Indian Patents. 241114:CHEMICAL PROCESS

Title of Invention	CHEMICAL PROCESS
Abstract	Abstract: Process for preparing compounds of Formula (I); and (IV); are described.

Full Text	FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION (See section 10, rule 13) 'CHEMICAL PROCESS' ASTRAZENECA AB, S-SE-15185 Sodertalje. Sweden; The following specification particularly describes the invention and the manner in which it is to be performed. WO 2005/080403 PCT/GB2005/000567 CHEMICAL PROCES The present invention relates to an improved chemical process for preparing intermediates. Certain of these intermediates are useful in the manufacture of compounds 5 which are useful in the treatment of, for example, cancer, pain and cardiovascular diseases in a warm-blooded animal such as man, particularly compounds which possess endothelin receptor antagonist activity. In particular, the present invention relates to a chemical process for preparing [4-(l,3,4-oxadiazol-2-yl)phenyl]boronic acid which is used in the manufacture of 10 N-(3-methoxy-5-methylpyrazin-2-yl)-2-(4-[l,3,4-oxadiazol-2-y!]phenyl)pyridine-3- sulphonamide which compound is disclosed as Example 36 of International Patent Application WO96740681. This compound possesses endothelin receptor antagonist activity, and accordingly is useful whenever such antagonist activity is desired, such as for research tools within pharmacological, diagnostic, and related studies or in the treatment of diseases 15 and medical conditions including, but not limited to hypertension, pulmonary hypertension, cardiac or cerebral circulatory disease and renal disease. In addition this compound is also useful in the treatment of cancer and pain, in a warm-blooded animal such as man. A route for preparing N-(3-methoxy-5-methylpyrazin-2-yl)-2-(4-tl,3,4-oxadiazol-2-yl] phenyl)pyridine-3-sulphonamide is disclosed in International Patent Applications 20 WO 96/40681 and WO 98/40332. The route involves the use of the compound N-(isobutoxycarbonyl)-2-(4-methoxycarbonylphenyl)-N-(3-methoxy-5-methylpyrazin-2-yl)pyridine-3-sulphonamide as an intermediate with the formation of the 1,3,4-oxadiazole in the 4-position of the phenyl group occurring at the end of the synthesis. This existing route is satisfactory for the synthesis of relatively small amounts of N-(3-methoxy-5-methylpyrazin-2- 25 yl)-2-(4-[ 1,3,4-oxadiazol-2-yI]phenyl) pyridine-3-sulphonamide but is a linear rather than convergent synthesis, involving the isolation of a substantial number of intermediates. As such, the overall yield of this synthesis is not high. Furthermore, as the heteroaryl moiety at the 4-position of the phenyl group is formed as the last step, it is necessary to undergo a linear synthesis approach with the rest of the 30 molecule made first. This is clearly undesirable when substituents in distinct parts of the molecule need to be varied in order to investigate structure-activity relationships. It would be highly desirable if a convergent approach to the synthesis of this type of compound could be devised. This would also be of significant benefit in the efficiency of manufacturing large WO 2005/080403 PCT/GB2005/000567 scale amounts of N-(3-methoxy-5-methylpyrazin-2-yl)-2-(4-[ 1,3,4-oxadiazol-2-yl]phenyl) pyridine-3-sulphonamide. We have now devised a much improved process for the manufacture of heteroaryl-phenyl boronic acids, in particular, [4-(l,3,4-oxadiazol-2-yl)phenyl]boronic acid. 5 The process allows exploitation of a more convergent route to N-(3-methoxy-5- methylpyrazin-2-yl)-2-(4-[l ,3,4-oxadiazol-2-yl]phenyl)pyridine-3-suIphonamide than the previously described route and allows a reduction in the number of intermediates that must be isolated. This provides significant advantages of time and cost of manufacture. In a further aspect of the present invention one of the heteroaryl-phenyl boronic acids, 10 [4-(l ,3,4-oxadiazol-2-yl)phenyl]boronic acid, produced according to the present invention, is used to prepare N-protected N-(3-methoxy-5-methylpyrazin-2-yl)-2-(4-[1,3,4-oxadiazol-2-yl)phenyl)pyridine-3-sulphonamides, in particular N-(isobutoxycarbonyi) N-(3-methoxy-5-methylpyrazin-2-yl)-2-(4-[l,3,4-oxadiazol-2-yl]phenyl) pyridine-3-sulphonamide. These intermediates may then be deprotected to form N-(3-methoxy-5-methyhpyrazin-2-yl)-2-(4- 15 [1,3,4-oxadiazol-2-yI]phenyl)pyridine-3-sulphonamide. The process for the manufacture of heteroaryl-phenyl boronic acids of the present invention utilises the increased acidity of the heteroaryl ring proton, and involves the sequential use of two bases. Initial attempts at adding one equivalent of a base to a heteroaryl-phenyl bromo compound in order to induce halogen-metal exchange led to 20 competing deprotonation of the beteroaryl ring. On quenching with a borate ester, a negligible yield of the desired product was achieved, together with starting material and by-products. The present inventors found, surprisingly, that the sequential use of two bases leads to good yields of the desired heteroaryl-phenyl boronic acids. In the process of the present invention the heteroaryl ring is initially deprotonated with a (typically) "weaker" base, before inducing 25 halogen-metal exchange with a (typically) "stronger" base. According to a first aspect of the present invention, there is provided a process for the preparation of a compound of the Formula I B(OH)2 (I) wherein, 30 X\| is selected from O, NR\| or S; and WO2005/0K0403 PCT/GB20O5/0OO567 X: is selected from CH or N; wherein R1is a nitrogen-protecting group, which comprises :- the sequential reaction of a compound of the Formula II N-X2 5 (ID with, (i) methyl- or an optionally substituted aryl- lithium; and then (ii) n-butyl-, s-butyl-, t-butyl- or n-hexyl- lithium; and then (iii) a borate ester. 10 For process steps (i), (ii) and (iii), the reactions may conveniently be carried out in an inert solvent or diluent or an ethereal solvent such as diethyl ether, tetrahydrofuran, diethoxymethane, 1,2-dimethoxyethane or 1,4-dioxan. Thus, for example, the reaction may be carried out by sequentially treating 2-(4-bromophenyl)-l,3,4-oxadiazole with 4-memylphenyllithium, followed by n-hexyllithium, and finally triisopropylborate in a 15 suitable solvent or diluent, for example, an ethereal solvent such as tetrahydrofuran, at a temperature in the range, for example, -90 to -50°C, more particularly -70 to -55°C, conveniently at or near -70°C. Optionally the heteroaryt-phenyl bromo compound of Formula II can be charged to a solution of the first base to enable deprotonation, followed by the addition of the second base 20 to induce transmetallation. This method although slightly less efficient in yield and quality does have advantages in cases where the first base must be generated in situ due to lack of stability at ambient temperatures. In this case only one cryogenic vessel is required to complete the processing. The molar ratios of the reagents used in process steps (i), (ii), and (iii), are preferably 25 in the range from 1.0-1.5: 1.0-1.5: 2.1 -3 respectively, but more preferably in the range 1.06-1.3: 1.07-1.1: 2.2-2.3 respectively. Conveniently, the lithiated intermediates formed during the conversion of compounds of the Formula II to compounds of Formula I are not isolated as such but are each prepared and used as a solution in an organic solvent. Thereby, compounds of Formula I may be manufactured from compounds of Formula II in a one-pot 30 procedure. WO 2005/080403 PCT/GB2005/000567 5 An aryl lithium is, for example, phenyl or naphthyl- lithium. An optional substituent for an aryl lithium is, for example, methyl. Particularly preferred optionally substituted aryl lithiums are, for example, phenyl-, 2-methyrpbenyl-, 4-methylphenyl-, mesityl- or naphthyl- lithium. 