Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07K—PEPTIDES
  • C07K5/00—Peptides containing up to four amino acids in a fully defined sequence; Derivatives thereof
  • C07K5/04—Peptides containing up to four amino acids in a fully defined sequence; Derivatives thereof containing only normal peptide links
  • C07K5/08—Tripeptides
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07K—PEPTIDES
  • C07K5/00—Peptides containing up to four amino acids in a fully defined sequence; Derivatives thereof
  • C07K5/04—Peptides containing up to four amino acids in a fully defined sequence; Derivatives thereof containing only normal peptide links
  • C07K5/08—Tripeptides
  • C07K5/0821—Tripeptides with the first amino acid being heterocyclic, e.g. His, Pro, Trp
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P7/00—Drugs for disorders of the blood or the extracellular fluid
  • A61P7/02—Antithrombotic agents; Anticoagulants; Platelet aggregation inhibitors
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07K—PEPTIDES
  • C07K5/00—Peptides containing up to four amino acids in a fully defined sequence; Derivatives thereof
  • C07K5/04—Peptides containing up to four amino acids in a fully defined sequence; Derivatives thereof containing only normal peptide links
  • C07K5/06—Dipeptides
  • C07K5/06139—Dipeptides with the first amino acid being heterocyclic

Definitions

• the present invention relates to a process for the preparation of acetyl-amidiniophenylalanyl-cyclohexylglycyl-pyridinioalaninamides of the formula I,
• the anions X are physiologically acceptable anions, and their analogs, which are effective inhibitors of the blood coagulation factor Xa and which can be used, for example, for preventing thromboses.
• the process according to the invention comprises the coupling of 2-[2-acetylamino-3-(4-amidinophenyl)propionylamino]-2-cyclohexylacetic acid, which is obtained from 2-[2-acetylamino-3-(4-cyanophenyl)acryloylamino]-2-cyclohexylacetic acid by asymmetric hydrogenation and conversion of the cyano group into the amidine, or a salt thereof, with a 3-(2-amino-2-carbamoylethyl)-1-methylpyridinium salt or a salt thereof.
• the invention furthermore provides starting materials and intermediates for this process, processes for their preparation and acetyl-(S)-4-amidiniophenylalanyl-(S)-cyclohexylglycyl-(S)-(1 -methyl-3-pyridinio)alaninamide as ditosylate salt.
• WO-A-95/29189 Compounds of the formula I and analogs thereof are described in WO-A-95/29189 and the corresponding U.S. Pat. No. 5,849,510. According to WO-A-95/29189, they are prepared by solid-phase synthesis using protective-group techniques where 3-pyridylalanine is coupled to a resin using a Knorr linker and then coupled with cyclohexylglycine, the pyridine nitrogen atom is quaternized, the dipeptide is coupled with acetyl-4-amidinophenylalanine, prepared from 4-cyanophenylalanine, and the product is, following cleavage from the resin, purified by chromatography. This solid-phase process is unsuitable for preparing multi-kg quantities required for development tasks, such as toxicological and clinical studies, or even for the synthesis on an industrial scale.
• a pharmaceutically active compound is acceptable as development product and for later use in patients only if the preparation can be carried out on the required scale and with adequate purity, where purity, in the case of compounds having centers of asymmetry, includes in particular also stereochemical purity.
• the compounds of the formula I contain a peptidic dication carrying positive charges in amidinium group and the N-methylpyridinium group.
• the amorphous nature of the salts is a considerable problem in the preparation of a compound of the formula I on a relatively large scale, since it renders recrystallization impossible and fractional precipitation is the only purification method feasable for use on a large scale.
• the purification efficiency of a precipitation is, of course, a lot lower than that of a crystallization, and it is therefore necessary to prepare even the crude compound of the formula I with a suitable anion X in a reaction that proceeds as smoothly as possible, so that in the end a product of clinically acceptable purity can be obtained by fractional precipitation.
• the preparation process naturally also has to be acceptable with respect to factors such as, for example, yield, the number of steps or the availability and the price of the starting materials.
• the product is isolated in the form of the trifluoroacetic acid salt, by evaporation of the reaction solution obtained in the last reaction step, dissolving the residue, addition of trifluoroacetic acid, filtration and freeze-drying.
• the purity of the product obtained by this process including the stereochemical purity, does not meet the requirements, necessitating a complicated chromatographic purification which involves heavy losses and is unacceptable when conducting the process on a large scale.
• the process has considerable technical disadvantages, for example the use of solvents such as diethyl ether or hexane or working at low temperatures, and the use of expensive starting materials (small amounts of the three enantiomerically pure unnatural a-amino acids (S)-3-pyridylalanine, (S)-cyclohexylglycine and (S)-4-amidinophenylalanine (or (S)-4-cyanophenylalanine; the amidino group can be formed from the cyano group) contained as building blocks in the compounds of the formula I are commercially available, but these compounds are very expensive). Accordingly, there is still a need for a smooth-running process for the large-scale preparation of compounds of the formula I having a suitable anion X.
• solvents such as diethyl ether or hexane or working at low temperatures
• expensive starting materials small amounts of the three enantiomerically pure unnatural a-amino acids (S)-3-pyridylalan
• the molecule of the formula I is constructed by coupling the C-terminal dipeptide of pyridylalanine and cyclohexylglycine with the N-terminal amino acid amidinophenylalanine (or cyanophenylalanine), in the process according to the invention, the molecule is synthesized by coupling the N-terminal dipeptide of amidinophenylalanine and cyclohexylglycine with the C-terminal amino acid pyridylalanine.
• the structural unit CH—CO—NH—CH—CO which has two centers of chirality which are sensitive to epimerization, is not formed in a coupling reaction of two chiral a-amino acids as in the known processes, but by asymmetric hydrogenation.
