Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D405/00—Heterocyclic compounds containing both one or more hetero rings having oxygen atoms as the only ring hetero atoms, and one or more rings having nitrogen as the only ring hetero atom
  • C07D405/02—Heterocyclic compounds containing both one or more hetero rings having oxygen atoms as the only ring hetero atoms, and one or more rings having nitrogen as the only ring hetero atom containing two hetero rings
  • C07D405/12—Heterocyclic compounds containing both one or more hetero rings having oxygen atoms as the only ring hetero atoms, and one or more rings having nitrogen as the only ring hetero atom containing two hetero rings linked by a chain containing hetero atoms as chain links

Definitions

• the present invention relates to an improved process for the preparation of alfuzosin hydrochloride.
• Alfuzosin hydrochloride has the chemical name N-[3-[(4-Amino-6,7-dimethoxy-2- quinazolinyl)methylamino]propyl]tetrahydro-2-furancarboxamide hydrochloride and has the structural formula as Formula I.
• Alfuzosin hydrochloride is an antagonist of the ⁇ -adrenergic receptor, and is useful as an antihypertensive agent and dysuria treatment agent.
• the patent 007' teaches the preparation of alfuzosin or a salt thereof by reacting 4-amino- 2-chloro-6,7-dimethoxy quinazoline of formula (II) with 3-methylaminopropionitrile of formula (III) in the presence of isoamyl alcohol to obtain N-(4-amino-6,7- dimethoxyquinazol-2-yl)-N-methyl-2-cyanoethylamine of formula (IV) which is further hydrogenated in the presence of Raney Nickel using 15% ammoniacal ethanol by applying 80 Kg pressure at 70 0 C for 96 hours to obtain N-(4-amino-6,7-dimethoxyquinazol-2-yl)-N- methylpropylenediamine of formula (V) which is then converted to the hydrochloride salt.
• N-(4-amino-6,7-dimethoxyquinazol-2-yl)-N-methylpropylenediamine hydrochloride is then treated with carbonyldiimidazole-activated tetrahydrofuroic acid by adding a diamine compound in the presence of carbonyldiimidazole to obtain alfuzosin base which is then converted into alfuzosin hydrochloride salt.
• the alfuzosin obtained in the next step on '880 by reaction of the compound of formula (V) with carbonyldiimidazole-activated tetrahydrofuroic acid is impure in nature and hence needs repetitive crystallization before converting it into the hydrochloride salt.
• Processes for the preparation of alfuzosin and its pharmaceutically acceptable salts have also been described in U.S. Pat. No. 5,545,738, GB Patent No. 2231571 , US2007/0066824.
• US 5,545,738 discloses a process for preparing the dihydrate form of alfuzosin hydrochloride.
• GB 2231571 discloses a process for preparing alfuzosin or salts thereof comprising reacting an isothiourea derivative with an amine and cyclising the resulting product to form alfuzosin.
• US2007/0066824 discloses a process for preparing salts of alfuzosin comprising a) esterifying tetrahydrofuroic acid; b) condensing the esterified product of step a) with 3-methyl amino propylene diamine to get N- ⁇ -methyl-N2- tetrahydrofuroyl propylene diamine; c) condensing Ni-methyl-N 2 -tetrahydrofuroyl propylene diamine with 4-amino-2-chloro-6,7-dimethoxyquinozoline to yield alfuzosin free base; d) treatment of alfuzosin free base of with a pharmaceutically acceptable acid to afford a pharmaceutically acceptable acid addition salt of alfuzosin.
• the present invention provides an improved process for synthesis of alfuzosin which avoids all the disadvantages associated with the prior art processes.
• One object of the present invention is to provide an improved process for preparing alfuzosin hydrochloride.
• Another object of the present invention is to provide a purification method to obtain high purity alfuzosin hydrochloride.
• Yet another object of the present invention is to provide a process for preparing alfuzosin hydrochloride which is simple, economical and suitable for industrial scale up.
