HK1149563B - 4-(acetylamino)-3-[(4-chlorophenyl)thio]-2-methyl-1h-indole-1-acetic acid ethyl ester intermediate compound - Google Patents

Description

The present invention relates to 4-(acetylamino)-3-[(4-chlorophenyl)thio]-2-methyl-1H-indole-acetic acid, ethyl ester and its use in the preparation of substituted indoles useful as pharmaceutical compounds for treating respiratory disorders

EPA 1 170 594 discloses methods for the identification of compounds useful for the treatment of disease states mediated by prostaglandin D2, a ligand for orphan receptor CRTh2. US 5,486,525 discloses a series of indoles said to possess PAF antagonist activity. It has now surprisingly been found that certain indole acetic acids are active at the CRTh2 receptor, and as a consequence are expected to be potentially useful for the treatment of various respiratory diseases, including asthma and COPD.

In a first aspect the invention therefore provides a compound 4-(acetylamino)-3-[(4-chlorophenyl)thio]-2-methyl-1H-indole-acetic acid, ethyl ester.

The compound of the invention may be used in the preparation of a compound of formula: and pharmaceutically acceptable salts and solvates thereof.

The invention will now be illustrated by the following non-limiting examples in which, unless stated otherwise:

1. (i) the title and sub-titled compounds of the examples and methods were named using the ACD labs/name program (version 6.0) from Advanced Chemical Development Inc, Canada;
2. (ii) unless stated otherwise, reverse phase preparative HPLC was conducted using a Symmetry, NovaPak or Ex-Terra reverse phase silica column;
3. (iii) Flash column chromatography refers to normal phase silica chromatography
4. (iv) solvents were dried with MgSO₄ or Na₂SO₄
5. (v) Evaporations were carried out by rotary evaporation in vacuo and work-up procedures were carried out after removal of residual solids such as drying agents by filtration;
6. (vi) Unless otherwise stated, operations were carried out at ambient temperature, that is in the range 18-25°C and under an atmosphere of an inert gas such as argon or nitrogen;
7. (vii) yields are given for illustration only and are not necessarily the maximum attainable;
8. (viii) the structures of the end-products of the formula (1) were confirmed by nuclear (generally proton) magnetic resonance (NMR) and mass spectral techniques; proton magnetic resonance chemical shift values were measured on the delta scale and peak multiplicities are shown as follows: s, singlet; d, doublet; t, triplet; m, multiplet; br, broad; q, quartet, quin, quintet;
9. (ix) intermediates were not generally fully characterised and purity was assessed by thin layer chromatography (TLC), high-performance liquid chromatography (HPLC), mass spectrometry (MS), infra-red (IR) or NMR analysis;
10. (x) mass spectra (MS): generally only ions which indicate the parent mass are reported when given, ¹H NMR data is quoted in the form of delta values for major diagnostic protons, given in parts per million (ppm) relative to tetramethylsilane (TMS) as an internal standard;
11. (xi) the following abbreviations are used:
    • M.p. = melting point
    • THF = tetrahydrofuran
    • EtOAc = ethyl acetate
    • MCPBA = meta chloroperbenzoic acid
    • DMF = N,N-dimethyl formamide
    • MgSO₄ = magnesium sulfate
    • Na₂SO₄= sodium sulfate
    • NaHCO₃ = sodium hydrogen carbonate

Example 1

Preparation of 4-(Acetylamino)-3-[(4-chlorophenyl)thio]-2-methyl-1H-indole-1-acetic acid i) 3-[(4-chlorophenyl)thio]-2-methyl-4-nitro-1H-indole

