Title of Invention	AN IMPROVED AND EFFICIENT PROCESS FOR THE PREPARATION OF MYCOPHENOLATE MOFETIL
Abstract	The present invention relates to an improved and efficient process for the preparation of Mycophenolate Mofetil in a high degree of pharmaceutically acceptable purity, which comprises the reaction of Mycophenolic acid or esters, or acid chlorides, or amides with metal salt of morpholino ethanoL A further aspect of the invention relates to the purification of Mycophenolate mofetil through salt formation and release of the free base which on recrystalized from suitable solvents to get highly pure Mycophenolate mofetil. The present invention provided a novel intermediate and process for preparation thereof. Also provided is new impurity of Mycophenolate mofetil and process for preparation thereof.

Title of Invention

AN IMPROVED AND EFFICIENT PROCESS FOR THE PREPARATION OF MYCOPHENOLATE MOFETIL

Abstract

The present invention relates to an improved and efficient process for the preparation of Mycophenolate Mofetil in a high degree of pharmaceutically acceptable purity, which comprises the reaction of Mycophenolic acid or esters, or acid chlorides, or amides with metal salt of morpholino ethanoL A further aspect of the invention relates to the purification of Mycophenolate mofetil through salt formation and release of the free base which on recrystalized from suitable solvents to get highly pure Mycophenolate mofetil. The present invention provided a novel intermediate and process for preparation thereof. Also provided is new impurity of Mycophenolate mofetil and process for preparation thereof.