5 A borate ester is an alky], alkenyl or aryl boronic ester, for example, trimethyl-, triethyl- or triisopropyl- borate. When R) is a nitrogen-protecting group, then, for example, suitable methods for protection are those known to those skilled in the art Conventional protecting groups may be used in accordance with standard practice (for illustration see T.W. Green, Protective Groups 10 in Organic Synthesis, John Wiley and Sons, 1991). A suitable nitrogen- protecting group, R1, is, for example, an (l-6C)alkyl, phenyl, allyl, methoxymethyl, benzyl, triphenylmethyl or dipbenylphosphinyl protecting group. This first aspect of the present invention provides compounds of Formula I in commercially acceptable yields and of high quality. 15 Further values of X\| and X2 are as follows. Such values may be used where appropriate with any definitions, claims or embodiments defined hereinbefore or hereinafter. X1 is O. X1 is NR1 X1 is S. 20 X2 is CH. X2 is N. X1is O, and X2 is CH. X1 is O, and X2 is N. X1 and X2 are N. 25 X1 is NR1, and X2 is CH. X1 is NR1, and X2 is N. X1, is S and X2 is CH. X1 is S and X2 is N. R1 is allyl or benzyl. 30 R1, is benzyl. Therefore in an additional aspect of the invention there is provided a process for the preparation of compounds of the Formula I WO 2005/080403 PCT/GB2005/000567 wherein, X1 is selected from O, NR1 or S; and X2 is selected from CH or N; 5 wherein R1 is a nitrogen-protecting group; which comprises :-the sequential reaction of compounds of the Formula II (i) (II) with, 10 (i) 4-metbylphenyllithium; and then (ii) n-hexyllithium; and then (iii) triisopropylborate. In a further aspect of the invention there is provided a process for the preparation of compounds of the Formula I X, 15 ^ (I) wherein, X1 is selected from O, NR1 or S; and X2 is selected from CH or N; wherein R1 is a nitrogen-protecting group; which comprises :- 20 the sequential reaction of compounds of the Formula II (II) with, (i) methyllithium; and then WO 2005/080403 PCT/GB2005/000567 (ii) n-hexyllithium; and then (iii) triisopropyiborate. In a further aspect of the invention there is provided a process for the preparation of compounds of the Formula I B(OH)2 5 wherein, X1 is O; and X2 is N; which comprises :- 10 the sequential reaction of compounds of the Formula II N-X2 o X, with, (I) methyllithium;and (ii) n-butyllithium; and then (iii) triisopropylborate. 15 In a further aspect of the invention there is provided a process for the preparation of compounds of the Formula I, Wherein, 20 X1 is O; and X2 is N; Which comprises:- The sequential reaction of compounds of the Formula II (i) methyllithium; and then methyHithium; and then n-butyllithium; and then triisopropyiborate. In a further aspect of the invention there is provided a process for the preparation of compounds of the Formula I, B(OH)2 wherein, 20 Xi is O; and X2isN; which comprises > the sequential reaction of compounds of the Formula II 0) WO 2005/080403 PCT7GB2005/1MM)567 (ii) with, (i) 4-methyphenyllitbium; and then (ii) n-butyllithium; and then 5 (iii) triisopropylborate. Compounds of the formula (II) may be prepared according to the experimental methods and procedures disclosed in Bioorganic & Medicinal Chemistry Letters, 2002, 72(20), 2879-2882; Eur. J. Med Chem., 2000,35,157-162; Helvetica Chimica Acta, 1950, 33,1271-1276; Eur. J. Med. Chem., 1985,20(3), 257-66 and J. Het. Chem., 1989,26,1341. 10 A further aspect of the present invention provides the use of [4-(l ,3,4-oxadiazol-2- yl)phenyl] boronic acid, prepared according to the present invention, in the preparation of compounds of Formula IV which are intermediates useful in the preparation of N-(3-memoxy-5-memylpyrazin-2-yI)-2-(4-[13,4-oxadiazol-2-yl]phenyl)pyridine-3-sulphonamide. N-(3-Methoxy-5-methylpyrazin-2-yl)-2-(4-[l,3,4-oxadiazol-2-yI]phenyl)pyridine-3-l 15 sulphonamide is prepared by deprotecting compounds of Formula IV. In this aspect of the invention [4-(l,3,4-oxadiazol-2-yi)phenyl]boronic acid is coupled with compounds of Formula III to form compounds of Formula IV. N' /^^B(OH)2 + ^- (IV) Particularly this reaction takes place in an aqueous solvent, for example methanol, 20 ethanol, isopropanol, industrial methylated spirit (IMS), isobutanol, NMP (N-methylpyrrolidinone), DMF; with or without an organic phase, for example toluene or xylenes at a temperature in the range, for example 60 to 100°C more particularly 75 to 85°C, in the presence of: (i) the boronic acid WO 2005/080403 PCT/GB2005/000567 (ii) a suitable source of palladium (0), for example PdCl2, Pd(Ph3P)4 or Pd(Oac)2; (iii) a suitable ligand, for example triphenylphosphine or 33'3"-phosphinidyne tris(benzenesulphonic acid) trisodium salt; (iv) a base, for example triethylamine, benzyldimethylamine, N-methylmorpholme, 5 N-methylpiperidine, triethanolamine, ethyldiethanolamine, diisopropylethylarmne, potassium acetate, cesium fluoride or potassium fluoride. Particularly the source of palladium is palladium acetate. Particularly the base is N-methyhnorpholine. In another aspect, particularly the base is 10 triethylamine. Particularly this reaction takes place in an aqueous solvent without an organic phase. In another aspect, particularly this reaction takes place in an aqueous solvent with an organic phase. Where this reaction takes place in an aqueous solvent with an organic phase, particularly the organic phase comprises toluene. In another aspect of the present invention, 15 where this reaction takes place in an aqueous solvent with an organic phase, particularly the organic phase comprises xylene. In another aspect, this reaction more specifically takes place in the presence of palladium acetate, 3,3'3"-phosphinidyne tris(benzenesulphonic acid) trisodium salt, N- methylmorpholine in water and isopropanol. 20 In another aspect, this reaction more specifically takes place in the presence of palladium acetate, 3>3,,3M-phosphinidyne tris(benzenesulphonic acid) trisodium salt, triethylamine, xylene, water and IMS. The molar ratios of the reagents used in process steps (i), (ii), (iii) and (iv), are preferably in the range from 1.0-2.0:0.02-0.3:0.06-0.9: 1.5-5.0 respectively, but more 25 preferably in the range 1.4-1.6:0.03-0.1:0.09-0.3: 2.0-3.0 respectively. In compounds of Formula IH or Formula IV, P is a nitrogen-protecting group. Suitable methods for protection are those known to those skilled in the art. Conventional protecting groups may be used in accordance with standard practice (for illustration see T.W. Green, Protective Groups in Organic Synthesis, John Wiley and Sons, 1991). 30 A suitable value for P is, for example, an acyl group, for example a C1-6 alkanoyl group such as acetyl; an aroyl group, for example benzoyl; a C1-6 alkoxycarbonyl group, for example a methoxycarbonyl, ethoxycarbonyl, isobutoxycarbonyl or tert-butoxycarbonyl group; an WO 2005/080403 PCT/GB2005/000567 arylmethoxycarbonyl group, for example benzyloxycarbonyl; a phosphinyl group, for example diphenylphosphinyl; a benzyl group or a C2^alkenyl group such as allyl. A suitable value for P is a Ci-ealkoxycarbonyl group. More suitable values for P are a methoxycarbonyl, ethoxycarbonyl or isobutoxycarbonyl group. More specifically a value for 5 P is isobutoxycarbonyl. The deprotection conditions for the nitrogen protecting groups described herein necessarily vary with the choice of protecting group. Thus, for example, an acyl group such as a C1-6alkanoyl or a C1-6alkoxycarbonyl group or an aroyl group may be removed for example, by hydrolysis with a suitable base such as an alkali metal hydroxide, for example lithium or 10 sodium hydroxide or an amine, for example ammonia. Alternatively an alkoxycarbonyl group such as a f-butoxycarbonyl group may be removed, for example, by treatment with a suitable acid as hydrochloric, sulphuric or phosphoric acid or trifluoroacetic acid and an arylmethoxycarbonyl group such as a benzyloxycarbonyl group may be removed, for example, by hydrogenation over a catalyst such as palladium-on-carbon, or by treatment with 15 a Lewis acid for example boron tris(trifluoroacetate). A phosphinyl group may be removed by base hydrolysis such as an alkali metal hydroxide, for example lithium or sodium hydroxide or an amine, for example ammonia. A benzyl group may be removed by hydrogenation over a catalyst such as palladium-on-carbon. A C2-6alkenyl group such as allyl may be removed palladium assisted hydrolysis. 