• a process for preparing N-(4-amino-6,7-dimethoxyquinazol-2-yl)-N-methyl-2-cyanoethylamine (IV) or a salt thereof comprising condensing 4-amino-2-chloro-6,7-dimethoxy quinazoline (II) with 3- methylaminopropionitrile (III) in the presence of a polar aprotic solvent selected from the group consisting of diglyme, dimethyl formamide, t-butanol, hexamethylphosphoramide or mixtures thereof, and optionally converting N-(4-amino-6,7-dimethoxyquinazol-2-yl)-N- methyl-2-cyanoethylamine (IV) to a salt thereof.
• the solvent is diglyme, t-butanol or a mixture thereof.
• the condensation reaction may be carried out in the presence or absence of a base such as an organic or inorganic base. Preferably, the condensation reaction is carried out in the absence of a base.
• the N-(4-amino-6,7-dimethoxyquinazol-2-yl)-N-methyl-2- cyanoethylamine (IV) prepared according to this process may have a purity greater than 95%, preferably greater than 98%.
• the use of a mixture of diglyme-and t-butanol reduces the amount of impurity A to about 2%, compared to an amount of around 12% according to the prior art process.
• the N-(4-amino-6,7-dimethoxyquinazol-2-yl)-N-methyl-2- cyanoethylamine (IV) is converted into an acid addition salt of the formula (IVa) in the presence of an acid HA
• the acid may be an inorganic acid or organic acid.
• a process for preparing N-(4-amino-6,7-dimethoxyquinazol-2-yl)- N-methyl propylenediamine (V) or a salt thereof comprising hydrogenating N-(4-amino-6,7-dimethoxyquinazol-2-yl)-N-methyl-2- cyanoethylamine (IV) using hydrogenating agent, for example Raney Nickel, under a pressure of less than 10 kg/cm 2 and optionally converting the N-(4-amino-6,7- dimethoxyquinazol-2-yl)- N-methyl propylenediamine (V) to a salt thereof.
• hydrogenating agent for example Raney Nickel
• the pressure is around 5-6 kg/cm'
• the hydrogenation is carried out in the presence of an alcohol and an aqueous ammonia solution.
• the alcohol may be methanol or ethanol, for example denatured ethanol.
• “wet” conditions i.e. aqueous ammonia rather than dry ammonia.
• “dry” conditions are used. More specifically, the hydrogenation processes in these prior art patents use ammoniacal isopropanol or ammoniacal ethanol, which is dry ammonia gas purged in either isopropanol or ethanol. The use of wet conditions make the process of the present invention more suitable for industrial application.
• the hydrogenation reaction takes place over a period of time ranging from about 2 hours to about 10 hours, preferably from about 2 hours to about 5 hours. Most preferably, the reaction takes place over a period of time of about 2 hours. In US'880, the reaction time is 6 hours.
• N-(4-amino-6,7-dimethoxyquinazol-2-yl)-N-methyl propylenediamine (V) is converted to an acid addition salt (Va)
• the acid may be an inorganic acid or organic acid.
• the N-(4-amino-6,7-dimethoxyquinazol-2-yl)-N-methyl-2- cyanoethylamine (IV) is prepared according to a process described in the first aspect of the invention.
• a process for preparing alfuzosin free base or alfuzosin hydrochloride comprising converting tetrahydrofuroic acid (Vl) to an intermediate form (VII)
• R is: (i) a halo group; (ii) OR 1 wherein Ri is a silyl group having the formula
• R 1 , R" and R'" are the same or different and are selected from hydrogen, optionally substituted Ci-C 6 alkyl, optionally substituted C 2 -Ce alkenyl; Y is selected from hydrogen, C-1-C 6 alkyl, C 2 -C 6 alkenyl and silyl , preferably substituted silyl; (iii) OR 2 wherein R 2 is a Ci to C 4 alkyl group; or (iv) OR 3 , wherein R 3 is N-hydroxysuccinimide or asparagine, and condensing the intermediate form (VII) with N-(4-amino-6,7- dimethoxyquinazol-2-yl)- N-methyl propylenediamine (V) or with acid addition salt (Va) to yield alfuzosin base and optionally converting alfuzosin base to alfuzosin hydrochloride (I), wherein the process is carried out without isolating the intermediate of formula (VII).
