WO2000012461A1

WO2000012461A1 - Process for making 2-amino-5-cyanophenol

Info

Publication number: WO2000012461A1
Application number: PCT/US1999/019494
Authority: WO
Inventors: Clifford S. Labaw; Susan C. Shilcrat
Original assignee: Smithkline Beecham Corporation
Priority date: 1998-08-28
Filing date: 1999-08-26
Publication date: 2000-03-09
Also published as: JP2003525856A; EP1107943A1; EP1107943A4; CA2341711A1

Abstract

This invention relates to a process for preparing 2-amino-5-cyanophenol.

Description

PROCESS FOR MAKING 2-AMINO-5-CYANOPHENOL Scope of the Invention This invention relates to a process for making intermediates useful for making certain phenyl urea compounds. The end-product phenyl urea compounds are useful in treating IL-8, GROα, GROβ, GROγ and NAP-2 mediated diseases. They are disclosed in PCT application serial number PCT/US96/13632, published 21 August 1997 as WIPO No. WO97/29743 and co-pending U.S. application 08/894291.

Area of the Invention Interleukin-8 is a chemoattractant for neutrophils, basophils, and a subset of

T-cells. It is produced by a majority of nucleated cells including macrophages, fibroblasts, endothelial and epithelial cells exposed to TNF, IL-la, IL-lb or LPS, and by neutrophils themselves when exposed to LPS or chemotactic factors such as FMLP. M. Baggiolini et al, J. Clin. Invest. 84, 1045 (1989); J. Schroder et al, J. Immunol. 139, 3474 (1987) and J. Immunol. 144, 2223 (1990) ; Strieter, et al,

Science 243, 1467 (1989) and /. Biol Chem. 264, 10621 (1989); Cassatella et al, J. Immunol. 148, 3216 (1992).

There is a need for treatment in this field, for compounds, which are capable of binding to the IL-8 α or β receptor. Therefore, conditions associated with an increase in IL-8 production (which is responsible for chemotaxis of neutrophil and T-cells subsets into the inflammatory site) would benefit by compounds, which are inhibitors of IL-8 receptor binding. Such compounds have been disclosed in published patent applications exemplified by the likes of PCT/US96/13632, published 21 August 1997 as WIPO No. WO97/29743. This invention provides a method for making 2-amino-5-cyano-phenol which is a useful intermediate for synthesising N-[2-hydroxy-4-cyanophenyl]-N'-[2-bromophenyl]urea, a compound disclosed in the aforementioned PCT application.

SUMMARY OF THE INVENTION This invention relates to a process for making 2-amino-5-cyanophenol. In particular, this process comprises preparing the phenol of Formula (I)

by demythelating a compound of Formula (II).

In addition, this invention comprises a process for preparing a compound of Formula (I) from o-anisidine, which process comprises treating o-anisidine with a halogenating agent to obtain Formula (III)

and displacing the bromide by a cyanide anion to obtain a compound of Formula (II) then demethylating Formula (II) to obtain the compound of Formula

(I).

Description of the Invention

Scheme 1 outlines the chemistry for preparing to 2-amino-5-cyanophenol, a third stage intermediate in a synthesis of N-[2-hydroxy-4-cyanophenyl]-N'-[2- bromophenyljurea. Scheme I

OMe stage a stage c_

(HI) (ID (I)

The pαrα bromination of o-anisidine (stage A) has been described in the literature, using several different reagents (Choudary, B. M.; Sudha, Y., and Reddy, P. N. Synlett., 1994, 450; Reeves, W. P.; and King, R. M. Synth. Comm. 1993, 23, 855; Fox, G. J.; Hallas, G.; Hepworth, J. D.; and Paskins, K. N. Org. Synth., Coll. Vol. 6, 181). The crude reaction product is typically a mixture of the starting material, Formula (III), the ortho isomer 2-bromo-6-methoxy-aniline (1) and the product of over bromination, 2,4-dibromo-6-methoxy-aniline (2) below.

1 2

The following reagents gave Formula (III) as the principle product in the reaction mixture: 2,4,4,6-tetrabromo-2,5-cyclohexadien-l-one, hexamethylenetetramine hydrobromide perbromide, benzyltrimethylammonium tribromide, tetrabutylammonium tribomide, pyridinium bromide perbromide, ammonium molybdate-potassium bromide-hydrogen peroxide-acetic acid, sodium tungstate-potassium bromide-hydrogen peroxide-acetic acid, and 48% hydrobromic acid in warm (60-80 °C) dimethyl sulfoxide. The preferred results were achieved with 2,4,4,6-tetrabromo-2,5-cyclohexadien-l-one and 48% hydrobromic acid in dimethyl sulfoxide. While 2,4,4,6-tetrabromo-2,5-cyclohexadien-l-one gave somewhat better isomer ratios, hydrobromic acid in dimethyl sulfoxide had the advantage of requiring no unusual reagent, only ordinary bulk chemicals. A typical crude GC product ratio for 2,4,4,6-tetrabromo-2,5-cyclohexadien-l-one was 15% o- anisidine/6% formula 1/61% o-anisidine/17% formula 2; for HBr-DMSO it was 13% o-anisidine/13% formula 1/53% Formula (II)/22% formula 2.

