The physical properties such as infra-red absorption values and X-ray Powder Diffraction data of the new intermediate, i. e. , sodium chloride associated 1,2-Benzisoxazole methanesulphonic acid sodium salt are reported to confirm its identity. The Zonisamide synthesized using the said intermediate is obtained in good quality.

BACKGROUND OF THE INVENTION Zonisamide is known as 1, 2-Benzisoxazole-3-methanesulphonamide by its chemical name. It has the following chemical structure as shown in Formula I : Formula I Zonisamide is currently available as an anti-epileptic agent which possesses anti- convulsant and ant-neurotoxic effects. Several routes for the manufacture of Zonisamide are reported in the literature, e. g. , [US Patent 4,172, 896; J. Heterocyclic Chem. 6, 279 (1969); Ibid, 8,397 (1971) ]. US Patent No. 4,172, 896 and Japanese Patent 53-77057 assigned to Dainippon Pharmaceutical Co. discloses the preparation of Zonisamide. These synthetic route involve the preparation of 1,2-Benzisoxazolemethanesulphonyl chloride, an intermediate in Zonisamide synthesis. First route discloses the synthesis of Zonisamide by brominating benzisoxazole acetic acid (hereinafter; BOA) followed by substitution of the bromine by sodium sulfite to give the advanced intermediate sodium salt of benzisoxazole methane sulphonic acid (hereinafter; BOS-Na) as shown below: OH NH20H. HCI N Br2 0 N H2so4 N ocoo Na/EtOH ACOH O COOH Br COOH Aq. Na2so3 POCI 3 I/I. N I/N MeOH + reflux, 3 hrs 5 °C, 4 hrs kS03Na so2c S03Na SOZCI EtAc/NH3 (9) to N cryst. EtAc S°2NH2 The manufacturing method of Zonisamide adopted in the above scheme is little bit difficult due to use of bromine and sensitivity of the intermediate product.

An alternative manufacturing process for Zonisamide starts from 4-hydroxy- coumarin. It may occur via the same intermediates 1,2-Benzisoxazole acetic acid and BOS- Na as shown below: OH C __HOH R CIS03H 01 N N O O NaOH/ BOOHOH BOS-Na g.3Na POCI NH coq/\, BOS-CI 2 Zonisamide S°2NH2 BOA is converted to the BOS-Na in reaction with CIS03H/dioxane in ethylene chloride at room temperature for about 3 hours followed by heating at 50 °C for 6 hours.

After the said reaction time water and NaOH are added and the product is isolated as sodium salt (BOS-Na) by evaporation of the aqueous layer. Using BOS-Na Zonisamide has been synthesized as discussed in above process.

On the other hand US Patent Application 2002/0183525 Al discloses a process for preparing 1, 2-Benzisoxazole-3-acetic acid, comprising the step reacting 4-hydroxy-coumarin with hydroxylamine in the presence of a sodium hydroxide which avoids the direct use of metallic sodium; and thus the process of this invention is substantially less hazards. This process further provides a process for preparing a salt of benzisoxazole methane sulphonic acid, comprising the steps of 1) sulphonating 1, 2-benzisoxazole-3-acetic acid using chlorosulphonic acid in a solvent mixture comprising dichloroethane and sodium hydroxide ; and 2) isolating the salt of benzisoxazole methane sulphonic acid. In this method the sulphonation involves the use of chlorosulphonic acid in large quantities actually used as reactant as well as solvent hence disulphonated product is formed as a major impurity.

Apart from these PCT application WO 03/072552 describes a different manufacturing process of benisoxazole methane sulphonic acid-chloride BOS-C1 and a process for preparing Zonisamide from BOS-C1. This process comprises the following steps as shown below: BOS-H or BOS-Na BOS-CI Zonisamide The above process discloses a) chlorinating 1, 2-benzisoxazole-3-methanesulphonic acid; salts or esters thereof; with thionyl chloride in an organic solvent and/or in the presence of a catalyst to form BOS-C1 ; and b) amidating BOS-C1 in the presence of ammonia selected from the group consisting of aqueous ammonia in a biphasic system, masked ammonia or dry ammonia to form Zonisamide.

It is therefore an objective of the present invention to provide an economical and industrially advantageous manufacturing method of Zonisamide.

SUMMARY OF THE INVENTION According to the present invention a process is provided for the manufacture of an anti-epileptic agent, Zonisamide (Formula I), via. a new crystalline 1,2-Benzisoxazole- methane-sulfonic acid sodium salt (BOS-Na;) associated with NaCl (Formula II) having chemical formulae as follows: Formula I Formula 11 Zonisamide BOS-Na: NaCl In a first embodiment, crystalline 1, 2-Benzisoxazole-3-methane sodium sulphonate (BOS-Na) associated with NaCl (Formula I) (hereinafter BOS-Na: NaCl) is isolated. The BOS-Na: NaCl is synthesized from 4-hydroxycoumarin. The first step of the synthesis involves the reaction of 4-hydroxycoumarin with hydroxylamine hydrochloride in presence of methanolic solution of sodium methoxide to form 1, 2-Benzisoxazole-3-acetic acid.

