selected from the group consisting of any one of the compounds in the table below, TABLE-US-00006

14. An isotopically substituted form of the compound or the pharmaceutically acceptable salt thereof according to claim 13, wherein preferably, the isotopically substituted form is a deuterated form.

15. A pharmaceutical composition, comprising a therapeutically effective amount of at least one of the compound or the pharmaceutically acceptable salt thereof according to claim 1 or the isotopically substituted form and a pharmaceutically acceptable excipient.

16. A method for treating or preventing chronic pain, comprising administering to a patient a therapeutically effective amount of the compound according to claim 1, or the isotopically substituted form, or the pharmaceutical composition.

17. Use of the compound according to claim 1, or the isotopically substituted form, or the pharmaceutical composition in the preparation of a medicament for treating or preventing chronic pain.

Description

DETAILED DESCRIPTION

[0073] The disclosure is further described below with reference to examples. However, these examples do not limit the scope of the disclosure.

[0074] Experimental methods without conditions specified in the examples of the disclosure were generally conducted under conventional conditions, or conditions recommended by the manufacturers of the starting materials or commercial products. Reagents without specific origins indicated were commercially available conventional reagents.

[0075] The structures of the compounds were determined by nuclear magnetic resonance (NMR) spectroscopy or/and mass spectrometry (MS). The NMR shifts () are given in 10.sup.6 (ppm). The NMR analyses were performed on a Bruker AVANCE-400 nuclear magnetic resonance instrument, with dimethyl sulfoxide-D6 (DMSO-d.sub.6), chloroform-D (CDCl.sub.3), and methanol-D4 (methanol-d.sub.4) as solvents and tetramethylsilane (TMS) as an internal standard.

[0076] The HPLC analyses were performed using an Agilent1100 high pressure liquid chromatograph, a GAS15B DAD ultraviolet detector, and a Water Vbridge C18 1504.6 mm 5 m chromatography column.

[0077] The MS analyses were performed using an Agilent6120 triple quadrupole mass spectrometer, a G1315D DAD detector, and a Waters Xbridge C18 4.650 mm, 5 m chromatography column, with scanning performed in positive/negative ion mode with a mass scan range of 80-1200.

[0078] The thin-layer chromatography silica gel plates used were Yantai Huanghai HSGF254 silica gel plates. The silica gel plates used in the thin-layer chromatography (TLC) analyses had a layer thickness of 0.2 mm0.03 mm, and those used in the thin-layer chromatography separation and purification had a layer thickness of 0.4 mm-0.5 mm.

[0079] The flash column purification system used was Combiflash Rf150 (TELEDYNE ISCO) or Isolara one (Biotage).

[0080] In the normal-phase column chromatography steps, a 200-300 mesh or 300-400 mesh Yantai Huanghai silica gel was generally used as the carrier, or a Changzhou Santai pre-fill ultrapure normal-phase silica gel column (40-63 m, 60 g, 24 g, 40 g, 120 g, or other specifications) was used.

[0081] The known starting materials in the disclosure may be synthesized by using or following methods known in the art, or may be purchased from Shanghai Titan Scientific, ABCR GmbH & Co. KG, Acros Organics, Aldrich Chemical Company, Accela ChemBio Inc., and Bide Pharmatech, among others.

[0082] In the examples, the reactions can all be performed in a nitrogen atmosphere unless otherwise specified.

[0083] The nitrogen atmosphere means that the reaction flask is connected to a balloon containing about 1 L of nitrogen gas.

[0084] The hydrogen atmosphere means that the reaction flask was connected to a balloon containing about 1 L of hydrogen gas.

[0085] The hydrogen gas was prepared by a QPH-IL hydrogen generator from Shanghai Quan Pu Scientific Instruments Inc.

[0086] The nitrogen atmosphere or the hydrogenation atmosphere was generally formed by 3 cycles of vacuumization and nitrogen or hydrogen filling.

[0087] In the examples, the solutions were aqueous solutions unless otherwise specified.

[0088] In the examples, the reaction temperature was room temperature, i.e., 20 C.-30 C., unless otherwise specified.