20 In a further aspect of the invention there is provided a process for preparing a compound of Formula IV which comprises reacting [4-(l,3,4-oxadiazol-2-yi)phenyl]boronic acid with a compound of Formula III. In a further aspect of the invention there is provided a process for preparing a compound of Formula IV which comprises reacting [4-(l,3,4-oxadiazol-2-yl)phenyl]boronic 25 acid, prepared according to the present invention, with a compound of Formula III. In this aspect of the invention, more specifically the invention provides the use of [4-0,3,4-oxadiazol-2-yl)phenyl] boronic acid, prepared according to the present invention, in the preparation of N-(isobutoxycarbonyl) N-(3-methoxy-5-methylpyrazin-2-yl)-2-(4-[ 1,3,4-oxadiazol-2-yl]phenyl) pyridine-3-sulphonamide a compound of Formula IV and an 30 intermediate useful in the preparation of N-(3-methoxy-5-methyIpyrazin-2-yl)-2-(4-[ l,3,4-oxadiazol-2-yl] phenyl)pyridine-3-sulphonamide. In this aspect of the invention [4-(l,3,4-oxadiazol-2-yl)phenyl]boronic acid is coupled with N-(isobutoxycarbonyl)-2-chloro-N-(3-methoxy-5-methylpyrazin-2-yl)pyridine-3- WO 2005/080403 PCT/GB2005/000567 11 sulphonamide to form N-(isobutoxycarbonyl) N-(3-methoxy-5-methylpyrazin-2-yI)-2-(4-[1,3,4-oxadiazol-2-yl]phenyl) pyridine-3-sulphonamide. The preparation of N-(isobutoxycarbonyl)-2-chIoro-N-(3-methoxy-5-methylpyra2in-2- yl) pyridine-3-sulphonamide is described in Example 1 of WO96/40681. 5 Thus according to this aspect of the invention there is provided a process for preparing N-(isobutoxycarbonyl)N-(3-methoxy-5-rnethylpyrazin-2-yl)-2-(4-[l,3,4-oxadiazol-2-yl]phenyl) pyridine-3-sulphonamide which comprises coupling (4-(l,3,4~oxadiazoI-2-yI)phenyl]boronic add with N-(isobutoxycarbonyI)-2-chloro-N-(3- methoxy-5-methylpyrazin-2-yl)pyridine-3-sulphonamide. 10 Therefore in a further aspect of the invention there is provided the use of [4-(13»4-oxadia2ol-2-yl)phenyl]boronic acid in the preparation of N-(isobutoxycarbonyl) N-(3-raethoxy-5-methylpyrazin-2-yl)-2-(4-[l ,3,4-oxadiazol-2-yl]phenyl) pyridine-3-sulphonamide. In a further aspect of the invention there is provided the use of 15 [4-(l ,3,4-oxadiazol-2-yl)phenyl]boronic acid, prepared according to die process of the present invention, in the preparation of N-(isobutoxycarbonyl) N-(3-methoxy-5-methylpyrazin-2-yl)-2-{4-[ 1,3,4-oxadiazol-2-yl]phenyl) pyridine-3-sulphonamide. In a further aspect of the invention there is provided a compound of Formula IV. In a further aspect of the invention there is provided £J-(isobutoxycarbonyI) N-(3- 20 methoxy-5-methylpyrazin-2-yl)-2-(4-[l3,4-oxadiazol-2-yllphenyl) pyridine-3-suIphonamide. In a further aspect of the invention there is provided the use of N-(isobutoxycarbonyl) N-(3-methoxy-5-niethylpyra23n-2-yl)-2-(4-[l,3,4-oxadiazo-2-yl]phenyl)pyridine-3- sulphonamide in the preparation of N-(3-methoxy-5-methylpyrazin-2-yl)-2-{4-[ 1,3,4- oxadiazol-2-yl] phenyl)pyridine-3-sulphonamide. 25 The invention will now be illustrated by the following non-limiting Examples in which, unless otherwise stated:- (i) yields are intended for the assistance of the reader only and are not necessarily the maximum attainable by diligent process development; (ii) 1H NMR spectra were determined at either 270MHz or 400MHz in DMSOd6 using 30 tetramethylsilane (TMS) as an internal standard, and are expressed as chemical shifts (delta values) in parts per million relative to TMS using conventional abbreviations for designation of major peaks: s, singlet; m, multiplet; t, triplet; br, broad; d, doublet. WO 2005/080403 PCT/GB2005/000567 - 12- Example 1 [4-ll3.4-oxadiazol-2-vOphenynboronicacid A solution of methyllithium (8% w/w in diethoxymethane) (65 ml) was added to a suspension of 2-(4-bromopherryl)-l,3,4-oxadiazole (40 g) in tetrahydrofuran (THF) (415 ml) at -65°C. 5 After an hour a solution of n-butyllithium (2.5M in hexanes) (78 ml) was then added at -65°C. After an hour, triisopropylborate (90 ml)) was then added maintaining the reaction mixture at -65°C. The reaction mixture was held at -65°C for an hour and then warmed to -20°C and drowned out into a mixture of acetic acid (28 ml) in water (222 ml). The resultant solid was isolated, washed with THF and water, and dried to yield the title compound (28.96 g @ 10 95.1% w/w, 82%); 400MHz NMR Spectrum: (DMSOd6) 8.00 (s, 4H), 8.31 (s, 2H), 9.35 (s, 1H); Mass Spectrum MH* 191.0628 (calc. using 11-B) Found 191.0633. The 2-(4-bromophenyl)-l,3,4-oxadiazoIe used as a starting material was prepared as follows: To a suspension of 4-bromobenzoic hydrazide (200 g) in industrial methylated spirit I5 (700 ml) was added triemylorthoformate (309 ml), industrial methylated spirit (100 ml) and sulphuric acid (0.8 ml). The reaction mixture was heated to reflux for 1 hour. The reaction mixture was cooled to 0-5°C and product crystallised. Product was isolated, washed and dried to yield 2-(4-bromophenyl)-l,3,4-oxadiazole (186.1 g, 89.9%). 400MHz NMR Spectrum: (DMSO6) 9.35 (s, 1H), 7.98 (d, 1H), 7.95 (d, 1H), 7.84 (d, 1H), 7.81 (d, 1H); Mass Spectrum 20 MH+ 224.9663 (calc. using 79-Br) Found 224.9701. Example 2 [4-(1.3.4-oxadiazol-2-vDphenvHboromcarid Lithium granules (8.2 g) and tetrahydrofuran (670 g) were charged to a reactor under an argon 25 atmosphere and the mixture cooled to -35°C. 4-Chlorotoluene (74.3 g) was added at -35°C and the mixture was held at this temperature for 6 hours. The resultant solution was added to a suspension of 2-(4-bromophenyl)-l,3,4-oxadiazole (124.4 g) in tetrahydrofuran (800 g) at -65°C. After 30 mins a solution of n-hexyllithium (33%w/w in hexanes) (240ml) was then added at -65°C. After a futher 30 min triisopropylborate (230.8 g) was then added 30 maintaining the reaction mixture at -65°C. The reaction mixture was allowed to warm to -35°C and drowned out into a solution of acetic acid (91.5 g) in water (688 g). The resultant WO 2005/080403 PCTVGB2005/000567 solid was isolated, washed with THF and water, and dried to yield the title compound (92.2 g, 88%). Example 3 5 [4-(1,3,4-oxadiazol-2-yl)phenyl]boronic acid Example 2 was repeated but the charge of 4-chlorotoluene increased from 1.06 moles to 1.30 moles. The yield of the title compound increased to 89.3%. Example 4 10 [4-(l,3,4-oxadiazol-2-yl)phenyl]boronic acid Tetrahydrofuran (250 g) was charged to a mixture of lithium granules (3.02 g) and biphenyl (0.01 g) under an argon atmosphere and the mixture cooled to -30°C. 2-Chlorotoluene (27.55 g) was slowly added at -30°C. The reaction was held at -30°C for 6 hours and then cooled to -65°C. A mixture of 2-(4-bromophenyl) 1,3,4-oxadiazole (50.0 g) in THF (300 g) 15 was slowly added at -65°C. The reaction was held at -65°C for 30 minutes then a solution of n-hexyllithium (33%w/w in hcxanes, 86 ml) was added at -65°C. The reaction was held at -65°C for 30 minutes and then trimethylborate (48.7 g) was added at -65°C. The reaction was held at -65°C for 10 minutes then methanol (55.3 g) was added followed by 4-methyl-2-pentanone (240 g). The reaction mixture was warmed and the low boiling solvents 20 distilled off under vacuum to a maximum temperature of 55°C. The residual mixture was cooled to 0°C and 10%w/w sulphuric acid (92 g) was added followed by water (92 g) whilst maintaining the temperature below 7°C. Product precipitated. The pH was adjusted to 6.5 by the addition of more I0%w/w sulphuric acid (85.3 g). The mixture was heated to 40°C then cooled back to 5-10°C. Product was isolated and washed with THF (56g) and water (60g), 25 yielding wet title compound (25.2 g, 60%). Example 5 [4-(1.3.4-oxadiazol-2-yl)phenyl]boronic acid Tetrahydrofuran was charged to lithium granules (7.6 g) under an argon atmosphere and the 30 mixture cooled to -30°C. 2-Chlorotoluene (69.4 g) was slowly added at -30°C. The reaction was held at -30°C for 6 hours then added to a suspension of 2-(4-bromophenyl)-l,3,4-oxadiazole (124.4 g) in tetrahydrofuran (800 g) at -65°C. The WO 2005/080403 PCT/GB20O5/000567 reaction was held at -65°C for 30 minutes then a solution of n-hexyllithium (33%w/w in hexanes, 245 ml) was added at -65°C. The reaction was held at -65°C for 30 minutes and then trimethylborate (230.8 g) was added at -65°C. The reaction was held at -65°C for 30 minutes then methanol (175 ml) was added followed by 4-methyl-2-pentanone (600 g). The reaction 5 mixture was warmed and the low boiling solvents distilled off under vacuum to a maximum temperature of 50°C. The reaction mixture was cooled to 5-10°C and the pH adjusted to 6.5 by the addition of 5%w/w sulphuric acid (990.5 g). Product precipitated. The mixture was heated to 40°C then cooled back to 10°C. Product was isolated, washed with THF and water, and dried yielding the title compound (79.3 g, 75.5%). 