WO2003095456A1 - A process for the preparation of zaleplon - Google Patents

A process for the preparation of zaleplon Download PDF

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Publication number
WO2003095456A1
WO2003095456A1 PCT/PL2003/000043 PL0300043W WO03095456A1 WO 2003095456 A1 WO2003095456 A1 WO 2003095456A1 PL 0300043 W PL0300043 W PL 0300043W WO 03095456 A1 WO03095456 A1 WO 03095456A1
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zaleplon
reaction
formic acid
ethyl
preparation
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Monika Korycinska
Tomasz Stawinski
Maciej Wieczorek
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Adamed Sp zoo
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Adamed Sp zoo
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Priority to DE60309159T priority patent/DE60309159D1/en
Priority to AU2003243061A priority patent/AU2003243061A1/en
Priority to BR0304837-3A priority patent/BR0304837A/en
Priority to US10/514,045 priority patent/US7057041B2/en
Priority to EP03750002A priority patent/EP1506199B1/en
Publication of WO2003095456A1 publication Critical patent/WO2003095456A1/en
Priority to UA20041109259A priority patent/UA77292C2/en
Priority to NO20040029A priority patent/NO20040029L/en
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D487/00—Heterocyclic compounds containing nitrogen atoms as the only ring hetero atoms in the condensed system, not provided for by groups C07D451/00 - C07D477/00
    • C07D487/02—Heterocyclic compounds containing nitrogen atoms as the only ring hetero atoms in the condensed system, not provided for by groups C07D451/00 - C07D477/00 in which the condensed system contains two hetero rings
    • C07D487/04—Ortho-condensed systems
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
    • A61P21/00—Drugs for disorders of the muscular or neuromuscular system
    • A61P21/02—Muscle relaxants, e.g. for tetanus or cramps
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
    • A61P25/00—Drugs for disorders of the nervous system
    • A61P25/20—Hypnotics; Sedatives
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
    • A61P25/00—Drugs for disorders of the nervous system
    • A61P25/22—Anxiolytics

Definitions

  • Patents EP 0776898 and EP 0208846 describe a process for the preparation of zaleplon, which consists in reaction of 3-din- ⁇ ethylamino- 1 - (3-N-ethyl-N-acetyla ⁇ inophenyl) -2-propen- 1 - one with 3-a ⁇ ninopyrazole-4-carbonitrile, by heating in acetic acid (EP 0208846) or in an aqueous solution of acetic acid (EP 0776898).
  • acetic acid EP 0208846
  • EP 0776898 carrying out the reaction in aqueous acetic acid would make it possible to obtain the product free from color impurities, in a much higher yield (ca. 90%) and of much better purity (above 98.77%), compared to the reaction carried out in neat acetic acid.
  • Such improved ap- proach would also allow one to shorten the reaction time and to lower the reaction temperature.
  • the allowed level of a single identified and qualified drug impurity should be no more than 0.5% (wt/wt), or 20 micrograms of the total daily dose. Due to a high degree of structural and chemical similarity between zaleplon and 'the isomef, these compounds are very difficult to separate by standard crystallization methods, particularly when the content of the isomer is above 10%. Moreover, the multiple crystallization necessary in such cases causes substantial losses of the desired active ingredient, zaleplon. Crude zaleplon may be crystallized from a polar solvent chosen from lower alkyl alcohols, such as methanol, ethanol and isopropanol.
  • the present invention relates to the process for the preparation of zaleplon, N-[3-(3-cyanopyrazolo[l,5-a]pyrimidin-7- yl)phenyl]-N-ethylacetamide 3, in the reaction of 3-dimethylarmno- l-(3-N-ethyl-N-acetyla ⁇ inophenyl)-2-propen-l-one 1 with 3-aminopyrazole-4-carbonitrile 2, which comprises carrying out the reaction in an aqueous solution of formic acid, at concentrations of formic acid in ⁇ he range of 20-80% (wt/wt), according to the Scheme presented below. Isomer 4 is formed with a very low yield.
  • the reaction is carried out by stii-Ting the reaction mixture at temperatures in the range of 20-60°C, preferably at 30-45°C. After the reaction is complete, the reaction optionally is diluted with water to give formic acid concentration below 40% (wt/wt), which causes zaleplon crystals to precipitate.
  • a 35-45% (wt/wt) solution of formic acid is used.
  • the low content of the isomer present in the crude zaleplon obtained from the reaction makes possible easy purification of zaleplon to purity levels in accordance with the standard require- ments established for pharmaceutical active ingredients.
  • the yield of the reaction carried out according to the present invention is increased by a few percent compared to the process described in EP 0776898. Isolating the product from the reaction mixture after completion of the reaction results in crude zaleplon of high purity. It can be additionaly crystallized from a polar solvent chosen from lower alkyl alcohols, e.g.
  • the zaleplon obtained by the process of the present invention, after one crystallization contains "the isomef in the amount of less than 5 micrograms per dosage unit containing 10 mg zaleplon.
  • 3-Dimethylamino- 1 -(3-N-ethyl-N-ace1ylaminophenyl)-2- propen-1-one (1) (104.14 g, 0.4 mol), 3-aminopyrazole-4-carbo- nitrile (2) (44.32 g, 0.41 mol) and 35% aqueous formic acid (1360 mL, 1500 g) are placed in a reactor.
  • the mixture is stirred (ca. 200 rpm) and slowly warmed up to 35°C over 1 hr. Then the mixture is warmed up to 40°C over 30 minutes and stirred at 40°C one more hour (total heating time is 2.5 hr from the beginning of heating).
  • the mixture is cooled to ca. 10°C and stirred at this temperature for ca. 30 minutes. Then it is filtered, the precipitate is thoroughly pressed and washed with water (3x 250mL). The precipitate-white to off-white crystals - is dried at 105°C. The yield is 87.5%) (106.86 g). The purity of the crude product is 99.69%) as determined by HPLC.

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  • Health & Medical Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Pharmacology & Pharmacy (AREA)
  • Animal Behavior & Ethology (AREA)
  • Veterinary Medicine (AREA)
  • Public Health (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Medicinal Chemistry (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Bioinformatics & Cheminformatics (AREA)
  • Engineering & Computer Science (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Neurology (AREA)
  • General Health & Medical Sciences (AREA)
  • Biomedical Technology (AREA)
  • Neurosurgery (AREA)
  • Anesthesiology (AREA)
  • Pain & Pain Management (AREA)
  • Orthopedic Medicine & Surgery (AREA)
  • Physical Education & Sports Medicine (AREA)
  • Nitrogen Condensed Heterocyclic Rings (AREA)
  • Steroid Compounds (AREA)
  • Pharmaceuticals Containing Other Organic And Inorganic Compounds (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Abstract

The invention relates to a process for the preparation of zaleplon (N-[3(3-cyanopyrazolo[1,5-a]pyrimidin-7-yl)phenyl]-N-ethyl-acetamide) in the reaction of 3-dimethylamino-1-(3-N-ethyl-N-acetylaminophenyl)-2-propen-1-one with 3-aminopyrazole-4-carbonitrile, which comprises carrying out said reaction in an aqueous solution of formic acid at formic acid concentrations in the range of 20-80% (w/w). Zaleplon is useful as an anxiolytic, a sedactive and a skeletal muscle relaxant.

Description

A process for the preparation of zaleplon
The invention relates to the field of the synthesis of N-[3-(3- cyanopyrazolo[ 1 ,5-a]pyriιnidin-7-yl)phenyl]-N-ethylacetaιnide (zaleplon), useful in medicine as an anxiolytic, sedative and skeletal muscle relaxing agent. Patents EP 0776898 and EP 0208846 describe a process for the preparation of zaleplon, which consists in reaction of 3-din-ιethylamino- 1 - (3-N-ethyl-N-acetylaπιinophenyl) -2-propen- 1 - one with 3-aιninopyrazole-4-carbonitrile, by heating in acetic acid (EP 0208846) or in an aqueous solution of acetic acid (EP 0776898). According to the teachings of EP 0776898, carrying out the reaction in aqueous acetic acid would make it possible to obtain the product free from color impurities, in a much higher yield (ca. 90%) and of much better purity (above 98.77%), compared to the reaction carried out in neat acetic acid. Such improved ap- proach would also allow one to shorten the reaction time and to lower the reaction temperature.
However, the present inventors have found that the reaction carried out under conditions described in EP 0776898, invariably resulted in zaleplon contaminated with a side product, N-[3-(3- cyanopyrazolo[ 1 , 5-a]pyιimidm-5-yl)phenyl]-N-ethylacetamide, which for the purpose of the present description is called "the iso- mer". The yield of this "isome , depending on the reaction parameters, is in the range of 10-20%.
The present inventors have isolated "the isomef from the re- action mixture and, in order to verify the structure, analyzed it by the usual spectroscopic methods, such as IR, Η-NMR, 13C-NMR, MS, UN and elemental analysis (IR (KBr): (cm'1) 3436,8, 3103,8, 3065, 1, 2977, 1, 2937, 1, 2228, 1, 1656,6, 1625,4, 1602,4, 1602, 1, 1553,9, 1521,8, 1469, 1, 1412, 1, 1302,7, 1280, 1, 1221,5, 1189,0, 1142,9, 1088, 1, 1004,6, 900, 1); UV (c=0,01042 mg/ml in MeOH, nm): 301,00 (0,3082), 261,20 (1, 1743), 219,20 (0,9612), 216,20 (0,9618). It has also been determined (using a differential scanning calorimeter) that the compound melts in the temperature range of 204-207°C, while the melting range for zaleplon is 185-188°C.
None of the prior art documents cited above mentions of the formation of the side product, N-[3-(3-cyaxιopyrazolo[l,5-a]- py-rimidin-5-yl)phenyl]-N-ethylacetamide. Nevertheless, the formation of this by-product creates a serious technological problem in the industrial scale production of zaleplon intended for use as an active ingredient in pharmaceutical formulations.
According to current standards, the allowed level of a single identified and qualified drug impurity, such as "the isomef, should be no more than 0.5% (wt/wt), or 20 micrograms of the total daily dose. Due to a high degree of structural and chemical similarity between zaleplon and 'the isomef, these compounds are very difficult to separate by standard crystallization methods, particularly when the content of the isomer is above 10%. Moreover, the multiple crystallization necessary in such cases causes substantial losses of the desired active ingredient, zaleplon. Crude zaleplon may be crystallized from a polar solvent chosen from lower alkyl alcohols, such as methanol, ethanol and isopropanol. The presence of impurities, such as "isomef, necessitates additional crystallization from a less polar solvent, e.g. chosen from among esters, such as ethyl acetate, butyl acetate, or similar. Thus, the methods known from the prior art do not allow to obtain the final product of required quality, in a simple way. The present inventors have undertaken an investigation of a solution of this problem by changing the reaction conditions, including changes to the reaction medium. Attempts to find appro- priate conditions in aqueous acetic acid did not result in decreased amounts of the isomer, similarly as in propionic acid solutions. However, the authors have unexpectedly found that the formation of such substantial amounts of the isomer can be avoided if the re- action is carried out in aqueous formic acid medium.
Thus, the present invention relates to the process for the preparation of zaleplon, N-[3-(3-cyanopyrazolo[l,5-a]pyrimidin-7- yl)phenyl]-N-ethylacetamide 3, in the reaction of 3-dimethylarmno- l-(3-N-ethyl-N-acetylaπιinophenyl)-2-propen-l-one 1 with 3-aminopyrazole-4-carbonitrile 2, which comprises carrying out the reaction in an aqueous solution of formic acid, at concentrations of formic acid in \he range of 20-80% (wt/wt), according to the Scheme presented below. Isomer 4 is formed with a very low yield.
Figure imgf000004_0001
The reaction is carried out by stii-Ting the reaction mixture at temperatures in the range of 20-60°C, preferably at 30-45°C. After the reaction is complete, the reaction optionally is diluted with water to give formic acid concentration below 40% (wt/wt), which causes zaleplon crystals to precipitate.
