PROCESS FOR PREPARING OMECAMTIV MECARBIL DIHYDROCHLORIDE HYDRATE

Abstract

Claim 1: A compound characterized in that it is methyl piperazine carboxylate phosphate hydrate (“PMEC”) of formula (1). Claim 2: A process for synthesizing methyl piperazine carboxylate phosphate hydrate (“PMEC”) of formula (1) characterized in that it comprises (a) mixing methyl chloroformate and piperazine to form PMEC; (b) mixing the PMEC and 0.5 molar equivalents of phosphoric acid to form PMEC phosphate hydrate; and (c) optionally filtering the PMEC phosphate hydrate from the mixture of step (b).

Description

SYNTHESIS OF OMECAMTIV MECARBIL FIELD Methods for preparing omecamtiv mecarbil and novel omecamtiv mecarbil intermediates and methods for synthesizing intermediates are provided. BACKGROUND The cardiac sarcomere is the basic unit of muscle contraction in the heart. It is a highly organized cytoskeletal structure composed of actin, cardiac muscle myosin, and a set of regulatory proteins. The discovery and development of small-molecule cardiac muscle myosin activators will lead to promising treatments for acute and chronic heart failure, dilated cardiomyopathy (DCM), and conditions associated with left and / or right ventricular systolic dysfunction or systolic reserve. Cardiac muscle myosin is the cytoskeletal motor protein in the cardiac muscle cell. It is directly responsible for converting chemical energy into mechanical force, resulting in cardiac muscle contraction. Current positive inotropic agents, such as beta-adrenergic receptor agonists or phosphodiesterase inhibitors, increase intracellular calcium concentration, thereby increasing cardiac sarcomere contractility. However, increased calcium levels increase the rate of cardiac muscle contraction and shorten systolic ejection time, which has been associated with potentially fatal side effects. In contrast, cardiac muscle myosin activators work by directly stimulating the activity of the cardiac muscle myosin motor protein without increasing intracellular calcium concentration. They accelerate the rate-limiting step of the myosin enzyme cycle, shifting it toward the force-producing state.Instead of increasing the speed of cardiac contraction, this mechanism, on the contrary, prolongs the systolic ejection time, resulting in a possibly more efficient cardiac muscle contractility and oxygen performance. U.S. Patent No. 7,507,735, incorporated herein by reference, describes a class of compounds, including omecamtiv mecarbil (AMG 423, CK-1827452), having the structure: Me Omecamtiv mecarbil is a first-in-class direct activator of cardiac myosin, the motor protein that triggers heart contraction. It is being evaluated as a potential treatment for heart failure in both intravenous and oral formulations, with the aim of establishing a new spectrum of patient care in both hospital and outpatient settings. There is a constant need for a commercial manufacturing process for omecamtiv mecarbil that considers the specific issues of API production, including Good Manufacturing Practice (GMP) requirements and regulatory body approval (e.g., the US FDA and EMA). COMPENDIUM This document provides a methyl piperazine carboxylate phosphate salt (PMEC), for example, a PMEC phosphate hydrate salt. Alternatively, PMEC is referred to as methyl piperazine-1-carboxylate. Processes for synthesizing the phosphate salt PMEC are also provided herein, comprising: (a) mixing methyl chloroformate and piperazine to form PMEC; (b) mixing the PMEC and 0.5 molar equivalents of phosphoric acid to form PMEC phosphate; and (c) optionally filtering the PMEC phosphate from the mixture of step (b). In some cases, step (a) is carried out in an aqueous solution, generating PMEC phosphate hydrate with a PMEC-to-water ratio of approximately 2:1. In various cases, step (a) is carried out at a temperature of 20 to 55 °C for 1 to 12 hours. In some cases, the PMEC formed in step (a) is isolated as a solution in methylene chloride, dichloroethane, 2-methyltetrahydrofuran, or a mixture thereof.More specifically, the isolation can be carried out by (i) washing the PMEC resulting from step (a) with an organic solvent; (ii) modifying the pH from 8 to 14 by adding a base to form a basic aqueous solution; and (iii) extracting the PMEC from the basic