Full Text	FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & The Patent Rules, 2003 COMPLETE SPECIFICATION (See section 10 and rule 13) TITLE OF THE INVENTION "AN IMPROVED AND EFFICIENT PROCESS FOR THE PREPARATION OF MYCOPHENOLATE MOFETIL" We, CADILA HEALTHCARE LTD., a company incorporated under the Companies Act, 1956, of Zydus Tower, Satellite Cross Roads, Ahmedabad - 380 015, Gujarat, India. The following specification particularly describes the nature of the invention and the manner in which it is to be performed: FIELD OF INVENTION The present invention discloses improved processes for preparing Mycophenolate Mofetil using basic reaction conditions, which reduces the reaction time and improves the purity of the product BACKGROUND OF THE INVENTION Mycophenolate mofetil is the morpholinoethyl ester of Mycophenolic acid; it has the following formula (I). Mycophenolate mofetil Mycophenolate mofetil is an immunosuppressant. It is derived from mycophenolic acid which was isolated from a fungus and chemically modified to improve oral absorption. Mycophenolate mofetil and its pharmaceutically acceptable salt thereof is used as an immunosuppressive agent, anti-inflammatory, anti-tumor and anti-viral agent. US 4753935 discloses Mycophenolate mofetil and also describes three different routes for synthesis. One of the routes disclosed therein is an acid halide condensation route (Scheme-1), which requires two steps and has a high dimeric impurity content, requiring a subsequent recrystallization step. Color problem with the finished product is also associated with this synthetic route due to trace iron contamination. Use of thionyl chloride for preparation of the acid chloride causes corrosion of plant and reactors. A second carbodiimide route is also disclosed in the same patent. This route has proven impractical for the synthesis of pharmaceutical grade Mycophenolate mofetil due to unacceptable percentage of impurity in the final product. Preparation of Mycophenolate mofetil via the direct esterification of mycophenolic acid in organic solvents that are capable of removing water during the course of the reaction is also disclosed in various patents. Thus, US Patent No. 5,247,083 describes preparation of Mycophenolate mofetil by refluxing Mycophenolic acid (MPA) and 2-rnorpholinoethanol in solvents such as toluene, xylene and dichloromethane or their mixtures with azeotropic water separation. The disadvantages of this process are long reaction period necessary to reach sufficient conversion depending on the solvent used (about 60 to 100 hrs) and presence of color in the product (light violet crystal). WO 0034503 discloses biochemical synthesis of Mycophenolate mofetil as well as chemical synthesis of Mycophenolate mofetil without the use of catalyst. The synthesis according to this specification also takes a long time, in hours or days for completion and when converting MPA to Mycophenolate mofetil, it was observed that a large part of the MPA is left unconverted, and impurities are formed. WO 02100855 teaches the use of high boiling dialkyl ethers such as dibutyl ether as solvents. This route also suffers from the disadvantages described above like long reaction periods and formation of colored Mycophenolate mofetil. WO 2004089946 disclosed synthesis of Mycophenolate mofetil using microwave irradiation. Obviously, the process is costly and difficult to practice on an industrial scale. WO 2003042393, WO 2000034503 and WO 2006024582 describes synthesis of Mycophenolate mofetil using enzyme as catalyst but there are several disadvantages of the use of enzymatic catalysis on an industrial scale, for instance in terms of volume, work-up and overall cost. US 20040167130 discloses a process for making Mycophenolate mofetil comprising the transesterification of mycophenolic acid with 2-(4-morpholinyl) ethanol using a catalyst selected from an alkaline or alkaline earth metal salt, tin oxide or stannous oxide. This method suffer from the disadvantage that the document only describes the use of one catalyst, dibutyl tin oxide, which is highly toxic, an irritant and expensive. No other alkaline or alkaline earth metal catalyst is used and no other examples are provided in the application. WO 2005023791 describes a process for making Mycophenolate mofetil as well as purification of Mycophenolate mofetil by treating it with a primary or secondary amine. In this process also the reaction takes place under acidic reaction condition. WO 2006076802 describes a process for making Mycophenolate mofetil using Zn and Ca salt or oxide as catalyst but this route also suffer from the disadvantage like long reaction time. WO 2005105769 (Teva) discloses a compound 2-(4-morpholinyl)ethyl(E)-6-(l,3-dmydro-4[2-(4-morpholinyl)emoxy]-6-memoxy-7-memyl-3-oxo-isoberizofuran-5-yl)-4-methyl-hex-4-enoate, as an impurity of Mycophenolate mofetil and a process for preparing the said impurity. However, no process for removal of the impurity is provided. WO 2008015693 (Concord Biotech) discloses an improved process for making Mycophenolate mofetil by reacting mycophenolic acid with 2-(4-morpholinyl) ethanol in presence of dipyridyl carbonate. This process also requires almost 24 hours for completion of the reaction. Thus, there remains a need for developing a process which overcomes one or more of the deficiencies of the prior art and thereby develop a modified process for preparing Mycophenolate mofetil which gives better yields, improved purity and reduces the overall reaction time. Further, in the prior art most or all the processes for making Mycophenolate mofetil take place under acidic or thermal reaction conditions. We herein disclose an improved process for preparing Mycophenolate mofetil using basic reaction conditions, which reduces the reaction time substantially and gives better purity. All of these makes the present process more commercially viable. OBJECTS OF THE INVENTION The objects of the present invention is to provide an improved process for preparing Mycophenolate mofetil. In an embodiment is provided a process for preparing Mycophenolate mofetil under basic conditions. In a further embodiment is provided a process for preparing Mycophenolate mofetil using new intermediates. In another aspect, the invention provides a novel intermediate for preparation of Mycophenolate mofetil and process for preparation of that novel intermediate. In another aspect, the invention encompasses 5-Methoxy-4-methyl-6-[2-(2rmethyl-5- oxo tetrahydro-furan-2-yl)-emyl]-7-(2-morpholin-4-yl-ethoxy)-3H-isobenzofuran-1-one (Compound-V) as a new impurity of Mycophenolate mofetil. In another aspect, the invention is directed to a process for synthesizing Compound-V. In yet another aspect, the invention encompasses Mycophenolate mofetil having an amount of compound V at about 0.01 to about 0.6% area by HPLC. In yet another aspect, the invention encompasses process for removal of Compound-V to obtain pure Mycophenolate mofetil. The above and other embodiments are further described in the following paragraphs. BRIEF DESCRIPTION OF THE FIGURES Fig. 1 is a representative 1H NMR spectrum for Compound V. Fig. 2 is a representative 13 C NMR spectrum for Compound V. Fig. 3 is a representative 1H NMR spectrum for Compound III. Fig. 4 is a representative 13C NMR spectrum for Compound HI. DETAILED DESCRIPTION The present invention provides an improved process for preparing Mycophenolate mofetil as described in the following Scheme 2: Step A: The hydroxy ethyl morpholine [(H), HEM, also referred to as 4-(2-hydroxyethyI)morpholine in the specification] was converted to the corresponding metal salt (III) by reacting with alkali metal in suitable alcohols preferably straight or branched chain (C1-C7) alcohols, more preferably straight or branched chain (C1-C6) alcohols, most preferably (C1-C4) alcohols. Subsequently excess alcohol was removed under reduced pressure. Step B: The metal salt thus obtained was reacted with compound of the formula (IV) wherein, 'Lv' is selected from carboxylic acid, esters, acid chlorides and amides, in suitable organic solvent(s). Suitable organic solvents may be selected from suitable hydrocarbons such as hexane, heptane, benzene, toluene, xylene, ethyl benzene, trimethyl benzene, duran, cyclohexane, eycloheptane or suitable halogenated solvents such as chloroform, dichloromethane, dichloroethane and the like or mixtures thereof. Preferably solvent can be selected from the group comprising of toluene, xylene, hexane, heptane, benzene, cyclohexane and the like or mixtures thereof. The reaction was carried out at temperature ranging from room temperature to reflux temperature of particular solvent used under anhydrous conditions to get E-6-(l,3-dihydro-4-hydroxy-6methoxy-7-methyl-3-oxo-5-isobenzofuranyl)-4-methyl-4-hexenoic acid 2-morpholin-4-yl-ethyl ester (Mycophenolate mofetil). In a preferred embodiment, Compound of formula (IV), represents alkyl esters of Mycophenolic acid. More preferably, alkyl ester of Mycophenolic acid is selected from (C1-C4) alkyl ester. The invention also provides a process for preparing metal salt of hydroxy ethyl morpholine. The hydroxy ethyl morpholine was converted to the corresponding metal salt by reacting it with alkali metal in suitable alcohols. Subsequently excess of alcohol was removed under reduced pressure. The invention also provides a novel intermediate 2-Morpholin-4-yl-potassium ethoxide, which was characterized as follows: % K(potassium)- 23-25 % (By acid / base titration), 13C Chemical Shift (67.6609, 61.7797, 59.5754, 55.0644) (Fig.4) and lH NMR spectrum is given below (Fig.3). lH -d(ppm) Hydrogen CHa 3.538(t) 1 2CH2 3.491(t) l1 CH2 2.350(t) 2 2CH2 2.312(t) 2l CH2 Surprisingly, it was found that when the reaction was carried out using the Compound "III, the reaction time was reduced substantially (from 16-24 hours reported earlier, to less than 2 hours in most of the cases as described below). In order to obtain marketing approval for a new drug product, manufacturers must submit to the regulatory authority evidence that the product is acceptable for administration to humans. Such a submission must include impurity profile of the product to demonstrate that the impurities are either absent, or present in a negligible amount. Different regulatory authorities have promulgated guidelines requiring applicants to identify the impurities present in the product and also disclose their concentration in the product. They also provide the maximum level of impurities allowable in the product. Thus for e.g. USFDA recommends that drug applicants identify all the impurities having concentration of 0.1 % or greater, in the active ingredient. Therefore, there is a need to check impurity profile and identify the impurities and also their concentration in the active ingredient. PHARMAEUROPA vol. No. 15, 4-October, 2003 lists eight possible impurities of Mycophenolate mofetil (from A to H). Subsequently, Teva in their patent application (WO2005105769) have disclosed one new impurity of Mycophenolate mofetil. Surprisingly, the present inventors have found that by the process of preparation of the present invention as described in Scheme 2, a new impurity was being formed not known earlier. The present invention thus provides a new impurity of Mycophenolate mofetil (MMF), Compound V and having chemical name 5-Methoxy-4-methyl-6-[2-(2-methyl-5-oxo-tetrahydro-furan-2-yl)-emyl]-7-(2-morpholin-4-yl-ethoxy)-3H-isobenzofuran-1-one, and has the following chemical structure: The Compound V was characterized by the following data: Compound V has the following 1H NMR (300MHz, CDC13) d (ppm): 1.3511(s), 1.8524(t), 1.9565(m), 2.1270(s), 2.491 l(t), 2.610(t), 2.785(q), 3.6933(t), 3.795(s), 4.1784(dt), 5.0735(s) (Fig.l). 