• the peptide coupling is clean and quantitative, with inexpensive reagents being used. Epimerization is very low.
• the compounds of the formula I are obtained in high yield and in high chemical purity and stereochemical purity by fractional precipitation. Chromatographic purifications or expensive and complicated technologies, such a freeze-drying, are not necessary to obtain the desired purities.
• the present invention also provides processes which are analogous to the above process and in which, using starting materials having a different configuration, stereoisomers of the compounds of the formula I are prepared, for example compounds in which the center of chirality in the amidinophenylalanine unit has the (R) configuration and/or the center of chirality in the cyclohexylglycine unit has the (R) configuration and/or the center of chirality in the pyridylalanine unit has the (R) configuration, or compounds which, on one or more of the centers of chirality, are present as (RS) mixtures.
• the invention furthermore provides processes which are analogous to the above processes and in which, using the appropriate starting materials, analogs of compounds of the formula I (and their stereoisomers) are prepared, for example compounds which, instead of the methyl group in the acetylamino group in the amidinophenylalanine unit, contain a (C 1 -C 4 )-alkyl group and/or, instead of the methyl group at the quarternary pyridine nitrogen atom, contain a (C 1 -C 4 )-alkyl group, examples of such (C 1 -C 4 )-alkyl groups being methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl.
• the invention also relates to processes for the preparation of compounds of the formula I′:
• R 1 is C 1 -C 4 alkyl
• R 2 is C 1 -C 4 alkyl
• A is CH in the R or S configuration
• B is CH in the R or S configuration
• G is CH in the R or S configuration.
• the processes for the preparation of a compound of the formula I′ comprise converting a compound of the formula II′ into a compound of the formula III′ or its salt with an acid HX, the compound of formula II′ having the structure:
• R 1 and B have the same meanings as in the formula I′,
• said converting comprises catalytic hydrogenation and conversion of the cyano group into an amidino group
• R 1 , A, and B have the same meanings as in the formula I′;
• R 2 and G have the same meanings as in the formula I′,
• anions X ⁇ of the formulae I′ and IV′ and of the acid HX are physiologically acceptable anions, and are identical or different.
• Physiologically acceptable anions X in the compounds of the formulae I and IV and in the acid HX can be, for example, chloride, bromide, iodide, methanesulfonate, toluene-4-sulfonate, acetate, benzoate and others.
• X is an anion equivalent.
• X is preferably an anion to which there are no objections from a physiological point of view, even if the compounds of the formula I are used in relatively high doses and for a relatively long period of time, and/or which imparts to the compounds of the formula I favorable properties with respect to pharmaceutical processing and the pharmacological action, for example a suitable solubility in water, and/or which imparts to the compounds of the formulae I and IV favorable properties with respect to technically conducting of the process according to the invention, for example simplicity of the process, suitable solubilities in the solvents used, the fact that they are easy to precipitate and/or easy to filter, etc.
• the invention relates to a process for the preparation of the compound of the formula I in the form of the ditosylate salt, i.e. the compound of the formula Ia,
• the compound of the formula Ia is easy to precipitate and easy to filter and is obtained in a particularly high yield and purity.
• the present invention also provides the compound of the formula la per se and its solvates, for example adducts with water or alcohols, the use of the compound of the formula la as an inhibitor of factor Xa or for the treatment, including therapy and prevention, of thromboembolic disorders, such as thromboses, myocardial infarction or angina pectoris, and the use of the compound of the formula Ia for preparing medicaments for these medical applications, and pharmaceutical preparations (or pharmaceutical compositions) comprising an effective amount of the compound of the formula Ia and a pharmaceutically acceptable carrier, i.e. one or more pharmaceutically acceptable excipients and/or additives.
• a pharmaceutically acceptable carrier i.e. one or more pharmaceutically acceptable excipients and/or additives.
• the present invention relates to a process for preparing the compound of the formula la, which comprises reacting the compound of the formula III or its toluene-4-sulfonic acid salt with the compound of the formula IVa or its toluene-4-sulfonic acid salt to give the compound of the formula Ia.
• the compounds can also be named in different ways, for example as dicationic pyridinium salts which contain a positively charged amidinio group as a substituent and two negatively charged anions X as counterions, or as acid addition salts of the acid HX and a monocationic pyridinium salt which contains a free amidino group as a substituent and a negatively charged anion X as counterion.
• the compound of the formula Ia could be referred to as 3- ⁇ (S)-2-[(S)-2-((S)-2-acetylamino-3-(4-amidiniophenyl)propionylamino)-2-cyclohexylacetylamino]-2-carbamoylethyl ⁇ -1-methylpyridinium ditosylate or as 3- ⁇ (S)-2-[(S)-2-((S)-2-acetylamino-3-(4-amidinophenyl)propionylamino)-2-cyclohexylacetylamino]-2-carbamoylethyl ⁇ -1-methylpyridinium tosylate toluene-4-sulfonic acid salt, or else as N-acetyl-4-(aminoimino-methyl)-L-phenylalanyl-L-2-cyclohexylglycyl-3-(1-methylpyridinium-3-yl)
• the compound of the formula II can be converted into the compound of the formula III by initially hydrogenating the compound of the formula II in a stereoselective manner to give the compound of the formula VI, followed by conversion of the cyano group into amidine, or by initially converting the cyano group into the amidine, followed by stereoselective hydrogenation.
• the hydrogenation to give the compound of the formula VI is carried out first, followed by conversion of the cyano group into the amidine.
• the stereocontrolled hydrogenation of the C ⁇ C double bond in the dehydrodipeptide of the formula II can be carried out using selective heterogeneous catalysts or chiral transition metal complexes. It is preferably carried out using chiral metal complexes of rhodium (I) or ruthenium (II), particularly preferably of rhodium (I).