aqueous solution of step (ii) with methylene chloride, dichloroethane, 2-methyltetrahydrofuran, or a mixture of these. Processes for synthesizing methyl 4(2-fluoro-3-nitrobenzyl)piperazine-l-carboxylate (PIPN) are also provided herein, comprising (a) mixing 2-fluoro-3-nitrotoluene, sodium bromate, and sodium bisulfite in isopropyl acetate and water to form 1-(bromomethyl)-2-fluoro-3-nitrobenzene (FNB); (b) optionally washing the FNB with aqueous sodium thiosulfate, aqueous sodium chloride, or both; and (c) mixing FNB, a trialalkylamine base, and piperazine carboxylate methyl phosphate (PMEC), e.g., PMEC phosphate hydrate, to form PIPN. In some cases, the FNB is washed with aqueous sodium thiosulfate and aqueous sodium chloride.Alternatively, PIPN can be prepared by (a) mixing 2-fluoro-3-nitrotoluene, benzoyl peroxide, N-bromosuccinimide, and acetic acid at a temperature of 70 to 95 °C to form 1-(bromomethyl)-2-fluoro-3-nitrobenzene (FNB); (b) optionally extracting FNB with toluene, washing FNB with an aqueous basic solution, or both; (c) mixing FNB, a trialkylamine base, and piperazine carboxylate methyl phosphate (PMEC), for example, PMEC phosphate hydrate, to form PIPN. In some cases, the FNB is extracted with toluene and washed with aqueous sodium hydroxide. In any process for preparing PIPN, PIPN can be formed as a hydrochloride salt. In any process for preparing PIPN, the PMEC phosphate, for example, PMEC phosphate hydrate, can be prepared as described herein. In any process for preparing PIPN, the trialalkylamine base comprises diisopropylethylamine or triethylamine.In any process for preparing PIPN, before mixing the FNB, the trialalkylamine base and the PMEC, the process may further comprise adding diethylphosphite and a trialalkylamine and mixing the resulting mixture at a temperature of 30 to 65 °C. Processes for synthesizing phenyl (6-methylpyridin-3-yl)carbamate (PCAR) are also provided herein, comprising mixing 5-amino-2-methylpyridine (APYR) and phenyl chloroformate in acetonitrile to form PCAR, wherein the mixing is carried out in the absence of N-methylpyrrolidinium (NMP). In some cases, the mixing is carried out at a temperature of 15 to 30 °C for 1 to 15 hours. In several cases, the PCAR is formed as a hydrochloride salt. In some cases, the process may further comprise preparing APYR by a process comprising: (i) hydrogenating 2-methyl-5-nitropyridine (NPYR) in the presence of a palladium catalyst to form crude APYR; and (ii) crystallizing APYR from crude APYR in isopropyl acetate and heptane. In several cases, the process may further comprise, prior to step (i), washing NPYR in isopropyl acetate with aqueous sodium hydroxide, followed by mixing the NPYR washed in isopropyl acetate with carbon.In some cases, the process may further comprise, prior to mixing APYR and phenyl chloroformate, purifying APYR by a process comprising: (i) washing an isopropyl acetate solution of crude APYR, wherein the crude APYR comprises up to 10 wt % APYR hydrochloride, con aqueous sodium hydroxide, and mix the washed APYR with charcoal to form, after filtration, a solution of APYR; and (ii) crystallize APYR from the solution of APYR from step (i) of isopropyl acetate and heptane. In various cases, the process may further comprise crystallizing PCAR. Processes for synthesizing methyl 4(3-amino-2-fluorobenzyl)piperazine-l-carboxylate (PIPA) are also provided herein, comprising (a) mixing methyl 4-(2-fluoro-3-nitrobenzyl)piperazine-l-carboxylate (PIPN), an aqueous solution of an inorganic base, and toluene to form a PIPN-free base solution; (b) hydrogenating the PIPN-free base solution in the presence of a palladium catalyst in a mixture of toluene and an alcohol solvent to form crude PIPA, wherein the alcohol comprises ethanol or isopropanol; and (c) crystallizing PIPA from crude PIPA in heptane and toluene. In various cases, the inorganic base comprises sodium hydroxide. Processes for preparing omecamtiv mecarbil dihydrochloride hydrate are also provided herein, comprising (a) mixing methyl 4-(3-amino-2-fluorobenzyl)piperazine-l-carboxylate (PIPA), phenyl (6-methylpyridin-3-yl)carbamate (PCAR), and a trialalkylamine in acetonitrile and tetrahydrofuran to form a crude omecamtiv mecarbil solution; (b) isolating the omecamtiv mecarbil free base