13C NMR (75MHz, CDC13) d (ppm): 10.989, 17.175, 23.492, 28.424, 30.640, .34.216, 53.811, 57.047, 60.121, 61.571, 66.878, 67.901, 76.130, 108.673, 115.218, 115.51, 147.144, 152.318, 161.990, 168.851,173.604 (Fig.2). I.R. (3018.4cm-1, 2860.2cm-1,1759.0cm-1, 1606.6cm-1,1282.6cm-1,1082cm-1, 740.6 cm-1). MS data for Compound V is given below. Peak Report Assignation Mmonois Calculated (Da) M measured (Da) [M+H]+ 434.34 434.0 [M+Na]+ 456,34 456.0 In another aspect, the invention encompasses a process for synthesizing Compound V by reacting Mycophenolic acid (VII) with 2-morpholin-4-yl-ethanol (II) in presence of suitable acid catalyst. Scheme-4 2-morpholin-4-yl-ethanol (II) was dissolved in excess of suitable solvent(s), to it was added suitable catalysts such as p-toluene sulfonic acid (PTSA) and the reaction mixture was stirred. Subsequently, Mycophenolic acid (VII) was added into it and the reaction mixture was further stirred under Dean Stark trap and solvent was removed continuously. The organic solvents used in above reaction may be selected from hydrocarbons such as hexane, heptane, benzene, toluene, xylene, ethyl benzene, trimethyl benzene, duran, cyclohcxanc, cyclohcptanc or halogcnated solvents such as chloroform, dichloromethane, dichloroethane and the like or mixtures thereof and more preferably toluene. The reaction is carried but at temperature ranging from room temperature to about reflux temperature of the solvents used under anhydrous condition and more preferably in the range of 160-180 °C. ' In an embodiment the invention encompasses Mycophenolate mofetil (I) having an amount of Compound V at about 0.01 to about 0.6% area by HPLC. This Mycophenolate mofetil (I) can be prepared according to the process described above and % impurity that was generated when using different solvent(s) and also using different reaction conditions are given below (Table-1). Table-1 Starting HEM Solvent Temperature Reaction Impurity After Material Mol. Equiv. as its alkali metal salt °C Time % (Compound V) purification % purity of MMF*by HPLC (Compound I) Methyl ester 1.3 Toluene 110 2h 0.13 99.9 of MP A ¦ • Methyl ester 1.3 Xylene 145 50 min 0.23 > 99.9 of MP A Methyl ester 1.3 Cyclohexane 80 10-12 h 0.03 99,9 ofMPA Methyl ester 1.3 Benzene 60 2h 0,10 .99.9 ofMPA Methyl ester 1.3 Toluene: 145 50 min 0.40 > 99.9 ofMPA Xylene ¦ - # MMF-Mycophenolate mofetil In an embodiment the invention encompasses process for purification of Mycophenolate mofetil having 0.01 to about 0.6 % total impurity. The process of purification comprises dissolving Mycophenolate mofetil having 0.01 to about 0.6% total impurity in dilute organic acid solution to obtain a clear solution, which was washed with suitable solvent such as xylene or toluene or mixtures thereof and basified with suitable aqueous solution of base and further recrystalized from suitable solvents selected from ethers, esters, ketones and mixtures thereof, more preferably ethers to obtained highly pure Mycophen lolate mofetil. The dilute organic acid used in the purification step is citric acid and base used is selected from suitable carbonate, bicarbonate or alkali base. In an embodiment, the invention encompasses Mycophenolate mofetil having at least 99.9 % purity by HPLC (as per table-1) prepared according to the process of the present invention. The invention is further described by the following non-limiting example, which is provided for illustration only and should not be construed to limit the scope of invention Example 1 Preparation of E-6-(l,3-dihydro-4-hydroxy-6methoxy-7-methyl-3-oxo-5- isobenzofuranyl)-4-methyl-4-hexenoic acid 2-morpholin-4-yl-ethyI ester. To a cooled solution (0-4 °C) of freshly prepared sodium methoxide in methanol (0.525 g), 4-(2-hydroxyethyl)morpholine (1.28g) was added and stirred at room temperature for 30 min. to 1 hrs. Subsequently excess of solvent was distilled out at reduced pressure to obtain 2-Morpholin-4-yl-sodium.ethoxide as viscous mass which was dissolved in toluene, to it was added 2.50g of 6-(l,3-dihydro-4-hydroxy-6-methoxy-7-methyl-3-oxo-5-isobenzofuranyl)-4-methyl-4-hexenoic acid methyl ester at 110 °C temperature with constant removal of solvent under Dean Stark trap for upto 2hr. It was cooled at room temperature. The reaction mixture was dumped into water, extracted with ethyl acetate and organic layer was separated. Aqueous layer was again extracted with ethyl acetate. The combined organic extracts were washed with water, dried and concentrated under reduced pressure to get E-6-(l,3-dihydro-4-hydroxy-6methoxy-7-memyl-3-oxo-5-isobenzofuranyl)-4-methyl-4-hexenoic acid 2-morpholin-4-yl-ethyl ester (Mycophenolate mofetil, Yield-80%). [% purity by HPLC=99.01%, HPLC Impurity Profile-Compound V=0.13%, Methyl ester of MPA-0.3%] Purification: Mycophenolate mofetil compound with 0.01-0.6 % total impurity (different batches as obtained above) was dissolved in aqueous solution of citric acid (citric acid-1.5mol equivalent). Clear solution was obtained which was washed with toluene and passed through hyflow and basified with aqueous sodium bicarbonate solution till pH-7-8. Solid obtained was filtered off and suck dried. The solid thus obtained was further purified by recrystallization from MTBE to get atleast 99.9% pure Mycophenolate mofetil or Mycophenolate mofetil without any detectable level of impurity. Example 2 Preparation of E-6-(13-dihydro-4-hydroxy-6methoxy-7-methyl-3-oxo-5- isobenzofuranyl)-4-methyI-4-hexenoic acid 2-morphoIin-4-yI-ethyI ester. In a round bottom flask 20ml of methanol was taken and 0.97mg sodium pieces were added at room temperature till it was dissolved. Subsequently, 4-(2-hydroxyethyl)morpholine (5.52g) was added at 0 °C and stirred the reaction mixture at 25 °C for 30min to 1hrs. Then excess of solvent was distilled out to obtain a viscous mass, which was dissolved in xylene. To it was added 10.82g of methyl ester of mycophenolic acid at 110 °C. Continuous removal of xylene, with continuous addition of fresh xylene was done at 145 °C forupto 50 minutes under Dean Stark assembly. Subsequently, the reaction mixture was cooled to 25-30 °C, dumped into water and xylene layer was separated out. Aqueous layer was further extracted with ethyl acetate. Organic layers obtained were combined, dried over sodium sulphate and distilled off to get Mycophenolate mofetil. (Yield 80%). [% purity by HPLC of Mycophenolate=99.1%, Compound V by HPLC -0.23%] Purification of Mycophenolate mofetil obtained above is carried out in a similar way as disclosed in Example-1, to obtain highly pure Mycophenolate mofetil. Example 3 Preparation of E-6-(13-dihydro-4-hydroxyr-6methoxy-7-methyl-3-oxo-5- isobenzofuranyl)-4-methyl-4-hexenoic acid 2-morpholin-4-yl-ethyl ester. To a freshly prepared sodium methoxide (0.525g) in methanol, 4-(2-hydroxyethyl)morpholine (1.275g) was added at 0-4 °C. It was stirred at room temperature for 30 min. to 1 hrs. and subsequently excess of solvent was distilled out under reduced pressure to obtain a viscous mass. To it was added a solution of methyl ester of mycophenolic acid (2.5g) in cyclohexane (10ml) at 80 °C with constant removal of solvent under Dean Stark trap for 8-12hrs. It was cooled to room temperature and dumped into water. Cyclohexane layer was separated out and aqueous layer extracted with ethyl acetate. Combined organic layers were dried and concentrated to obtain Mycophenolate mofetil. [% purity by HPLC of Mycophenolate mofetil=99.06%, Compound V by HPLC=0.03%] Purification of Mycophenolate mofetil obtained above is carried out in a similar way as disclosed in Example-1, to obtained highly pure Mycophenolate mofetil. Example 4 Preparation of E-6-(l,3-dihydro-4-hydroxy-6methoxy-7-methyl-3-oxo-5- isobenzofuranyl)-4-methyl-4-hexenoic acid 2-morpholin-4-yl-ethyl ester. 6.7g of freshly prepared sodium ethoxide in ethanol was taken and 12.75g of 4-(2-hydroxyethyl)morpholine was added at 0 °C and it was kept under stirring for 30 min to 1 hrs. at 25 °C. Subsequently excess of ethanol was distilled out to obtain 2-Morpholin-4-yl-sodium o ethoxide and into it 250 ml of toluene:xylene (50:50) mixture was added at 70 C. 25g methyl ester of mycophenolic acid was added in to the reaction mixture and the temperature of reaction mixture was gradually increased to 145 °C. Solvents were distilled out continuously with continuous addition of toluene:xylene (50:50) mixture at 145 °C for 50 min. After 50 min. reaction mixture containing 100ml toluene:xylene (50:50) mixture was cooled to room temperature and dumped into water. Organic layer was separated and aqueous layer extracted with ethyl acetate. Organic layers were combined, dried and distilled out to get Mycophenolate mofetil. [Yield 85%, % purity by HPLO 99.2%, Compound V= 0.40%]. Purification of Mycophenolate mofetil obtained above is carried out in a similar way as disclosed in Example-1, to obtain highly pure Mycophenolate mofetil. Example 5 Preparation of E-6-(l,3-dihydro-4-hydroxy-6methoxy-7-methyI-3-oxo-5- isobenzofuranyl)-4-methyl-4-hexenoie acid 2-morpholin-4-yl-ethyl ester. Into freshly prepared sodium tert. butoxide (5.85g), 8.1g of 4-(2-hydroxyethyl)morpholine was added at 0 °C and stirred for 30 min. to 2-hrs. to obtain 2-Morpholin-4-yl-sodium ethoxide. To it was added 150ml of benzene at 60 C. To this mixture, 15.7g of methyl ester of MPA was added, and subsequently reaction mixture was heated at 80 °C with constant removal of solvent under Dean Stark trap for 2hrs. It was cooled at room temperature and reaction mixture was dumped into water. The benzene layer was separated out and aqueous layer was extracted with ethyl acetate. Organic layers were combined, dried and distilled out. [Yield: 70 % purity by HPL099.13%, Compound V=0.22%.] Purification of Mycophenolate mofetil obtained above is carried out in a similar way as disclosed in Example-1, to obtain highly pure Mycophenolate mofetil. Example 6 Preparation of E-6-(l,3-dihydro-4-hydroxy-6methoxy-7-methyI-3-oxo-5- isobenzofuranyl)-4-methyl-4-hexenoic acid 2-morpholin-4-yl-ethyl ester. 31.9 g 4-(2-hydroxyethyl)morpholine was added to 13.125g sodium methoxide in methanol at 0-4 °C, and then further stirred for 30 min to 1 hrs. at 25 -30 °C. Excess of solvent was distilled out at reduced pressure and methyl ester of Mycophenolic acid (62.5g) in 250 ml toluene was added at 135 -145 °C. The reaction mixture was refluxed with constant removal of solvent under Dean Stark trap for 2 hrs and cooled at room temperature. After suitable work up (in a similar way as per example 1) Mycophenolate mofetil was obtained. [Yield=82%, % purity by HPLC 99.05%, Compound V=0.52%] Purification of Mycophenolate mofetil obtained above is carried out in a similar way as disclosed in Example-1, to obtained highly pure Mycophenolate mofetil. Example 7 Preparation of E-6-(l,3-dihydro-4-hydroxy-6methoxy-7-methyl-3-oxo-5- isobenzofuranyl)-4-methyl-4-hexenoic acid 2-morpholin-4-yl-ethyl ester. Into freshly prepared potassium tert. butoxide (6.83g), 8.1g of 4-(2-hydroxyethyl)morpholine was added at 0 °C and stirred for 30 min. to 2-hrs, to obtain 2-Morpholin-4-yl-potassium ethoxide and into it 150ml of benzene was added at 60 °C. To the mixture, 15,7g of methyl ester of MPA was added, and subsequently reaction mixture was heated at 80 °C with constant removal of solvent under Dean Stark trap for 2hrs. It was cooled to room temperature and reaction mixture was dumped into water. Benzene layer was separated out and aqueous layer was extracted with ethyl acetate. Organic layers were combined, dried and distilled out to get Mycophenolate mofetil. [Yield:71 % purity by HPLC=99.14% Compound V=0.28%], Purification of Mycophenolate mofetil obtained above is carried out in a similar way as disclosed in Example-1, to obtain highly pure Mycophenolate mofetil. Example 8 Preparation of E-6-(l,3-dihydro-4-hydroxy-6methoxy-7-methyl-3-oxo-5- isobenzofuranyl)-4-methyl-4-hexenoic acid 2-morpholin-4-yl-ethyl ester. 