Title of Invention	A PROCESS FOR THE PREPARATION OF AMIFOSTINE DIHYDRATE
Abstract	The present invention relates to a novel dihydrate form of Amifostine of formula (I) and process for its preparation.

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NOVEL DIHYDRATE FORM OF AMIFOSTINE AND A PROCESS FOR ITS PREPARATION Field of Invention: The present invention relates to a novel dihydrate form of Amifostine of formula (I) and process for its preparation. Amifostine is S-2-(3-aniinopropylamino)ethyl dihydrogen phosphorothioate of formula-I(a) useful in cancer chemotherapy and exists normally as the trihydrate. Background of the invention: Amifostine is originally developed as a radiation protector and the only drug that has been approved by the FDA for Xerostomia (dry mouth) in patients receiving radiation therapy for cancers of the head and neck. Xerostomia is a chronic dry-mouth condition, which is caused by damage to the salivary glands during radiation therapy. In addition to its utility as radioprotectant, it has been reported that Amifostine is used experimentally to protect HIV infected patients from the harmful side effects of 3'-azido-3'deoxythymidine (AZT) therapy. Amifostine and its derivatives exert their protective effects without significantly affecting the beneficial properties of the administered therapeutic agents. This is in part due to the selective uptake of the protective thiol into normal tissue. Amifostine is commercially available as an injection dosage form containing a lyophilized powder of Amifostine trihydrate for intravenously. Amifostine having chemical name, S-2-(3-aminopropylamino)ethyl dihydrogen phosphorothioate is also known as WR-2721 and similar aminoalkylamino dihydrogen phosphorothioates are first reported in US patent 3892824 (1968) and later it was published in J. Med chem., 12, 236-243 (1969). In the above said article and patent (US 3892824), the manufacturing process for Amifostine monohydrate is described as shown in scheme-1. Scheme-1 In this process, 2-(3-aminopropylamino)ethanol(II) and aqueous hydrobromic acid were reacted and the resulting crystalline 2-(3-aminopropylamino)ethyl bromide dihydrobromide(III) was then reacted with anhydrous trisodium phosphorothioate (IV) in dimethyl formamide and water medium to get S-2-(3-aminopropylamino)ethyl dihydrogen phosphorothioate monohydrate (V). The product was isolated by the addition of methanol. Its melting point was 160-161° C. In this patent (US 3892824), neither physical characterization parameters like differential scanning calorimetry(DSC), X-ray diffraction(XRD) data, IR spectral data nor analytical purity of the substance have been furnished for monohydrate form. In the patent DD 289448 (1983), the product was synthesized by following the same methodology but by using trisodium phosphorothioate dodecahydrate (VI) instead of anhydrous reagent (IV) in dimethyl formamide and water medium to get Amifostine trihydrate(I(a)) as crystals (Scheme-2). In this patent (DD 289448), the purity of Amifostine trihydrate was reported as 100% based on Thin layer chromatography. Along with this result no analytical details like DSC, X-ray diffraction studies or FTIR were reported to further confirm the structure. In the patent DD 289449 (1983), the product was synthesized by following the same methodology but by using trisodium phosphorothioate dodecahydrate (VI) instead of anhydrous reagent (IV) in aqueous alcoholic medium to get Amifostine trihydrate(I(a)) as crystals (Scheme-3). In this patent (DD 289449) also, the purity of Amifostine trihydrate was reported as 100% based on Thin layer chromatography. Along with this result no analytical details like DSC, X-ray diffraction studies or FTIR were reported to further confirm the structure. However in the patent WO 9403179 (1994), the details of stability data. Differential scanning calorimetry(DSC) data, FTIR spectral data and X-ray diffraction (XRD) data and molecular and crystal structure of Amifostine trihydrate drug substance have been disclosed. According to this patent, the moisture content of Amifostine trihydrate is reported as 