Second step of the synthesis comprises sulphonation of 1, 2-Benisoxazole-3-acetic acid with chlorosulfonic acid dioxane complex. The reaction is carried out in ethylene chloride at 75 to 85 °C for 5 to 8 hrs. The reaction mixture after the treatment by 25 % sodium hydroxide solution is poured slowly into refluxing acetone which forms crystalline BOS-Na: NaCl. HPLC purity = 95 %.

In a second embodiment the crystalline BOS-Na: NaCl is heated with phosphorous oxychloride at 70-80 °C for 6-to 8 hours. After the said time excess of POC13 is distilled off under vacuum. The remaining mixture is taken in ethyl acetate and treated with anhydrous ammonia gas at low temperature to afford crude 1, 2-Bezisoxazole-3-methanesulphonamide.

The crude product after re-crystallization in methanol yields pure Zonisamide as white crystalline solid. HPLC purity = 99 %.

DETAILED DESCRIPTION OF THE INVENTION Zonisamide being an important and active anti-epileptic agent possessing anti- convulsant and anti-neurotoxic effects, a systematic study for its large scale manufacture of high purity is under taken. The present invention is directed towards a process for the manufacture of sodium chloride associated 1, 2-Benzisoxazole-3-methane sodium sulphonate (BOS-Na: NaCl). The BOS-Na: NaCl thus prepared is directly converted to 1,2- Benzisoxazole-3-methanesulphonamide in good yield.

According to one embodiment the present invention, 1, 2-Benzisoxazole-3- methanesulphonamide is prepared according the following synthetic reaction scheme: (a) Reaction of4-hydroxycoumarin and hvdroxvlamine hydrochloride 1, 2-Benzisoxazole-3-acetic acid is prepared by reacting 4-Hydroxycoumarin with NH20H. HC1 in presence of CH30Na in alcoholic solution as shown below: 4-Hydroxy-coumari 1, 2-Benzisoxazole-3-acetic acid 4-Hydroxymethylcoumarin is taken in methanol followed by addition of hydroxylamine hydrochloride and sodium methoxide. The molar excess of hydroxylamine hydrochloride and sodium methoxide used in this reaction is typically between about 1 and about 4 fold preferably between about 2 to 3 fold, relative to the 4-hydroxycoumarin.

The resulting mixture is refluxed till the reaction is completed. The reflux time for this reaction is between 5 to 10 hours. It is noted that as soon reaction is completed heating should be avoided to minimize the impurities. The resultant reaction mixture is cooled and filtered to separate inorganic solids. The methanol layer thus collected is concentrated to get solid mass. Using aqueous sodium bicarbonate solution the resultant solid is made alkaline and extracted with organic solvent more preferably diethyl ether. Organic layer containing 2- hydroxyacetophenone oxime is discarded. Acidification of aqueous layer with 2N hydrochloric acid 1, 2-Benzisoxazole-3-acetic acid is obtained in crystalline form having melting point 122-124 °C and HPLC purity between 95-98 %.

(b) Sulfonation of 12-Benzisoxazole-3-acetic acid 1, 2-Benzisoxazole-3-acetic acid is sulphonated under mild conditions using chlorosulphonic acid: dioxane complex to form 1, 2-Benzisoxazole-3-methane sodium sulphonate associated with sodium chloride (BOS-Na: NaCl). The pictorial process is outlined below: COOH S03Na CIS03H-Dioxane N : NaCI NaOH/ 1, 2-Benzisoxazole-3-acetic acid BOS-Na: CI A mixture of 1, 2-Benzisoxazole-3-acetic acid and a complex of chlorosulphonic acid and 1,4-dioxane is refluxed for 5-8 hours. Complex mixture of chlorosulphonic acid and 1,4- dioxane is prepared by admixing chlorosulphonic acid and 1,4-dioxane between about 0.5 to about 3.0 more preferably between about 1.0 to about 2.0 w/w ratio. The significant observation made in this invention is the limited use (1.3 to 2.0 mole) of chlorosulphonic acid with respect to 1, 2-benzisoxazole-3-acetic acid. The molar ratio used in the present invention leads to reduction in disulphonated product. In the present invention the solvent selected is alkyl halide more particularly ethylene dichloride.