1.09g of freshly prepared sodium methoxide (in methanol) was dissolved in 25 ml toluene. Then into it 2.62% of 4-(2-hydroxyethyl)morpholine was added and stirred for 30min. to lhr. at room temperature. Further reaction mixture was stirred for 30min-lhrs. at 70 °C to give a clear solution of 2-Morpholin-4-yl-sodium ethoxide. In a separate round bottom flask 5g of Mycophenolic acid and 10ml of toluene was taken, equipped with Dean Stark assembly and it was heated at 110 °C. Then into it a solution of 2-Morpholin-4-yl-sodium ethoxide in toluene was added drop wise with constant removal and addition of fresh toluene under Dean Stark trap for 30min. to 80 min., after that removal of toluene stopped and reaction mass left at this temperature for 4hr. TLC checked, for reaction completion. From reaction mass toluene was removed and water was added. Then reaction mass was extracted thrice with ethyl acetate. Combined organic layers were dried over sodium sulphate and distilled out under reduced pressure at 40 °C. Purification of Mycophenolate mofetil obtained as above is carried out in a similar way as disclosed in Example-1, to obtained highly pure Mycophenolate mofetil. [Yield-70%, HPLC Purity- 99.8%] Example 9 Preparation of E-6-(l,3-dihydro-4-hydroxy-6methoxy-7-methyl-3-oxo-5- isobenzofuranyl)-4-methyl-4-hexenoic acid 2-morpholin-4-yl-ethyl ester. In a round bottom flask Mycophenolic acid (5g) was dissolved into 40ml DCM and into it 1-2 drops of DMF was added at room temperature, then thionyl chloride(l,71ml) was added at 10 °C and reaction mixture was stirred at 25 °C for 3hr. Excess of solvent and volatile impurities were removed by distillation under reduced pressure to get acid chloride of Mycophenolic acid (5.29g). In a separate round bottom flask l.lg of sodium methoxide in 20ml toluene was taken, 2,67g of 2-morpholin-4-yl-ethanol was added and stirred for 30 min. to 1-hrs. at 25 °C. Further the reaction mixture was stirred for 30 min to 1 hrs. at 70 °C to give a clear solution of 2-Morpholin-4-yl-sodium ethoxide. 5.29g of acid chloride of Mycophenolic acid was dissolved in 10ml toluene and into it clear solution of 2-Morpholin-4-yl-sodium ethoxide was added dropwise at 110 °C. and refluxed for 4hr. TLC checked for the completion of reaction. Reaction mass dumped into water and toluene layer was separated. Aqueous layer extracted twice with ethyl acetate. All organic layers were combined, dried over sodium sulphate and distilled out under reduced pressure. Oily mass obtained was dissolved in 3% aqueous HC1 solution, when a clear solution was obtained which was washed with toluene. Aqueous layer was basifled with sodium bicarbonate solution till pH-7.2. The solid obtained was filtered off, suck dried to obtain Mycophenolate mofetil. Purification of Mycophenolate mofetil obtained as above is carried out in a similar way as disclosed in Example-1, to obtain highly pure Mycophenolate mofetil. [Yield-69%, HPLC Purity- 99.7%] Example 10 Preparation of 2-Morpholin-4-yl-potasslum ethoxide 1.64 g potassium metal is dissolved in 20ml of methanol, 5.52g of 4-(2-hydroxyethyl)morpholine is added at 0 °C, stir for 30 min. to 2 hrs. and subsequently excess methanol is distilled out. The 2-Morpholin-4-yl-potassium ethoxide obtained is characterized by potassium ion analysis and NMR data (traces of methanol remains). % potassium = 23-25 % (By acid /base titration). Example 11 Preparation of 2-MorphoIin-4-yl- potassium ethoxide Into 10 ml t-butanol, 0.43 g of potassium metal is dissolved at room temperature and to it was added 1.44g of 2-morpholin-4-yk-ethanol at 0 °C, stirred for 30min. to 2hrs. and subsequently excess of t-butanol is distilled out to give 2-Morpholin-4-yl-potassium ethoxide in 100% yield, which was characterized by potassium ion analysis and NMR data (traces of methanol remained) (Figure 3). % potassium = 23-25 % (By acid /base titration). Example 12 Preparation of 2-Morpholin-4-yI- potassium ethoxide 0.3 8g potassium metal is dissolved in 10ml of ethanol, 1.28g 4-(2-hydroxyethyl)morpholine was added at 0 C, stirred for 30 min. to 2 hrs. and subsequently excess ethanol was distilled out to give 2-Morpholin-4-yl-potassium ethoxide (Yield 100%) which was characterized by potassium ion analysis and NMR data. % potassium = 23-25 % (By acid /base titration) Example 13 Preparation of 5-methoxy-4-methyI-6-[2-(2-methyl-5-oxo-tetrahydro-furan-2-yl)-ethyl]-7-(2-morpholin-4-yl-ethoxy)-3H-isobenzofuran-l-one(Impurity-compound V) 5.24 g 4-(2-hydroxyethyl)morpholine was dissolved in 2.5 ml toluene and 9.48 g of p-toluene sulfonic acid was added, stirred for 5-10min. at 70 °C and subsequently 6.4g of Mycophenolic acid was added. Reaction mixture was stirred for 9hr under Dean Stark trap at 130 °C. For initial lhr, toluene was continuously removed. After nine hours, reaction mixture was dumped into dilute sodium bicarbonate solution and toluene layer was separated out. Subsequently aqueous layer was again washed with ethyl acetate. Combined organic layer was dried and distilled off to get 98 % pure 5-methoxy-4-methyl-6-[2-(2-methyl-5-oxo-tetrahyoVo-ruran-2-yl)-emyl]-7-(2-moipholm-4-yl-emoxy)-3H-isobenzofuran-l-one(Compound V), which on purification gave Compound-V with more than 99% purity. Benefits of the present process: The improved process of the present invention has the following advantages: 1. It uses basic reaction conditions, which reduces the reaction time substantially; 2. The process gives Mycophenolate mofetil with very high purity; 3. It identifies a new impurity of Mycophenolate mofetil and also discloses a process for purification of the impurity. We Claim: 1. A process for the preparation of Mycophenolate mofetil of formula-(I) comprising: (a) reacting a compound of formula-(IV) with metal salt of hydroxy ethyl morpholine of formula-(III), wherein, Lv is selected from carboxylic acid, esters, acid chlorides or amides; and (b) if desired, purifying compound (I). 2. The process as claimed in claim 1, wherein said metal is an alkali metal selected from lithium, sodium or potassium. 3. The process as claimed in claim 1 or 2. wherein reaction is carried out in organic solvents selected from the group comprising of hydrocarbons or halogenated solvents or their mixtures. 4. The process as claimed in claim 3, wherein said hydrocarbon is selected from hexane, heptane, benzene, toluene, xylene, ethyl benzene, trimethyl benzene, duran, cyclohexane, cycloheptane or their mixtures. 5. The process as claimed in any preceding claim, wherein the reaction is carried out at temperature ranging from room temperature to reflux temperature of the solvents used. 6. The process as claimed in claim 5, wherein the temperature range is from 40-200°C. 7. The process as claimed in claim 1. wherein the compound of formula-(III) is prepared by treating a compound of formula-(II) with an alkali metal in an organic solvent. The process as claimed in claim 7, wherein organic solvent is (C1-C7) alcohols, preferably selected from (C1-C6) alcohols, most preferably selected from methyl alcohol or butyl alcohol. 9. The process as claimed in claim 7, wherein 2-morpholin-4-yl-ethanol is added at 0-5°C. 10. The process as claimed in claim 1. wherein the leaving group is an alkyl ester selected from (C1-C4) alkyl ester, more preferably methyl ester. 11. The process as claimed in any preceding claim, wherein the leaving group is an acid chloride. 12. The process as claimed in claim 1, wherein the leaving group is a carboxylic acid. 13. The process as claimed in claim 1, wherein the leaving group is a carboxamide group. 14. A compound of structural formula-(III): wherein M = K. 15. The compound as claimed in claim 14, characterized by % Potassium = 23-25% by acid /base titration. 16. The compound as claimed in claim 14, characterized by H NMR spectrum as provided in Fig.3 and 13C Chemical Shift as provided in Fig.4. 17. A process for preparing Mycophenolate mofetil of formula (I) using the compound of formula (III) as claimed in any preceding claim. 18. A compound of formula-(V): 19. The compound as claimed in formula (V) as claimed in claim 18, characterized by 1H NMR (300 MHz, CDC13) d (ppm) values of 1.351 l(s), 1.8524(t), 1.9565(m), 2.1270(s), 2.4911(t), 2.610(t), 2.785(q), 3.6933(t), 3.795(s). 4.1784(dt), 5.0735(s). 20. The compound as claimed in claim 18, characterized by 13C NMR (75 MHz, CDCI3) d (ppm) values of 10.989, 17.175, 23.492, 28.424, 30.640, 34.216, 53.811, 57.047, 60.121, 61.571, 66.878, 67.901, 76.130, 108.673, 115.218, 115.51, 147.144, 152.318, 161.990, 168.851, 173.604. 21. The compound as claimed in claim 18, characterized by MS(Da) [M+H]+ 434.0, 456.0 [M+Na]+. 22. The compound as claimed in claim 18, which is an impurity of Mycophenolate mofetil. 23. The impurity as claimed in claim 18 which is obtained in the process of preparing Mycophenolate mofetil as claimed in the present invention, wherein it is present in the range of 0.01 to 0.6 % area by HPLC. 24. A process for preparing compound V comprising reacting 2-morpholin-4-yl-ethanoI of formula-(II) with Mycophenolic acid (VII) in organic solvents and in presence of acid catalyst. 25. The process as claimed in claim 24, wherein reaction is carried out in organic solvents selected from the group comprising of hydrocarbons or halogenated solvents or their mixtures. 26. The process as claimed in claim 24, wherein said acid catalyst is p-toluene sulfonic acid. 27. The process as claimed in claim 24, wherein said reaction is carried out at temperature in the range from room temperature to reflux temperature of the solvents used. 28. The process for purification of Mycophenolate mofetil prepared as claimed in claim 1 comprising the steps of: (a) reacting Mycophenolate mofetil prepared as claimed in the process of claim 1, with dilute aqueous solution of a organic acid; (b) washing the solution with a solvent; (c) basifying the solution with base until pH 7-8; (d) recrystallization of the solid obtained in (c), from solvent to obtain highly pure Mycophenolate mofetil. 29. The process as claimed in claim 28, wherein said aqueous organic acid used in step (a) is citric acid. 30. The process as claimed in claim 28, wherein solvent used for washing in step (b) is selected from toluene or xylene. 31. The process as claimed in claim 28. wherein said aqueous base used in step (c) is selected from carbonate, bicarbonate or alkali base. 32. The process as claimed in claim 28, wherein solvent used for recrystallization in step (d) is selected from ethers, ketones, esters or their mixtures, more preferably ethers. 33. The process as claimed in claim 28, wherein Mycophenolate mofetil obtained is with at least 99.9% purity by HPLC.