12.1% w/w. But according to theoretical calculation, the moisture content must be 20.1% w/w. Also other analytical reports like DSC, FTIR and X-ray diffraction studies revealed that the reported crystalline Amifostine is a trihydrate form. In the subsequent patent WO 0218396 (2002) a comparative data for Amifostine monohydrate and trihydrate with respect to FTIR, DSC and XRD have been furnished. Recently, we developed a novel and industrially feasible process for Amifostine trihydrate as shown in the scheme-4. Accordingly, 2-(3-aminopropylamino)ethyl bromide dihydrobromide(III) and commercially available thiophosphoryl chloride(VIII) were reacted in presence of aqueous alkali to afford Amifostine trihydrate. The product was then crystallized in aqueous alcohol to get pure Amifostine trihydrate. During our studies on Amifostine trihydrate, the following difficulties were observed i) It is very difficult to control the moisture content of Amifostine trihydrate during drying to meet the pharmacopoeial limit of 19.2-21.2%. ii) Amifostine trihydrate is known to be unstable at temperatures above 40° C. This puts severe constraints on the operating temperatures of drying for this drug substance. By employing lower temperatures (less than 30° C) for drying, it is very difficult to eliminate the residual organic solvent methanol and at the same time keeping the water content within permissible limits for this drug substance, iii) Prolonged drying hours(6-8 hrs) causes hydrolysis of phosphorothioate ester function of Amifostine. In the present manufacturing conditions of Amifostine trihydrate, a great difficulty is encountered to control the moisture content (19.2-21.2%) and keeping the residual solvents in the specified limits during the drying process. Hence there is a need to develop an alternate hydrate form of Amifostine to overcome the above difficulties. In order to maintain a balance between optimum moisture content and acceptable residual solvent content, a new dihydrate form of Amifostine is now invented and found suitable to overcome the above mentioned difficulties. Accordingly, we disclose a novel and industrially viable process for the synthesis of Amifostine dihydrate, which was not disclosed earlier. It has been found that the new dihydrate form of Amifostine is devoid of the difficulties mentioned above. To meet the requirement for high purity Amifostine, we wish to disclose a simple and commercially viable process comprising the reaction of 2-(3-aminopropylamino) ethylbromide dihydrobromide (III) and thiophosphoryl chloride (VII) in aqueous alkaline medium (Scheme-5; Route A). Also we wish to disclose another route of synthesis of the same target molecule by condensing trisodium phosphorothioate dodecahydrate (VI) with 2-(3-aminopropylamino) ethyl bromide dihydrobromide (III) in presence of water (Scheme-5; Route B). Objectives of the present invention: The main objective of the present invention is to provide a new stable dihydrate form of A^mifostine, which obviates the following difficulties associated with handling the known \mifostine trihydrate. (i) It is very difficult to control the moisture content of Amifostine trihydrate during drying operation to meet the pharmacopoeial limit of 19.2-21.2% (ii) Amifostine trihydrate is known to be unstable at temperatures above 40° C. This puts severe constraints on the operating temperatures for drying of this drug substance, (iii) By employing lower temperatures (less than 30° C) for drying, it is very difficult to eliminate the residual organic solvent methanol and also water, (iv) Prolonged drying (6-8 hrs) causes hydrolysis of phosphorothioate ester function of Amifostine. Accordingly, another objective of the present invention is to provide a novel crystallization and isolation technique which affords a stable crystalline Amifostine dihydrate containing 12.5-14.5% moisture content. Accordingly yet another objective of the present invention is to provide a novel and new dihydrate form of Amifostine of high purity. Accordingly yet another objective of the present invention is to provide a new process for the preparation