10 Example 6 14-(1,3,4-oxadiazol-2-yl)phenyl]boronic acid Example 4 was repeated but chlorobenzene (61.6 g) was used instead of 2-chlorotoluene. The isolated yield of the title compound was 87.8 g, (83.8%). 15 Example 7 N-(Isobutoxycarbonyl) N-(3-methoxy-5-methylpyrazin-2-yl)-2-{4-[1,3,4-oxadiazol-2- Yl]phenyl) pvridine-3-sulphonamide Palladium acetate (0.4l44g) and 3,3\3"-phosphinidyne tris(benzenesulphonic acid) 20 trisodium salt 30% w/w aq sol (3.26g) were dissolved in water (35ml) over 6 minutes in an ultrasonic barn. The yellow solution was added to a stirred slurry of [4-(l,3,4-oxadiazol-2-yl)phenyl] boronic acid (10g) and isobutyl [(2-chloropyridin-3-yl)sulfonyI](3-methoxy-5-methylpyra2in-2-yl)carbamate (16.86g) in xylene (100ml), industrial methylated spirit (50ml) and triethylamine (17ml). The catalyst dissolution flask 25 was then washed in with water (5ml) and the reaction mixture heated to reflux (80°C) on an oil bath (105°C) and stirred at reflux for 24.5 hours. The reaction mixture was cooled to 30°C and filtered through a Whatman GF/B glass filter paper and the lower aqueous phase separated off. The reaction flask and filter cake was washed with xylene (20ml). The xylene wash was used to re-extract the aqueous phase. The combined organic phases were stirred and 30 heated to reflux (85°C) in a clean 500ml 4-necked flask equipped with overhead stirrer, water condenser, and nitrogen atmosphere. Essochem solvent 30 (hydrocarbons Bp 100-130°C) (100ml) was added dropwise over 6 min and the mixture was allowed to self cool to ambient temperature and then further cooled to -5°C and held for 1 hour. The product was filtered off WO 2005/080403 PCT/GB2005/000567 and washed with Essochem solvent 30 (50ml). The cake was dried on the filter for 3 hours to give 15.20g @100% strength, yield 76.8%. 270 MHz 1H-NMR Spectrum: 0.70 (d, 6H), 1.72 (m, 1H), 2.51 (s, 3H), 3.84 (d, 2H), 4.00 (s, 3H), 7.59 (m, 1H); 7.80 (d, 2H), 7.90 (s, 1H), 8.17 (d, 2H), 8.50 (s, 1H), 8.90 (m, 1H) and 9.00 (d, 1H). Mass Spectrum MH* = 525.2 5 (C24H25N606S = 525.16). Example 8 N-(lsobutoxycarbonyl) N-(3-methoxv-5-methylpyrazin-2-yl)-2-(4-1,3.4-oxadiazol-2- Yl]phenyl) pyridine-3-sulphonamide 10 To a nitrogen purged 500mL multi necked flask equipped with an overhead stirrer was charged isobutyl [(2-chloropyridin-3-yl]sulfonyl](3-methoxy-5-methylpyrazin-2-yl)carbamate (22.15g), [4-(l,3,4-oxadiazol-2-yl)phenyl)boronic acid (12.26g), isopropanol (60ml), water (140ml) and 3,3',3"-phosphinidyne tris(benzenesulphonic acid) trisodium salt 30% w/w aq sol (13.7g). Agitation was started and palladium acetate (0.54lg) was added after 10 minutes. 15 N-Methylmorpholine (13.25ml) was added and the temperature was adjusted to 80°C. After 4h 20min toluene (140ml) was added and the temperature adjusted to 60°C. After a further 45 min the mixture was filtered through a 1 um glass fibre filter paper and the aqueous phase separated off. The reaction flask and filter cake was washed with toluene (22ml). The toluene wash was used to re-extract the aqueous phase and the organic layers were combined. These 20 contained the title compound (22.8g, 90%) which was not isolated. Example 9 N-(lsobutoxycarbonyl)N-(3-methoxy-5-methylpyrazin-2-yl)-2-(4-[1,3,4-oxadiazol-2-yl]phenyl) pyridine-3-sulphonamide 25 To a nitrogen purged 150ml multi necked flask equipped with an overhead stirrer was charged isobutyl [(2-chloropyridin-3-yl)sulfonyl](3-methoxy-5-methylpyrazin-2-yl)carbamate(7.75g), [4-(l,3,4-oxadiazol-2-yl)phenyl] boronic acid (4.29g), isopropanol (21ml), water (49ml) and 3,3'3"-phosphinidyne tris(benzenesulphonic acid) trisodium salt 30% w/w aq sol (2.88g). Agitation was started and palladium acetate (0.114g) was added after 10 minutes. Potassium 30 fluoride (2.48g) was added and the temperature was adjusted to 80°C. After 5h toluene (49ml) was added and the temperature adjusted to 60°C. After a further 10min the mixture was filtered through a 1 p.m glass fibre filter paper and the aqueous phase separated off. The organic phase contained the title compound (7.36g, 83%) which was not isolated. WO 2005/080403 PCT/GB2005/000567 16 CLAIMS 1. A process for the preparation of a compound of the Formula I (I) 5 wherein, X1 is selected from O, NR1 or S; and X2 is selected from CH or N; wherein R1 is a nitrogen-protecting group, which comprises :- 10 the sequential reaction of a compound of the Formula II N-X2 (II) with, (i) methyl- or an optionally substituted aryl- lithium; and then (ii) n-butyl-, s-butyl-, t-butyl- or n-hexyl- lithium; and then 15 (iii) a borate ester. 2 The process according to claim 1 wherein X1 is O. 2. The process according to claim 1 or 2 wherein X2 is N. 20 4. The process according to any one of claims 1-3 wherein said methyl- or an optionally substituted aryl- lithium is 4-methylphenyllithium or methyllithium. 5. The process according to any one of claims 1-4 wherein said n-butyl-, s-butyl-, 25 t-butyl- or n-hexyl- lithium is n-hexyllithium or n-butyllithium. 6. The process according to any one of claims 1-5 wherein said borate ester is triisopropylborate. WO 2005/080403 PCT/GB2005/000567 7. [4-( 1,3,4-Oxadiazol-2-yl)phenyl]boronic acid prepared by the process as claimed in any one of claims 1-6. 8. A process for preparing compounds of Formula IV: 5 (IV) which comprises coupling [4-(l,3,4-oxadiazol-2-yl)phenyl]boronic acid with a compound of Formula III: o=s. ,p 6 5 CH3 (III) wherein P is a nitrogen-protecting group. 10 9. The process according to claim 8 which takes place in the presence of (i) a source of palladium (0) selected from PdCl2, Pd(Ph3P)4 or Pd(OAc)2; ( (ii) a suitable ligand selected from triphenylphosphine or 3,3',3"-phosphinidyne tris(benzenesulphonic acid) trisodium salt; 15 (iii) a base selected from triethylamine, benzyldimethylamine, N-methylmorpholine, N-methylpiperidine, triethanolamine, ethyldiethanolamine, diisopropylethylamine, potassium acetate, cesium fluoride or potassium fluoride. WO 2005/080403 PCr/GB2tft5/mM567 18 10. The process according to claim 8 or claim 9wherein said [4-(l ,3,4-oxadiazol-2-yl) phenyl]boronic acid is prepared according to the process as claimed in any one of claims 1-7. 11. The process according to any one of claims 8-10 wherein P is isobutoxycarbonyl. 5 12. A compound of Formula IV: wherein P is a nitrogen-protecting group. 10 13. A compound of Formula IV as claimed 11 claim 11 which is N-(isobutoxycarbonyl)N-(3-methoxy-5-methylpyrazin-2-yl)-2-(4-[1,3,4-oxadaizol-2-yl)phenyl)pyridine-3-. sulphonamide 14. Compounds of Formula I and IV and process for preparing the same, substantially as herein described with reference to for going description and examples. G Dated this 05th day of August, 2006 VIBHA SHUKLA OF K&S PARTNERS AGENT FOR THE APPLICANT(S) Abstract: Process for preparing compounds of Formula (I); and (IV); are described. * BCOH), (I) (IV)