Full Text

FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patent Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
"AN IMPROVED AND EFFICIENT PROCESS FOR THE PREPARATION OF
MYCOPHENOLATE MOFETIL"
We, CADILA HEALTHCARE LTD., a company incorporated under the Companies Act, 1956, of Zydus Tower, Satellite Cross Roads, Ahmedabad - 380 015, Gujarat, India.
The following specification particularly describes the nature of the invention and the manner in which it is to be performed:

FIELD OF INVENTION
The present invention discloses improved processes for preparing Mycophenolate Mofetil using basic reaction conditions, which reduces the reaction time and improves the purity of the product BACKGROUND OF THE INVENTION
Mycophenolate mofetil is the morpholinoethyl ester of Mycophenolic acid; it has the following formula (I).

Mycophenolate mofetil
Mycophenolate mofetil is an immunosuppressant. It is derived from mycophenolic acid which was isolated from a fungus and chemically modified to improve oral absorption. Mycophenolate mofetil and its pharmaceutically acceptable salt thereof is used as an immunosuppressive agent, anti-inflammatory, anti-tumor and anti-viral agent. US 4753935 discloses Mycophenolate mofetil and also describes three different routes for synthesis. One of the routes disclosed therein is an acid halide condensation route (Scheme-1), which requires two steps and has a high dimeric impurity content, requiring a subsequent recrystallization step. Color problem with the finished product is also associated with this synthetic route due to trace iron contamination. Use of thionyl chloride for preparation of the acid chloride causes corrosion of plant and reactors.
A second carbodiimide route is also disclosed in the same patent. This route has proven impractical for the synthesis of pharmaceutical grade Mycophenolate mofetil due to unacceptable percentage of impurity in the final product.

Preparation of Mycophenolate mofetil via the direct esterification of mycophenolic acid in organic solvents that are capable of removing water during the course of the reaction is also disclosed in various patents. Thus, US Patent No. 5,247,083 describes preparation of Mycophenolate mofetil by refluxing Mycophenolic acid (MPA) and 2-rnorpholinoethanol in solvents such as toluene, xylene and dichloromethane or their mixtures with azeotropic water separation. The disadvantages of this process are long reaction period necessary to reach sufficient conversion depending on the solvent used (about 60 to 100 hrs) and presence of color in the product (light violet crystal).
WO 0034503 discloses biochemical synthesis of Mycophenolate mofetil as well as chemical synthesis of Mycophenolate mofetil without the use of catalyst. The synthesis
according to this specification also takes a long time, in hours or days for completion and
when converting MPA to Mycophenolate mofetil, it was observed that a large part of the
MPA is left unconverted, and impurities are formed.
WO 02100855 teaches the use of high boiling dialkyl ethers such as dibutyl ether as
solvents. This route also suffers from the disadvantages described above like long reaction
periods and formation of colored Mycophenolate mofetil.
WO 2004089946 disclosed synthesis of Mycophenolate mofetil using microwave
irradiation. Obviously, the process is costly and difficult to practice on an industrial scale.
WO 2003042393, WO 2000034503 and WO 2006024582 describes synthesis of
Mycophenolate mofetil using enzyme as catalyst but there are several disadvantages of the
use of enzymatic catalysis on an industrial scale, for instance in terms of volume, work-up
and overall cost.

US 20040167130 discloses a process for making Mycophenolate mofetil comprising the transesterification of mycophenolic acid with 2-(4-morpholinyl) ethanol using a catalyst selected from an alkaline or alkaline earth metal salt, tin oxide or stannous oxide. This method suffer from the disadvantage that the document only describes the use of one catalyst, dibutyl tin oxide, which is highly toxic, an irritant and expensive. No other alkaline or alkaline earth metal catalyst is used and no other examples are provided in the application.
WO 2005023791 describes a process for making Mycophenolate mofetil as well as purification of Mycophenolate mofetil by treating it with a primary or secondary amine. In this process also the reaction takes place under acidic reaction condition.
WO 2006076802 describes a process for making Mycophenolate mofetil using Zn and Ca salt or oxide as catalyst but this route also suffer from the disadvantage like long reaction time.
WO 2005105769 (Teva) discloses a compound 2-(4-morpholinyl)ethyl(E)-6-(l,3-dmydro-4[2-(4-morpholinyl)emoxy]-6-memoxy-7-memyl-3-oxo-isoberizofuran-5-yl)-4-methyl-hex-4-enoate, as an impurity of Mycophenolate mofetil and a process for preparing the said impurity. However, no process for removal of the impurity is provided.
WO 2008015693 (Concord Biotech) discloses an improved process for making Mycophenolate mofetil by reacting mycophenolic acid with 2-(4-morpholinyl) ethanol in presence of dipyridyl carbonate. This process also requires almost 24 hours for completion of the reaction.
Thus, there remains a need for developing a process which overcomes one or more of the deficiencies of the prior art and thereby develop a modified process for preparing Mycophenolate mofetil which gives better yields, improved purity and reduces the overall reaction time. Further, in the prior art most or all the processes for making Mycophenolate mofetil take place under acidic or thermal reaction conditions. We herein disclose an improved process for preparing Mycophenolate mofetil using basic reaction conditions, which reduces the reaction time substantially and gives better purity. All of these makes the present process more commercially viable. OBJECTS OF THE INVENTION
The objects of the present invention is to provide an improved process for preparing Mycophenolate mofetil.
In an embodiment is provided a process for preparing Mycophenolate mofetil under basic conditions.
In a further embodiment is provided a process for preparing Mycophenolate mofetil using new intermediates.

In another aspect, the invention provides a novel intermediate for preparation of Mycophenolate mofetil and process for preparation of that novel intermediate.
In another aspect, the invention encompasses 5-Methoxy-4-methyl-6-[2-(2rmethyl-5-
oxo tetrahydro-furan-2-yl)-emyl]-7-(2-morpholin-4-yl-ethoxy)-3H-isobenzofuran-1-one
(Compound-V) as a new impurity of Mycophenolate mofetil.
In another aspect, the invention is directed to a process for synthesizing Compound-V. In yet another aspect, the invention encompasses Mycophenolate mofetil having an amount of compound V at about 0.01 to about 0.6% area by HPLC.
In yet another aspect, the invention encompasses process for removal of Compound-V to obtain pure Mycophenolate mofetil.
The above and other embodiments are further described in the following paragraphs. BRIEF DESCRIPTION OF THE FIGURES Fig. 1 is a representative 1H NMR spectrum for Compound V. Fig. 2 is a representative 13 C NMR spectrum for Compound V. Fig. 3 is a representative 1H NMR spectrum for Compound III. Fig. 4 is a representative 13C NMR spectrum for Compound HI.
DETAILED DESCRIPTION
The present invention provides an improved process for preparing Mycophenolate mofetil as described in the following Scheme 2:

Step A: The hydroxy ethyl morpholine [(H), HEM, also referred to as 4-(2-hydroxyethyI)morpholine in the specification] was converted to the corresponding metal salt (III) by reacting with alkali metal in suitable alcohols preferably straight or branched chain (C1-C7) alcohols, more preferably straight or branched chain (C1-C6) alcohols, most preferably (C1-C4) alcohols. Subsequently excess alcohol was removed under reduced pressure.
Step B: The metal salt thus obtained was reacted with compound of the formula (IV) wherein, 'Lv' is selected from carboxylic acid, esters, acid chlorides and amides, in suitable organic solvent(s). Suitable organic solvents may be selected from suitable hydrocarbons such as

hexane, heptane, benzene, toluene, xylene, ethyl benzene, trimethyl benzene, duran, cyclohexane, eycloheptane or suitable halogenated solvents such as chloroform, dichloromethane, dichloroethane and the like or mixtures thereof. Preferably solvent can be selected from the group comprising of toluene, xylene, hexane, heptane, benzene, cyclohexane and the like or mixtures thereof. The reaction was carried out at temperature ranging from room temperature to reflux temperature of particular solvent used under anhydrous conditions to get E-6-(l,3-dihydro-4-hydroxy-6methoxy-7-methyl-3-oxo-5-isobenzofuranyl)-4-methyl-4-hexenoic acid 2-morpholin-4-yl-ethyl ester (Mycophenolate mofetil).
In a preferred embodiment, Compound of formula (IV), represents alkyl esters of Mycophenolic acid. More preferably, alkyl ester of Mycophenolic acid is selected from (C1-C4) alkyl ester.
The invention also provides a process for preparing metal salt of hydroxy ethyl morpholine.