• the transition metal catalyst can be cationic or neutral, and it can be employed in isolated form or be formed in situ in the hydrogenation medium from the chiral ligand and a precatalyst, for example a rhodium salt such as [Rh(COD)Cl] 2 or [Rh(COD) 2 ] + Y ⁇ (COD is 1,5-cyclooctadiene, Y here is, for example, tetrafluoroborate).
• the hydrogenation catalyst can be present in the hydrogenation medium in homogeneously dissolved form, or it can be heterogenized by attachment to a solid support, as a result of which it can be removed easily by filtration after the hydrogenation has ended and be re-used for the next hydrogenation batch.
• chiral ligands for the transition metal complex numerous different compounds are suitable. A review of such chiral ligands can be found, for example, in I. Ojima, Catalytic Asymmetric Synthesis, pages 445-447, VCH, New York 1993.
• a rhodium (I) complex with a chiral phosphine as ligand is used for the asymmetric hydrogenation of the compound of the formula II to give the compound of the formula VI.
• a Rh(I)-(+)-BPPM catalyst i.e.
• the catalyst is preferably prepared in situ from a rhodium salt and the ligand.
• Suitable solvents for the stereoselective hydrogenation of the compound of the formula II to give the compound of the formula VI are, for example, ethers, in particular water-miscible ethers, or lower alcohols, such as methanol, ethanol or isopropanol.
• the hydrogenation is particularly preferably carried out in methanol.
• the hydrogenation is preferably carried out at temperatures of from about 20 to about 60° C., particularly preferably from about 30 to about 50° C., for example at about 40° C.
• the hydrogen pressure that is established depends on the apparatus used; it is preferred to establish a hydrogen pressure of from about 1 to about 20 bar, particularly preferably from about 5 to about 15 bar, for example about 10 bar.
• the reaction is carried out with substantial exclusion of oxygen and very intensive mixing.
• the hydrogenation product can be isolated in a simple manner by adding water and filtering off or centrifuging off the resulting precipitate.
• the asymmetric hydrogenation proceeds with very high stereoselectivity and yield and gives the compound of the formula VI with a diastereomeric excess of 98.4% d.e. of (S,S)-isomer in the crude product and 99.5% d.e. in the isolated product, at an isolated yield of 97%.
• these excellent results are obtained at very high substrate/catalyst ratios of about 2000:1 to about 5000:1.
• the present invention also provides the compound of the formula VI per se, i.e. (S)-2-[(S)-2-acetylamino-3-(4-cyanophenyl)propionylamino]-2-cyclohexylacetic acid and its salts, for example alkali metal or alkaline earth metal salts, such as the sodium salt or the potassium salt, the above process for its preparation and its use as intermediate, in particular as intermediate for pharmaceutically active substances.
• salts for example alkali metal or alkaline earth metal salts, such as the sodium salt or the potassium salt
• the cyano group in the compound of the formula VI can be converted into the amidine by various methods known per se to the person skilled in the art, for example by the method described in WO-A-97/22712 which does, however, have a number of disadvantages when carried out on an industrial scale, for example the use of hydrogen sulfide.
• the conversion is preferably carried out by initially adding hydroxylamine to the cyano group in the compound of the formula VI, with formation of the N-hydroxyamidine intermediate of the formula VII.
• the compound of the formula VII is then converted in a simple manner by hydrogenolysis, i.e. by reaction with hydrogen in the presence of a hydrogenation catalyst, into the amidine of the formula III.
• the principle of this reaction sequence is described, for example, in H. Jendralla et al., Tetrahedron 51 (1995) 12047.
• the required hydroxylamine is advantageously prepared in situ from a hydroxylammonium salt, for example hydroxylammonium chloride or hydroxylammonium sulfate, and a base, for example a basic sodium or potassium compound or a tertiary amine.
• a hydroxylammonium salt for example hydroxylammonium chloride or hydroxylammonium sulfate
• a base for example a basic sodium or potassium compound or a tertiary amine.
• the base used for the reaction of the compound of the formula VI with a hydroxylammonium salt is preferably sodium hydrogen carbonate.
• the hydroxylamine or the hydroxylammonium salt is preferably employed in excess, for example in an amount of from about 1 to about 2 mol per mole of the compound of the formula VI.
• Suitable solvents for the reaction with hydroxylamine or a hydroxylammonium salt are, for example, lower alcohols. A particularly preferred solvent is methanol.
• the compound of the formula VII is preferably prepared at temperatures of from about 20 to about 65° C., particularly preferably at temperatures from about 40 to about 60° C. If a hydroxylammonium salt is employed, the added base also converts the carboxylic acid function in the compound of the formula VI or that in the compound of the formula VII into the corresponding salt.
• this compound can be isolated in an advantageous manner in the form of a salt at the carboxylic acid function, i.e., if the base used is a sodium compound, in the form of the sodium salt of the carboxylic acid, which can be precipitated by concentrating the reaction mixture and/or admixing with a relatively nonpolar solvent and removed by filtration or centrifugation.
• Preferred solvents for the hydrogenolysis are, in particular if the N-hydroxyamidine is employed in the form of a salt, polar solvents, for example lower alcohols or acetic acid.
• a particularly preferred solvent is acetic acid.
• the resulting amidine compound of the formula III can be isolated as such (i.e., in free form) or in the form of an acid addition salt (the amidine compound of the formula III as such might not be present in the form having a free amidino group and a carboxylic acid group, which is represented by the formula Ill, but in the tautomeric form of the formula IIIa, i.e. as betaine or zwitterion, in which the carboxylic acid group is dissociated to the carboxylate anion and the amidine unit is protonated to the amidinium cation).
• the compound of the formula III is obtained as acid addition salt.
• an acid of the formula HX a salt of the formula VIII is formed, in which the anion X is preferably a physiologically acceptable anion, for example iodide or tosylate.