It was possible to isolate and purify Formula (III) through its sulfate salt. An ethyl acetate solution of the crude reaction mixture was treated with an ethyl acetate solution of concentrated sulfuric acid. The sulfate salt of Formula (II) crystallized from solution in enhanced purity. Recrystallization of Formula (II) from an alcohol solvent gave material of high chemical and isomeric purity. The free base was regenerated by standard aqueous extractive methodology.

Using HBr-DMSO as the brominating agent, and purifying via the sulfate salt, 100 g o-anisidine was transformed to 46 g or Formula (III).

Cyanation, (stage b) was effected by treating Formula (III) with copper (I) cyanide in either refluxing NN-dimethylformamide or l-methyl-2-pyrrolidinone for 3-5 hours. While the reaction proceeded faster in l-methyl-2-pyrrolidinone, workup was difficult and it was easiest to carry the crude reaction mixture through stage c, then purify by crystallization Stage c provided a crude recovery of 75%.

Demethylation of crude Formula (II) (stage c) was effected by several reagents: boron tribromide, sodium ethyl thiolate, and sodium cyanide in refluxing dimethyl sulfoxide. Where boron tribromide is used, the reaction is carried out in an aprotic solvent such as methylene chloride. Preferably the reaction is carried out under an inert gas such as nitrogen. This reaction goes to completion at a reduced temperature, i.e., about -10 to +10 °C in about 1-3 hours. The sodium cyanide reaction proceeds best in dimethyl sulfoxide. The reaction is run under an inert gas such as nitrogen. Refluxing for 3-7 hours is needed to effect the reaction. If sodium ethyl thiolate is used, dimethyl formamide is the solvent of choice. Again the reaction is carried out under an inert gas, nitrogen for example. Mildy elevated temperatures are needed to run the reaction; 75 to 125 °C for 30 minutes to 2 hours or so should cause the reaction to go to completion. An experimental procedure for each stage of the reaction set out in Scheme I is detailed below.

Examples Example 1 2-Methoxy-4-Bromo-Aniline

A stirred solution of o-anisidine; (104.6 g; 0.85 mol; Aldrich) in dry DMSO (1000 mL) under nitrogen, was treated with 48% HBr (185 mL; 1.64 mol; 1.9 eq; Aldrich) over 10-12 min. The reaction mixture spontaneously exothermed to -50 °C. After addition was complete, the reaction was heated to 80 °C and maintained at that temperature for 20 min. The reaction mixture was cooled to 5 °C, then partitioned between EtOAc (2L) and 1.5 N NaOH (2.4 L). After separating the phases, the aqueous layer was washed with additional EtOAc (1 L). The combined EtOAc layers were washed with H₂O (2 x 2 L) and saturated brine (1 L), dried over magnesium sulfate (100 g), filtered, and concentrated in vacuo to a dark oil (163.9 g).

The crude product mixture was redissolved in EtOAc (1 L) and transfered to a stirred 2 L vessel. A solution of 18 N sulfuric acid (100 mL; 1.8 mol) in EtOAc (400 mL) was added in one portion. The EtOAc solution spontaneously exothermed to -50 °C. (If necessary to dissolve all solids, the reaction mixture was heated to reflux.) The mixture was allowed to cool slowly to ambient temperature. The resultant white crystals were collected by filtration, washed with EtOAc (100 mL) and dried to give 120.8 g Formula(III)-sulfate salt. This was recrystallized from 2- propanol (900 mL). The resultant crystals were filtered, washed with cold 2- propanol (100 mL), and force-air dried (58.7 g). To liberate the free base, the crystalline sulfate salt was partitioned between 1

N NaOH (1 L) and EtOAc (1 L). The mixture was stirred until all solids disappeared, then the phases were separated. The aqueous phase was washed with additional EtOAc (500 mL). The combined EtOAc phases were washed with H₂O (1 L) and saturated brine (500 mL), then dried over magnesium sulfate (50 g). The solution was filtered, and concentrated in vacuo to produce Forumla (III) as a white solid (46.25 g; 27% yield), mp 56-58 °C. ^lU NMR (DMSO-d₆) δ 3.75 (s, 3H), 4.86 (b, 2H), 6.55 (d, J = 8.3 Hz, IH), 6.80 (dd, J = 8.3, 2.2 Hz, IH), 6.89 (d, J = 2.2 Hz, IH). ¹³C NMR (DMSO-d₆) δ 147.1, 137.2, 123.2, 114.7, 113.4, 106.2, 55.6.