The hydroxy ethyl morpholine was converted to the corresponding metal salt by reacting it with alkali metal in suitable alcohols. Subsequently excess of alcohol was removed under reduced pressure.
The invention also provides a novel intermediate 2-Morpholin-4-yl-potassium ethoxide, which was characterized as follows:
% K(potassium)- 23-25 % (By acid / base titration), 13C Chemical Shift (67.6609, 61.7797, 59.5754, 55.0644) (Fig.4) and lH NMR spectrum is given below (Fig.3).

lH -d(ppm) Hydrogen CHa
3.538(t) 1 2CH2
3.491(t) l1 CH2
2.350(t) 2 2CH2

2.312(t) 2l CH2
Surprisingly, it was found that when the reaction was carried out using the Compound "III, the reaction time was reduced substantially (from 16-24 hours reported earlier, to less than 2 hours in most of the cases as described below).
In order to obtain marketing approval for a new drug product, manufacturers must submit to the regulatory authority evidence that the product is acceptable for administration to humans. Such a submission must include impurity profile of the product to demonstrate that the impurities are either absent, or present in a negligible amount. Different regulatory authorities have promulgated guidelines requiring applicants to identify the impurities present in the product and also disclose their concentration in the product. They also provide the maximum level of impurities allowable in the product. Thus for e.g. USFDA recommends that drug applicants identify all the impurities having concentration of 0.1 % or greater, in the active ingredient. Therefore, there is a need to check impurity profile and identify the impurities and also their concentration in the active ingredient.
PHARMAEUROPA vol. No. 15, 4-October, 2003 lists eight possible impurities of Mycophenolate mofetil (from A to H). Subsequently, Teva in their patent application (WO2005105769) have disclosed one new impurity of Mycophenolate mofetil. Surprisingly, the present inventors have found that by the process of preparation of the present invention as described in Scheme 2, a new impurity was being formed not known earlier.
The present invention thus provides a new impurity of Mycophenolate mofetil (MMF), Compound V and having chemical name 5-Methoxy-4-methyl-6-[2-(2-methyl-5-oxo-tetrahydro-furan-2-yl)-emyl]-7-(2-morpholin-4-yl-ethoxy)-3H-isobenzofuran-1-one, and
has the following chemical structure:

The Compound V was characterized by the following data: Compound V has the following 1H NMR (300MHz, CDC13) d (ppm): 1.3511(s), 1.8524(t), 1.9565(m), 2.1270(s), 2.491 l(t), 2.610(t), 2.785(q), 3.6933(t), 3.795(s), 4.1784(dt), 5.0735(s) (Fig.l).
13C NMR (75MHz, CDC13) d (ppm): 10.989, 17.175, 23.492, 28.424, 30.640, .34.216, 53.811, 57.047, 60.121, 61.571, 66.878, 67.901, 76.130, 108.673, 115.218, 115.51, 147.144, 152.318, 161.990, 168.851,173.604 (Fig.2).
I.R. (3018.4cm-1, 2860.2cm-1,1759.0cm-1, 1606.6cm-1,1282.6cm-1,1082cm-1, 740.6 cm-1). MS data for Compound V is given below.

Peak Report
Assignation Mmonois Calculated (Da) M measured (Da)
[M+H]+ 434.34 434.0
[M+Na]+ 456,34 456.0
In another aspect, the invention encompasses a process for synthesizing Compound V by reacting Mycophenolic acid (VII) with 2-morpholin-4-yl-ethanol (II) in presence of suitable acid catalyst.

Scheme-4
2-morpholin-4-yl-ethanol (II) was dissolved in excess of suitable solvent(s), to it was added suitable catalysts such as p-toluene sulfonic acid (PTSA) and the reaction mixture was stirred. Subsequently, Mycophenolic acid (VII) was added into it and the reaction mixture was further stirred under Dean Stark trap and solvent was removed continuously.
The organic solvents used in above reaction may be selected from hydrocarbons such as hexane, heptane, benzene, toluene, xylene, ethyl benzene, trimethyl benzene, duran, cyclohcxanc, cyclohcptanc or halogcnated solvents such as chloroform, dichloromethane, dichloroethane and the like or mixtures thereof and more preferably toluene.

The reaction is carried but at temperature ranging from room temperature to about reflux temperature of the solvents used under anhydrous condition and more preferably in the range of 160-180 °C. '
In an embodiment the invention encompasses Mycophenolate mofetil (I) having an amount of Compound V at about 0.01 to about 0.6% area by HPLC. This Mycophenolate mofetil (I) can be prepared according to the process described above and % impurity that was generated when using different solvent(s) and also using different reaction conditions are given below (Table-1). Table-1

Starting HEM Solvent Temperature Reaction Impurity After
Material Mol. Equiv. as its alkali metal salt °C Time % (Compound
V) purification %
purity of
MMF*by
HPLC
(Compound I)
Methyl ester 1.3 Toluene 110 2h 0.13 99.9
of MP A ¦ •
Methyl ester 1.3 Xylene 145 50 min 0.23 > 99.9
of MP A
Methyl ester 1.3 Cyclohexane 80 10-12 h 0.03 99,9
ofMPA
Methyl ester 1.3 Benzene 60 2h 0,10 .99.9
ofMPA
Methyl ester 1.3 Toluene: 145 50 min 0.40 > 99.9
ofMPA Xylene ¦ -
# MMF-Mycophenolate mofetil
In an embodiment the invention encompasses process for purification of
Mycophenolate mofetil having 0.01 to about 0.6 % total impurity.
The process of purification comprises dissolving Mycophenolate mofetil having 0.01 to about
0.6% total impurity in dilute organic acid solution to obtain a clear solution, which was
washed with suitable solvent such as xylene or toluene or mixtures thereof and basified with
suitable aqueous solution of base and further recrystalized from suitable solvents selected
from ethers, esters, ketones and mixtures thereof, more preferably ethers to obtained highly
pure Mycophen lolate mofetil.

The dilute organic acid used in the purification step is citric acid and base used is selected from suitable carbonate, bicarbonate or alkali base.
In an embodiment, the invention encompasses Mycophenolate mofetil having at least 99.9 % purity by HPLC (as per table-1) prepared according to the process of the present invention.
The invention is further described by the following non-limiting example, which is provided for illustration only and should not be construed to limit the scope of invention
Example 1
Preparation of E-6-(l,3-dihydro-4-hydroxy-6methoxy-7-methyl-3-oxo-5-
isobenzofuranyl)-4-methyl-4-hexenoic acid 2-morpholin-4-yl-ethyI ester.
To a cooled solution (0-4 °C) of freshly prepared sodium methoxide in methanol (0.525 g), 4-(2-hydroxyethyl)morpholine (1.28g) was added and stirred at room temperature for 30 min. to 1 hrs. Subsequently excess of solvent was distilled out at reduced pressure to obtain 2-Morpholin-4-yl-sodium.ethoxide as viscous mass which was dissolved in toluene, to it was added 2.50g of 6-(l,3-dihydro-4-hydroxy-6-methoxy-7-methyl-3-oxo-5-isobenzofuranyl)-4-methyl-4-hexenoic acid methyl ester at 110 °C temperature with constant removal of solvent under Dean Stark trap for upto 2hr. It was cooled at room temperature. The reaction mixture was dumped into water, extracted with ethyl acetate and organic layer was separated. Aqueous layer was again extracted with ethyl acetate. The combined organic extracts were washed with water, dried and concentrated under reduced pressure to get E-6-(l,3-dihydro-4-hydroxy-6methoxy-7-memyl-3-oxo-5-isobenzofuranyl)-4-methyl-4-hexenoic acid 2-morpholin-4-yl-ethyl ester (Mycophenolate mofetil, Yield-80%). [% purity by HPLC=99.01%, HPLC Impurity Profile-Compound V=0.13%, Methyl ester of MPA-0.3%] Purification:
Mycophenolate mofetil compound with 0.01-0.6 % total impurity (different batches as obtained above) was dissolved in aqueous solution of citric acid (citric acid-1.5mol equivalent). Clear solution was obtained which was washed with toluene and passed through hyflow and basified with aqueous sodium bicarbonate solution till pH-7-8. Solid obtained was filtered off and suck dried. The solid thus obtained was further purified by recrystallization from MTBE to get atleast 99.9% pure Mycophenolate mofetil or Mycophenolate mofetil without any detectable level of impurity.