• the compounds of the formula VIII are the abovementioned salts of the acid HX and the compound of the formula III. If the compound of the formula III is to be isolated in the form of an acid addition salt, the acid HX is preferably chosen such that the compound of the formula VII contains the same anion as the compound of the formula I to be prepared.
• the ditosylate salt of the formula la is to be prepared and the compound of the formula III is to be isolated as a salt
• preference is given to preparing the amidinium tosylate of the formula VIII where X ⁇ TosO ⁇ for example by adding toluene-4-sulfonic acid during work-up.
• the present invention also provides the compounds of the formula III and their salts and the compounds of the formulae IIIa and VIII per se, i.e. (S)-2-[(S)-2-acetylamino-3-(4-amidinophenyl)propionylamino]-2-cyclohexylacetic acid as betaine (zwitterion) and in the form of their salts, the above process for their preparation and their use as intermediates, in particular as intermediates for pharmaceutically active compounds.
• the peptide coupling of the amidine of the formula III (in the form of a salt or preferably in the form of the betaine of the formula IIIa) with the pyridinioalaninamide of the formula IV or a salt thereof to give the compound of the formula I can be carried out by customary coupling methods known to the person skilled in the art.
• the pyridinioalaninamide is preferably employed in the form of a salt with the acid HX, i.e. in the form of the dication salts of the formula IX, in which the anions X are preferably physiologically acceptable anions.
• the second equivalent of the anion X which is required for preparing the compound of the formula I in addition to the equivalent of the anion X introduced by the compound of the formula IV, can be added in the form of an equivalent of the acid HX or a salt of the acid HX during work-up of the reaction mixture of the peptide coupling.
• Examples of peptide coupling agents suitable for activating the carboxylic acid function or carboxylate function in the compound of the formula III (or IIIa or VIII) which may be mentioned are carbodiimides, such as, for example, dicyclohexylcarbodiimide (DCC) or diisopropylcarbodiimide (DIC), or uronium salts, such as O-[(cyano-ethoxycarbonyl-methylene)amino]-N,N,N′,N′-tetramethyluronium tetrafluoroborate (TOTU) or O-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate (HATU).
• carbodiimides such as, for example, dicyclohexylcarbodiimide (DCC) or diisopropylcarbodiimide (DIC), or uronium salts, such as O-[(cyano
• Activating agents which are particularly preferred in this respect are HATU, DCC/HOObt and DCC/HObt.
• HATU HATU
• DCC/HOObt the coupling gives a product which contains only 0.7-1.5% of the diastereomer in the crude product.
• DCC/HOObt specially preferred, owing to its considerably lower price, is DCC/HOObt.
• HOObt is preferably employed on a support, for example on Dicalite®.
• the coupling reaction is preferably carried out in a polar solvent (or a solvent mixture).
• Suitable solvents are protic solvents, such as lower alcohols, for example methanol, ethanol or isopropanol, and from among these alcohols, preference is given to isopropanol, since the risk of a conversion of the C-terminal amide group into the ester is lower than with methanol or ethanol.
• the coupling is carried out in aprotic polar solvents in which the coupling proceeds particularly rapidly and cleanly, for example in amides, such as N,N-dimethylformamide (DMF) or N-methyl-2-pyrrolidone (NMP), or in dimethyl sulfoxide (DMSO).
• amides such as N,N-dimethylformamide (DMF) or N-methyl-2-pyrrolidone (NMP)
• DMSO dimethyl sulfoxide
• the coupling is carried out in DMF or NMP, both of which give excellent coupling results and isolated yields of the compound of the formula I of 85-95% (after two product precipitations).
• the coupling is carried out in DMF, since this can be removed more easily from the product.
• the coupling is preferably carried out at temperatures of from about 0 to about 30° C., particularly preferably at from about 0 to about 25° C., for example by initially stirring the reaction mixture at about 10° C. and then allowing it to warm to room temperature.
• a favorable pH (from about 3.3 to 4.2 if X in the compound of the formula IX is tosylate) is generally present during the entire course of the coupling, without the addition of an additional base being required.
• the pH can be adjusted appropriately by adding a base, such as a tertiary amine.
• the peptide coupling requires the addition of at least one equivalent of a base, for example a tertiary amine, such as triethylamine or, preferably, N-ethyldiisopropylamine.
• a base for example a tertiary amine, such as triethylamine or, preferably, N-ethyldiisopropylamine.
• the activating agent used is a carbodiimide together with an N-hydroxybenzotriazine or N-hydroxybenzotriazole reagent, such as, for example, HOObt
• this reagent can be present in substoichiometric amounts or only catalytic amounts, since the N-hydroxy reagent is regenerated during the reaction of the compound of the formula IV with the activated ester intermediately formed from the compound of the formula III and the N-hydroxy reagent.
• the HOObt is preferably employed in an amount of from about 0.15 to about 1 mol per mole of the compound of the formula III, particularly preferably in an amount of from about 0.2 to about 0.3 mol, for example about 0.25 mol, per mole of the compound of the formula III.
• the carbodiimide is preferably employed in a slight excess.
• the coupling is carried out using DCC/HOObt, for example, preferably an amount of from about 1.1 to about 1.4 mol per mole of the compound of the formula III, particularly preferably an amount from about 1.2 to about 1.3 mol, for example about 1.25 mol, per mole of the compound of the formula III is employed.
• the order in which the reactants are added is variable. Preference is given to initially charging the compounds of the formula III and IV or their salts, any base that may be added and the N-hydroxy reagent, and to meter in the carbodiimide, for example in the form of a solution in a solvent such as DMF or NMP, over a period of several hours, for example from about 5 to about 10 hours.
• the coupling at a reaction temperature of about 10° C. followed by stirring at room temperature, is generally completed rapidly, takes place virtually quantitatively and gives the product in high purity.