In the US Patent 4,172, 896 the same complex of chlorosulphonic acid and 1,4- dioxane is used for sulphonation but the quantity of chlorosulphonic acid was alarmingly high and this resulted in significant formation of disulphonated product. The removal of disulphonated product needs additional purification steps which costs time, solvent and labor etc.

In the present invention due to controlled use of chlorosulphonic acid the formation of disulphonated product is not observed.

The sulphonated product so obtained in ethylene dichloride is extracted in water.

Organic layer is discarded and aqueous layer is basified with 25% caustic lye solution. The aqueous reaction mixture is partially concentrated and it is poured in warm anti solvent like acetone. Sodium salt of benzisoxazole methane sulphonic acid is obtained in solid form and is isolated by filtration and dried.

The isolated product, e. g., 1, 2-Benzisoxazole-3-methane sodium sulphonate is associated with sodium chloride (BOS-Na: NaCl) which is confirmed by their characteristic X-Ray powder diffraction and IR absorption frequencies.

The present invention provides BOS-Na: Cl, characterized by having the following X- Ray Powder Diffraction main peaks at about 18.64, 19.02, 19. 80, 22.62, 23.14, 23. 58, 25.52, 28. 02,29. 00,31. 80, 32.10, 32.38, 32.96, 37.84, 38. 28 and 38.60, 0.2.

IR Spectrum of BOS-Na: NaCl is characterized by the following peaks at about 3455, 1630,1136, 955,747, 638 and 619 cm-1.

US Patent application no. 2003/0144527 Al discloses the different polymorphic forms of 1, 2-Benzisoxazole-3 methane sodium sulphonate (BOS-Na). The different polymorphs of the BOS-Na are characterized by their characteristic XRD and IR peak values.

However, in the present study the IR and XRD peak values of BOS-Na: NaCl are very different from polymorphic forms I, II, III, IV and V of BOS-N. The XRD and IR values are compared from the values reported in US Patent application no. 2003/0144527 Al. A comparative XRD and IR values of different polymorphic forms of BOS-Na and sodium chloride associated BOS-Na is set forth in Table 1.

TABLE 1: XRD and IR peak values of different polymorphic forms of BOS-Na and BOS- Na: NaCl (XRD and IR peak values are reported in 29 and cm-1 respectively). BOS-Na BOS-Na BOS-Na BOS-Na BOS-Na BOS-Na: Cl Form I Form II Form III Form IV Form V XRD IR XRD IR XRD IR XRD IR XRD IR XRD IR 5. 0 3546 5. 3 3597 5.0 3604 4. 5 3431 6. 7 3601 18.64 3455 15.7 3485 16.6 3535 5. 3 3495 5. 9 1567 10.9 3520 19.02 1630 16.5 3440 21.3 3496 15.7 3067 8. 8 1416 16.1 1587 19. 80 1136 17. 3 1612 26.7 3067 17. 8 2998 11. 3 924 21. 0 1055 22.62 955 18.6 1513 2998 21. 4 2951 16. 3 862 21. 2 793 23. 14 747 19.1 1439 2951 1605 16. 9 586 22. 2 753 23. 58 638 19.7 1410 1606 1516 19. 0 25. 52 619 21.5 1382 1516 1438 22. 5 28. 02 22.8 1234 1438 1382 23. 9 29. 00 23.2 1199 1382 1215 24.7 31. 80 23.5 1048 1213 1136 25. 0 32. 10 24. 3 918 1064 1065 26. 8 32. 38 855 1055 1052 28. 1 32. 96 760 743 777 29. 7 37. 84 669 663 747 30. 9 38. 28 593 588 696 32. 6 38. 60 541 588 33. 6 522 521 35.5 36. 6 It is appreciated for the present study that whatever BOS-Na is isolated by acetone precipitation is associated with sodium chloride. Characteristic XRD peak of pure sodium chloride is observed at (29) 31. 82°. However a strong peak at (20) 31. 80 is observed in BOS- Na: NaCl which gives very clear cut information about the association of sodium chloride with BOS-Na.

(c) Chlorination and Amidation reactions BOS-Na: NaCl is converted to Zonisamide after making its acid chloride followed by amidation as shown in the reaction below: BOS-Na: CI 1, 2-Benzisoxazole-3-methanesulphonamide (Zonisamide) The isolated product from step (b) namely, 1, 2-Benzisoxazole-3-methane sodium sulphonate associated with sodium chloride (BOS-Na: NaCl) is chlorinated without further purification using phosphorous oxychloride between about 60 to 80 °C for about 4 to about 10 hours. The ratio of POC13 used in this reaction is about 3 times excess (by weight) in comparison to BOS-Na: NaCl. The excess of oxychloride present in the solution is distilled under vacuum leaving crude 1, 2-Benzisoxazole-3-methanesulfonyl chloride. Further, ethyl acetate is added as solvent to the mixture and anhydrous ammonia is passed to afford crude Zonisamide. The Zonisamide thus obtained is re-crystallized in methanol to obtain white crystalline solid. After drying at 60-70 °C under vacuum yielded dry crystalline Zonisamide having meting point 160-164 °C. HPLC Purity = 99 %.