from the crude omecamtiv mecarbil solution; and (c) mixing the isolated omecamtiv mecarbil free base with 2 to 1 molar equivalents of hydrochloric acid in isopropanol and water to form omecamtiv mecarbil dihydrochloride hydrate. In various cases, the trialalkylamine comprises diisopropylethylamine or triethylamine. In some cases, the isolation of step (b) comprises crystallizing the omecamtiv mecarbil free base by adding water to the crude omecamtiv mecarbil solution from step (a) and filtering the crystallized omecamtiv mecarbil free base.In several cases, the process may further involve crystallizing the isopropanol dihydrochloride hydrate from water. In some cases, PCAR is prepared using a process as described herein. Processes for preparing omecamtiv mecarbil dihydrochloride hydrate are also provided herein, comprising (a) mixing methyl 4-(3-amino-2-fluorobenzyl)piperazine-l-carboxylate (PIPA), triphosgene, and a trialalkylamine in acetonitrile and tetrahydrofuran to form PIPA isocyanate; (b) mixing the PIPA isocyanate and 5-amino-2-methylpyridine (APYR) to form omecamtiv mecarbil free base; (c) mixing the omecamtiv mecarbil free base with 2 to 3 molar equivalents of hydrochloric acid in isopropanol and water to form omecamtiv mecarbil dihydrochloride hydrate. In some cases, step (a) is carried out by continuous manufacturing comprising mixing a first solution comprising PIPA and the trialalkylamine in acetonitrile and a second solution comprising triphosgene in tetrahydrofuran by using a micromixer chip and reaction loop to form PIPA isocyanate.In several cases, step (b) is carried out by continuous manufacturing comprising mixing a solution comprising PIPA isocyanate and a solution comprising APYR using a Y-blender and a reaction loop. In some cases, APYR is prepared by a process as described herein. In some cases, PIPA is prepared by a process as described herein. BRIEF DESCRIPTION OF THE FIGURES Figure 1 shows a dynamic vapor sorption (DVS) isothermal plot for three forms of piperazine-l-methyl carboxylate (PMEC) salt: a phosphate hydrate salt, a hemisulfate salt, and an acetate salt. The onset of DVS weight gain for each salt was measured as highlighted: 35% relative humidity (RH) for hemisulfate; 50% RH for acetate; and 65% RH for phosphate hydrate. Phosphate hydrate is referred to as phosphate or hemiphosphate, and hemisulfate is referred to as sulfate or hemisulfate in the figure. Figure 2 shows a differential scanning calorimetry spectrum of PMEC phosphate hydrate. Figure 3 shows an X-ray powder diffraction pattern for PMEC phosphate hydrate (square) and PMEC suspension (circle). DETAILED DESCRIPTION Omecamtiv mecarbil dihydrochloride hydrate is used in an oral formulation as a treatment for heart failure. Specific conditions include, but are not limited to: acute (or decompensated) congestive heart failure, chronic congestive heart failure; diseases particularly associated with systolic cardiac dysfunction. A previous process for manufacturing omecamtiv mecarbil dihydrochloride hydrate is described in WO 2014 / 152270. The GMP manufacturing sequence described herein differs from that previous synthesis sequence in several ways. The GMP sequence is lengthened from two to six steps. This longer GMP sequence provides alternative production sequences, including avoiding solvents during production that are difficult to remove (e.g., N-methylpyrrolidone, NMP), avoiding the use of evaporative crystallization, and isolating intermediates to avoid challenging solvent exchanges. The above process for manufacturing omecamtiv mecarbil dihydrochloride hydrate is represented in Scheme 1 and described in detail in WO 2014 / 152270. That process involves the non-GMP preparation of the regulatory API starting materials piperazine nitro-HCl (PIPN) and phenyl carbamate-HCl (PCAR) from commercially available raw materials, FN-toluene (FNT) and 5-amino-2-methylpyridine (APYR), respectively. The isolated GMP intermediate piperazine aniline (PIPA) is prepared from PIPN by hydrogenation and subsequently combined with PCAR to generate omecamtiv mecarbil. The dihydrochloride hydrate salt of omecamtiv mecarbil is manufactured from the corresponding freebase by a shortened process (i.e., the omecamtiv mecarbil freebase is not isolated) and isolated as