of S-2-(3-aminopropylamino)ethyl dihydrogen phosphorothioate dihydrate which comprises the usage of 2-(3-aminopropylamino) ethyl bromide dihydrobromide, thiophosphoryl chloride and sodium hydroxide as principle raw materials. Accordingly still yet another objective of the present invention is to provide a new process for the preparation of S-2-(3-aminopropylaniino)ethyl dihydrogen phosphorothioate dihydrate, which comprises the usage of 2-(3-aminopropylamino)ethyl bromide dihydrobromide, trisodium phosphorothioate dodecahydrate in water medium. Accordingly still another objective of the present invention is to provide an improved commercial preparation of Amifostine dihydrate of high purity (99.9-99.95%) Accordingly yet another objective of the present invention is to provide a new method of elimination or minimization of Amifostine thiol impurity (VIII) (Limit: Accordingly still another objective of the present invention is to provide a new method of minimization of total impurity content of Amifostine (Limit: Pharmacopoeia 2005 monograph) from Amifostine dihydrate using a novel crystallization technique. Accordingly still another objective of the present invention is to provide a novel dihydrate form of Amifostine, which is characterized by the following analytical data. a) Wave numbers (cm"') of characteristic Infrared absorption bands in potassium bromide are 595.8, 769.5, 844.1, 990.0, 1160.5, 1277.0, 1531.4, 1600.4, 1623.6, 1690.7, 2744.2, 3414.6 cm-1-[Fig 1] b) Differential scarming calorimetry data (^ C) -[ Fig 2] First endotherm at 55.1-67.1° C and second endotherm at 146.2-154.5° C c) Characteristic Peaks in the powder X-ray diffraction pattern are [Fig 3] Diffraction angles (29°) i d value (A°) 1 Intensity (%) 3.082 28.64655 15 8.668 10.19330 8J 12.614 7.01212 4l0 15.386 5.75435 6^8 17.409 5.08986 29^9 17.884 4.95590 4^9 20.190 4.39456 14A 22.012 4.03480 O 23.833 3.73052 209 29.074 3.06887 iOOO 45.097 2.00878 16 Brief Description of the Figures: Fig 1: FTIR spectrum of Amifostine dihydrate Fig 2: DS C of Amifostine dihydrate Fig 3: X-ray diffraction of Amifostine dihydrate Summary of the present invention: The present invention discloses a novel dihydrate form of Amifostine and a novel method of making the same, which comprises of: a) Reacting 2-(3-aminopropylamino) ethyl bromide dihydrobromide and commercially available thiophosphoryl chloride in the presence of aqueous alkali to afford Amifostine dihydrate. (or) by reacting 2-(3-aminopropylamino) ethyl bromide dihydrobromide and trisodium phosphorothioate dodecahydrate in the presence of water to afford Amifostine dihydrate. b) Isolating the resulting Amifostine dihydrate by the addition of alcohol c) Purifying Amifostine dihydrate thus obtained, in water-methanol or water-ethanol. d) Filtering and triturating wet Amifostine dihydrate with 5-15% aqueous alcohol to get Amifostine dihydrate of high purity. d) Drying the above wet crystalline Amifostine dihydrate at 25-30° C under vacuum (710-750 mm of Hg) to remove the residual solvents like methanol / ethanol and keeping the optimum moisture content at 12.5-14.5%(w/w). Detailed description of the present invention: The details of the present invention for the commercial manufacture of Amifostine dihydrate (I) are as follows: According to the present process of the invention as outlined in Scheme-5 (Route 'A'), thiophosphoryl chloride (VII) is treated with aqueous alkali solution at room temperature and after getting uniform solution, 2-(3-aminopropylamino)ethyl bromide dihydrobromide (III) (prepared according to the procedure reported in US 3892824) is added to get S-2-(3-aminopropylamino)ethyl phosphorothioate as an aqueous solution. According to the present process of the invention as outlined in Scheme-5 (Route 'B'), trisodium phosphorothioate dodecahydrate (VI) is reacted with 2-(3-aminopropylamino) ethylbromide dihydrobromide in the presence of aqueous alcohol to get S-2-(3-aminopropylamino)ethyl dihydrogen phosphorothioate as an aqueous solution. Accordingly, the present invention provides a new method of manufacture of novel Amifostine dihydrate of