• the reaction mixture is advantageously initially filtered, and the product is then precipitated by adding a suitable organic solvent.
• the precipitation is preferably carried out using an excess of a lower ketone, such as acetone or methyl ethyl ketone, particularly preferably the DMF solution or NMP solution being added dropwise or by means of a pump to an excess of acetone or methyl ethyl ketone.
• the precipitated product is isolated by filtration or centrifugation, washed and, if desired for increasing the purity, precipitated a second time or else a third time in an analogous manner (for example by dissolving the product in DMF and precipitating it by pumping the solution into acetone or methyl ethyl ketone).
• a third time in an analogous manner (for example by dissolving the product in DMF and precipitating it by pumping the solution into acetone or methyl ethyl ketone).
• the starting materials of the formulae II and IV or their salts, which are used in the process according to the invention described above, can be prepared, for example, by the processes described below.
• the starting material of the formula II and/or the starting material of the formula IV or their salts used are prepared by the processes described below or are in part prepared by the processes described below.
• the compound of the formula II can be obtained by reacting the azlactone of the formula XI with (S)-cyclohexylglycine (formula XII).
• the azlactone of the formula XI which is essentially present as Z isomer, is formed under standard conditions for the Erlenmeyer azlactone synthesis from 4-formylbenzonitrile (formula X) and N-acetylglycine, for example by heating with sodium acetate and acetic anhydride in a solvent, preferably by heating in acetone under reflux.
• the reaction of the compounds of the formulae XI and XII to give the dehydrodipeptide of the formula II is preferably carried out in alkaline solution, for example with addition of one equivalent (based on the cyclohexylglycine) of a base such as sodium hydroxide or potassium hydroxide, in a mixture of water and a water-miscible organic solvent, for example a ketone, such as acetone, or an ether, particularly preferably in a mixture of acetone and water, at temperatures of from about 30 to about 50° C., for example, at about 40° C.
• a base such as sodium hydroxide or potassium hydroxide
• a water-miscible organic solvent for example a ketone, such as acetone, or an ether, particularly preferably in a mixture of acetone and water
• the reaction mixture is acidified, for example with hydrochloric acid, to a pH of about 2.3 and diluted with water, and the precipitate is filtered off or centrifuged off.
• the resulting compound of the formula II is present mainly as Z isomer, the percentage of E isomer is ⁇ 2%.
• the present invention also provides the compounds of the formulae II and XI and salts of the compound of the formula II per se, in particular the Z forms, the above processes for their preparation and their use as intermediates, in particular as intermediates for pharmaceutically active compounds.
• Salts of the compound of the formula II which may be mentioned are, for example, alkali metal and alkaline earth metal salts, such as the sodium salt or the potassium salt.
• the optically pure (S)-cyclohexylglycine (formula XII) required is advantageously prepared by one of the following three routes.
• the starting material used is racemic phenylglycine (formula XIII) which is converted, by hydrogenation of the aromatic ring under standard conditions, into racemic cyclohexylglycine (formula XIV), for example by hydrogenation in the presence of a noble metal catalyst, such as rhodium on carbon, in hydrochloric acid at from about 80 to about 120° C., for example at about 100° C., and at a hydrogen pressure of from about 10 to about 30 bar.
• a noble metal catalyst such as rhodium on carbon
• racemic cyclohexylglycine is then acetylated under standard conditions at the amino group using, for example, acetic anhydride in the presence of a base, such as sodium hydroxide, in water at a temperature of from about 0 to about 30° C. and at a pH of at least 11.
• a base such as sodium hydroxide
• the racemic N-acetyl-cyclohexylgycine (formula XV) is then subjected to an enzymatic racemate resolution using an acylase (L-specific aminoacylase, E.C.3.5.1.14), to give optically pure (S)-cyclohexylglycine (formula XII) and N-acetylcyclohexylglycine containing a high excess of the (R) antipode (formula XVI)
• acylase L-specific aminoacylase
• the selective enzymatic deacetylation of the (S)-N-acetyl-cyclohexylglycine in the (RS) mixture can be carried out, for example, using the acylase “Amano” 30 000 in the presence of cobalt(ll) chloride in water at a pH of about 7.8 and a temperature of about 38 to 40° C.
• the cyclohexylglycine that precipitates out is virtually enantiomerically pure (S) isomer.
• the (R)-N-acetylcyclohexylglycine which remains in the filtrate, can, after racemization, for example by heating with acetic acid and acetic anhydride at about 115° C., again be subjected to enzymatic deacetylation, so that in the end virtually all of the racemic N-acetylcyclohexylglycine is converted into optically pure (S)-cyclohexylglycine.
• a second possibility of preparing (S)-cyclohexylglycine comprises preparing racemic N-acetylcyclohexylglycine (formula XV) in a one-step process by palladium-catalyzed amidocarbonylation from cyclohexanecarbaldehyde, carbon monoxide and acetamide, followed by the described racemate resolution with an acylase (see M. Beller et al., Chem. Eur. J. 4 (1998) 935).
• the phenyl group in enantiomerically pure (S)-phenylglycine (formula XVII) is hydrogenated under racemization-free conditions to the cyclohexyl group.
• suitable catalysts are noble metal catalysts, such as, for example, rhodium on carbon.
• the hydrogenation is preferably carried out in acidic medium, for example in a carboxylic acid, such as glacial acetic acid, particularly preferably in a strong acid, such as, for example, 2N hydrochloric acid or sulfuric acid.
• the hydrogenation proceeds rapidly and without any significant racemization at a temperature of from about 60 to about 80° C. and a hydrogen pressure of, for example, about 20 bar.
• the resulting product is of a similar quality to the product that is obtained from racemic phenylglycine by the process described above.