Elemental analysis of the isolated Zonisamide is shown below: Elements Zonisamide Calculated Found Nitrogen 13.2 13.73 Carbon 45.28 45.70 Hydrogen 03. 77 03. 50 Sulfur 15. 09 14. 38 The proton NMR of Zonisamide shows the following peaks (ppm relative to d6- DMSO, integration values in parentheses): 4.9 (2H), 7.25 (2H) and 7.4-8. 0 (4H).

IR spectrum of Zonisamide of the present invention is characterized by the following peaks at about 3322.34, 3165.79, 3084.01, 2990.54, 2946.34, 1564.32, 1516. 68, 1384.28, 1339.46, 1151.50, 1131.93, 936.72, 916.78, 869.08, 763.46, 747.39, 660.45 and 557. 83 cm~l.

X-Ray powder diffraction of Zonisamide of the present invention is characterized by the following peaks (20) at about 11.420, 13.400, 14.400, 14.720, 16.300, 18. 520,18. 820, 19.720, 22.180, 22.520, 22.920, 23.900, 24.260, 25.620, 26.560, 27.220, 27.660, 28.780, 29.160, 29.660, 29.960, 31.120, 31.700, 32.040, 32.920, 33.400, 34.180, 34.680, 35.200, 36.460, 37.180, 37.500, 38.220 and 38.860°.

Molecular weight of the Zonaside (Mw 212) of the present invention is characterized by scanning mass of the finally crystallized product, which is found exactly the same of theoretical value.

The following examples illustrate the invention, but is not limiting thereof.

EXAMPLE 1 1, 2-Benisoxazole-3-acetica acid Methanolic solution of 4-Hydroxycoumarin (59 Kg, 314.19 moles) is refluxed with hydroxylamine hydrochloride (75.98 Kg, 1093.23 moles) and sodium methoxide 26.18% w/v solution (225. 38 Ltr, 1092.27 mole) for 5 to 10 hours. After the said time inorganic solid is filtered off and filtrate containing 1, 2-Bezisoxazole-3-acetic acid in methanol is concentrated to afford solid which is made alkaline with sodium bicarbonate and extracted with diethyl ether. In ether extract 2-hydroxyacetophenone oxime is found, which is discarded. By further acidification of aqueous layer with 2N hydrochloric acid, 1, 2-Benzisoxazole-3-acetic acid (49. 18 Kg) is obtained as a crystalline solid with melting point 122 to 124 °C and having HPLC purity about 95 to 98%.

EXAMPLE 2 1, 2-Be7zzisoxazole-3-methane sodium sulphonate (BOS-Na : NaCIJ A mixture of 1, 2-Benzisoxazole-3-acetic acid (49.18 Kg, 277.85 moles) and chlorosulphonic acid: l, 4-dioxane complex (132.50 Ltr) [prepared by addition at low temperature 1,4-dioxane (105. 30 Kg) in chlorosulphonic acid (53.50 Kg, 459.15 mole) ] in dichloroethane is refluxed for 5 to 8 hours.

Then the reaction is completed the is mixture cooled to room temperature and quenched by chilled water. Organic layer separated out was discarded and aqueous layer is made alkaline with 25% sodium hydroxide solution is partially concentrated, upto 150 to 200 Ltr and the aqueous solution is added to refluxing acetone. Solid mass thus separated is filtered and dried at 65 to 70°C under vacuum for 6 to 8 hours to afford 90 Kg material having melting point 266 to 270 °C and HPLC purity NLT 95%. This product is associated with sodium chloride which is used in the next stage to manufacture Zonisamide without further purification.

EXAMPLE 3 1, 2-Benzisoxazole-3-methanesulphonamide (Zonisamide) 1, 2-Benisoxazole-3-methane sodium sulphonate (90 Kg) associated with sodium chloride and phosphorous oxychloride (282 Kg) is heated at 70 to 80 °C temperature for 6 to 8 hours to form acid chloride. Excess POC13 is distilled off under vacuum and remaining mass is taken is taken in ethyl acetate. It is then treated with anhydrous ammonia gas at lower temperature to afforded crude Zonisamide, which is re-crystallized in methanol to get pure Zonisamide (30 Kg) as a white crystalline solid. The isolated product is dried at 60 to 70 °C under vacuum for 8 to 10 hours having melting point 160 to 164 °C and HPLC purity = 99%.