Full Text

FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION (See section 10, rule 13)
'CHEMICAL PROCESS'
ASTRAZENECA AB, S-SE-15185 Sodertalje. Sweden;
The following specification particularly describes the invention and the manner in which it is to be performed.

WO 2005/080403 PCT/GB2005/000567
CHEMICAL PROCES
The present invention relates to an improved chemical process for preparing intermediates. Certain of these intermediates are useful in the manufacture of compounds
5 which are useful in the treatment of, for example, cancer, pain and cardiovascular diseases in a warm-blooded animal such as man, particularly compounds which possess endothelin receptor antagonist activity.
In particular, the present invention relates to a chemical process for preparing [4-(l,3,4-oxadiazol-2-yl)phenyl]boronic acid which is used in the manufacture of
10 N-(3-methoxy-5-methylpyrazin-2-yl)-2-(4-[l,3,4-oxadiazol-2-y!]phenyl)pyridine-3- sulphonamide which compound is disclosed as Example 36 of International Patent Application WO96740681. This compound possesses endothelin receptor antagonist activity, and accordingly is useful whenever such antagonist activity is desired, such as for research tools within pharmacological, diagnostic, and related studies or in the treatment of diseases
15 and medical conditions including, but not limited to hypertension, pulmonary hypertension, cardiac or cerebral circulatory disease and renal disease. In addition this compound is also useful in the treatment of cancer and pain, in a warm-blooded animal such as man.
A route for preparing N-(3-methoxy-5-methylpyrazin-2-yl)-2-(4-tl,3,4-oxadiazol-2-yl] phenyl)pyridine-3-sulphonamide is disclosed in International Patent Applications
20 WO 96/40681 and WO 98/40332. The route involves the use of the compound N-(isobutoxycarbonyl)-2-(4-methoxycarbonylphenyl)-N-(3-methoxy-5-methylpyrazin-2-yl)pyridine-3-sulphonamide as an intermediate with the formation of the 1,3,4-oxadiazole in the 4-position of the phenyl group occurring at the end of the synthesis. This existing route is satisfactory for the synthesis of relatively small amounts of N-(3-methoxy-5-methylpyrazin-2-
25 yl)-2-(4-[ 1,3,4-oxadiazol-2-yI]phenyl) pyridine-3-sulphonamide but is a linear rather than convergent synthesis, involving the isolation of a substantial number of intermediates. As such, the overall yield of this synthesis is not high.
Furthermore, as the heteroaryl moiety at the 4-position of the phenyl group is formed as the last step, it is necessary to undergo a linear synthesis approach with the rest of the
30 molecule made first. This is clearly undesirable when substituents in distinct parts of the molecule need to be varied in order to investigate structure-activity relationships. It would be highly desirable if a convergent approach to the synthesis of this type of compound could be devised. This would also be of significant benefit in the efficiency of manufacturing large

WO 2005/080403 PCT/GB2005/000567
scale amounts of N-(3-methoxy-5-methylpyrazin-2-yl)-2-(4-[ 1,3,4-oxadiazol-2-yl]phenyl) pyridine-3-sulphonamide.
We have now devised a much improved process for the manufacture of heteroaryl-phenyl boronic acids, in particular, [4-(l,3,4-oxadiazol-2-yl)phenyl]boronic acid.
5 The process allows exploitation of a more convergent route to N-(3-methoxy-5-
methylpyrazin-2-yl)-2-(4-[l ,3,4-oxadiazol-2-yl]phenyl)pyridine-3-suIphonamide than the previously described route and allows a reduction in the number of intermediates that must be isolated. This provides significant advantages of time and cost of manufacture.
In a further aspect of the present invention one of the heteroaryl-phenyl boronic acids,
10 [4-(l ,3,4-oxadiazol-2-yl)phenyl]boronic acid, produced according to the present invention, is used to prepare N-protected N-(3-methoxy-5-methylpyrazin-2-yl)-2-(4-[1,3,4-oxadiazol-2-yl)phenyl)pyridine-3-sulphonamides, in particular N-(isobutoxycarbonyi) N-(3-methoxy-5-methylpyrazin-2-yl)-2-(4-[l,3,4-oxadiazol-2-yl]phenyl) pyridine-3-sulphonamide. These intermediates may then be deprotected to form N-(3-methoxy-5-methyhpyrazin-2-yl)-2-(4-
15 [1,3,4-oxadiazol-2-yI]phenyl)pyridine-3-sulphonamide.
The process for the manufacture of heteroaryl-phenyl boronic acids of the present invention utilises the increased acidity of the heteroaryl ring proton, and involves the sequential use of two bases. Initial attempts at adding one equivalent of a base to a heteroaryl-phenyl bromo compound in order to induce halogen-metal exchange led to
20 competing deprotonation of the beteroaryl ring. On quenching with a borate ester, a negligible yield of the desired product was achieved, together with starting material and by-products. The present inventors found, surprisingly, that the sequential use of two bases leads to good yields of the desired heteroaryl-phenyl boronic acids. In the process of the present invention the heteroaryl ring is initially deprotonated with a (typically) "weaker" base, before inducing
25 halogen-metal exchange with a (typically) "stronger" base.
According to a first aspect of the present invention, there is provided a process for the preparation of a compound of the Formula I

B(OH)2
(I) wherein, 30 X| is selected from O, NR| or S; and

WO2005/0K0403 PCT/GB20O5/0OO567
X: is selected from CH or N; wherein R1is a nitrogen-protecting group,
which comprises :-
the sequential reaction of a compound of the Formula II
N-X2
5 (ID
with,
(i) methyl- or an optionally substituted aryl- lithium; and then (ii) n-butyl-, s-butyl-, t-butyl- or n-hexyl- lithium; and then (iii) a borate ester.
10 For process steps (i), (ii) and (iii), the reactions may conveniently be carried out in an
inert solvent or diluent or an ethereal solvent such as diethyl ether, tetrahydrofuran, diethoxymethane, 1,2-dimethoxyethane or 1,4-dioxan. Thus, for example, the reaction may be carried out by sequentially treating 2-(4-bromophenyl)-l,3,4-oxadiazole with 4-memylphenyllithium, followed by n-hexyllithium, and finally triisopropylborate in a
15 suitable solvent or diluent, for example, an ethereal solvent such as tetrahydrofuran, at a temperature in the range, for example, -90 to -50°C, more particularly -70 to -55°C, conveniently at or near -70°C.
Optionally the heteroaryt-phenyl bromo compound of Formula II can be charged to a solution of the first base to enable deprotonation, followed by the addition of the second base
20 to induce transmetallation. This method although slightly less efficient in yield and quality does have advantages in cases where the first base must be generated in situ due to lack of stability at ambient temperatures. In this case only one cryogenic vessel is required to complete the processing.
The molar ratios of the reagents used in process steps (i), (ii), and (iii), are preferably
25 in the range from 1.0-1.5: 1.0-1.5: 2.1 -3 respectively, but more preferably in the range 1.06-1.3: 1.07-1.1: 2.2-2.3 respectively. Conveniently, the lithiated intermediates formed during the conversion of compounds of the Formula II to compounds of Formula I are not isolated as such but are each prepared and used as a solution in an organic solvent. Thereby, compounds of Formula I may be manufactured from compounds of Formula II in a one-pot
30 procedure.

WO 2005/080403 PCT/GB2005/000567
5
An aryl lithium is, for example, phenyl or naphthyl- lithium.
An optional substituent for an aryl lithium is, for example, methyl.
Particularly preferred optionally substituted aryl lithiums are, for example, phenyl-,
2-methyrpbenyl-, 4-methylphenyl-, mesityl- or naphthyl- lithium.

5 A borate ester is an alky], alkenyl or aryl boronic ester, for example, trimethyl-,
triethyl- or triisopropyl- borate.
When R) is a nitrogen-protecting group, then, for example, suitable methods for protection are those known to those skilled in the art Conventional protecting groups may be used in accordance with standard practice (for illustration see T.W. Green, Protective Groups
10 in Organic Synthesis, John Wiley and Sons, 1991).
A suitable nitrogen- protecting group, R1, is, for example, an (l-6C)alkyl, phenyl, allyl, methoxymethyl, benzyl, triphenylmethyl or dipbenylphosphinyl protecting group.
This first aspect of the present invention provides compounds of Formula I in
commercially acceptable yields and of high quality.
15 Further values of X| and X2 are as follows. Such values may be used where
appropriate with any definitions, claims or embodiments defined hereinbefore or hereinafter.
X1 is O.
X1 is NR1
X1 is S.
20 X2 is CH.
X2 is N.
X1is O, and X2 is CH.
X1 is O, and X2 is N.
X1 and X2 are N.
25 X1 is NR1, and X2 is CH.
X1 is NR1, and X2 is N.
X1, is S and X2 is CH.
X1 is S and X2 is N.
R1 is allyl or benzyl.
30 R1, is benzyl.
Therefore in an additional aspect of the invention there is provided a process for the preparation of compounds of the Formula I