• the term "without isolation” means that the product being referred to as not being isolated is not isolated as a solid, for example it is not isolated from the reaction mass and dried to form a solid.
• “without isolation” may mean that the product remains in solution and is then used directly in the next synthetic step, or it may mean that solvent is substantially removed from a solution of the product such that the product is present as a residue, but not as a solid.
• alfuzosin base is isolated.
• the isolated alfuzosin base may be converted to the hydrochloride salt of alfuzosin.
• alfuzosin base is not isolated before being converted to alfuzosin hydrochloride.
• tetrahydrofuroic acid (VI) is 5 treated with a halogenating agent; preferably a chlorinating agent, to yield tetrahydrofuroyl chloride (Vila).
• a halogenating agent preferably a chlorinating agent
• Preferred chlorinating agents are, for example thionyl chloride, phosphorus oxychloride,0 phosphorus trichloride, phosphorus pentachloride, phosgene and oxalyl chloride.
• the chlorination is performed in a manner known to those skilled in the art. In general it is ⁇ preferred to heat the tetrahydrofuroic acid (Vl) with the chlorinating agent, which will either be used neat or in a solution with a suitable solvent such as, for example toluene, methylenechloride, acetonitrile, tetrahydrofuran, diglyme, dimethylforamide or dioxane or5 the like. It is preferred to perform chlorination by refluxing with neat thionyl chloride, any excess of which can later be conveniently removed by evaporation.
• the intermediate When the intermediate is condensed with the diamine (V), the any residual chlorinating agent if first removed, as this would react with the diamine (V). If chlorination is performed0 in a solvent, then it is preferable to employ a high boiling point solvent, so that the chlorinating agent may be removed by evaporation.
• tetrahydrofuroic acid is converted to tetrahydrofuroyl chloride (Vila)
• a preferred method for preparing alfuzosin base or hydrochloride comprises5 reacting diamine (V) in situ with tetrahydrofuroyl chloride (Vila) in the presence of an anhydrous solvent, i.e. without isolation of tetrahydrofuroyl chloride (Vila).
• a base either organic or inorganic, may be added to the reaction mixture as an acid scavenger. The reaction rate may be increased by heating the reaction mass to the boiling point of the solvent.
• R 2 When R is OR 2 , wherein R2 is a Ci to C 4 alkyl group, R 2 may be methyl, ethyl, n-propyl, isopropyl, n-butyl or tertiary butyl.
• the formation of the intermediate (VII) may comprise esterfying tetrahydrofuroic acid (Vl) with an alcohol of the formula R 2 OH, wherein R 2 has the same meanings as given above, in the presence of an acid.
• the acid may be selected from the group consisting of acetic acid, sulfuric acid and nitric acid.
• the process for preparing alfuzosin may comprise reacting tetrahydrofuroic acid (Vl) with diamine (V) in the presence of a silicon amine based on the silyl group of the formula.
• silyl group is nitrogen-bonded to the oxygen of the OR 1 group.
• C-i-C ⁇ alkyl represents straight-chain or branched-chain alkyl having 1 to 6 carbon atoms.
• silyl represents -SU-I 3 .
• Silyl can be substituted with one or more substitutents such as C1-C-6 alkyl and hydroxyl.
• the silicon amine is selected from alkali metal disilazane or alkali metal monosilazane.
• the alkali metal may be selected from lithium, sodium or potassium.
• HMDS hexamethyldisilazane
• the condensation reaction is preferably carried out under an inert atmosphere at a temperature ranging from 50 to 200 0 C. The process is preferably carried out for several hours until the condensation reaction completes.
• the condensation reaction may be carried out by reacting tetrahydrofuroic acid (Vl) with ethyl chloroformate in the presence of a base and a polar protic solvent.
• R 3 is preferably N- hydroxysuccinimide (VIIc).