To a stirred solution of 3-nitroaniline (8 g) in THF (700 ml) cooled to -78 °C was added tert-butyl hypochlorite (6.3 g) dropwise over 5 minutes. The reaction was allowed to warm to -65 ° C over 20 minutes before 1-[4-chlorophenyl)thio]-2-propanone (11.6 g) was added as a solution in THF (20 ml). After 2 hours triethylamine (8.1 ml) was added and the reaction allowed to warm to room temperature. 2M HCl (aq) was added to the reaction mixture before concentration in vacuo. The residue was slurried in methanol and the solid which precipitated isolated by filtration to give the sub-title compound (5.8 g). ¹H NMR (DMSO-d6) δ 12.55 (s, 1H), 7.76 (dd, 1H), 7.63 (dd, 1H), 7.31-7.22 (m, 3H), 6.91 (dd, 2H), 2.47 (s, 3H)

ii) 3-[(4-chlorophenyl)thio]-2-methyl-4-nitro-1H-indole-acetic acid, ethyl ester

To a stirred suspension of sodium hydride, 60% dispersion in mineral oil, (0.85 g) in THF (100 ml) was added the product from part (i) (5.6 g) as a solution in THF (50 ml). After stirring at room temperature for 30 minutes ethyl bromoacetate (2.3 ml) was added dropwise over 10 minutes. After 2 hours the reaction was concentrated in vacuo, the residue dissolved in ethyl acetate, washed with water, brine, dried (MgSO₄) and concentrated in vacuo. Recrystallisation from ethanol gave the sub-title compound (5 g). ¹H NMR (DMSO-d6) δ 7.97 (dd, 1H), 7.65 (dd, 1H), 7.35 (t, 1H), 7.26 (dt, 2H), 6.92 (dt, 2H), 5.40 (s, 2H), 4.19 (q, 2H), 2.45 (s, 3H), 1.22 (t, 3H).

iii) 4-amino-3-[(4-chlorophenyl)thio]-2-methyl-1H-indole-acetic acid, ethyl ester

A suspension of the product from part (ii) (2.25 g) in ethanol (170 ml) was stirred in the presence of 5% Pt/C (0.5 g) under 2 bar pressure of H₂. After stirring overnight the catalyst was removed by filtration and the filtrates concentrated in vacuo. Purification by flash column chromatography (14% EtOAc/hexane as eluent) to give the sub-title compound (1.4 g). ¹H NMR (DMSO-d6) δ 7.30 (dd, 2H), 7.00 (dt, 2H), 6.85 (t,1H), 6.68 (dd, 1H), 6.23 (dd, 1H), 5.33 (s, 2H), 5.09 (s, 2H), 4.16 (q, 2H), 2.33 (s, 3H), 1.21 (t, 3H).

3-[(4-chlorophenyl)thio]-4-(ethylamino)-2-methyl-1H-indole-1-acetic acid, ethyl ester was also isolated as a by product from the reaction (0.33g).

¹H NMR (DMSO-d6) δ 7.32 (dd, 2H), 7.01 (dd, 2H), 6.95 (t, 1H), 6.73 (d, 1H), 6.16 (d, 1H), 5.70 (t, 1H), 5.11 (s, 2H), 4.16 (q, 2H), 3.05 (dt, 2H), 2.34 (s, 3H), 1.21 (t, 3H), 1.02 (t, 3H).

iv) 4-(acetylamino)-3-[(4-chlorophenyl)thiol-2-methyl-1H-indole-acetic acid, ethyl ester

To a solution of the product from part (iii) (0.5 g) in dichloromethane (10 ml) was added triethylamine (0.18 ml) and acetyl chloride (0.1 ml), the reaction was stirred at room temperature for 30 minutes. The mixture was then adsorbed onto silica gel and purified by column chromatography (33% EtOAc/hexane as eluent) to give the sub-title compound (0.52 g). ¹H NMR (DMSO-d6) δ 9.51 (s, 1H), 7.46 (d, 1H), 7.34 - 7.27 (m, 3H), 7.11(t, 1H), 6.97 (d, 2H), 5.24 (s, 2H), 4.18 (q, 2H), 2.39 (s, 3H), 1.86 (s, 3H), 1.21 (t, 3H).

v) 4-(acetylamino)-3-[(4-chlorophenyl)thio]-2-methyl-1H-indole-acetic acid

To a solution of the product from part (iv) (0.31 g) in THF (10 ml) was added a 1M solution of NaOH (aq) (0.75 ml). The reaction was stirred overnight at room temperature. The reaction mixture was concentrated in vacuo and the residue dissolved/suspended in water. The pH was adjusted to 2 using dilute HCl (aq) and the solid which precipitated isolated by filtration. Recrystallisation from acetonitrile gave the title compound (0.16 g). ¹H NMR (DMSO-d6) δ 13.21 (s, 1H), 9.51 (s, 1H), 7.46 (d, 1H), 7.33 - 7.27 (m, 3H), 7.11 (t, 1H), 6.98 (d, 2H), 5.12 (s, 2H), 2.39 (s, 3H), 1.85 (s, 3H).