WO 2005/080403 PCT/GB2005/000567

wherein,
X1 is selected from O, NR1 or S; and
X2 is selected from CH or N;
5 wherein R1 is a nitrogen-protecting group;
which comprises :-the sequential reaction of compounds of the Formula II

(i)

(II)
with,

10 (i) 4-metbylphenyllithium; and then
(ii) n-hexyllithium; and then (iii) triisopropylborate.
In a further aspect of the invention there is provided a process for the preparation of compounds of the Formula I

X,
15 ^ (I)
wherein,
X1 is selected from O, NR1 or S; and
X2 is selected from CH or N;
wherein R1 is a nitrogen-protecting group; which comprises :-
20 the sequential reaction of compounds of the Formula II

(II)

with,
(i) methyllithium; and then

WO 2005/080403

PCT/GB2005/000567

(ii) n-hexyllithium; and then (iii) triisopropyiborate.
In a further aspect of the invention there is provided a process for the preparation of compounds of the Formula I

B(OH)2
5
wherein,
X1 is O; and
X2 is N;
which comprises :-
10 the sequential reaction of compounds of the Formula II
N-X2
o
X,

with,
(I) methyllithium;and
(ii) n-butyllithium; and then
(iii) triisopropylborate.
15 In a further aspect of the invention there is provided a process for the preparation of compounds of the Formula I,
Wherein,
20 X1 is O; and
X2 is N;
Which comprises:-
The sequential reaction of compounds of the Formula II
(i) methyllithium; and then

methyHithium; and then n-butyllithium; and then triisopropyiborate.
In a further aspect of the invention there is provided a process for the preparation of compounds of the Formula I,

B(OH)2
wherein,
20 Xi is O; and
X2isN;
which comprises > the sequential reaction of compounds of the Formula II

0)

WO 2005/080403 PCT7GB2005/1MM)567

(ii)

with,
(i) 4-methyphenyllitbium; and then
(ii) n-butyllithium; and then
5 (iii) triisopropylborate.
Compounds of the formula (II) may be prepared according to the experimental
methods and procedures disclosed in Bioorganic & Medicinal Chemistry Letters, 2002,
72(20), 2879-2882; Eur. J. Med Chem., 2000,35,157-162; Helvetica Chimica Acta, 1950,
33,1271-1276; Eur. J. Med. Chem., 1985,20(3), 257-66 and J. Het. Chem., 1989,26,1341.

10 A further aspect of the present invention provides the use of [4-(l ,3,4-oxadiazol-2-
yl)phenyl] boronic acid, prepared according to the present invention, in the preparation of compounds of Formula IV which are intermediates useful in the preparation of N-(3-memoxy-5-memylpyrazin-2-yI)-2-(4-[13,4-oxadiazol-2-yl]phenyl)pyridine-3-sulphonamide.
N-(3-Methoxy-5-methylpyrazin-2-yl)-2-(4-[l,3,4-oxadiazol-2-yI]phenyl)pyridine-3-l 15 sulphonamide is prepared by deprotecting compounds of Formula IV.
In this aspect of the invention [4-(l,3,4-oxadiazol-2-yi)phenyl]boronic acid is coupled with compounds of Formula III to form compounds of Formula IV.

N'
/^^B(OH)2
+
^-
(IV)

Particularly this reaction takes place in an aqueous solvent, for example methanol,
20 ethanol, isopropanol, industrial methylated spirit (IMS), isobutanol, NMP
(N-methylpyrrolidinone), DMF; with or without an organic phase, for example toluene or xylenes at a temperature in the range, for example 60 to 100°C more particularly 75 to 85°C, in the presence of:
(i) the boronic acid

WO 2005/080403 PCT/GB2005/000567
(ii) a suitable source of palladium (0), for example PdCl2, Pd(Ph3P)4 or Pd(Oac)2;
(iii) a suitable ligand, for example triphenylphosphine or 33'3"-phosphinidyne
tris(benzenesulphonic acid) trisodium salt;
(iv) a base, for example triethylamine, benzyldimethylamine, N-methylmorpholme,

5 N-methylpiperidine, triethanolamine, ethyldiethanolamine,
diisopropylethylarmne, potassium acetate, cesium fluoride or potassium fluoride. Particularly the source of palladium is palladium acetate.
Particularly the base is N-methyhnorpholine. In another aspect, particularly the base is
10 triethylamine.
Particularly this reaction takes place in an aqueous solvent without an organic phase. In another aspect, particularly this reaction takes place in an aqueous solvent with an organic phase. Where this reaction takes place in an aqueous solvent with an organic phase, particularly the organic phase comprises toluene. In another aspect of the present invention,
15 where this reaction takes place in an aqueous solvent with an organic phase, particularly the organic phase comprises xylene.
In another aspect, this reaction more specifically takes place in the presence of
palladium acetate, 3,3'3"-phosphinidyne tris(benzenesulphonic acid) trisodium salt, N-
methylmorpholine in water and isopropanol.
20 In another aspect, this reaction more specifically takes place in the presence of
palladium acetate, 3>3,,3M-phosphinidyne tris(benzenesulphonic acid) trisodium salt, triethylamine, xylene, water and IMS.
The molar ratios of the reagents used in process steps (i), (ii), (iii) and (iv), are preferably in the range from 1.0-2.0:0.02-0.3:0.06-0.9: 1.5-5.0 respectively, but more
25 preferably in the range 1.4-1.6:0.03-0.1:0.09-0.3: 2.0-3.0 respectively.
In compounds of Formula IH or Formula IV, P is a nitrogen-protecting group. Suitable
methods for protection are those known to those skilled in the art. Conventional protecting
groups may be used in accordance with standard practice (for illustration see T.W. Green,
Protective Groups in Organic Synthesis, John Wiley and Sons, 1991).
30 A suitable value for P is, for example, an acyl group, for example a C1-6 alkanoyl group
such as acetyl; an aroyl group, for example benzoyl; a C1-6 alkoxycarbonyl group, for example a methoxycarbonyl, ethoxycarbonyl, isobutoxycarbonyl or tert-butoxycarbonyl group; an

WO 2005/080403 PCT/GB2005/000567
arylmethoxycarbonyl group, for example benzyloxycarbonyl; a phosphinyl group, for example diphenylphosphinyl; a benzyl group or a C2^alkenyl group such as allyl.
A suitable value for P is a Ci-ealkoxycarbonyl group. More suitable values for P are a methoxycarbonyl, ethoxycarbonyl or isobutoxycarbonyl group. More specifically a value for
5 P is isobutoxycarbonyl.
The deprotection conditions for the nitrogen protecting groups described herein necessarily vary with the choice of protecting group. Thus, for example, an acyl group such as a C1-6alkanoyl or a C1-6alkoxycarbonyl group or an aroyl group may be removed for example, by hydrolysis with a suitable base such as an alkali metal hydroxide, for example lithium or
10 sodium hydroxide or an amine, for example ammonia. Alternatively an alkoxycarbonyl group such as a f-butoxycarbonyl group may be removed, for example, by treatment with a suitable acid as hydrochloric, sulphuric or phosphoric acid or trifluoroacetic acid and an arylmethoxycarbonyl group such as a benzyloxycarbonyl group may be removed, for example, by hydrogenation over a catalyst such as palladium-on-carbon, or by treatment with
15 a Lewis acid for example boron tris(trifluoroacetate). A phosphinyl group may be removed by base hydrolysis such as an alkali metal hydroxide, for example lithium or sodium hydroxide or an amine, for example ammonia. A benzyl group may be removed by hydrogenation over a catalyst such as palladium-on-carbon. A C2-6alkenyl group such as allyl may be removed palladium assisted hydrolysis.
20 In a further aspect of the invention there is provided a process for preparing a
compound of Formula IV which comprises reacting [4-(l,3,4-oxadiazol-2-yi)phenyl]boronic acid with a compound of Formula III.
In a further aspect of the invention there is provided a process for preparing a compound of Formula IV which comprises reacting [4-(l,3,4-oxadiazol-2-yl)phenyl]boronic
25 acid, prepared according to the present invention, with a compound of Formula III.
In this aspect of the invention, more specifically the invention provides the use of [4-0,3,4-oxadiazol-2-yl)phenyl] boronic acid, prepared according to the present invention, in the preparation of N-(isobutoxycarbonyl) N-(3-methoxy-5-methylpyrazin-2-yl)-2-(4-[ 1,3,4-oxadiazol-2-yl]phenyl) pyridine-3-sulphonamide a compound of Formula IV and an
30 intermediate useful in the preparation of N-(3-methoxy-5-methyIpyrazin-2-yl)-2-(4-[ l,3,4-oxadiazol-2-yl] phenyl)pyridine-3-sulphonamide.
In this aspect of the invention [4-(l,3,4-oxadiazol-2-yl)phenyl]boronic acid is coupled with N-(isobutoxycarbonyl)-2-chloro-N-(3-methoxy-5-methylpyrazin-2-yl)pyridine-3-