Example 2
Preparation of E-6-(13-dihydro-4-hydroxy-6methoxy-7-methyl-3-oxo-5-
isobenzofuranyl)-4-methyI-4-hexenoic acid 2-morphoIin-4-yI-ethyI ester.
In a round bottom flask 20ml of methanol was taken and 0.97mg sodium pieces were added at room temperature till it was dissolved. Subsequently, 4-(2-hydroxyethyl)morpholine (5.52g) was added at 0 °C and stirred the reaction mixture at 25 °C for 30min to 1hrs. Then excess of solvent was distilled out to obtain a viscous mass, which was dissolved in xylene.
To it was added 10.82g of methyl ester of mycophenolic acid at 110 °C. Continuous removal of xylene, with continuous addition of fresh xylene was done at 145 °C forupto 50 minutes under Dean Stark assembly. Subsequently, the reaction mixture was cooled to 25-30 °C, dumped into water and xylene layer was separated out. Aqueous layer was further extracted with ethyl acetate. Organic layers obtained were combined, dried over sodium sulphate and distilled off to get Mycophenolate mofetil. (Yield 80%). [% purity by HPLC of Mycophenolate=99.1%, Compound V by HPLC -0.23%] Purification of Mycophenolate mofetil obtained above is carried out in a similar way as disclosed in Example-1, to obtain highly pure Mycophenolate mofetil.
Example 3
Preparation of E-6-(13-dihydro-4-hydroxyr-6methoxy-7-methyl-3-oxo-5-
isobenzofuranyl)-4-methyl-4-hexenoic acid 2-morpholin-4-yl-ethyl ester.
To a freshly prepared sodium methoxide (0.525g) in methanol, 4-(2-hydroxyethyl)morpholine (1.275g) was added at 0-4 °C. It was stirred at room temperature for 30 min. to 1 hrs. and subsequently excess of solvent was distilled out under reduced pressure to obtain a viscous mass. To it was added a solution of methyl ester of mycophenolic acid (2.5g) in cyclohexane (10ml) at 80 °C with constant removal of solvent under Dean Stark trap for 8-12hrs. It was cooled to room temperature and dumped into water. Cyclohexane layer was separated out and aqueous layer extracted with ethyl acetate. Combined organic layers were dried and concentrated to obtain Mycophenolate mofetil. [% purity by HPLC of Mycophenolate mofetil=99.06%, Compound V by HPLC=0.03%] Purification of Mycophenolate mofetil obtained above is carried out in a similar way as disclosed in Example-1, to obtained highly pure Mycophenolate mofetil.
Example 4
Preparation of E-6-(l,3-dihydro-4-hydroxy-6methoxy-7-methyl-3-oxo-5-
isobenzofuranyl)-4-methyl-4-hexenoic acid 2-morpholin-4-yl-ethyl ester.

6.7g of freshly prepared sodium ethoxide in ethanol was taken and 12.75g of 4-(2-hydroxyethyl)morpholine was added at 0 °C and it was kept under stirring for 30 min to 1 hrs. at 25 °C. Subsequently excess of ethanol was distilled out to obtain 2-Morpholin-4-yl-sodium
o
ethoxide and into it 250 ml of toluene:xylene (50:50) mixture was added at 70 C. 25g methyl ester of mycophenolic acid was added in to the reaction mixture and the temperature of reaction mixture was gradually increased to 145 °C. Solvents were distilled out continuously with continuous addition of toluene:xylene (50:50) mixture at 145 °C for 50 min. After 50 min. reaction mixture containing 100ml toluene:xylene (50:50) mixture was cooled to room temperature and dumped into water. Organic layer was separated and aqueous layer extracted with ethyl acetate. Organic layers were combined, dried and distilled out to get Mycophenolate mofetil. [Yield 85%, % purity by HPLO 99.2%, Compound V= 0.40%].
Purification of Mycophenolate mofetil obtained above is carried out in a similar way as disclosed in Example-1, to obtain highly pure Mycophenolate mofetil.
Example 5
Preparation of E-6-(l,3-dihydro-4-hydroxy-6methoxy-7-methyI-3-oxo-5-
isobenzofuranyl)-4-methyl-4-hexenoie acid 2-morpholin-4-yl-ethyl ester.
Into freshly prepared sodium tert. butoxide (5.85g), 8.1g of 4-(2-hydroxyethyl)morpholine was added at 0 °C and stirred for 30 min. to 2-hrs. to obtain 2-Morpholin-4-yl-sodium ethoxide. To it was added 150ml of benzene at 60 C. To this mixture, 15.7g of methyl ester of MPA was added, and subsequently reaction mixture was heated at 80 °C with constant removal of solvent under Dean Stark trap for 2hrs. It was cooled at room temperature and reaction mixture was dumped into water. The benzene layer was separated out and aqueous layer was extracted with ethyl acetate. Organic layers were combined, dried and distilled out.
[Yield: 70 % purity by HPL099.13%, Compound V=0.22%.]
Purification of Mycophenolate mofetil obtained above is carried out in a similar way as disclosed in Example-1, to obtain highly pure Mycophenolate mofetil.
Example 6
Preparation of E-6-(l,3-dihydro-4-hydroxy-6methoxy-7-methyI-3-oxo-5-
isobenzofuranyl)-4-methyl-4-hexenoic acid 2-morpholin-4-yl-ethyl ester.
31.9 g 4-(2-hydroxyethyl)morpholine was added to 13.125g sodium methoxide in methanol at 0-4 °C, and then further stirred for 30 min to 1 hrs. at 25 -30 °C. Excess of

solvent was distilled out at reduced pressure and methyl ester of Mycophenolic acid (62.5g) in 250 ml toluene was added at 135 -145 °C. The reaction mixture was refluxed with constant removal of solvent under Dean Stark trap for 2 hrs and cooled at room temperature. After suitable work up (in a similar way as per example 1) Mycophenolate mofetil was obtained. [Yield=82%, % purity by HPLC 99.05%, Compound V=0.52%]
Purification of Mycophenolate mofetil obtained above is carried out in a similar way as disclosed in Example-1, to obtained highly pure Mycophenolate mofetil.
Example 7
Preparation of E-6-(l,3-dihydro-4-hydroxy-6methoxy-7-methyl-3-oxo-5-
isobenzofuranyl)-4-methyl-4-hexenoic acid 2-morpholin-4-yl-ethyl ester.
Into freshly prepared potassium tert. butoxide (6.83g), 8.1g of 4-(2-hydroxyethyl)morpholine was added at 0 °C and stirred for 30 min. to 2-hrs, to obtain 2-Morpholin-4-yl-potassium ethoxide and into it 150ml of benzene was added at 60 °C. To the mixture, 15,7g of methyl ester of MPA was added, and subsequently reaction mixture was heated at 80 °C with constant removal of solvent under Dean Stark trap for 2hrs. It was cooled to room temperature and reaction mixture was dumped into water. Benzene layer was separated out and aqueous layer was extracted with ethyl acetate. Organic layers were combined, dried and distilled out to get Mycophenolate mofetil. [Yield:71 % purity by HPLC=99.14% Compound V=0.28%],
Purification of Mycophenolate mofetil obtained above is carried out in a similar way as disclosed in Example-1, to obtain highly pure Mycophenolate mofetil.
Example 8
Preparation of E-6-(l,3-dihydro-4-hydroxy-6methoxy-7-methyl-3-oxo-5-
isobenzofuranyl)-4-methyl-4-hexenoic acid 2-morpholin-4-yl-ethyl ester.
1.09g of freshly prepared sodium methoxide (in methanol) was dissolved in 25 ml toluene. Then into it 2.62% of 4-(2-hydroxyethyl)morpholine was added and stirred for 30min. to lhr. at room temperature. Further reaction mixture was stirred for 30min-lhrs. at 70 °C to give a clear solution of 2-Morpholin-4-yl-sodium ethoxide. In a separate round bottom flask 5g of Mycophenolic acid and 10ml of toluene was taken, equipped with Dean Stark assembly and it was heated at 110 °C. Then into it a solution of 2-Morpholin-4-yl-sodium ethoxide in toluene was added drop wise with constant removal and addition of fresh toluene under Dean Stark trap for 30min. to 80 min., after that removal of toluene stopped and reaction mass left at this temperature for 4hr. TLC checked, for reaction completion. From reaction mass toluene was removed and water was added. Then reaction mass was extracted thrice with

ethyl acetate. Combined organic layers were dried over sodium sulphate and distilled out under reduced pressure at 40 °C.
Purification of Mycophenolate mofetil obtained as above is carried out in a similar way as disclosed in Example-1, to obtained highly pure Mycophenolate mofetil. [Yield-70%, HPLC Purity- 99.8%]
Example 9
Preparation of E-6-(l,3-dihydro-4-hydroxy-6methoxy-7-methyl-3-oxo-5-
isobenzofuranyl)-4-methyl-4-hexenoic acid 2-morpholin-4-yl-ethyl ester.
In a round bottom flask Mycophenolic acid (5g) was dissolved into 40ml DCM and into it 1-2 drops of DMF was added at room temperature, then thionyl chloride(l,71ml) was added at 10 °C and reaction mixture was stirred at 25 °C for 3hr. Excess of solvent and volatile impurities were removed by distillation under reduced pressure to get acid chloride of Mycophenolic acid (5.29g). In a separate round bottom flask l.lg of sodium methoxide in 20ml toluene was taken, 2,67g of 2-morpholin-4-yl-ethanol was added and stirred for 30 min. to 1-hrs. at 25 °C. Further the reaction mixture was stirred for 30 min to 1 hrs. at 70 °C to give a clear solution of 2-Morpholin-4-yl-sodium ethoxide. 5.29g of acid chloride of Mycophenolic acid was dissolved in 10ml toluene and into it clear solution of 2-Morpholin-4-yl-sodium ethoxide was added dropwise at 110 °C. and refluxed for 4hr. TLC checked for the completion of reaction. Reaction mass dumped into water and toluene layer was separated. Aqueous layer extracted twice with ethyl acetate. All organic layers were combined, dried over sodium sulphate and distilled out under reduced pressure. Oily mass obtained was dissolved in 3% aqueous HC1 solution, when a clear solution was obtained which was washed with toluene. Aqueous layer was basifled with sodium bicarbonate solution till pH-7.2. The solid obtained was filtered off, suck dried to obtain Mycophenolate mofetil.
Purification of Mycophenolate mofetil obtained as above is carried out in a similar way as disclosed in Example-1, to obtain highly pure Mycophenolate mofetil. [Yield-69%, HPLC Purity- 99.7%]
Example 10 Preparation of 2-Morpholin-4-yl-potasslum ethoxide 1.64 g potassium metal is dissolved in 20ml of methanol, 5.52g of 4-(2-hydroxyethyl)morpholine is added at 0 °C, stir for 30 min. to 2 hrs. and subsequently excess methanol is distilled out. The 2-Morpholin-4-yl-potassium ethoxide obtained is characterized by potassium ion analysis and NMR data (traces of methanol remains). % potassium = 23-25 % (By acid /base titration).