APCI+ [M+H] 389

M.p. dec > 266°C

Reference Examples: Reference Example 5

3-[(2-Chlorophenyl)thio]-2-methyl-5-[(methylsulfonyl)amino]-1H-indole-1-acetic acid i) 2-methyl-5-nitro-1H-indole-1-acetic acid, ethyl ester

2-Methyl-5-nitro-1H-indole (5.3 g) was dissolved in dimethyl formamide (20 ml) and to it added sodium hydride (1.2 g) for the mixture to be stirred for 1 hour. Ethyl bromoacetate (6.8 g) was added all at once and a precipitate started to form. The mixture was quenched with 1 % aqueous acetic acid and the precipitate collected by filtration and washed thoroughly with water, triturated with diethyl ether and dried under vacuum to give pure sub-title product (6.2 g). ¹H NMR (DMSO-d6) δ 8.45 (d, 1H), 7.96 (dd,1H), 7.59 (d, 1H), 6.56 (s, 1H), 5.21 (s, 2H), 4.16 (q, 2H), 2.37 (s, 3H), 1.19 (t, 3H). APCI- [M-H] 263

ii) 5-amino-2-methyl-1H-indole-1-acetic acid, ethyl ester

A suspension of 2-methyl-5-nitro-1H- indole-1-acetic acid, ethyl ester (6.2 g) in ethanol (600 ml) in the presence of 10% palladium on charcoal (0.6 g) was stirred under a hydrogen atmosphere at 3 bar for 4 hours. The mixture was filtered through celite and the filtrate evaporated to give the sub-title compound as a pink viscous oil (5.3 g). APCI- [M-H] 233

iii) 2-methyl-5-[(methylsulfonyl)amino]-1H-indole-1-acetic acid, ethyl ester

Methanesulfonyl chloride (1.15 g) was added to a solution of 5-amino-2-methyl-1H-indole-1-acetic acid, ethyl ester (2.3 g) in triethylamine (1.7 ml) and dichloromethane (20 ml) at 0 °C a pink viscous oil for a pink viscous oil for and stirred at 20 °C for 1 hour. Water was added and the mixture extracted with dichloromethane, dried (Na₂SO₄) and evaporated to give the crude solid. This was purified by chromatography using silica (40:1 dichloromethane/ethyl acetate as eluent) to give the sub-title compound as a pink solid (1.4 g). ¹H NMR (DMSO-d6) δ 9.23 (s, 1H), 7.30 (m, 2H), 6.94 (dd, 1H), 6.23(s, 1H), 5.03 (s, 2H), 4.14 (q, 2H), 2.85 (s, 3H), 2.31 (s, 3H), 1.19 (t, 3H). APCI- [M-H] 311

iv) 3-[(2-chlorophenyl)thio]-2-methyl-5-[(methylsulfonyl)amino]-1H-indole-1-acetic acid, ethyl ester

2-methyl-5-[(methylsulfonyl)amino]-1H-indole-1-acetic acid, ethyl ester (0.31 g) and 2-chlorobenzenethiol (0.27 g) were dissolved in dimethyl formamide (3 ml) followed by addition of iodine 0.30 g) for the whole to be stirred at room temperature overnight. The mixture was poured into aqueous sodium thiosulphate (50 ml) and the resultant white precipitate collected by filtration and rinsed with water, dried under vacuum to be recrystallised from ethanol. The crystals were harvested and rinsed with isohexane and dried under vacuum to give the sub-title compound (0.20 g) ¹H NMR (DMSO-d6) δ 9.34 (s, 1H), 7.55 (d, 1H), 7.45 (m, H), 7.21 (d, 1H), 7.23-7.06 (m, 3H), 6.44 (m,1H), 5.26 (s, 2H), 4.18 (q, 2H), 2.83 (s, 3H), 2.38 (s, 3H), 1.22 (t,3H). APCI- [M-H] 453/455

v) 3-[(2-chlorophenyl)thio]-2-methyl-4-[(methylsulfonyl)amino]-1H-indole-1-acetic acid