WO 2005/080403 PCT/GB2005/000567
11
sulphonamide to form N-(isobutoxycarbonyl) N-(3-methoxy-5-methylpyrazin-2-yI)-2-(4-[1,3,4-oxadiazol-2-yl]phenyl) pyridine-3-sulphonamide.
The preparation of N-(isobutoxycarbonyl)-2-chIoro-N-(3-methoxy-5-methylpyra2in-2-
yl) pyridine-3-sulphonamide is described in Example 1 of WO96/40681.
5 Thus according to this aspect of the invention there is provided a process for preparing
N-(isobutoxycarbonyl)N-(3-methoxy-5-rnethylpyrazin-2-yl)-2-(4-[l,3,4-oxadiazol-2-yl]phenyl) pyridine-3-sulphonamide which comprises coupling
(4-(l,3,4~oxadiazoI-2-yI)phenyl]boronic add with N-(isobutoxycarbonyI)-2-chloro-N-(3-
methoxy-5-methylpyrazin-2-yl)pyridine-3-sulphonamide.
10 Therefore in a further aspect of the invention there is provided the use of
[4-(13»4-oxadia2ol-2-yl)phenyl]boronic acid in the preparation of N-(isobutoxycarbonyl) N-(3-raethoxy-5-methylpyrazin-2-yl)-2-(4-[l ,3,4-oxadiazol-2-yl]phenyl) pyridine-3-sulphonamide.
In a further aspect of the invention there is provided the use of
15 [4-(l ,3,4-oxadiazol-2-yl)phenyl]boronic acid, prepared according to die process of the present invention, in the preparation of N-(isobutoxycarbonyl) N-(3-methoxy-5-methylpyrazin-2-yl)-2-{4-[ 1,3,4-oxadiazol-2-yl]phenyl) pyridine-3-sulphonamide.
In a further aspect of the invention there is provided a compound of Formula IV.
In a further aspect of the invention there is provided £J-(isobutoxycarbonyI) N-(3-
20 methoxy-5-methylpyrazin-2-yl)-2-(4-[l3,4-oxadiazol-2-yllphenyl) pyridine-3-suIphonamide.
In a further aspect of the invention there is provided the use of N-(isobutoxycarbonyl)
N-(3-methoxy-5-niethylpyra23n-2-yl)-2-(4-[l,3,4-oxadiazo-2-yl]phenyl)pyridine-3-
sulphonamide in the preparation of N-(3-methoxy-5-methylpyrazin-2-yl)-2-{4-[ 1,3,4-
oxadiazol-2-yl] phenyl)pyridine-3-sulphonamide.
25 The invention will now be illustrated by the following non-limiting Examples in
which, unless otherwise stated:-
(i) yields are intended for the assistance of the reader only and are not necessarily the maximum attainable by diligent process development;
(ii) 1H NMR spectra were determined at either 270MHz or 400MHz in DMSOd6 using
30 tetramethylsilane (TMS) as an internal standard, and are expressed as chemical shifts (delta values) in parts per million relative to TMS using conventional abbreviations for designation of major peaks: s, singlet; m, multiplet; t, triplet; br, broad; d, doublet.

WO 2005/080403 PCT/GB2005/000567
- 12-
Example 1
[4-ll3.4-oxadiazol-2-vOphenynboronicacid
A solution of methyllithium (8% w/w in diethoxymethane) (65 ml) was added to a suspension
of 2-(4-bromopherryl)-l,3,4-oxadiazole (40 g) in tetrahydrofuran (THF) (415 ml) at -65°C.
5 After an hour a solution of n-butyllithium (2.5M in hexanes) (78 ml) was then added at -65°C. After an hour, triisopropylborate (90 ml)) was then added maintaining the reaction mixture at -65°C. The reaction mixture was held at -65°C for an hour and then warmed to -20°C and drowned out into a mixture of acetic acid (28 ml) in water (222 ml). The resultant solid was isolated, washed with THF and water, and dried to yield the title compound (28.96 g @
10 95.1% w/w, 82%); 400MHz NMR Spectrum: (DMSOd6) 8.00 (s, 4H), 8.31 (s, 2H), 9.35 (s, 1H); Mass Spectrum MH* 191.0628 (calc. using 11-B) Found 191.0633.
The 2-(4-bromophenyl)-l,3,4-oxadiazoIe used as a starting material was prepared as follows:
To a suspension of 4-bromobenzoic hydrazide (200 g) in industrial methylated spirit
I5 (700 ml) was added triemylorthoformate (309 ml), industrial methylated spirit (100 ml) and sulphuric acid (0.8 ml). The reaction mixture was heated to reflux for 1 hour. The reaction mixture was cooled to 0-5°C and product crystallised. Product was isolated, washed and dried to yield 2-(4-bromophenyl)-l,3,4-oxadiazole (186.1 g, 89.9%). 400MHz NMR Spectrum: (DMSO6) 9.35 (s, 1H), 7.98 (d, 1H), 7.95 (d, 1H), 7.84 (d, 1H), 7.81 (d, 1H); Mass Spectrum
20 MH+ 224.9663 (calc. using 79-Br) Found 224.9701.
Example 2
[4-(1.3.4-oxadiazol-2-vDphenvHboromcarid
Lithium granules (8.2 g) and tetrahydrofuran (670 g) were charged to a reactor under an argon
25 atmosphere and the mixture cooled to -35°C. 4-Chlorotoluene (74.3 g) was added at -35°C and the mixture was held at this temperature for 6 hours. The resultant solution was added to a suspension of 2-(4-bromophenyl)-l,3,4-oxadiazole (124.4 g) in tetrahydrofuran (800 g) at -65°C. After 30 mins a solution of n-hexyllithium (33%w/w in hexanes) (240ml) was then added at -65°C. After a futher 30 min triisopropylborate (230.8 g) was then added
30 maintaining the reaction mixture at -65°C. The reaction mixture was allowed to warm to -35°C and drowned out into a solution of acetic acid (91.5 g) in water (688 g). The resultant

WO 2005/080403 PCTVGB2005/000567
solid was isolated, washed with THF and water, and dried to yield the title compound (92.2 g, 88%).
Example 3
5 [4-(1,3,4-oxadiazol-2-yl)phenyl]boronic acid
Example 2 was repeated but the charge of 4-chlorotoluene increased from 1.06 moles to 1.30 moles. The yield of the title compound increased to 89.3%.
Example 4
10 [4-(l,3,4-oxadiazol-2-yl)phenyl]boronic acid
Tetrahydrofuran (250 g) was charged to a mixture of lithium granules (3.02 g) and biphenyl (0.01 g) under an argon atmosphere and the mixture cooled to -30°C. 2-Chlorotoluene (27.55 g) was slowly added at -30°C. The reaction was held at -30°C for 6 hours and then cooled to -65°C. A mixture of 2-(4-bromophenyl) 1,3,4-oxadiazole (50.0 g) in THF (300 g)
15 was slowly added at -65°C. The reaction was held at -65°C for 30 minutes then a solution of n-hexyllithium (33%w/w in hcxanes, 86 ml) was added at -65°C. The reaction was held at -65°C for 30 minutes and then trimethylborate (48.7 g) was added at -65°C. The reaction was held at -65°C for 10 minutes then methanol (55.3 g) was added followed by 4-methyl-2-pentanone (240 g). The reaction mixture was warmed and the low boiling solvents
20 distilled off under vacuum to a maximum temperature of 55°C. The residual mixture was cooled to 0°C and 10%w/w sulphuric acid (92 g) was added followed by water (92 g) whilst maintaining the temperature below 7°C. Product precipitated. The pH was adjusted to 6.5 by the addition of more I0%w/w sulphuric acid (85.3 g). The mixture was heated to 40°C then cooled back to 5-10°C. Product was isolated and washed with THF (56g) and water (60g),
25 yielding wet title compound (25.2 g, 60%).
Example 5
[4-(1.3.4-oxadiazol-2-yl)phenyl]boronic acid
Tetrahydrofuran was charged to lithium granules (7.6 g) under an argon atmosphere and the
30 mixture cooled to -30°C. 2-Chlorotoluene (69.4 g) was slowly added at -30°C. The reaction was held at -30°C for 6 hours then added to a suspension of 2-(4-bromophenyl)-l,3,4-oxadiazole (124.4 g) in tetrahydrofuran (800 g) at -65°C. The