• the starting material (S)-phenylglycine is more expensive than the starting material (RS)-phenylglycine, but owing to the lower production costs, the process which uses (S)-phenylglycine as starting material is more advantageous.
• the enantiomerically pure starting material of the formula IV or its salt of the formula IX is advantageously prepared starting from pyridine-3-carbaldehyde (formula XVIII), which can be converted under similar conditions as those stated above for the conversion of the compound of the formula X into the compound of the formula XI, into the azlactone of the formula XIX, for example by heating with N-acetylglycine and acetic anhydride in acetone.
• the azlactone of the formula XIX can be solvolyzed with water to give N-acetyldehydropyridylalanine, i.e.
• the carboxylic acid or with a lower alcohol, for example a (C 1 -C 3 )-alkanol, such as methanol or ethanol, to give a carboxylic acid ester, preferably with methanol to give the methyl ester (compare formula XX).
• a lower alcohol for example a (C 1 -C 3 )-alkanol, such as methanol or ethanol
• the subsequent asymmetric hydrogenation is particularly advantageously carried out in an alcohol under acidic conditions, where most or all carboxylic acid functions are converted into the ester, and as the solvolysis of the azlactone of the formula XIX with alcohols proceeds more smoothly than that with water, the compound of the formula XIX is preferably solvolyzed using a lower alcohol, particularly preferably methanol.
• the alcoholysis is preferably carried out in the presence of a weak base, for example a tertiary amine, such as triethylamine, at temperatures of from about 50 to about 65° C.
• a weak base for example a tertiary amine, such as triethylamine
• the methyl ester is preferably isolated in the form of an acid addition salt with a strong acid, i.e. in the form of a compound of the formula XX, where the anion Y here is the anion of a strong acid, for example tetrafluoroborate or tosylate.
• the product of the methanolysis of the azlactone of the formula XIX is precipitated as tetrafluoroborate salt by adding tetrafluoroboric acid, for example an aqueous tetrafluoroboric acid solution, up to a pH of about 1.5 to about 2, for example about 1.9, and the product is, after the precipitation has been brought to completion by addition of a nonpolar solvent, for example an ether, such as methyl tert-butyl ether, filtered off or centrifuged off.
• a nonpolar solvent for example an ether, such as methyl tert-butyl ether
• the next step is an asymmetric catalytic hydrogenation of the dehydropyridylalanine derivative of the formula XX to give the optically active amino acid derivative of the formula XXI.
• this hydrogenation is preferably carried out under acidic conditions, for example in acetic acid, particularly preferably in the presence of a strong acid, for example toluene-4-sulfonic acid or tetrafluoroboric acid, which is employed in at least the stoichiometric amount, for example 1- to 2-times the molar amount, thus converting the pyridine group completely into the pyridinium salt.
• the hydrogenation preference is given to using a pyridinium salt of the formula XX and, if appropriate, additional acid.
• Preferred acids in whose presence the hydrogenation of the salt of the formula XX is carried out are tetrafluoroboric acid and toluene-4-sulfonic acid, in particular tetrafluoroboric acid, which can be used in the form of an aqueous solution.
• the illustrations given above for the catalysts for the hydrogenation of the compound of the formula II to that of the formula VI apply correspondingly.
• the stereocontrolled hydrogenation of the C ⁇ C double bond in the compound of the formula XX can likewise be carried out using selective heterogeneous catalysts or using chiral transition metal complexes. It is preferably carried out using chiral metal complexes of rhodium(I) or ruthenium(II), in particular of rhodium(I).
• the transition metal catalyst can be employed in isolated form or can be formed in situ in the hydrogenation medium, from a chiral ligand and a precatalyst, for example, a rhodium salt, such as [Rh(COD)Cl] 2 .
• the catalyst is preferably prepared in situ.
• chiral ligands for the transition metal complex again numerous different compounds are suitable.
• the catalyst used for the asymmetric hydrogenation of the compounds of the formula XX to the compounds of the formula XXI is a rhodium(l) complex having a chiral phosphine as ligand, particularly preferably an Rh(I)-(+)-phenyl-CAPP catalyst, i.e.
• Further ligands for suitable catalytically active transition metal complexes are listed, for example, in I. Ojima, Catalytic Asymmetric Synthesis, pages 445-447, VCH, New York 1993.
• the hydrogenation of the compound of the formula XX is preferably carried out at temperatures of from about 20 to about 60° C., particularly preferably between about 30 and about 50° C., for example at about 40° C.
• the hydrogen pressure employed depends on the apparatus used; preference is given to a hydrogen pressure of from about 0.2 to about 20 bar, particularly preferably from about 0.2 to about 10 bar, especially preferably of from about 0.5 to about 1 bar, for example about 0.8 bar.
• the hydrogenation is, to increase enantioselectivity, preferably carried out at relatively low hydrogen pressure.
• the hydrogenation product of the formula XXI is, in particular in the case of the tetrafluoroborate salt, preferably isolated by crystallization, for example from an alcohol, such as isopropanol.
• the isolated yield is from about 86 to about 95%, the enantiomeric purity is, depending on the chosen conditions, from about 70% to about 95% e.e. of (S) isomer.
• substrate/catalyst ratios of from about 5 000:1 to about 10 000:1, for example about 8 000:1.
• the methyl ester group in the compounds of the formula XXI is hydrolyzed to give the carboxylic acid group, the acetyl group at the amino group is removed and the amino group is protected in a suitable manner, so that it does not cause any side-reactions during the formation of the carboxamide function.
• Removal of the acetyl group and hydrolysis of the methyl ester to the free carboxylic acid can be carried out simultaneously by treatment with an acid, for example aqueous hydrochloric acid, such as 1N hydrochloric acid, or 4N hydrochloric acid, at temperatures of, for example, from about 60 to about 85° C. or of from about 85 to about 90° C.
• the free amino group is then advantageously immediately converted into an acylamino group which later can be easily deprotected, for example into the benzyloxycarbonylamino group.
• the organic solvent is distilled off, a slightly acidic pH, preferably a pH of about 5, is established and the precipitated compound of the formula XXII is filtered off or centrifuged off. If desired, the purity of the compound of the formula XXII can be increased by recrystallization, for example from water, prior to the preparation of the amide of the formula XXIII.
• the enantiomeric purity of the compounds of the formula XXI or the compound of the formula XXII obtainable therefrom by the process described above is insufficient, it is advantageous to cleave the acetyl group from the amino group in the compound of the formula XXI not by using hydrochloric acid, but enzymatically and thus enantioselectively.
• the enzymatic deacetylation is preferably carried out analogously to the enzymatic deacetylation of (RS)-N-acetylcyclohexylglycine described above, using the acylase “Amano” 30 000.
• the salt of the formula XXI isolated following the hydrogenation is initially dissolved in water and, after addition of a base, for example sodium hydroxide, stirred in the alkaline range, for example at a pH of from about 10 to about 11, to hydrolyze the methyl ester.
• a base for example sodium hydroxide
• the acylase is added at a pH of from about 7.8 to about 7.9 and at a temperature of from about 38 to about 40° C., for example in an amount of from about 5 to about 6 g per kg of the compound of the formula XXI, and the mixture is stirred until the (S)-isomer is deacetylated.
• a water-miscible solvent such as THF
• Z—OSu is added to the reaction mixture
• the reaction with Z—OSu is carried out at a pH of from about 8.0 to about 8.5
• the organic solvent is distilled off
• the mixture is acidified to a pH of about 5
• the precipitated enantiomerically pure product of the formula XXII is then isolated.
• the conversion of the Z-protected amino acid of the formula XXII into the Z-protected amino acid amide of the formula XXIII can be carried out using methods which are customary for such reactions and known to the person skilled in the art.
• the acid of the formula XXII is activated by conversion into the mixed anhydride using an alkyl chloroformate, particularly preferably isobutyl chloroformate.
• This reaction is preferably carried out in the presence of a tertiary amine, for example, N-ethyldiisopropylamine, in an ether such as THF as solvent, at temperatures of from about ⁇ 10 to about 0° C., preferably from about ⁇ 10 to about ⁇ 5° C.
• a tertiary amine for example, N-ethyldiisopropylamine
• an ether such as THF as solvent
• ammonia is introduced, at a temperature of from about ⁇ 10 to about 0° C., preferably from about ⁇ 10 to about ⁇ 5° C., into the solution of the mixed anhydride.
• the compound of the formula XXIII is obtained in a yield of about 87%, with a chemical purity and enantiomeric purity of in each case virtually 100%.
• the methylation of the pyridine nitrogen atom in the compound of the formula XXIII, with formation of the pyridinium salt of the formula XXIV, can be carried out smoothly with numerous methylating agents, for example methyl iodide, methyl bromide, methyl chloride or methyl toluene-4-sulfonate, in a number of solvents, for example alcohols, such as isopropanol, amides, such as DMF, N,N,N′,N′-tetramethylurea, ketones, such as acetone, or ethers, such as THF, preferably at temperatures of from about 40 to about 60° C.
• methylating agents for example methyl iodide, methyl bromide, methyl chloride or methyl toluene-4-sulfonate
• solvents for example alcohols, such as isopropanol, amides, such as DMF, N,N,N′,N′-tetramethylurea
• a further aspect in the selection of the methylating agent is the effect of the anion X, contained in the compounds of the formulae IV, IX and I and originating from the methylating agent, on the properties of these compounds, for example on the solubility of the compound of the formula IV or a salt thereof, which is of importance in the coupling reaction of the compounds of the formulae III and IV, or on the solubilities, the precipitation properties and the physiological compatibility of the compound of the formula I.
• the toluene-4-sulfonates are distinguished, in the case of the compound of the formula IV or the toluene-4-sulfonic acid salt thereof, by the fact that they can be isolated easily, are highly soluble and have a high peptide coupling rate, and in the case of the compound of the formula I, in particular by surprisingly good precipitation properties, purity and yield.
• a particularly preferred methylating agent for the conversion of the compound of the formula XXIII into the compound of the formula XXIV thus is methyl toluene-4-sulfonate.
• the methylation of the compound of the formula XXIII with methyl toluene-4-sulfonate is preferably carried out in a lower alcohol as solvent, for example in isopropanol, at temperatures of from about 40 to about 60° C., for example, at about 50° C.
• the methyl toluene-4-sulfonate is preferably employed in a small excess, for example in about 1 to about 1.2 times the molar amount, based on the compound of the formula XXIII.
• the methylation of the compound of the formula XXIII and the subsequent removal of the benzyloxycarbonyl protective group in the compound of the formula XXIV by hydrogenolysis can be carried out separately.
• the methylation and hydrogenolysis are carried out in a one-pot reaction, without intermediate isolation of the compound of the formula XXIV.
• the compound of the formula XXIV is dissolved, for example by adding water, if it has precipitated from the reaction medium of the methylation, and then hydrogenated under customary conditions, for example in the presence of a customary noble metal catalyst, such as palladium on carbon, at temperatures from about 20 to about 40° C., preferably about 20 to about 30° C., and at a hydrogen pressure of from about 1 to about 20 bar, preferably from about I to about 5 bar, particularly preferably at about 1 bar, i.e. not under hydrogen overpressure.
• a customary noble metal catalyst such as palladium on carbon
• the monocation salt comprising the 3-((S)-2-amino-2-carbamoylethyl)-1-methylpyridinium cation (having a free amino group NH 2 in the 2-position) and an anion X, for example tosylate, iodide or chloride, as counterion, i.e. the compound of the formula IV, can be isolated as such.