• the reaction may be carried out in the presence of a catalyst such as dimethylaminopyridine, using an organic solvent in an inert atmosphere.
• a catalyst such as dimethylaminopyridine
• the ester (VIIc) may then be condensed with diamine (V) in a suitable organic solvent preferably dichloromethane using a suitable organic base or an inorganic base, suitably under an inert atmosphere to form alfuzosin base or hydrochloride.
• the condensation reaction may be carried out by isolating intermediate ester (VIIc).
• the reaction is carried out without isolating ester (VIIc).
• the process involves reacting a solution of compound (Vl) or (VII) with diamine compound (V) or vice versa in a solvent at a suitable temperature to yield alfuzosin.
• the mixture may be basified, extracted in a suitable solvent, neutralized, washed with water and dried.
• the solvent may be evaporated partially or completely to provide a residue or solution of alfuzosin base in a solvent.
• the residue of alfuzosin is dissolved in methanol and acidified with hydrochloric acid either as gas or as an aqueous solution or as alcoholic solution to yield alfuzosin hydrochloride.
• the solid alfuzosin hydrochloride may be obtained by distilling the solvent under reduced pressure and adding an antisolvent to the residue of alfuzosin base in a solvent. Suitable antisolvents may be selected from esters or ethers.
• the alfuzosin hydrochloride may be isolated by filtration and may be purified further using known crystallization techniques.
• Still another aspect of the present invention is to provide pharmaceutical composition containing a therapeutically effective amount of pure alfuzosin hydrochloride, along with one or more pharmaceutically acceptable carriers, diluents and excipients.
• Such pharmaceutical compositions are well known to those skilled in the art and processes for preparing them are also well known.
• the present invention provides an improved process for the synthesis of alfuzosin hydrochloride as depicted in reaction scheme 2 below:
• step a 4-amino-2-chloro-6,7-dimethoxy quinazoline (II) is condensed with 3- methylaminopropionitrile (III) in the presence of a polar aprotic solvent to yield N-(4-amino- 6,7-dimethoxyquinazol-2-yl)-N-methyl-2-cyanoethylamine (IV).
• polar aprotic solvents are selected from the group consisting of diglyme, dimethyl formamide, t-butanol, or mixtures thereof.
• Preferred solvents for the reaction are diglyme, t-butanol or a mixture thereof, more preferably a mixture thereof.
• the solvents used in the process of present invention the reduce formation of "alfuzosin impurity A" to a level below 2% instead of 10- 12% when the prior art process is followed. This consequently improves the yield, colour and purity of N-(4-amino-6,7-dimethoxyquinazol-2-yl)-N-methyl-2-cyanoethylamine (IV).
• the reaction may be carried out optionally in the presence of, either organic or inorganic base. In an embodiment, the reaction is carried out without base.
• N-(4-amino- 6,7-dimethoxyquinazol-2-yl)-N-methyl-2-cyanoethylamine (IV) prepared according to this embodiment and salts thereof may have purity greater than 95%, preferably greater than 98%.
• the free base obtained may be optionally purified by converting into acid addition salt (IVa).
• a ⁇ is an anion.
• the anion corresponds to the acid used.
• the acid used may be selected from inorganic acids and organic acids and the like.
• step b N-(4-amino-6,7-dimethoxyquinazol-2-yl)-N-methyl-2-cyanoethylamine (IV) is hydrogenated to yield N-(4-amino-6, 7-dimethoxyquinazol-2-yl)- N-methyl propylenediamine (V).
• the reaction is carried out at pressure of less than 10 kg/cm 2 , preferably at 5-6 kg/cm 2 .
• the reaction does not require anhydrous conditions as reported in the prior art.
• the prior art teaches use of absolute ethanol or tetrahydrofuran which require dry ammonia gas or solution of dry ammonia gas either in ethanol or in isopropanol.
• the preferred solvent is denatured alcohol along with aqueous ammonia solution.
• the improved reaction condition reduces reaction hours from 96 hours to about 10 hours, preferably about 2 hours, making the process more feasible on an industrial scale. This forms another aspect of the present invention.