[0089] The monitoring of reaction progress in the examples was performed using thin-layer chromatography (TLC). For the developing solvents used in the reactions, the eluent systems used in the column chromatography purification, and the developing solvent systems used in the thin-layer chromatography analyses, the volume ratio of the solvents was adjusted depending on the polarity of the compound, or by adding a small amount of basic or acidic reagents such as triethylamine and acetic acid.

EXAMPLES

[0090] Example 1: ((2R,3S,4R,5R)-5-(2-Chloro-6-(cyclopentylamino)-9H-purin-9-yl)-3,4-dihydroxytetrahydrofuran-2-yl)methyl pentadecanoate (Compound 1)

##STR00056## ##STR00057##

Step 1) Preparation of (2R,3R,4S,5R)-2-(2-chloro-6-(cyclopentylamino)-9H-purin-9-yl)-5-(hydroxymethyl)tetrahydrofuran-3,4-diol (1-c)

[0091] 1-a (6.0 g, 13.4 mmol), ethanol (40 mL), 1-b (1.370 g, 16.1 mmol), and TEA (2.2 mL, 16.1 mmol) were sequentially added to a 250 mL three-necked flask. Stirring was started, and the system was purged with nitrogen gas three times and heated at reflux (internal temperature: 70 C.) for 2 h. Analysis showed that the reaction of the starting material was complete, and the reaction was stopped and cooled until the internal temperature was 20 C. The reaction mixture was concentrated under reduced pressure to give an oil. Methanol (120 mL) and potassium carbonate (12.9 g, 93.4 mmol) were sequentially added, and the mixture was stirred at room temperature for 3 h. The reaction was stopped, and the reaction mixture was concentrated under reduced pressure to give an oil. Water (50 mL), saturated ammonium chloride (150 mL), and dichloromethane were sequentially added. Extraction was performed with dichloromethane three times, 60 mL each time. The organic phases were combined, extracted and washed with saturated brine (50 mL), dried over anhydrous sodium sulfate (5 g), filtered, and concentrated to give an oil. The oil was purified by column chromatography (MeOH/DCM=0-10%) to give a yellow solid (4.750 g, yield: 95.9%).

[0092] MS-ESI: 370.1[M+H].sup.+.

[0093] .sup.1H NMR (400 MHZ, CD.sub.3OD) 8.22 (s, 1 H), 5.89 (d, J=6.0 Hz, 1 H), 4.66 (t, J=5.2 Hz, 1 H), 4.53-4.49 (m, 1 H), 4.31 (t, J=3.2 Hz, 1 H), 4.15-4.13 (m, 1 H), 3.88 (dd, J=12.4 Hz, J=2.4 Hz, 1 H), 4.74 (dd, J=12.4 Hz, J=4.0 Hz, 1 H), 2.11-2.05 (m, 2 H), 1.82-1.76 (m, 2 H), 1.73-1.58 (m, 4 H)

Step 2) Preparation of ((3aR,4R,6R,6aR)-6-(2-chloro-6-(cyclopentylamino)-9H-purin-9-yl)-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methanol (1-d)

[0094] 1-c (4.0 g, 10.8 mmol), acetone (40 mL), 2,2-dimethoxypropane (5.637 g, 54.2 mmol), and PTSA (0.372 g, 2.16 mmol) were sequentially added to a 100 mL three-necked flask, and the system was purged with nitrogen gas three times and heated at reflux for 1 h. Analysis showed that the reaction was complete, and heating was stopped. The reaction mixture was cooled to room temperature (20 C.) and concentrated under reduced pressure to give an oil. Dichloromethane (150 mL) was added, and the mixture was extracted and washed with saturated sodium bicarbonate (60 mL2) and saturated brine (50 mL) in sequence, dried over anhydrous sodium sulfate (5 g), filtered, and concentrated to give 4.0 g of a yellow solid crude product. The crude product was directly used in the next step. Yield: 96.6%.

[0095] MS-ESI: 410.2[M+H].sup.+.