formula-I by following routes 'A or B' (Scheme-5) which comprises of the following steps, i) dissolution of thiophosphoryl chloride (VII) in aqueous alkali suspending trisodium phosphorothioate dodecahydrate (VI) in water ii) addition of 2-(3-aminopropylamino) ethylbromide dihydrobromide (III) to above aqueous alkali solution or aqueous solution iii) Isolation of Amifostine dihydrate by the addition of lower alcohols such as methanol, ethanol, isopropyi alcohol, ketonic solvents like acetone or ester solvents like ethyl acetate or dipolar aprotic solvents like acetonitrile or tetrahydrofuran. iv) Purification of Amifostine dihydrate is carried out by dissolving the product in water at 35-40° C, decolorizing the resulting solution with activated charcoal at 20-30° C followed by filtration and crystallization of Amifostine dihydrate by the addition of lower alcohols like methanol, ethanol, isopropyi alcohol or ketonic solvent like acetone or an aliphatic ester like ethyl acetate or a dipolar aprotic solvents like acetonitrile or tetrahydrofuran. v) Drying the above wet crystalline Amifostine dihydrate at 25-30° C under vacuum (710-750 mm of Hg) to remove the residual solvents like methanol / ethanol and keeping the optimum moisture content 12.5-14.5%(w/w). vi) Analysis of the above obtained Amifostine dihydrate using moisture content (by KF method), FTIR, DSC and Powdered X-ray diffraction technique. The alkali solution used in step (i) to dissolve thiophosphoryl chloride is selected from alkali metal hydroxides like sodium hydroxide, potassium hydroxide and lithium hydroxide preferably sodium hydroxide. The molar ratio between thiophosphoryl chloride and alkali metal hydroxide used in step (i) is 1: 6.0 or 1: 6.25 preferably 1: 6.0. The temperature at which dissolution of thiophosphoryl chloride in aqueous alkali metal hydroxide in step (i) is 25-40 °C preferably 25-35° C. The time of addition of thiophosphoryl chloride to the alkali metal hydroxide solution in step (i) is 3-6 hours preferably 4-5 hours. In step (ii), the temperature at which the addition of 2-(3-aminopropylamino)ethyl bromide dihydrobromide to the above aqueous alkali solution or aqueous solution is 10-25° C preferably 15-20° C. In step (ii), The time of maintenance of the above aqueous solution to react may be in the range of 2-6 hours preferably for 4 hours. In step (iii), solvent employed for isolation Amifostine dihydrate is selected from alcohols such as methanol, ethanol, isopropyl alcohol or ketonic solvents like acetone or ester solvents like ethyl acetate or dipolar aprotic solvent like acetonitrile or tetrahydrofuran. The preferred solvent is methanol. In step (iii), the temperature at which the addition of the above said solvent to the reaction mixture for isolation Amifostine dihydrate is 0-20° C preferably 5-10° C. In step (iii), the temperature at which isolation of Amifostine dihydrate is 0-10° C preferably 5-10° C. In step (iv), the solvent mixture for crystallization of Amifostine dihydrate is selected from Water-methanol, water-ethanol, water-isopropyl alcohol, water-acetone, water-ethyl acetate, water-acetonitrile or water-tetrahydrofuran preferably water-methanol. In step (iv), the volume of water used for dissolution of Amifostine dihydrate may be in the range of 1.5-4.0 times to its weight preferably 2.5 times. In step (iv), the temperature at which the dissolution of Amifostine dihydrate in water may be in the range of 25-40° C preferably 35-40° C. In step (iv), the temperature at which, the resulting aqueous solution of Amifostine dihydrate is clarified using activated charcoal may be in the range of 20-30° C preferably 25-30° C. In step (iv), the temperature at which, alcohol is added to the aqueous solution may be in the range of 20-30° C preferably 25-30° C. In step (iv), the volume of alcohol used to crystallize Amifostine dihydrate may be in the range of 0.5-1.5 times to its weight, preferably 0.5-1.0 and most preferably 0.5 times. In step (iv), the temperature at which isolation of crystalline Amifostine dihydrate is 0-10° C preferably 5-10° C. In step (iv), the percentage of water