The title compound was prepared by the method of Example 1 part (v) except that recrystallisation was not required. (0.10 g) ¹H NMR (DMSO-d6) δ 13.25 (s, 1H), 9.33 (s, 1H), 7.54 (d, 1H), 7.45 (dd, 1H), 7.21 (d, 1H), 7.08 (m, 3H), 6.45 (d, 1H), 5.13 (s, 2H), 2.83 (s, 3H), 2.38 (s, 3H). APCI- [M-H] 425/427 M.p. 212 °C

Reference Example 17

4-(Acetylamino)-3-[(3-chlorophenyl)thiol-2-methyl-1H-indole-1-acetic acid i) 4-(acetylamino)-2-methyl-1H-indole-1-acetic acid, ethyl ester

Thiosalicylic acid was added to a solution of the product from Example 1 part (iv) (474 mg) in trifluoroacetic acid (10 ml) was added thiosalicylic acid (351 mg) and the resulting suspension was heated to 60°C for 4 hours. The mixture was concentrated in vacuo and the residue dissolved in EtOAc and washed with NaHCO₃ (aq), brine, dried (MgSO₄) and evaporated to give crude material. Purification by column chromatography (50% EtOAc/hexane as eluent) gave the sub-title compound (0.13 g). ¹H NMR (DMSO-d6) δ 9.51 (s, 1H), 7.54 (d, 1H), 7.07 (d, 1H), 6.96 (t, 1H), 6.50 (s, 1H), 5.02 (s, 2H), 4.14 (q, 2H), 2.33 (d, 3H), 2.12 (s, 3H), 1.20 (t, 3H).

ii) 4-(acetylamino)-3-[(3-chlorophenyl)thio]-2-methyl-1H-indole-1-acetic acid

The sub-title compound was prepared by the method of Reference Example 5 part (iv) using the product from part (i) (0.11 g) and 3-chlorobenzenethiol (0.048 g), then purified by preparative hplc (eluent MeCN/NH₃ (aq)) to give the title compound (70 mg). ¹H NMR (DMSO-d6) δ 9.49 (s, 1H), 7.43 (d, 1H), 7.29 (d, 1H), 7.24 (t, 1H), 7.14 (dd, 1H), 7.08 (t, 1H), 6.97 - 6.95 (m, 2H), 4.96 (s, 2H), 2.38 (s, 3H), 1.86 (s, 3H). APCI- [M-H] 387

Reference Example 18

3-[(4-Chlorophenyl)thio]-4-[[(dimethylamino)sulfonyl]amino]-2-methyl-1H-indole-1-acetic acid i) 3-[(4-chlorophenyl)thio]-4-[[(dimethylamino)sulfonyl]amino]-2-methyl-1H-indole-1-acetic acid, ethyl ester

Triethylamine (55 µl) and dimethylsulfamoyl chloride (43 µl) were added to a solution of the product from Example 1 part (iv) (150 mg) in acetonitrile (5 ml). The mixture was heated at reflux for 24 hours, adsorbed onto silica and purified using column chromatography (33% EtOAc/hexane as eluent) to give the sub-title compound (95 mg). ¹H NMR (DMSO-d6) δ 8.80 (s, 1H), 7.35 - 7.29 (m, 3H), 7.13 (t, 1H), 7.07 (dd, 1H), 6.99 (dt, 2H), 5.25 (s, 2H), 4.18 (q, 2H), 2.56 (s, 6H), 2.37 (s, 3H), 1.21 (t, 3H).

ii) 3-[(4-chlorophenyl)thio]-4-[[(dimethylamino)sulfonyl]amino]-2-methyl-1H-indole-1-acetic acid

The title compound was prepared using the method of Example 1 part (v) and the product from part (i). ¹H NMR (DMSO-d6) δ 8.79 (s, 1H), 7.31 (m, 2H), 7.14 (dd, 1H), 7.04 - 6.99 (m, 4H), 4.51 (s, 2H), 2.54 (s, 6H), 2.34 (s, 3H). APCI- [M-H] 452