• N-(4-amino-6,7-dimethoxyquinazol-2-yl)-N-methyl propylenediamine (V) can be isolated as acid addition salt (Va)
• step c tetrahydrofuroic acid (Vl) is activated to an intermediate of formula (VII) and condensed with N-(4-amino-6,7-dimethoxyquinazol-2-yl)-N-methyl propylenediamine (V) or with acid addition salt (Va) to yield alfuzosin hydrochloride (I).
• alfuzosin base can be isolated.
• condensation is carried out without isolating intermediate of formula (VII).
• step c where R is a halo group, tetrahydrofuroic acid (Vl) is treated with a halogenating agent; preferably a chlorinating agent, to yield tetrahydrofuroyl chloride (Vila).
• a halogenating agent preferably a chlorinating agent
• Preferred chlorinating agents are, for example thionyl chloride, phosphorus oxychloride, phosphorus trichloride, phosphorus pentachloride, phosgene and oxalyl chloride.
• the chlorination is performed in a manner known to those skilled in the art.
• Ri is a hydroxy protective group, such as an ester group and the process to prepare alfuzosin comprises; esterfying tetrahydrofuroic acid (Vl) with alcohol in the presence of an acid to form ester of formula (VIIb)
• R 2 is Ci to C 4 alkyl group and; condensing esterified intermediate without isolating it, with diamine (V) optionally in the presence of solvent.
• the alcohol suitable for the process is selected from CrC 4 alcohols like methanol, ethanol, butanol, isopropanol, n- propanol, tertiary butanol and the like.
• the acid used selected from the group comprising of acetic acid, sulfuric acid, nitric acid and the like.
• step c the process for preparing alfuzosin involves: reacting tetrahydrofuroic acid (Vl) with diamine (V) in the presence of a silicon amine based on a si IyI group of the formula
• R is OR 1 and Ri is the radical shown above.
• CrC ⁇ alkyl represents straight or branched-chain alkyl groups having 1 to 6 carbon atoms, for example methyl, ethyl, n-propyl, isopropyl, n-butyl, tertiary butyl, pentyl or hexyl.
• C2-C 6 alkenyl represents straight or branched-chain alkenyl groups having 2 to 6 carbon atoms, such as ethenyl and n-propenyl
• sil represents -SiH 3 . SiIyI may be substituted with one or more substitutents such as C-i-C ⁇ alkyl and hydroxyl.
• the silicon amine may be selected from alkali metal disilazane or alkali metal monosilazane.
• the alkali metal may be selected from lithium, sodium or potassium.
• preferable silicon amine used is 1 ,1 ,1 ,3,3,3-hexamethyldisilazane (HMDS).
• HMDS 1 ,1 ,1 ,3,3,3-hexamethyldisilazane
• the step c involves activation of tetrahydrofuroic acid (Vl) with an amide such as N-hydroxysuccinimide, asparagine, preferably N-hydroxy succinimide to obtain corresponding ester of formula (VIIc).
• the reaction may be carried out in the presence of catalyst such as dimethylaminopyridine, using an organic solvent in an inert atmosphere.
• the ester (VIIc) is then condensed with diamine (V) in a suitable organic solvent preferably dichloromethane using a suitable organic base or an inorganic base, in an inert atmosphere to form alfuzosin hydrochloride.
• the condensation reaction may be carried out by isolating intermediate ester (VIIc). In the process of the present invention the reaction is carried out without isolating ester (VIIc).
• the present invention provides a novel process for preparing alfuzosin hydrochloride comprising reacting tetrahydrofuroic acid (Vl) with ethyl chloroformate in the presence of a suitable base using polar protic solvent and condensing with a solution of diamine (V).
• the condensation of compounds (VII) and (V) may involve reacting a solution of compound (Vl) or (VII) with diamine compound (V) or vice versa in a solvent at a suitable temperature to yield alfuzosin.
• the mixture may be basified, extracted in a suitable solvent, neutralized, washed with water and dried. In this way, the alfuzosin base is isolated.