in aqueous alcohol used to triturate the wet cake of crystalline Amifostine dihydrate may be in the range of 5-20%, preferably 5-15%. In step (iv), the temperature at which, trituration of wet cake of Amifostine dihydrate may be in the range of 20-30° C preferably at 25-30° C. In step (v), the temperature at which drying of crystalline Amifostine dihydrate of USP grade may be in the range of 15-30° C preferably 20-25° C. In step (vi), Amifostine dihydrate is characterized by its moisture content (12.5-14.5%) analysis by Karl-Fisher method. In step (vi), Amifostine dihydrate is characterized by its FTIR spectrum, a representative example of which is provided in the spectrum of Fig 1. Particularly characteristic peaks in the FTIR spectrum occur at 595.8, 769.5, 844.1, 990.0, 1160.5, 1277.0, 1531.4, 1600.4, 1623.6,1690.7, 2744.2, 3414.6 ± 2 cm-1. In step (vi), Amifostine dihydrate is characterized by its Differential scanning calorimetric (DSC) analysis, a representative example of which is provided in Fig 2. Particularly characteristic first endotherm appear at 55.1-67.1±4° C and second endotherm appear at 146.2-154.5 ± 2° C. In step (vi), Amifostine dihydrate is characterized by its powdered X-ray diffraction (XRD) technique, a representative example of which is provided in diffractogram of Fig 3. Particularly characteristic peaks in the powdered X-ray diffraction pattern occur at 3.08, 8.66, 12.61, 15.38, 17.40, 17.88,20.19, 22.01, 23.83, 29.07,45.09 ± 2 degrees two-theta. Advantages associated with the present invention: i) The novel dihydrate form of Amifostine of this invention is easy to handle and may be used as alternate drug substance in place of Amifostine trihydrate. This is possible in practice as Amifostine is an injectable drug product and is used ultimately in aqueous solution form, ii) It is easier to maintain a balance between optimum moisture content level (12.5- 14.5%) and acceptable residual solvent content while handling Amifostine dihydrate as finished drug substance, iii) The phosphorothioate ester function of Amifostine is susceptible to hydrolysis by the bound water on prolonged drying. This deterioration is minimized in the case of Amifostine dihydrate. Having thus described the present invention with reference to certain preferred embodiments, the invention will be further illustrated by the examples, which follow. These examples are provided for illustrative purposes only and are not intended to limit the scope of the invention in any way. Example-1: Preparation of Amifostine Dihydrate (I): To a stirred solution of trisodium phosphorothioate (VI) (3.52 Kg; 8.89 mole) in Water (7.96 Lt), 2-(3-aminopropylamino)ethyl bromide dihydrobromide (III) (2.5 Kg; 7.29 mole) is added lot wise under cooling at 15-20° C. After addition, the reaction mixture is stirred for another 4 hours and further cooled to 5° C. To this solution, methanol (10.2 Lt) is added drop-wise to get Amifostine dihydrate (I). Yield: 1.4 Kg Purification of Amifostine Dihydrate(I): The above wet product of Amifostine dihydrate (I) (1.4 Kg) is dissolved in water (3.5 Lt) at 35-40°C under nitrogen atmosphere. After complete dissolution, the solution is cooled to room temperature (25°C) and the solution is treated with activated charcoal (0.1 Kg) for 10-15 minutes and to the filtered solution is added methanol (37 ml) at 25-30° C. The clear solution is fiirther cooled to 0-5° C and stirred for 2 hours and filtered. The wet cake is then triturated with aqueous methanol (5% water) and dried at 20-25° in a vacuum oven at 710-750 mm Hg until the moisture content limit (12.5-14.5%) is reached. The purity of Amifostine dihydrate is 99.95% and the thiol impurity is 0.03%. Yield: 1.2 Kg (61.4%) The Amifostine dihydrate crystals thus obtained is analyzed for various physico-chemical characteristics as follows. Moisture content :13.5%w/w FTIR(cm-l) : 595.8, 769.5, 844.1, 990.0, 1160.5, 1277.0, 1531.4, 1600.4, 1623.6, 1690.7,2744.2, 3414.6 cm-1 [Fig 1] DSC : First endotherm at 55.1-67.1° and second endotherm at 146.2 - 154.5° C [Fig 2] Powdered XRD : 3.08, 8.66, 12.61, 15.38, 17.40, 17.88,20.19,22.01,23.83,29.07, 