Reference Example 21

4-(Acetylamino)-2-methyl-3-[[4-(methylsulfonyl)phenyl]thiol-1H-indole-1-acetic acid i) 4-(methylsulfonyl)benzenethiol

1-fluoro-4-(methylsulfonyl)benzene and sodium bisulphide (10 g) were heated in NMP (10 ml) at 80°C for 2h. The mixture was poured into water, washed with EtOAc, acidified with concentrated hydrochloric acid and extracted with EtOAc. The organics were washed with water, dried (MgSO₄) and evaporated to give the sub-title compound, which was used in the next step without characterisation.

ii) 4-(acetylamino)-2-methyl-3-[[4-(methylsulfonyl)phenyl]thio]-1H-indole-1-acetic acid, ethyl ester.

The sub-title compound was prepared by the method of Reference Example 5 part (iv) using the product from part (i) and the product from Reference Example 17 part (i), and purified by chromatography (50% EtOAc/hexane increasing to 66% EtOAc/hexane as eluent) to give the sub-title compound. ¹H NMR (DMSO-d6) δ 9.45 (s, 1H), 7.72 (dt, 2H), 7.38 (d, 1H), 7.32 (d, 1H), 7.16 - 7.11 (m, 3H), 5.27 (s, 2H), 4.19 (q, 2H), 3.14 (s, 3H), 2.38 (s, 3H), 1.82 (s, 3H), 1.22 (t, 3H).

iv) 4-(acetylamino)-2-methyl-3-[[4-(methylsulfonyl)phenyl]thio]-1H-indole-1-acetic acid

The title compound was prepared using the method of Example 1 part (v) and the product from part (ii). ¹H NMR (DMSO-d6) δ 9.44 (s, 1H), 7.72 (dd, 2H), 7.38 (d, 1H), 7.31 (d, 1H), 7.17 - 7.10 (m, 3H), 5.14 (s, 2H), 3.14 (s, H), 2.38 (s, 3H), 1.82 (s, 3H). APCI- [M-H] 431

Reference Example 22

4-(Acetylamino)-3-[(2-chlorophenyl)thio]-2-methyl-1H-indole-1-acetic acid 4-(acetylamino)-3-[(2-chlorophenyl)thio]-2-methyl-1H-indole-1-acetic acid

The title compound was prepared by the method of Reference Example 5 parts (iv) and using the product from Reference Example 17 part (i) and 2-chlorothiophenol, and purified by column chromatography (33% EtOAc/hexane as eluent). The resulting product was treated as outlined in example 1 part (v) to give the title compound. ¹H NMR (DMSO-d6) δ 9.43 (s, 1H), 7.46 (dd, 1H), 7.37 (dd, 2H), 7.14 - 7.05 (m, 3H), 6.42 (dd, 1H), 5.14 (s, 2H), 2.37 (s, 3H), 1.81 (s, 3H) APCI+ [M+H] 389

Reference Example 23

4-(Acetylamino)-2-methyl-3-[[4-(ethylsulfonyl)phenyl]thio]-1H-indole-1-acetic acid i) 4-(acetylamino)-2-methyl-3-[[4-(ethylsulfonyl)phenyl]thio]-1H-indole-1-acetic acid

The title compound was prepared by the method of Reference Example 5 part (iv) using the product from Reference Example 17 part (i) and 4-(ethylsulfonyl)benzenethiol. The product was purified by preparative hplc (eluent MeCN/NH₃ (aq)). ¹H NMR (DMSO-d6) δ 9.41 (s, 1H), 7.66 (d, 2H), 7.30 (d, 2H), 7.17 (d, 2H), 7.08 (t, 1H), 4.85 (s, 2H), 3.20 (q, 2H), 2.37 (s, 3H), 1.78 (s, 3H), 1.05 (t, 3H). APCI- [M-H] 445

Claims (1)

1. The compound 4-(acetylamino)-3-[(4-chlorophenyl)thio]-2-methyl-1H-indoleacetic acid, ethyl ester.