• the solvent may be evaporated partially or completely to provide a residue or solution of alfuzosin base in a solvent. In this way, the alfuzosin base is not isolated.
• a residue of alfuzosin is dissolved in methanol and acidified with hydrochloric acid either as gas or as an aqueous solution or as alcoholic solution.
• the solid alfuzosin hydrochloride can be obtained by distilling solvent under reduced pressure, adding antisolvent to the residue of alfuzosin base in a solvent.
• a suitable antisolvent may be selected from an ester or ether.
• the alfuzosin hydrochloride can be isolated by filtration and may be purified further by using known crystallization techniques.
• Still another aspect of the present invention is to provide a pharmaceutical composition containing a therapeutically effective amount of pure alfuzosin hydrochloride, along with one or more pharmaceutically acceptable carriers, diluents and excipients.
• pharmaceutical compositions and carriers, diluents and excipients are well known to those skilled in the art.
• reaction mass was further stirred for 15 minutes, filtered and washed with 50 ml isopropanol and subjected to drying at 50 0 C for 7- 8 hours to yield N-(4-amino-6,7-dimethoxyquinazol-2-yl)-N-methyl-2-cyanoethylamine hydrochloride (50 gms).
• reaction mass was further stirred for 15 minutes, filtered and washed with 50 ml isopropanol and subjected to drying at 50 0 C for 7-8 hours to yield N-(4-amino-6,7-dimethoxyquinazol-2-yl)- N-methyl-2-cyanoethylamine hydrochloride (43 gms).
• the solid obtained was further refluxed in 1000 ml methanol for 30 minutes, then cooled to 15 25°C, stirred for 1 hour at 25°C, filtered, washed with 200 ml methanol and dried under suction.
• the compound N-(4-amino-6,7-dimethoxyquinazol-2-yl)-N-methyl-2- cyanoethylamine hydrochloride was dried under vacuum at 50 0 C for 5 hours. Yield- 102 gms. (75.55 %).
• the reaction mixture was hydrogenated at 70 0 C under a pressure of 5 kg/cm 2 (70psi) for 2 hours.
• the reaction mass was cooled to room temperature and filtered on hyflo bed.
• the reaction mixture was hydrogenated at 70 0 C under a pressure of 5 kg/cm 2 (70psi) for 2 hours.
• the reaction mass was cooled to room temperature and filtered on hyflo bed.
• the solvent was distilled under reduced pressure.
• the residue obtained was stirred in 125 ml acetonitrile at 45-50 0 C, filtered and concentrated under reduced pressure at 60 0 C.
• the residue was dissolved in 150 ml isopropanol and acidified to pH 1-2 with isopropanolic
• This example illustrates the preparation of alfuzosin hydrochloride without isolation of alfuzosin base.
• HMDS (42.16ml, 0.199 moles) was charged in a 100 ml round-bottom flask under argon at room temperature. After cooling to 10°C, tetrahydrofuran-2-carboxylic acid (3.98gms, 0.0343moles) was added drop wise and the reaction mass was stirred and heated to 50- 55°C. After 5 hours of stirring, the reaction mass was cooled to 0-5 0 C and N-(4-amino-6,7- dimethoxyquinazol-2-yl)-N-methylpropylenediamine (10 gms, 0.0343 moles) was added drop wise maintaining temperature below 5°C. The reaction mass was heated to 110°C.
• the clear MDC layer was dried on sodium sulfate and distilled completely under reduced pressure to obtain residue.
• the residue was dissolved in 50 ml methanol, acidified to pH 2-3 with IPA-HCI at room temperature. The solvent was removed under reduced pressure, 50 ml acetone charged, heated to reflux and cooled to room temperature. The solids were filtered and dried under vacuum at 6O 0 C to yield 9.5 gms of alfuzosin hydrochloride. ( 73.24%)
• This example illustrates the preparation of alfuzosin hydrochloride without isolation alfuzosin base.

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• 2008
  • 2008-08-01 EP EP08788253.6A patent/EP2178864B1/en not_active Not-in-force
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