45.09 [Fig 3] CiXampie z: Preparation of Amifostine Dihydrate (I): To a stirred solution of sodium hydroxide(124g; 3.1 mole) and water(336 ml), thiophosphoryl chloride (VII) (84g; 0.49 mole) is added drop-wise over a period of 4-5 hours at 30-40° C. After addition, the solution is stirred till uniform solution is observed (approximately 2-6 hours). After getting uniform solution, 2-(3-aminopropylamino)ethyl bromide dihydrobromide (III) (lOOg; 0.29 mole) is added lot wise under cooling at 15-20° C. After addition the reaction mixture is stirred for another 4 hours and further cooled to 5° C. To this solution, methanol (1.4 Lt) is added drop-wise to precipitate Amifostine dihydrate (I). Yield: 78 g Purification of Amifostine Dihydrate(I): The above wet product of Amifostine dihydrate (I) (78g) is dissolved in water (195 ml) at 35-40°C under nitrogen atmosphere. After complete dissolution, the solution is cooled to room temperature (25°C) and the solution is treated with activated charcoal (2g) for 10-15 minutes and to the filtered solution is added methanol (39 ml) at 25-30° C. The clear solution is further cooled to 0-5° C and stirred for 2 hours and filtered. The wet cake is then triturated with aqueous methanol (90% methanol), filtered and dried at 20-25° C in a vacuum oven at 710-750 mm Hg until the moisture content limit (12.5-14.5%) is reached. The HPLC purity of Amifostine dihydrate is 99.90% and the thiol impurity is 0.04%. Yield: 45 g (57.7%) The Amifostine dihydrate crystals thus obtained is analyzed for various physico-chemical characteristics as follows. Moisture content : 13.26 % (w/w) FT IR(cm-l) : 597.0, 767.9, 843.9, 990.9, 1162.0, 1275.6,1532.7, 1601.0, 1620.8, 1692.0, 2742.9, 3414.0 cm-1 DSC : First endotherm at 54.1-70.7° and second endotherm at 148.6 - 154.9° C Powdered XRD : 3.59, 8.69,12.35, 16.16, 17.27, 18.09,20.87, 22.55, 23.89, 30.02, 45.51 ExainpIe-3: Preparation of Amifostine Dihydrate (I): To a stirred solution of sodium hydroxide(124g; 3.1 mole) and water(336 ml), thiophosphoryl chloride (VII) (84g; 0.49 mole) is added drop-wise over a period of 4-5 hours at 30-40° C. After addition, the solution is stirred till uniform solution is observed (approximately 2-6 hours). After getting uniform solution, 2-(3-aminopropylamino)ethyl bromide dihydrobromide (III) (lOOg; 0.29 mole) is added lot wise under cooling at 15-20° C. After addition, the reaction mixture is stirred for another 4 hours and further cooled to 5° C. To this solution, ethanol (1.4 Lt) is added drop-wise to precipitate Amifostine dihydrate (I). Yield: 76.5 g Purification of Amifostine Dihydrate(I): The above wet product of Amifostine dihydrate (I) (76g) is dissolved in water (195 ml) at 35-40°C under nitrogen atmosphere. After complete dissolution, the solution is cooled to room temperature (25°C) and the solution is treated with activated charcoal (2g) for 10-15 minutes and to the filtered solution is added ethanol (38 ml) at 25-30° C. The clear solution is further cooled to 0-5° C and stirred for 2 hours and filtered. The wet cake is then washed with aqueous ethanol (90 % ethanol) and dried at 20-25° in a vacuum oven at 710-750 mm Hg until the moistiu-e content limit (12.5-14.5%) is reached. The HPLC purity of Amifostine dihydrate is 99.95% and the thiol impurity is 0.03%. Yield: 42.3 g (54.2%) The Amifostine dihydrate crystals thus obtained is analyzed for various physico-chemical characteristics as follows. Moisture content : 13.51 % (w/w) FTIR(cm-l) : 598.0,768.5,844.9,991.0,1162.5,1276.8,1532.0,1601.0,1621.0, 1692.1,2742.8, 3414.5 cm-1 DSC : First endotherm at 55.6-67.0° and second endotherm at 146.1 - 154.5° C Powdered XRD : 3.50, 8.71, 12.49, 16.01, 17.20, 18.05,20.92, 22.15, 23.80, 29.94, 45.55 Example-4: Preparation of Amifostine Dihydrate (I): To a stirred solution of sodium hydroxide(3.1Kg; 77.5 mole) and water(8.4 Lt), thiophosphoryl chloride (VII) (2.IKg; 12.38 mole) is added drop-wise over a period of 4-5 hours at 30-40° C. After addition, the solution is stirred till uniform solution is observed (approximately 2-6 hours). After getting uniform solution, 2-(3-aminopropylamino)ethyl bromide dihydrobromide (III) (2.5 Kg; 7.28 mole) is added lot wise under cooling at 15-20° C. After addition, the reaction mixture is stirred for another 4 hours and further cooled to 5° C. To this solution, methanol (35 Lt) is added drop-wise to precipitate Amifostine dihydrate (!)