• the resulting pyridinioalaninamide is isolated in the form of a salt with the acid HX, i.e. in the form of the dication salt of the formula IX, and to this end, the reaction mixture of the hydrogenolysis is admixed with about one equivalent of the acid HX, i.e.
• the hydrogenation catalyst is filtered off, and the product can then be isolated by concentration and crystallization of the residue, for example from an alcohol such as isopropanol.
• Acetone (80.0 I) was introduced into a mixture of 4-formylbenzonitrile (15.0 kg, 114.5 mol), N-acetylglycine (19.2 kg, 162.4 mol) and anhydrous sodium acetate (9.4 kg, 114.5 mol) followed by introduction, with stirring, of acetic anhydride (35.0 I, 370.5 mol).
• the reaction mixture was stirred under reflux for 1 h.
• the resulting thin yellow suspension was cooled to 50° C. and ice-water (200 I) was added as quickly as possible, with stirring and cooling.
• the mixture was stirred at 20° C. for another 1 h.
• the mixture was heated to an internal temperature of 80° C., and 20 bar of hydrogen were applied.
• the total hydrogenation time was 5-6 h, the hydrogen uptake was about 37 I.
• the mixture was allowed to further hydrogenate at 20 bar for an extra 30-60 min.
• the mixture was then cooled to an internal temperature of 50° C., and the catalyst was filtered off at 50° C. using a pressure filter.
• reaction solution was then filtered through a pressure nutsch covered with a Seitz filter K1000 and activated carbon (1 kg), and the filter residue was washed with 10 1 of acetone.
• the filtrate was then cooled to 14° C.
• 2N hydrochloric acid (about 10 I) was then added over a period of 10 min until a pH of 2.3 had been reached. Stirring was continued for 15 min, and the pH was readjusted using 2N HCl. Over a period of 20 min, the solution was then admixed with stirring with deionized water (160 I), whereupon the title compound precipitated. With stirring, the mixture was cooled to 0° C. and stirred at this temperature for 1 h.
• the precipitated sodium chloride was filtered off with suction using a Seitz filter and washed with methanol (4 I).
• the methanol solution was concentrated to about 10 I using a rotary evaporator at a bath temperature of about 40° C., and added dropwise, with vigorous stirring, to isopropanol (60 I). This resulted in the precipitation of the sodium salt of the N-hydroxyamidine.
• the mixture was concentrated under reduced pressure, at about 40° C. and with vigorous stirring, to a volume of about 50 I. Stirring was then continued at 15° C. for 1 h, and the product was filtered off through a pressure nutsch.
• the precipitate was washed with isopropanol (10 I) and dried on the nutsch filter overnight, in a stream of nitrogen.
• the reaction mixture was allowed to cool to room temperature and filtered under nitrogen through a clarifying layer Seitz filter covered with activated carbon, and the filter residue was washed with glacial acetic acid (2 I).
• the filtrate was concentrated on a rotary evaporator at a bath temperature of 50° C. until no more glacial acetic acid distilled off and crystallization started.
• the mixture was then allowed to cool to about 25° C. and, whilst the mixture was still rotating, ethyl acetate (20 I) was soaked into the flask of the rotary evaporator, whereupon the amidine precipitated as acetic acid salt. After 0.5 h of extra stirring time, the precipitate was filtered off with suction by means of a paper filter and dried thoroughly with suction.
• Ice-water ( ⁇ 2° C., 200.0 I) was added as quickly as possible ( ⁇ 5 min), with stirring and cooling, and the mixture was then stirred at 5-10° C. for 1 h.
• the beige suspension was introduced into a centrifuge which had been inertized with nitrogen.
• the precipitate was centrifuged, washed with deionized water (80.0 I) and dried under reduced pressure at 40° C. Yield: 24.8 kg (131.9 mol, 70.6% of theory).
• acylase “Amano” 30 000 (38.0 g) in deionized water (400 ml) was added at 39° C., and the mixture was then stirred at a constant pH of 7.9 and a constant temperature of 39° C. for 40 h.
• TLC mobile phase as above
• the vessel was inertized with nitrogen, and tetrahydrofuran (22.0 I) was then added and the reaction mixture was, over a period of 1 h, cooled to an internal temperature of 10° C.
• tetrahydrofuran (22.0 I) was then added, over a period of 1 h, cooled to an internal temperature of 10° C.
• a solution of N-(benzyloxycarbonyloxy)succinimide (4.63 kg, 18.6 mol) in tetrahydrofuran (23.0 I) was added, during which time the pH was kept at 8.0-8.5 by continuous addition of concentrated aqueous sodium hydroxide solution (33% strength).
• the mixture was then stirred at 20° C. for 1.5 h.
• TLC mobile phase as above
• the reaction solution was diluted with deionized water (0.33 I), and palladium/carbon (10%, 50% water; 50 g) was then added.
• the hydrogenation was carried out under atmospheric pressure by passing through hydrogen (about 10 I/min), with continuous metered addition of a solution of toluene-4-sulfonic acid monohydrate (0.63 kg, 3.33 mol) in deionized water (1.0 I) at 20-25° C., over a period of about 3 h. After the hydrogenation had ended, the autoclave was flushed with nitrogen and the hydrogenation solution was filtered through a Seitz filter and washed with deionized water (0.5 I).
• the filtrate was pumped into a vessel which had been initially charged with acetone (1200 I), which was stirred vigorously under nitrogen, at 18° C. The mixture was stirred at room temperature for 10 min and the suspension was then pressed with nitrogen through a pressure nutsch which had been covered with a filter cloth made of polypropylene and a Seitz filter. The residue was washed with acetone (3 ⁇ 100 I), the solid on the pressure nutsch was dried overnight using nitrogen, and the precipitation of the product from acetone was then repeated.

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