a dihydrochloride hydrate by filtration after wet milling. All API starting materials are highlighted in the boxes. Scheme 1: NH2 I. APrOAc / NaHCOj (aq.) ii. Hj / Pd-C / / -PrOAc III. Heptane Stage 1 GMP OMe Plperazine Aniline (PIPA) Intermediate GMP yield 90 % phenl carbamate to+HCI (PCAR) I. APr2NElfTHF II. 2*PrOH / H2O / HCI Stage 2 GMP For the synthesis described herein, the API starting materials were moved upstream in the sequence to meet the selection and justification requirements of various regulatory bodies, such as the EMA and FDA. As such, the process described herein comprises six steps, compared to the two-step sequence described in WO 2014 / 152270. This elongated GMP sequence provides several advantages over the shorter sequence. Piperazine-L-carboxylate methyl phosphate (PMEC) is used instead of PMEC freebase in the formation of the piperazine nitro-HCl (PIPN) intermediate. PMEC freebase is an oil containing varying levels of piperazine, which leads to the formation of impurities (e.g., BISN in the PIPN product, see Scheme 3). In contrast, PMEC phosphate is a stable crystalline salt with low and constant levels of piperazine.Therefore, using PMEC hemiphosphate hemihydrate instead of PMEC freebase significantly reduces the formation of impurities. The process described herein also allows for the elimination of N-methylpyrrolidone (NMP) during PCAR preparation, an advantage considering that NMP is difficult to remove and is listed under the EU REACH protocol (a list of chemical safety materials). Furthermore, the process described herein alters the solvent used in the hydrogenation of PIPN to generate PIPA, since the use of isopropyl acetate in the previous process involved an evaporative crystallization operation, which often leads to material contamination and inconsistent results.The process described herein replaces a challenging solvent exchange, taking into account the very low solubility of the free base omecamtiv mecarbil in isopropanol (~12 mg / mL) at 20 °C and the formation of a suspension that cannot be stirred during the solvent exchange of tetrahydrofuran (THF) to isopropanol. The new commercial process described herein for preparing omecamtiv mecarbil dihydrochloride hydrate is shown in Scheme 2. It involves six GMP steps. The designated commercial API starting materials are 2-fluoro-3-nitrotoluene (FNT), 5-amino-2-methylpyridine (APYR), and PMEC phosphate hydrate. Scheme 2 FN-Toluene (FNT) Commercially available API SM V.......................1 L NBS. (BzO)2 AcOH ¡j. HPO(OEt)2 Toluene Stage 1 GMP Not isolated Manipulated as a solution Plperazine Nitro+HCl (PIPN) Intermediate GMP crystalline yield 82 % Aminoplridine (APYR) Available at commercial level API SM Phenyl chloroformate Acetonitrile Stage 3 GMP OR PhO^NH Phenyl carbamate+HCI (PCAR) Intermediate GMP crystalline yield 95 % her. Toluene / NaOH (ac.) II. Hz / Pd-C / Tbluene / Ethanol ill. Heptane Stage 4 GMP Plperazine Nitro+HCl (PIPN) Phenyl carbamate+HCI (PCAR) her. / -P^NEt / THF ACN í¡. h2o Intermediate GMP yield 90 % H Stage 5 GMP yield 85 % FN-toluene is a raw material manufactured from toluene using a shorter synthesis sequence. Fractional distillation of the resulting isomer mixture yields the desired regioisomer, 2-fluoro-3-nitrotoluene, at acceptable purity, with a maximum of 0.5% GC area of ​​any of the other isomers. 2-Fluoro-3-nitrotoluene (FNT) manufactured by this process has reproducible quality and can be designated as a commercial API starting material. PIPN Manufacturing: PMEC phosphate, for example, PMEC phosphate hydrate, is an API starting material prepared in a single step from piperazine. The previous process for preparing PIPN used PMEC freebase as a raw material, which can be purchased, but is an oil containing varying amounts of piperazine. After storage at 25 °C, piperazine levels of up to 18% LC area were observed in the PMEC freebase. As illustrated in Scheme 3, the residual piperazine leads to the formation of the impurity BISN in the PIPN product. Scheme 3 A stable crystalline salt of PMEC with low and consistent piperazine levels was sought as a commercial API starting material. Therefore, various salts were analyzed to identify a suitable candidate. PMEC phosphate, for example, PMEC phosphate hydrate, was found to be