• Yield: 2.1 Kg Purification of Amifostine Dihydrate(I): The above wet product of Amifostine dihydrate (I) (2.1 Kg) is dissolved in water (5.25 Lt) at 35-40°C under nitrogen atmosphere. After complete dissolution, the solution is cooled to room temperature (25°C) and the solution is treated with activated charcoal (50g) for 10-15 minutes and to the filtered solution is added methanol (1.05 Lt) at 25-30° C. The clear solution is ftirther cooled to 0-5° C and stirred for 2 hours and filtered. The wet cake is then triturated with aqueous methanol (90% methanol) and dried at 20-25° in a vacuum oven at 710-750 mm Hg until the moisture content limit (12.5-14.5%) is reached. The HPLC purity of Amifostine dihydrate is 99.93% and the thiol impurity is 0.04%. Yield: 1.2 Kg (61.4%) The Amifostine dihydrate crystals thus obtained is analyzed for various physico-chemical characteristics as follows. Moisture content : 13.46% (w/w) FTIR(cm-l) : 597.0, 769.5, 844.0, 990.5, 1161.9, 1276.0,1532.4, 1600.1, 1622.0, 1690.0,2743.8, 3414.0 cm-1 DSC : First endotherm at 55.3-67.2° and second endotherm at 146.5 - 154.0° C Powdered XRD : 3.05, 8.60,12.64, 15.31,17.40,17.97,20.19,22.11,23.88,29.40, 45.65 Example 5: Preparation of Amifostine Dihydrate (I): To a stirred solution of trisodium phosphorothioate (VI) (125 g; 0.315 mole) in Water (250 ml), 2-(3-aminopropylamino)ethyl bromide dihydrobromide (III) (lOOg; 0.29 mole) is added lot wise under cooling at 15-20° C. After addition, the reaction mixture is stirred for another 4 hours and fiuther cooled to 5° C. To this solution, methanol (1.4 Lt) is added drop-wise to get Amifostine dihydrate (I). Yield: 74.1 g Purification of Amifostine Dihydrate(I): The above wet product of Amifostine dihydrate (I) (74g) is dissolved in water (195 ml) at 35-40°C under nitrogen atmosphere. After complete dissolution, the solution is cooled to room temperature (25 °C) and the solution is treated with activated charcoal (2g) for 10-15 minutes and to the filtered solution is added methanol (37 ml) at 25-30° C. The clear solution is further cooled to 0-5° C and stirred for 2 hours and filtered. The wet cake is then triturated with aqueous methanol (5% water) and dried at 20-25° in a vacuum oven at 710-750 mm Hg until the moisture content limit (12.5-14.5%) is reached. The purity of Amifostine dihydrate is 99.95% and the thiol impurity is 0.03%. Yield: 42.0 g (53.8%) The Amifostine dihydrate crystals thus obtained is analyzed for various physico-chemical characteristics as follows. Moisture content : 13.61 % FTIR(cm-l) : 597.1, 769.1, 844.0, 990.2, 1161.0, 1276.8, 1532.0, 1600.0, 1622.2, 1690.5,2744.0, 3414.3 cm-1 DSC : First endotherm at 55.5-67.0° and second endotherm at 146.0 - 153.9° C Powdered XRD : 3.06, 8.65,12.60, 15.35,17.42, 17.90,20.17, 22.06,23.80,29.00, 45.06 We claim: 1. Crystalline solid Amifostine dihydrate of the following structure 2. Crystalline solid Amifostine dihydrate characterized by FTIR spectrum substantially as depicted in Fig 1. 3. Crystalline solid Amifostine dihydrate characterized by DSC analysis substantially as depicted in Fig 2. 4. Crystalline solid Amifostine dihydrate characterized by powdered X-ray diffractogram substantially as depicted in Fig 3. 5. Crystalline solid Amifostine dihydrate characterized by moisture content by Karl-Fisher method. 6. The crystalline soHd Amifostine of Claims 1-5 is a dihydrate. 7. The crystalline solid Amifostine dihydrate of claim 2 is characterized by FTIR having peaks at 595.8, 769.5, 844.1, 990.0, 1160.5, 1277.0, 1531.4, 1600.4, 1623.6, 1690.7, 2744.2, 3414.6 ± 2 cm-1. 8. The crystalline solid Amifostine dihydrate of claim 3 is characterized by DSC having first endotherm at 55.1-67.1 ± 4° C and second endotherm at 146.2-154.5 + 2° C. 9. The crystalline solid Amifostine dihydrate of claim 4 is characterized by powdered X-ray diffraction pattern having peaks at 3.08, 8.66, 12.61, 15.38, 17.40, 17.88, 20.19, 22.01,23.83, 29.07, 45.09 ± 2 degrees two-theta. 