[0096] .sup.1H NMR (400 MHZ, CD.sub.3OD) 8.22 (s, 1 H), 6.09 (d, J=3.6 Hz, 1 H), 5.23 (dd, J=6.0 Hz, J=3.2 Hz, 1 H), 5.01 (dd, J=6.4 Hz, J=2.4 Hz, 1 H), 4.53-4.49 (m, 1 H), 4.34 (dd, J=6.0 Hz, J =4.0 Hz, 1 H), 3.78 (dd, J =12.0 Hz, J =4.0 Hz, 1 H), 3.71 (dd, J=12.0 Hz, J=4.0 Hz, 1 H), 2.16-2.04 (m, 2 H), 1.83-1.76 (m, 2 H), 1.72-1.56 (m, 7 H), 1.37 (s, 3 H).

Step 3) Preparation of ((3aR,4R,6R,6aR)-6-(2-chloro-6-(cyclopentylamino)-9H-purin-9-yl)-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methyl pentadecanoate (1-e)

[0097] DCM (6 mL), 1-d (600 mg, 1.46 mmol), DCC (453 mg, 2.2 mmol), and DMAP (18 mg, 0.146 mmol) were sequentially added to a 25 mL single-necked flask, and the system was purged with nitrogen gas three times and stirred at room temperature (19-26 C.) for 5 h. Analysis showed that the reaction was complete, and the reaction was stopped. The reaction mixture was filtered, and the filter cake was washed with dichloromethane twice, 20 mL each time. The filtrate was concentrated under reduced pressure to give an oil, and the oil was purified by column chromatography (EA/PE=0- 1/1) to give a white solid (896 mg, yield: 96%).

[0098] .sup.1H NMR (400 MHZ, CD.sub.3OD) 8.13 (s, 1 H), 6.13 (d, J=2.0 Hz, 1 H), 5.48-5.44 (m, 1 H), 5.43 (s, 1 H), 5.08-5.05 (m, 1 H), 4.53-4.48 (m, 1 H), 4.45-4.42 (m, 1 H), 4.27-4.25 (m, 2 H), 2.23-2.18 (m, 2 H), 2.11-2.04 (m, 2 H), 1.82-1.78 (m, 2 H), 1.72-1.58 (m, 6 H), 1.50-1.47 (m, 2 H), 1.39 (s, 3 H), 1.35-1.23 (m, 20 H), 0.89 (t, J=6.8 Hz, 3 H).

Step 4) Preparation of ((2R,3S,4R,5R)-5-(2-chloro-6-(cyclopentylamino)-9H-purin-9-yl)-3,4-dihydroxytetrahydrofuran-2-yl)methyl pentadecanoate (Compound 1)

[0099] Dichloromethane (6 mL) and 1-e (600 mg, 0.946 mmol) were sequentially added to a 50 mL three-necked flask, and the system was purged with nitrogen gas three times and cooled in an ice-water bath until the internal temperature was 5 C. TFA (6 mL) was added dropwise over about 5 min, with the internal temperature not higher than 5 C. The ice-water bath was removed, and the mixture was stirred at room temperature for 3 h. Analysis showed that the reaction was complete, and the reaction was stopped. The reaction mixture was concentrated under reduced pressure to give an oil. Saturated brine (60 mL) was added, and extraction was performed with dichloromethane (60 mL3). The organic phases were combined, dried over anhydrous sodium sulfate (5 g), filtered, and concentrated to give an oil. The oil was purified by column chromatography (MeOH/DCM=0% to 10%) to give a white solid (289 mg, yield: 51%).

[0100] MS-ESI: 594.3[M+H].sup.+.

[0101] .sup.1H NMR (400 MHZ, CDCI.sub.3) 7.87 (s, 1 H), 6.01 (d, J=3.2 Hz, 1 H), 5.90 (d, J=5.2 Hz, 1 H), 5.43 (s, 1 H), 4.58-4.57 (m, 1 H), 4.54 (t, J=5.2 Hz, 1 H), 4.52-4.47 (m, 1 H), 4.46-4.37 (m, 2 H), 4.28 (dd, J=12.4 Hz, J=4.0 Hz, 1 H), 3.26 (d, J=1.6 Hz, 1 H), 2.28-2.20 (m, 2 H), 2.18-2.10 (m, 2 H), 1.57-1.43 (m, 2 H), 1.51-1.48 (m, 4 H), 1.31-1.22 (m, 22 H), 0.87 (t, J=6.8 Hz, 3 H).