Example 11 Preparation of 2-MorphoIin-4-yl- potassium ethoxide
Into 10 ml t-butanol, 0.43 g of potassium metal is dissolved at room temperature and to it was added 1.44g of 2-morpholin-4-yk-ethanol at 0 °C, stirred for 30min. to 2hrs. and subsequently excess of t-butanol is distilled out to give 2-Morpholin-4-yl-potassium ethoxide in 100% yield, which was characterized by potassium ion analysis and NMR data (traces of methanol remained) (Figure 3). % potassium = 23-25 % (By acid /base titration).
Example 12 Preparation of 2-Morpholin-4-yI- potassium ethoxide 0.3 8g potassium metal is dissolved in 10ml of ethanol, 1.28g 4-(2-hydroxyethyl)morpholine was added at 0 C, stirred for 30 min. to 2 hrs. and subsequently excess ethanol was distilled out to give 2-Morpholin-4-yl-potassium ethoxide (Yield 100%) which was characterized by potassium ion analysis and NMR data. % potassium = 23-25 % (By acid /base titration)
Example 13 Preparation of 5-methoxy-4-methyI-6-[2-(2-methyl-5-oxo-tetrahydro-furan-2-yl)-ethyl]-7-(2-morpholin-4-yl-ethoxy)-3H-isobenzofuran-l-one(Impurity-compound V)
5.24 g 4-(2-hydroxyethyl)morpholine was dissolved in 2.5 ml toluene and 9.48 g of p-toluene sulfonic acid was added, stirred for 5-10min. at 70 °C and subsequently 6.4g of Mycophenolic acid was added. Reaction mixture was stirred for 9hr under Dean Stark trap at 130 °C. For initial lhr, toluene was continuously removed. After nine hours, reaction mixture was dumped into dilute sodium bicarbonate solution and toluene layer was separated out. Subsequently aqueous layer was again washed with ethyl acetate. Combined organic layer was dried and distilled off to get 98 % pure 5-methoxy-4-methyl-6-[2-(2-methyl-5-oxo-tetrahyoVo-ruran-2-yl)-emyl]-7-(2-moipholm-4-yl-emoxy)-3H-isobenzofuran-l-one(Compound V), which on purification gave Compound-V with more than 99% purity. Benefits of the present process: The improved process of the present invention has the following advantages:
1. It uses basic reaction conditions, which reduces the reaction time substantially;
2. The process gives Mycophenolate mofetil with very high purity;
3. It identifies a new impurity of Mycophenolate mofetil and also discloses a process for purification of the impurity.

We Claim:
1. A process for the preparation of Mycophenolate mofetil of formula-(I) comprising:

(a) reacting a compound of formula-(IV) with metal salt of hydroxy ethyl morpholine of formula-(III),

wherein, Lv is selected from carboxylic acid, esters, acid chlorides or amides; and (b) if desired, purifying compound (I).
2. The process as claimed in claim 1, wherein said metal is an alkali metal selected from lithium, sodium or potassium.
3. The process as claimed in claim 1 or 2. wherein reaction is carried out in organic solvents selected from the group comprising of hydrocarbons or halogenated solvents or their mixtures.
4. The process as claimed in claim 3, wherein said hydrocarbon is selected from hexane, heptane, benzene, toluene, xylene, ethyl benzene, trimethyl benzene, duran, cyclohexane, cycloheptane or their mixtures.
5. The process as claimed in any preceding claim, wherein the reaction is carried out at temperature ranging from room temperature to reflux temperature of the solvents used.
6. The process as claimed in claim 5, wherein the temperature range is from 40-200°C.
7. The process as claimed in claim 1. wherein the compound of formula-(III)

is prepared by treating a compound of formula-(II) with an alkali metal in an organic solvent.

The process as claimed in claim 7, wherein organic solvent is (C1-C7) alcohols, preferably selected from (C1-C6) alcohols, most preferably selected from methyl alcohol or butyl alcohol.
9. The process as claimed in claim 7, wherein 2-morpholin-4-yl-ethanol is added at 0-5°C.
10. The process as claimed in claim 1. wherein the leaving group is an alkyl ester selected from (C1-C4) alkyl ester, more preferably methyl ester.
11. The process as claimed in any preceding claim, wherein the leaving group is an acid chloride.
12. The process as claimed in claim 1, wherein the leaving group is a carboxylic acid.
13. The process as claimed in claim 1, wherein the leaving group is a carboxamide group.
14. A compound of structural formula-(III):

wherein M = K.
15. The compound as claimed in claim 14, characterized by % Potassium = 23-25% by acid /base titration.
16. The compound as claimed in claim 14, characterized by H NMR spectrum as provided in Fig.3 and 13C Chemical Shift as provided in Fig.4.
17. A process for preparing Mycophenolate mofetil of formula (I) using the compound of formula (III) as claimed in any preceding claim.
18. A compound of formula-(V):

19. The compound as claimed in formula (V) as claimed in claim 18, characterized by 1H NMR
(300 MHz, CDC13) d (ppm) values of 1.351 l(s), 1.8524(t), 1.9565(m), 2.1270(s), 2.4911(t),
2.610(t), 2.785(q), 3.6933(t), 3.795(s). 4.1784(dt), 5.0735(s).
20. The compound as claimed in claim 18, characterized by 13C NMR (75 MHz, CDCI3) d (ppm) values of 10.989, 17.175, 23.492, 28.424, 30.640, 34.216, 53.811, 57.047, 60.121, 61.571, 66.878, 67.901, 76.130, 108.673, 115.218, 115.51, 147.144, 152.318, 161.990, 168.851, 173.604.
21. The compound as claimed in claim 18, characterized by MS(Da) [M+H]+ 434.0, 456.0
[M+Na]+.
22. The compound as claimed in claim 18, which is an impurity of Mycophenolate mofetil.
23. The impurity as claimed in claim 18 which is obtained in the process of preparing Mycophenolate mofetil as claimed in the present invention, wherein it is present in the range of 0.01 to 0.6 % area by HPLC.
24. A process for preparing compound V comprising reacting 2-morpholin-4-yl-ethanoI of formula-(II) with Mycophenolic acid (VII) in organic solvents and in presence of acid catalyst.

25. The process as claimed in claim 24, wherein reaction is carried out in organic solvents selected from the group comprising of hydrocarbons or halogenated solvents or their mixtures.
26. The process as claimed in claim 24, wherein said acid catalyst is p-toluene sulfonic acid.
27. The process as claimed in claim 24, wherein said reaction is carried out at temperature in the range from room temperature to reflux temperature of the solvents used.
28. The process for purification of Mycophenolate mofetil prepared as claimed in claim 1 comprising the steps of:
(a) reacting Mycophenolate mofetil prepared as claimed in the process of claim 1, with dilute aqueous solution of a organic acid;
(b) washing the solution with a solvent;
(c) basifying the solution with base until pH 7-8;
(d) recrystallization of the solid obtained in (c), from solvent to obtain highly pure Mycophenolate mofetil.

29. The process as claimed in claim 28, wherein said aqueous organic acid used in step (a) is citric acid.
30. The process as claimed in claim 28, wherein solvent used for washing in step (b) is selected from toluene or xylene.
31. The process as claimed in claim 28. wherein said aqueous base used in step (c) is selected from carbonate, bicarbonate or alkali base.
32. The process as claimed in claim 28, wherein solvent used for recrystallization in step (d) is selected from ethers, ketones, esters or their mixtures, more preferably ethers.
33. The process as claimed in claim 28, wherein Mycophenolate mofetil obtained is with at least 99.9% purity by HPLC.

AN IMPROVED AND EFFICIENT PROCESS FOR THE PREPARATION OF MYCOPHENOLATE MOFETIL

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