WO 2005/080403 PCT/GB20O5/000567
reaction was held at -65°C for 30 minutes then a solution of n-hexyllithium (33%w/w in hexanes, 245 ml) was added at -65°C. The reaction was held at -65°C for 30 minutes and then trimethylborate (230.8 g) was added at -65°C. The reaction was held at -65°C for 30 minutes then methanol (175 ml) was added followed by 4-methyl-2-pentanone (600 g). The reaction
5 mixture was warmed and the low boiling solvents distilled off under vacuum to a maximum temperature of 50°C. The reaction mixture was cooled to 5-10°C and the pH adjusted to 6.5 by the addition of 5%w/w sulphuric acid (990.5 g). Product precipitated. The mixture was heated to 40°C then cooled back to 10°C. Product was isolated, washed with THF and water, and dried yielding the title compound (79.3 g, 75.5%).
10
Example 6
14-(1,3,4-oxadiazol-2-yl)phenyl]boronic acid
Example 4 was repeated but chlorobenzene (61.6 g) was used instead of 2-chlorotoluene. The isolated yield of the title compound was 87.8 g, (83.8%).
15
Example 7
N-(Isobutoxycarbonyl) N-(3-methoxy-5-methylpyrazin-2-yl)-2-{4-[1,3,4-oxadiazol-2-
Yl]phenyl) pvridine-3-sulphonamide
Palladium acetate (0.4l44g) and 3,3\3"-phosphinidyne tris(benzenesulphonic acid)
20 trisodium salt 30% w/w aq sol (3.26g) were dissolved in water (35ml) over 6 minutes in an ultrasonic barn. The yellow solution was added to a stirred slurry of [4-(l,3,4-oxadiazol-2-yl)phenyl] boronic acid (10g) and isobutyl [(2-chloropyridin-3-yl)sulfonyI](3-methoxy-5-methylpyra2in-2-yl)carbamate (16.86g) in xylene (100ml), industrial methylated spirit (50ml) and triethylamine (17ml). The catalyst dissolution flask
25 was then washed in with water (5ml) and the reaction mixture heated to reflux (80°C) on an oil bath (105°C) and stirred at reflux for 24.5 hours. The reaction mixture was cooled to 30°C and filtered through a Whatman GF/B glass filter paper and the lower aqueous phase separated off. The reaction flask and filter cake was washed with xylene (20ml). The xylene wash was used to re-extract the aqueous phase. The combined organic phases were stirred and
30 heated to reflux (85°C) in a clean 500ml 4-necked flask equipped with overhead stirrer, water condenser, and nitrogen atmosphere. Essochem solvent 30 (hydrocarbons Bp 100-130°C) (100ml) was added dropwise over 6 min and the mixture was allowed to self cool to ambient temperature and then further cooled to -5°C and held for 1 hour. The product was filtered off

WO 2005/080403 PCT/GB2005/000567
and washed with Essochem solvent 30 (50ml). The cake was dried on the filter for 3 hours to give 15.20g @100% strength, yield 76.8%. 270 MHz 1H-NMR Spectrum: 0.70 (d, 6H), 1.72 (m, 1H), 2.51 (s, 3H), 3.84 (d, 2H), 4.00 (s, 3H), 7.59 (m, 1H); 7.80 (d, 2H), 7.90 (s, 1H), 8.17 (d, 2H), 8.50 (s, 1H), 8.90 (m, 1H) and 9.00 (d, 1H). Mass Spectrum MH* = 525.2
5 (C24H25N606S = 525.16).
Example 8
N-(lsobutoxycarbonyl) N-(3-methoxv-5-methylpyrazin-2-yl)-2-(4-1,3.4-oxadiazol-2-
Yl]phenyl) pyridine-3-sulphonamide
10 To a nitrogen purged 500mL multi necked flask equipped with an overhead stirrer was
charged isobutyl [(2-chloropyridin-3-yl]sulfonyl](3-methoxy-5-methylpyrazin-2-yl)carbamate (22.15g), [4-(l,3,4-oxadiazol-2-yl)phenyl)boronic acid (12.26g), isopropanol (60ml), water (140ml) and 3,3',3"-phosphinidyne tris(benzenesulphonic acid) trisodium salt 30% w/w aq sol (13.7g). Agitation was started and palladium acetate (0.54lg) was added after 10 minutes.
15 N-Methylmorpholine (13.25ml) was added and the temperature was adjusted to 80°C. After 4h 20min toluene (140ml) was added and the temperature adjusted to 60°C. After a further 45 min the mixture was filtered through a 1 um glass fibre filter paper and the aqueous phase separated off. The reaction flask and filter cake was washed with toluene (22ml). The toluene wash was used to re-extract the aqueous phase and the organic layers were combined. These
20 contained the title compound (22.8g, 90%) which was not isolated.
Example 9
N-(lsobutoxycarbonyl)N-(3-methoxy-5-methylpyrazin-2-yl)-2-(4-[1,3,4-oxadiazol-2-yl]phenyl) pyridine-3-sulphonamide
25 To a nitrogen purged 150ml multi necked flask equipped with an overhead stirrer was charged isobutyl [(2-chloropyridin-3-yl)sulfonyl](3-methoxy-5-methylpyrazin-2-yl)carbamate(7.75g), [4-(l,3,4-oxadiazol-2-yl)phenyl] boronic acid (4.29g), isopropanol (21ml), water (49ml) and 3,3'3"-phosphinidyne tris(benzenesulphonic acid) trisodium salt 30% w/w aq sol (2.88g). Agitation was started and palladium acetate (0.114g) was added after 10 minutes. Potassium
30 fluoride (2.48g) was added and the temperature was adjusted to 80°C. After 5h toluene (49ml) was added and the temperature adjusted to 60°C. After a further 10min the mixture was filtered through a 1 p.m glass fibre filter paper and the aqueous phase separated off. The organic phase contained the title compound (7.36g, 83%) which was not isolated.

WO 2005/080403 PCT/GB2005/000567
16 CLAIMS
1. A process for the preparation of a compound of the Formula I

(I)
5 wherein,
X1 is selected from O, NR1 or S; and
X2 is selected from CH or N;
wherein R1 is a nitrogen-protecting group,
which comprises :-
10 the sequential reaction of a compound of the Formula II
N-X2
(II) with,
(i) methyl- or an optionally substituted aryl- lithium; and then
(ii) n-butyl-, s-butyl-, t-butyl- or n-hexyl- lithium; and then
15 (iii) a borate ester.

2 The process according to claim 1 wherein X1 is O.
2. The process according to claim 1 or 2 wherein X2 is N.
20
4. The process according to any one of claims 1-3 wherein said methyl- or an optionally
substituted aryl- lithium is 4-methylphenyllithium or methyllithium.
5. The process according to any one of claims 1-4 wherein said n-butyl-, s-butyl-,
25 t-butyl- or n-hexyl- lithium is n-hexyllithium or n-butyllithium.
6. The process according to any one of claims 1-5 wherein said borate ester is
triisopropylborate.

WO 2005/080403 PCT/GB2005/000567
7. [4-( 1,3,4-Oxadiazol-2-yl)phenyl]boronic acid prepared by the process as claimed in any one of claims 1-6.
8. A process for preparing compounds of Formula IV:

5

(IV)
which comprises coupling [4-(l,3,4-oxadiazol-2-yl)phenyl]boronic acid with a compound of Formula III:

o=s. ,p
6 5
CH3
(III)
wherein P is a nitrogen-protecting group. 10
9. The process according to claim 8 which takes place in the presence of
(i) a source of palladium (0) selected from PdCl2, Pd(Ph3P)4 or Pd(OAc)2; (
(ii) a suitable ligand selected from triphenylphosphine or 3,3',3"-phosphinidyne tris(benzenesulphonic acid) trisodium salt;
15
(iii) a base selected from triethylamine, benzyldimethylamine, N-methylmorpholine, N-methylpiperidine, triethanolamine, ethyldiethanolamine, diisopropylethylamine, potassium acetate, cesium fluoride or potassium fluoride.

WO 2005/080403

PCr/GB2tft5/mM567

18

10. The process according to claim 8 or claim 9wherein said [4-(l ,3,4-oxadiazol-2-yl) phenyl]boronic acid is prepared according to the process as claimed in any one of claims 1-7.
11. The process according to any one of claims 8-10 wherein P is isobutoxycarbonyl.

5
12. A compound of Formula IV:

wherein P is a nitrogen-protecting group.
10 13. A compound of Formula IV as claimed 11 claim 11 which is N-(isobutoxycarbonyl)N-(3-methoxy-5-methylpyrazin-2-yl)-2-(4-[1,3,4-oxadaizol-2-yl)phenyl)pyridine-3-.
sulphonamide
14. Compounds of Formula I and IV and process for preparing the same, substantially as herein described with reference to for going description and examples.

G
Dated this 05th day of August, 2006

VIBHA SHUKLA
OF K&S PARTNERS
AGENT FOR THE APPLICANT(S)

Abstract:
Process for preparing compounds of Formula (I); and (IV); are described.

*
BCOH),
(I)

(IV)

CHEMICAL PROCESS

Documents:

Inventors:

PCT Conventions: