Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
1999-07-27
2001-01-09
Higel, Floyd D. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
active
06172237
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for preparing eprosartan. This compound is described in U.S. Pat. No. 5,185,351 as being an angiotensin II receptor antagonist useful in the treatment of hypertension, congestive heart failure and renal failure.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 5,185,351 describes processes for the preparation of imidazole compounds. One of the processes described in this application is the reaction of an aldehyde with a substituted half-acid, half-ester derivative of a malonate. Although this process produces the imidazoles claimed therein, there was a need to improve this process when preparing compounds, such as eprosartan, on a commercial scale.
It has now been found that eprosartan can be prepared by reacting 4-[(2-n-butyl-5-formyl-1H-imidazol-1-yl)methyl]benzoic acid or the bisulfite addition compound of 4-[(2-n-butyl-5-formyl-1H-imidazol-1-yl)methyl]benzoic acid (PCT Application WO 95/32189) with (2-thienylmethyl)propanedioic acid, mono-ethyl ester to produce eprosartan efficiently in high yield and high purity. The efficiency of this process and the quality and yield of the imidazole product are particularly important when preparing said product on a large scale for therapeutic use.
DESCRIPTION OF THE INVENTION
The present invention provides a process for the preparation of eprosartan, which is (E)-&agr;-[[2-butyl-1-[(4-carboxyphenyl)methyl]-1H-imidazol-5-yl]methylene]-2-thiophene propanoic acid, a compound of formula (I):
or a pharmaceutically acceptable salt thereof, which process comprises reacting a compound of formula (II):
or an acid or a base addition salt thereof, with a compound of formula (III):
wherein R′ is C
1-4
alkyl, at reduced pressure in the presence of a catalyst, such as piperidine or piperidinium propionate in an excess of propionic acid, and thereafter hydrolyzing the R′ ester and optionally forming a pharmaceutically acceptable salt.
Alternately, a formula (I) compound can be prepared by reacting a compound of formula (IV):
with a formula (III) compound at reduced pressure in the presence of a catalyst, such as piperidine or piperidinium propionate in an excess of propionic acid, and thereafter hydrolyzing the R′ ester and optionally forming a pharmaceutically acceptable salt.
Acid addition salts of formula (I) and (II) compounds are formed with the appropriate inorganic or organic acids by methods known in the art. Representative examples of suitable acids are maleic, fumaric, acetic, succinic, hydrochloric, hydrobromic, sulfuric, phosphoric or methanesulfonic. Preferably, the pharmaceutically acceptable acid addition salt for the formula (I) compound is the methanesulfonic acid addition salt.
Base addition salts of formula (I) and (II) compounds are formed with the appropriate inorganic or organic bases by methods known in the art. Cationic salts are prepared by treating the parent compound with an excess of an alkaline reagent, such as hydroxide, carbonate or alkoxide, containing the appropriate cation; or with an appropriate organic amine. Representative examples of cations are Li
+
, Na
+
, K
+
, Ca
++
, Mg
++
and NH
4
+
. The preferred salt form for the formula (II) compound is
As used herein, C
1-4
alkyl means an alkyl group of 1-4 carbons, branched or unbranched. C
1-4
alkyl includes methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and t-butyl. The preferred R′ C
1-4
alkyl group is ethyl.
Typically the process is carried out by combining 4-[(2-n-butyl-5-formyl-1H-imidazol-1-yl)methyl]benzoic acid or the bisulfite addition compound of 4-[(2-n-butyl-5-formyl-1H-imidazol-1-yl)methyl]benzoic acid with (2-thienylmethyl)-propanedioic acid, mono-ethyl ester in a suitable solvent, such as toluene, in the presence of a catalyst, for example, in the presence of piperidinium propionate and an excess of propionic acid, at a suitable temperature, such as at a temperature of about 75° C. to about 100° C., preferably at a temperature of 80° C.-85° C., at reduced pressure, such as at an internal pressure reduced to about 9-13 inches of Hg, preferably 11 inches of Hg. The ester precursors to the formula (I) compound are hydrolyzed to the corresponding formula (I) carboxylic acid using base, such as aqueous sodium or potassium hydroxide. Thereafter, pharmaceutically acceptable salts may be prepared as described above.
Alternately, 4-[(2-n-butyl-5-formyl-1H-imidazol-1-yl)methyl]benzoic acid or the bisulfite addition compound of 4-[(2-n-butyl-5-formyl-1H-imidazol-1-yl)methyl]benzoic acid and (2-thienylmethyl)propanedioic acid, mono-ethyl ester are reacted to give (E)-&agr;-[[2-butyl-1-[(4carboxyphenyl)methyl]-1H-imidazol-5-yl]methylene]-2-thiophene propanoic acid by heating the two substrates in toluene at reflux under reduced pressure and in the presence of piperidine as catalyst followed by hydrolysis of the intermediate ester ethyl (ethyl (E)-&agr;-[[2-butyl-1-[(4-carboxyphenyl)methyl]-1H-imidazol-5-yl]methylene]-2-thiophenepropanoate). In this preparation, 4-[(2-n-butyl-5-formyl-1H-imidazol-1-yl)methyl]benzoic acid or the bisulfite addition compound of 4-[(2-n-butyl-5-formyl-1H-imidazol-1-yl)methyl]benzoic acid, (2-thienylmethyl)propanedioic acid, mono-ethyl ester, and toluene are charged to a glass lined steel vessel and are initially heated to 55-60° C. to afford a homogenous solution. The catalyst (66 mol % piperidine) is added and the reaction is heated to reflux (70-75° C.) under reduced pressure. Reflux conditions are maintained for 20-35 hours and additional (2-thienylmethyl)-propanedioic acid, mono-ethyl ester is added. Once the reaction is complete, water and aqueous sodium hydroxide are added to the vessel and the reaction mixture heated at reflux under atmospheric conditions for 1-3 hours. The reaction is deemed complete when the level of ethyl (E)-&agr;-[[2-butyl-1-[(4-carboxyphenyl)-methyl]-1H-imidazol-5-yl]methylene]-2-thiophene propanoate is less than 2.0%. The reaction is cooled to 45-50° C. and the aqueous and organic phases separated. The toluene phase is discarded. Ethanol is added to the aqueous phase and the solution is acidified with aqueous hydrochloric acid until a pH of 5.0 to 5.4 is achieved, maintaining the temperature at 50-55° C. The product slurry is cooled and allowed to stir at 10-15° C. for 2 hours. The product is isolated by centrifugation, washed and stored. Thereafter, pharmaceutically acceptable salts may be prepared as described above.
The reaction between 4-[(2-n-butyl-5-formyl-1H-imidazol-1-yl)methyl]benzoic acid or the bisulfite addition compound of 4-[(2-n-butyl-5-formyl-1H-imidazol-1-yl)methyl]benzoic acid and (2-thienylmethyl)propanedioic acid, mono-ethyl ester catalyzed with piperidine can be run successfully in solvents (and/or solvent systems) other than toluene; these solvents include cyclohexane, cyclohexane:dichloroethane (12:5 or 1:1), cyclohexane:pyridine (12:5), and cyclohexane:ethyl acetate:pyridine (8:3:1).
Other catalysts which successfully promote the reaction between 4-[(2-n-butyl-5-formyl-1H-imidazol-1-yl)methyl]benzoic acid or the bisulfite addition compound of 4-[(2-n-butyl-5-formyl-1H-imidazol-1-yl)methyl]benzoic acid and (2-thienylmethyl)propanedioic acid, mono-ethyl ester in toluene under reduced pressure besides piperidine include morpholine, 1-methylpiperazine, and pyrrolidine.
The invention is illustrated by the following examples. The examples are not intended to limit the scope of this invention as defined hereinabove and as claimed hereinbelow.
REFERENCES:
patent: 5185351 (1993-02-01), Finkelstein et al.
patent: 5395847 (1995-03-01), Weinstock et al.
patent: 5444080 (1995-08-01), Girard et al.
Flisak Joseph Robert
Labaw Clifford S.
Liu Li
Higel Floyd D.
Kinzig Charles M.
McCarthy Mary E.
SmithKline Beecham Corporation
Venetianer Stephen
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