Example 2: ((2R,3S,4R,5R)-5-(2-Chloro-6-(cyclopentylamino)-9H-purin-9-yl)-3,4-dihydroxytetrahydrofuran-2-yl)methyl benzoate (Compound 2)

##STR00058##

Step 1) Preparation of ((3aR,4R,6R,6aR)-6-(2-chloro-6-(cyclopentylamino)-9H-purin-9-yl)-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methyl benzoate (2-a)

[0102] In a nitrogen atmosphere, 1-d (550 mg, 1.34 mmol, 1.0 eq) was added to DCM (25 mL) and stirred until the compound dissolved, and benzoic acid (196 mg, 1.74 mmol, 1.3 eq), DMAP (16.5 mg, 0.134 mmol, 0.1 eq), and DCC (418 mg, 2.01 mmol, 1.5 eq) were sequentially added. The mixture was left to react for 3-4 h, and in-process monitoring showed that the reaction was complete. The reaction mixture was directly concentrated under reduced pressure and then purified by reversed-phase column chromatography (ACN:H.sub.2O (1% TFA)=0-95%) to give 2-a (610 mg, yield: 88%).

[0103] MS-ESI: 514.2 [M+H].sup.+.

Step 2) Preparation of ((2R,3S,4R,5R)-5-(2-chloro-6-(cyclopentylamino)-9H-purin-9-yl)-3,4-dihydroxytetrahydrofuran-2-yl)methyl benzoate (Compound 2)

[0104] 2-a (610 mg, 1.1 mmol, 1.0 eq) was dissolved in DCM (3 mL), and TFA (3 mL) was then added. The mixture was stirred in a nitrogen atmosphere for 2-3 h, and in-process monitoring showed that the reaction was complete. The reaction mixture was concentrated under reduced pressure to remove the solvent, and the residue was dissolved in DCM (30 mL). Then the solution was washed with saturated sodium bicarbonate (40 mL) and concentrated under reduced pressure, and the residue was purified by column chromatography (EA:PE=0-75%) to give compound 2 (130 mg, yield: 23.11%).

[0105] MS-ESI: 474.1 [M+H].sup.+.

[0106] .sup.1H NMR (400 M, CDCl.sub.3): 7.86-7.84 (m, 3 H), 7.52 (t, J=7.6 Hz, 1 H), 7.38-7.26 (m, 2 H), 6.10-6.08 (bs, 1 H), 5.91 (d, J=7.6 Hz, 1 H), 5.48 (s, 1 H), 4.72-4.47 (m, 6H), 3.26-3.23 (m, 1 H), 2.22-2.17 (m,2H), 1.77-1.72 (m, 2 H), 1.55-1.53 (m,2 H), 1.33-1.31 (m, 1H).

Example 3 ((2R,3S,4R,5R)-5-(2-Chloro-6-(cyclopentylamino)-9H-purin-9-yl)-3,4-dihydroxytetrahydrofuran-2-yl)methyl isobutyrate (Compound 3)

##STR00059##

Step 1) Preparation of ((3aR,4R,6R,6aR)-6-(2-chloro-6-(cyclopentylamino)-9H-purin-9-yl)-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methyl isobutyrate (3-a)

[0107] In a nitrogen atmosphere, 1-d (550 mg, 1.34 mmol, 1.0 eq) was added to DCM (25 mL) and stirred, and then isobutyric acid (154 mg, 1.74 mmol, 1.3 eq), DMAP (16.5 mg, 0.134 mmol, 0.1 eq), and DCC (418 mg, 2.01 mmol, 1.5 eq) were sequentially added. The mixture was left to react for 3-4 h, and in-process monitoring showed that the reaction was complete. The reaction mixture was directly concentrated under reduced pressure and then purified by reversed-phase column chromatography (ACN:H.sub.2O (1% TFA)=0-95%) to give 3-a (613 mg, yield: 95%).

[0108] MS-ESI: 480.2 [M+H].sup.+.