Preferably, a 35-45% (wt/wt) solution of formic acid is used. The low content of the isomer present in the crude zaleplon obtained from the reaction makes possible easy purification of zaleplon to purity levels in accordance with the standard require- ments established for pharmaceutical active ingredients. Moreover, the yield of the reaction carried out according to the present invention is increased by a few percent compared to the process described in EP 0776898. Isolating the product from the reaction mixture after completion of the reaction results in crude zaleplon of high purity. It can be additionaly crystallized from a polar solvent chosen from lower alkyl alcohols, e.g. from methanol, ethanol or isopropanol, or from a less polar solvent, e.g. belonging to the ester group, such as ethyl acetate, butyl acetate, or similcir. When required, additional crystallization can be carried out. However, generally one crystallization affords zaleplon of sufficient purity.
When carrying the reaction according to the present process, usually one crystallization of crude zaleplon is sufficient. However, if necessary, it is possible to recrystallize zaleplon from a less polar solvent e.g. belonging to the ester group, such as ethyl acetate, butyl acetate or the like.
The zaleplon obtained by the process of the present invention, after one crystallization contains "the isomef in the amount of less than 5 micrograms per dosage unit containing 10 mg zaleplon. The present invention will now be described with reference to the following specific, illustrative and non-limiting embodiments.
Example 1. Preparation of crude zaleplon.
3-Dimethylamino- 1 -(3-N-ethyl-N-ace1ylaminophenyl)-2- propen-1-one (1) (104.14 g, 0.4 mol), 3-aminopyrazole-4-carbo- nitrile (2) (44.32 g, 0.41 mol) and 35% aqueous formic acid (1360 mL, 1500 g) are placed in a reactor. The mixture is stirred (ca. 200 rpm) and slowly warmed up to 35°C over 1 hr. Then the mixture is warmed up to 40°C over 30 minutes and stirred at 40°C one more hour (total heating time is 2.5 hr from the beginning of heating). Subsequently, the mixture is cooled to ca. 10°C and stirred at this temperature for ca. 30 minutes. Then it is filtered, the precipitate is thoroughly pressed and washed with water (3x 250mL). The precipitate-white to off-white crystals - is dried at 105°C. The yield is 87.5%) (106.86 g). The purity of the crude product is 99.69%) as determined by HPLC.
Example 2.
Crystallization of crude zaleplon Crude zaleplon obtained in the above Example 1 is placed in a reactor equipped with a stirrer, methanol (8: 1, v/w) is added and the mixture is heated to reflux (temperature ca. 65°C). After the crystals completely dissolved, stirring is continued under reflux for another 20-30 minutes. Then the solution is cooled to 10°C and stirred at this temperature for 2 hours, until all the product crystallized. The precipitate is separated from the mother liquor under reduced pressure, washed with methanol (5°C, lx 250 ml), thoroughly pressed and dried at 80°C. Yield of crystallization: 90%. Purity of the product (as determined by HPLC): 99.98%.
Example 3 (comparative)
A comparative study of the processes for zaleplon preparation was conducted, using as the reaction medium aqueous solutions of formic acid (according to the present invention), acetic acid (prior art) and propionic acid (as reference), at various acid concentrations.
The selectivity of these reactions was assayed by HPLC (C18, Luna 250x5 mm column; mobile phase: pH 6.8 buffer- acetonitrile mixture, 2: 1 v/v; a Waters chromatograph with a PDD detector). The results are summarized in the Table below.
Figure imgf000007_0001
As it can be seen from the above Table, by replacing acetic acid with its higher homologue- propionic acid, the formation of the undesirable isomer is not avoided. However, by running the reaction in formic acid solutions the desired product is obtained practically free from the isomer.
Example 4.
Crystallization of crude zaleplon in a large scale Technical zaleplon (5 kg) is placed in a reactor equipped with a stirrer, 40 1 of methanol is added and the mixture is heated to reflux and maintained under these conditions until all the product dissolves (ca 30 min). Then the solution while still hot is filtered through candle filter to remove mechanical impurities and obtained clear solution is cooled to 10°C and stirred at this temperature for 2 hours. Precipitated solid is filtered under reduced pressure, washed with cold (5°C) methanol (2x 500 ml) and dried in a shelf dryer at 80°C. 4,52 kg of the pure product is obtained (yield of crystallization: 90%). Purity of the product (as determined by HPLC): 99.98%.

Claims

1. A process for the preparation of zaleplon (N-[3-(3-cyano- pyrazolo[l,5-a]pyrinύdin-7-yl)phenyl]-N-ethylacetan ide), which comprises reaction 3-dl ethyla-mino-l-(3-N-ethyl-N-acetylaπιino- phenyl)-2-propen-l-one with 3-a-rninopyrazole-4-carbonitrile, characterized in that the reaction is carried out in an aqueous solu- tion of formic acid, at formic acid concentrations in the range of 20-80% (w/w).
2. The process of claim 1, wherein the concentration of said formic acid solution is in the range of 35-45% (w/w).
3. The process of claim 1, wherein after the reaction is complete, the reaction mixture is diluted with water to achieve a concentration of formic acid below 40% (w/w).
4. The process of any of the claims 1, 2 or 3, additionally comprising crystallization of crude zaleplon, preferably from a lower al- kyl alcohol selected from methanol, ethanol or isopropanol or from lower organic ester such as ethyl acetate or butyl acetate.
PCT/PL2003/000043 2002-05-14 2003-05-12 A process for the preparation of zaleplon Ceased WO2003095456A1 (en)

Priority Applications (8)

Application Number Priority Date Filing Date Title
CA002482545A CA2482545A1 (en) 2002-05-14 2003-05-12 A process for the preparation of zaleplon
DE60309159T DE60309159D1 (en) 2002-05-14 2003-05-12 PROCESS FOR THE PREPARATION OF ZALEPLONE
AU2003243061A AU2003243061A1 (en) 2002-05-14 2003-05-12 A process for the preparation of zaleplon
BR0304837-3A BR0304837A (en) 2002-05-14 2003-05-12 Process for the preparation of n- [3- (3-cyano-pyrazolo [1,5-a] pyrimidin-7-yl) phenyl] -n-ethylacidamide) (zaleplon)
US10/514,045 US7057041B2 (en) 2002-05-14 2003-05-12 Process for the preparation of zaleplon
EP03750002A EP1506199B1 (en) 2002-05-14 2003-05-12 A process for the preparation of zaleplon
UA20041109259A UA77292C2 (en) 2002-05-14 2003-12-05 A process for the preparation of zaleplon
NO20040029A NO20040029L (en) 2002-05-14 2004-01-05 Process for the preparation of zaleplon

Applications Claiming Priority (2)

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PLP-353870 2002-05-14
PL353870A PL207322B1 (en) 2002-05-14 2002-05-14 Method of manufacture of zaleplone

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EP (1) EP1506199B1 (en)
AT (1) ATE342903T1 (en)
AU (1) AU2003243061A1 (en)
BR (1) BR0304837A (en)
CA (1) CA2482545A1 (en)
DE (1) DE60309159D1 (en)
ES (1) ES2275110T3 (en)
NO (1) NO20040029L (en)
PL (1) PL207322B1 (en)
RU (1) RU2004136843A (en)
UA (1) UA77292C2 (en)
WO (1) WO2003095456A1 (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1406871A4 (en) * 2001-06-12 2005-01-26 Biogal Gyogyszergyar Process for the production of n- 3-(3-cyanopyrazolo 1,5-a] pyrimidin-7-yl)phenyl]-n-ethylacetamide (zaleplon)
WO2005073235A3 (en) * 2004-02-02 2005-10-06 Richter Gedeon Vegyeszet Process for the synthesis of n- [3-(3-cyanopyrazolo [1,5a] pyrimidin-7-yl)-phenyl]-n-ethyl-acetamide
US7348429B2 (en) 2001-06-12 2008-03-25 TEVA Gyógyszergyár Zártköruen Muködö Részvénytársaság Process for purifying N-[3-(3-cyanopyrazolo[1,5-a]pyrimidin-7-yl)phenyl]-N-ethylacetamide(zaleplon) and crystalline forms of zaleplon accessible with the process

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9618162B2 (en) 2014-04-25 2017-04-11 Cree, Inc. LED lamp

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0208846A1 (en) * 1983-06-23 1987-01-21 American Cyanamid Company [7-(3-Disubstituted amino)phenyl]pyrazolo[1,5-a]pyrimidines
EP0776898A1 (en) * 1995-12-01 1997-06-04 American Cyanamid Company Process improvement in the synthesis of N-[3-(3-cyanopyrazolo [1,5-a]pyrimidin-7-yl)phenyl]-N-ethyl-acetamide
WO2002100828A2 (en) * 2001-06-12 2002-12-19 Biogal Gyogyszergyar Rt Process for the production of zaleplon

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0208846A1 (en) * 1983-06-23 1987-01-21 American Cyanamid Company [7-(3-Disubstituted amino)phenyl]pyrazolo[1,5-a]pyrimidines
EP0776898A1 (en) * 1995-12-01 1997-06-04 American Cyanamid Company Process improvement in the synthesis of N-[3-(3-cyanopyrazolo [1,5-a]pyrimidin-7-yl)phenyl]-N-ethyl-acetamide
WO2002100828A2 (en) * 2001-06-12 2002-12-19 Biogal Gyogyszergyar Rt Process for the production of zaleplon

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1406871A4 (en) * 2001-06-12 2005-01-26 Biogal Gyogyszergyar Process for the production of n- 3-(3-cyanopyrazolo 1,5-a] pyrimidin-7-yl)phenyl]-n-ethylacetamide (zaleplon)
US7348429B2 (en) 2001-06-12 2008-03-25 TEVA Gyógyszergyár Zártköruen Muködö Részvénytársaság Process for purifying N-[3-(3-cyanopyrazolo[1,5-a]pyrimidin-7-yl)phenyl]-N-ethylacetamide(zaleplon) and crystalline forms of zaleplon accessible with the process
WO2005073235A3 (en) * 2004-02-02 2005-10-06 Richter Gedeon Vegyeszet Process for the synthesis of n- [3-(3-cyanopyrazolo [1,5a] pyrimidin-7-yl)-phenyl]-n-ethyl-acetamide
EA010830B1 (en) * 2004-02-02 2008-12-30 Рихтер Гедеон Ведьесети Дьяр Рт. Process for the synthesis of n- [3-(3-cyanopyrazolo [1,5a] pyrimidin-7-yl)-phenyl]-n-ethyl-acetamide

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CA2482545A1 (en) 2003-11-20
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US7057041B2 (en) 2006-06-06
RU2004136843A (en) 2005-07-20
US20050234237A1 (en) 2005-10-20
BR0304837A (en) 2004-08-17
EP1506199A1 (en) 2005-02-16
PL353870A1 (en) 2003-11-17
NO20040029L (en) 2004-01-05
UA77292C2 (en) 2006-11-15
ATE342903T1 (en) 2006-11-15
EP1506199B1 (en) 2006-10-18
AU2003243061A1 (en) 2003-11-11
DE60309159D1 (en) 2006-11-30

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