10. The crystalline solid Amifostine dihydrate of claim 5 is characterized by moisture content of 12.5-14.5% (w/w). 11. A novel process for the manufacture of high purity Amifostine dihydrate of the formula-I, which comprises: (i) reacting 2-(3-aminopropylamino) ethyl bromide dihydrobromide of formula-Ill with thiophosphoryl chloride of formula VII dissolved in alkali metal hydroxide solution (or) by reacting 2-(3-aminopropylamino)ethyl bromide dihydrobromide of formula III with trisodium phosphorothioate dodecahydrate of formula (VI) in aqueous (ii) isolation of Amifostine dihydrate from aqueous solution by addition of solvents such as a lower alcohol or a ketonic solvent or an ester of lower alcohol or a dipolar aprotic solvent. (iii) purification of the resulting Amifostine dihydrate by dissolving it in water at 35-40° C, decolorizing with activated carbon and adding a lower alcohol or a ketonic solvent or an ester or lower alcohol or a dipolar aprotic solvent at 25-30° C and allowing the resulting clear solution to cool to 0-5° C following by filtration to get high purity Amifostine dihydrate of formula-I meeting the pharmacopoeial requirements. 12. A novel process for Amifostine dihydrate (I) as claimed in claim (11) where in the alkali metal hydroxide in step (i) is selected from sodium hydroxide or potassium hydroxide or lithium hydroxide. 13. An alternate novel process for Amifostine dihydrate (I) as claimed in claim (11) where in step (i) the solvent medium is selected from water. 14. A novel process for Amifostine dihydrate (1) as claimed in claims 11-13 where in isolation of Amifostine dihydrate from aqueous solution in step (ii) is carried out by addition of solvents like methanol, ethanol, isopropyl alcohol or a ketonic solvent like acetone or an aliphatic ester like ethyl acetate or dipolar aprotic solvents like acetonitrile or tetrahydrofuran. 15. An improved process for Amifostine dihydrate of formula (I) as claimed in claims 11-14, where in purification of Amifostine dihydrate in step (iii) is carried out by dissolving the product in water at 35-40° C, decolorizing the resulting solution with activated carbon at 20-30° C followed by filtration and crystallization of Amifostine dihydrate by the addition of lower alcohols like methanol, ethanol, isopropyl alcohol or ketonic solvent like acetone or an aliphatic ester like ethyl acetate or a dipolar aprotic solvents like acetonitrile or tetrahydrofuran. 16. A novel process for Amifostine dihydrate of formula (I) as claimed in claims 11-15 where in the purity of Amifostine dihydrate (I) is 99.9-99.95 by HPLC. 17. A novel process for Amifostine dihydrate of formula (I) as claimed in claims 11-16, where in the thiol impurity of formula (VIII) does not exceed 0.05% by HPLC. 18. A novel process for Amifostine dihydrate of formula (I) as claimed in claims 11-17 where in the purity of Amifostine dihydrate (I) complies the pharmacopoeial requirements specified in USP-28. 19. A novel process for the manufacture of high purity Amifostine dihydrate of formula (I) substantially as reported here in with reference to examples 1-5. 20. A novel dihydrate form of Amifostine of formula-I having pharmaceutical application.

Documents:

0306-che-2006 abstract 09-02-2007.pdf

0306-che-2006 claims 09-02-2007.pdf

0306-che-2006 drawings 09-02-2007.pdf

0306-che-2006 description(complete) 09-02-2007.pdf

0306-che-2006 form-2 09-02-2007.pdf

306-CHE-2006 AMENDED PAGES OF SPECIFICATION 21-09-2011.pdf

306-CHE-2006 AMENDED CLAIMS 21-09-2011.pdf

306-CHE-2006 AMENDED PAGES OF SPECIFICATION 02-04-2012.pdf

306-CHE-2006 AMENDED CLAIMS 02-04-2012.pdf

306-CHE-2006 CORRESPONDENCE OTHERS 02-04-2012.pdf

306-CHE-2006 DRAWINGS.pdf

306-CHE-2006 DRAWINGS.tif

306-CHE-2006 EXAMINATION REPORT REPLY RECEIVED 21-09-2011.pdf

306-CHE-2006 FORM-3 02-04-2012.pdf

306-che-2006-description(provisional).pdf

306-che-diagrams.pdf

306-che-form 1.pdf

306-correspondence-others.pdf

abs-306-che-2006.jpg