Step 2) Preparation of ((2R,3S,4R,5R)-5-(2-chloro-6-(cyclopentylamino)-9H-purin-9-yl)-3,4-dihydroxytetrahydrofuran-2-yl)methyl isobutyrate (Compound 3)

[0109] In a nitrogen atmosphere, 3-a (610 mg, 1.1 mmol, 1.0 eq) was dissolved in DCM (3 mL), and TFA (3 mL) was then added. The mixture was stirred for 2-3 h, and in-process monitoring showed that the reaction was complete. The reaction mixture was concentrated under reduced pressure to remove the solvent, and the residue was dissolved in DCM (30 mL). Then the solution was washed with saturated sodium bicarbonate (40 mL) and concentrated under reduced pressure, and the residue was purified by column chromatography (EA:PE=0-75%) to give compound 3 (291 mg, yield: 23.11%).

[0110] MS-ESI: 440.2 [M+H].sup.+.

[0111] .sup.1H NMR (400 MHZ, CDCl.sub.3) 7.89 (s, 1 H), 6.10 (bs, 1 H), 5.92 (d, J=4.8 Hz, 1 H), 5.54 (bs, 1 H), 4.58-4.108 (m, 6 H), 3.38 (bs, 1 H), 2.55-2.48 (m, 1 H), 2.17-2.10 (m, 2 H), 1.80-1.66 (m, 7 H), 1.57-1.53 (m, 2 H), 1.13-0.96 (m, 3 H).

Example 4: ((2R,3S,4R,5R)-5-(2-Chloro-6-(cyclopentylamino)-9H-purin-9-yl)-3,4-dihydroxytetrahydrofuran-2-yl)methyl L-valinate (Compound 4)

##STR00060##

Step 1) Preparation of ((3aR,4R,6R,6aR)-6-(2-chloro-6-(cyclopentylamino)-9H-purin-9-yl)-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)L-valine (4-a)

[0112] DCM (10 mL), 1-d (500 mg, 1.22 mmol), Boc-D-valine (345 mg, 1.59 mmol), DCC (377 mg, 1.83 mmol), and DMAP (15 mg, 0.122 mmol) were sequentially added to a 25 mL single-necked flask, and the system was purged with nitrogen gas three times and stirred at room temperature (19-26 C.) for 5 h. Analysis showed that the reaction was complete, and the reaction was stopped. The reaction mixture was filtered, and the filter cake was washed with dichloromethane twice, 20 mL each time. The filtrate was concentrated under reduced pressure to give an oil, and the oil was purified by column chromatography (EA/PE=0:1-1:1) to give a white solid (718 mg, yield: 96%).

[0113] MS-ESI: 609.3 [M+1].sup.+.

Step 2) Preparation of ((2R,3S,4R,5R)-5-(2-chloro-6-(cyclopentylamino)-9H-purin-9-yl)-3,4-dihydroxytetrahydrofuran-2-yl)methyl L-valinate (Compound 4)

[0114] TFA (6 mL) and 1-d (600 mg, 0.946 mmol) were sequentially added to a 50 mL three-necked flask, and the system was purged with nitrogen gas three times and stirred at room temperature (19-26 C.) for 2 h. Analysis showed that the reaction was complete. The reaction mixture was concentrated under reduced pressure to give an oil. Saturated sodium bicarbonate (60 mL) was added, and extraction was performed with dichloromethane (60 mL3). The organic phases were combined, dried over anhydrous sodium sulfate (5 g), filtered, and concentrated to give an oil. The oil was purified by column chromatography (MeOH/DCM=0%-10%) to give a white solid (206 mg, yield: 44.6%).

[0115] MS-ESI: 469.2 [M+1].sup.+.

[0116] .sup.1H NMR (400 MHZ, CD.sub.3OD) 8.16 (s, 1 H), 5.92 (d, J=4.4 Hz, 1 H), 4.78 (t, J=4.8 Hz, 1 H), 4.51-4.46 (m, 1 H), 4.44-4.38 (m, 3 H), 4.27-4.23 (m, 1 H), 2.10-2.05 (m, 2 H), 1.97-1.92 (m, 1 H), 1.82-1.76 (m, 2 H), 1.73-1.35 (m, 4 H), 0.91 (d, J=7.2 Hz, 3 H), 0.87 (d, J=6.8 Hz, 3 H).