Example 2 2-Methoxy-4-Cyano- Aniline A solution of 2-methoxy-4-bromoaniline (8.66 g; 42.9 mmol) in N,N- dimethylformamide (100 mL) under nitrogen was treated with copper (I) cyanide (5.75 g; 64.3 mmol; 1.5 eq). The reaction mixture was refluxed 5-6 h. After cooling, 10% aq FeCl₃ (100 mL) and EtOAc (100 mL) were added. Stirring was continued 10 min, followed by filtration through Celite. The aqueous phase was washed with additional EtOAc (50 mL). The combined organic phases were washed with H₂O (100 mL) and saturated brine (50 mL), and dried over magnesium sulfate (2.5 g). Upon concentration in vacuo, the captioned compound was isolated as a crude oil and used without further purification. ^lU NMR (CDC1₃) δ 3.76 (s, 3H), 4.75 (b), 6.57 (d, J = 8.1 Hz, IH), 6.86 (d, 7 = 1.7 Hz, IH), 7.04 (dd, 7 = 8.1, 1.7 Hz, 1H);¹³C NMR (CDC1₃) δ 146.1, 141.1, 126.6, 120.3, 113.5, 112.8, 99.2, 55.6.

Example 3 2-Amino-5-Cyano-PhenoI2-Methoxy-4-cyanoaniline was demethylated to form 2-amino-5-cyano-phenol by several reagents (a-c).

3a - Boron Tribromide: A solution of crude 2-methoxy-4-cyanoaniline (1.78 g; 12 mmol) in methylene chloride (25 mL) under nitrogen was cooled to 0 °C. A 1 M solution of boron tribromide in methylene chloride (24 mL; 24 mmol; 2 eq; Aldrich) was added dropwise over 20 min; the temperature was maintained below 5 °C. Stirring continued 2 hours at 0 °C. 5% aq NaHCO₃ (100 mL)was added, followed by extraction with EtOAc (2 x 50 mL). The organic phases were washed with H₂O (50 mL) and sat brine (50 mL) and dried over magnesium sulfate (4 g). The solution was filtered and concentrated in vacuo. The residue was stirred with methylene chloride (10 mL) to give the captioned compound as a solid (0.57 g; 35% yield) emerged from solution, mp 128-130 °C (d); ^lH NMR (DMSO-d₆) δ 5.74 (s, IH), 6.62 6.63 (d, J = 8.1 Hz, IH), 6.85 (d, I = 1.8 Hz, IH), 6.98 (dd, J = 8.1, 1.8 Hz, IH), 9.78 (b, 2H); ¹³C NMR (DMSO-d₆) δ 143.4, 142.5, 125.3, 120.7, 116.2, 113.3, 95.8.

3b - Sodium Cyanide in DMSO: Under nitrogen, a solution of crude 2- methoxy-4-cyanoaniline (0.41 g; 2.77 mmol) in dry DMSO (4 mL) was treated with solid sodium cyanide (0.68 g; 13.85 mmol; 5 eq) and heated to reflux for 5 hours. The cooled mixture was partitioned between H₂O (20 mL) and EtOAc (20 mL). The pH of the aqueous phase was adjusted to 7 with 1 N HC1, and the phases were separated. The organic phase was washed with H₂O (10 mL) and sat. brine (10 mL), and dried over magnesium sulfate (2 g). Concentration in vacuo gave the title compound as a tan solid (240 mg; 65% yield).

3c - Sodium Ethyl Thiolate in DMF: Under nitrogen, a solution of crude 2- methoxy-4-cyanoaniline (0.33 g; 2.23 mmol) in DMF (4 mL) was treated with a solution of sodium ethyl thiolate (0.29 g; 3.45 mmol; 1.55 eq; Aldrich) in DMF (1 mL). The reaction mixture was heated to 100 °C for 1 hour. The mixture was cooled and partitioned between saturated NH₄C1 soln(10 mL) and EtOAc (10 mL). The pH of the aqueous phase was adjusted to 5 with 1 N HC1, and the phases were separated. The organic phase was washed with H₂O (10 mL), saturated brine (10 mL), and dried over magnesium sulfate (1 g). Concentration in vacuo gave the title compound as a tan solid (230 mg; 77% yield).

Claims

What is claimed is:

1. A process for preparing a compound of Formula (I),

which process comprises demythelating a compound of Formula (II).

2. The process of claim 1 wherein the demethylation is carried out using boron tribromide in an aprotic solvent, sodium cyanide in dimethyl sulfoxide, or sodium ethyl thiolate in dimethyl formamide.

3. The process of claim 2 wherein the demethylation is carried out using boron tribromide in an aprotic solvent under an inert gas at temperatures between - 10 and +10 °C for about 1-3 hours.

4. The process of claim 2 wherein the demethylation is carried out using sodium cyanide in an aprotic solvent under an inert gas at reflux for about 3-7 hours.

5. The process of claim 2 wherein the demethylation is carried out using sodium ethyl thiolate in an aprotic solvent under an inert gas and heating the solution to about 75 to 125 °C for about 30 minutes to 2 hours.

6. A process for preparing a compound of Formula (I)