BIOLOGICAL EVALUATIONS

Test Example 1

1. Exprimental Materials

TABLE-US-00002 Cat. No./ Reagent/instrument Manufacturer Specification Complete Freund's Sigma-Aldrich, St. Louis, F5881 adjuvant (CFA) MO 0.9% sodium chloride Anhui Double-Crane 500 mL injection Pharmaceutical Co., Ltd. 2-Chloro-N6- Sigma-Aldrich, St. Louis, 37739-05-2 cyclopentyladenosine MO (CCPA) VonFrey electronic Bioseb, Vitrolles, France BIO-EVF4 aesthesiometer

[0117] Experimental animals: SPF male Sprague-Dawley (SD) rats, weighing 18030 g, obtained from Shanghai Sippe-Bk Lab Animal Co., Ltd.

[0118] Experimental samples: Compounds 1, 2, and 3 and CCPA were used to prepare the corresponding pharmaceutical compositions according to the following formulation amounts and method.

TABLE-US-00003 TABLE 1 Formulations of pharmaceutical compositions Formulation Amount 1 2 3 4 Compound 1 30 mg / / / Compound 2 / 30 mg / / Compound 3 / / 30 mg / CCPA / / / 30 mg DMPC 485.7 mg Cholesterol 138.6 mg

[0119] Preparation method: Formulation amounts of compounds 1, 2, and 3 and CCPA were separately weighed out, added to a proper amount of tert-butanol/water mixed solution, and dissolved by stirring. Then formulation amounts of dimyristoylphosphatidylcholine (DMPC) and cholesterol were added and dissolved by stirring.

[0120] The above solutions were made up to volume (25-40 mL), added to vials, and lyophilized in a lyophilizer for later use. When used, the lyophilizates were dissolved in normal saline to 1 mg/mL, 2 mg/mL, 4 mg/mL, and 8 mg/mL.

2. Experimental Method

2.1. Animals and Administration

[0121] SD rats, 6 to 8-week-old and weighing 150 g-200 g, were divided into a control group, a model control group, and an administration group. A CFA inflammatory pain model was obtained 24 h after 100 L of complete Freund's adjuvant was injected into the soles of the left feet of the rats in the model control group and the administration group. The injection was performed at left Zusanli, and the injection volume was 100 L. Specific administration information is shown in Table 2.

TABLE-US-00004 TABLE 2 Administration information Number of Route of Concentration Volume animals Group administration (mg/mL) (100 L) (rats) Control group Injection 6 Model control 100 6 group Administration 1 mg/mL 100 6 group 2 mg/mL 100 6 4 mg/mL 100 6 8 mg/mL 100 6

[0122] Note: For the control group, 100 L of normal saline was injected into the soles of the feet. For the model control group, 100 L of normal saline was injected into Zusanli after the model was successfully established.

2.2. Evaluation Indices and Data

[0123] A VonFrey electronic aesthesiometer was used to measure the pain threshold, and mechanical pain was used as an evaluation index. Observations of the basal pain threshold were started 1 day before the model was established and ended 14 days after the model was established.

[0124] Pain thresholds before and after administration for different groups of animals were plotted using Graph Pad Prism 8.3.0 software. Based on the dose-response curve 48 h after administration, the EC.sub.50 and EC.sub.90 were obtained through fitting.

TABLE-US-00005 TABLE 3 Activity data for formulation samples No. EC.sub.50 (mg/mL) EC50(M) EC.sub.90 (mg/mL) EC90(M) Formulation 1 1.001 1.687 1.082 1.824 Formulation 2 2.082 4.446 2.285 4.880 Formulation 3 1.807 4.115 2.106 4.796 Formulation 4 2.352 6.494 3.474 10.799

[0125] Conclusion: Biological activity data show that after fatty alkanoyl modification at the 5 site, the EC.sub.50 and EC.sub.90 values of compound 1 significantly decreased, and increased 4-fold and 6-fold, respectively, compared to CCPA. In addition, compared to compound 2, the EC.sub.50 and EC.sub.90 also increased nearly 3-fold. Unlike the prior art (or common sense), the activity of the fatty compound is comparable to or worse than that of the compounds.