less hygroscopic than the corresponding acetate and sulfate salts, as shown in Figure 1. It can be stored in tightly sealed aluminum bags to prevent contact with moisture. As a benefit, PMEC phosphate, for example, PMEC phosphate hydrate, can be added directly to a reaction mixture to prepare PIPN. In contrast, PMEC acetate must be converted to the free base PMEC before being added to the reaction mixture, taking into account the formation of the byproduct FN-Bromide (FNB) and the acetate anion. PMEC phosphate, for example, PMEC phosphate hydrate, It contains low levels of piperazine (<0.4% of the GC area) that do not increase after storage. PMEC phosphate, for example, PMEC phosphate hydrate, has been successfully used for the manufacture of PIPN. The PIPN batch manufactured in this way (5 kg) contained less than 0.1% of the LC area of ​​the residual BISN. A process was developed for the production of PMEC phosphate hydrate involving the treatment of piperazine with methyl chloroformate followed by the extraction of PMEC as a free base from the organic layer after neutralization with aqueous sodium hydroxide, as shown in Scheme 4. Following solvent exchange from dichloromethane to tert-butyl methyl ether, the target salt was crystallized by the addition of phosphoric acid and filtration. The PMEC phosphate hydrate was isolated in a yield of 45–50% piperazine and >99% GC area. Piperazine levels in the PMEC phosphate hydrate samples were observed to be <0.4% GC area. The DSC spectrum and XRPD pattern for the PMEC phosphate hydrate are shown in Figures 2 and 3, respectively.PMEC phosphate has a stoichiometry of approximately 2:1 PMEC:phosphate and is therefore referred to herein interchangeably as PMEC phosphate, PMEC hemiphosphate, or PMEC phosphate salt. A PMEC phosphate hydrate can be formed as detailed herein, and this hydrate has a stoichiometry of approximately 2:1:1 PMEC:phosphate:water and is referred to herein interchangeably as PMEC phosphate hydrate, PMEC hemiphosphate hemihydrate, or PMEC phosphate hydrate. It is understood that the ratio of PMEC, phosphate, and water in the PMEC phosphate hydrate may differ slightly from the 2:1:1 stoichiometric ratio highlighted above, for example, to a ratio of 6:4:3 or similar. Elemental analysis and / or structural analysis by X-ray crystallography can be carried out on the material prepared by the processes described herein.The ratio of PMEC, phosphate, and water in the isolated salt is constant, and determining the exact PMEC:phosphate:water ratio does not negatively impact the suitability of the hydrate salt. PMEC phosphate herein for the intended use as a starting material in the preparation of omecamtiv mecarbil dihydrochloride hydrate. Scheme 4 (1.0 equiv.) Water 15-25 °C Piperazine il. Extraction with CH2CI2 Bis-PMEC (yield, trial -20%) CH2CI2 i Layer PMEC Piperazine salt (yield, test -60%) (yield, test -20%) Aqueous layer iii. pH adjustment with aq. NaOH. IV. NaCI v. Extraction with CH2CI2 Piperazine Aqueous layer MeO EITHER VI. Solvent exchange MTBE + 1 / 2 H2O ¿H21 / 2HPO42· PMEC Hemiphosphate Hemihydrate H3PO4 (0.50 equiv.) vii. MTBE 40-45°C PMEC CH2CI2 layer: yield 45-50% >99% of the GC area The general synthesis method for preparing PMEC phosphate, for example, PMEC phosphate hydrate, comprises mixing piperazine and methyl chloroformate to form PMEC, adding 0.5 molar equivalents of phosphoric acid (for example, in an aqueous solution) to form the phosphate salt, and optionally filtering the salt. The reaction of piperazine and methyl chloroformate can be carried out at a temperature of 20 to 55 °C for 1 to 12 hours. The specific extraction methods and post-reaction treatment procedures are shown in Scheme 4 for purifying phosphate from PMEC. However, other treatment procedures may be employed. PMEC can be purified from the bis-PMEC formed in the piperazine and methyl chloroformate reaction mixture by extraction with an organic solvent such as methylene chloride, dichloroethane, or 2-methyltetrahydrofuran, or a mixture thereof. In some embodiments, the organic solvent comprises methylene chloride. The unwanted bis-PMEC is separated in the organic solvent layer, and the desired PMEC is retained in the aqueous layer. The PMEC may be further purified. For example, the PMEC in the aqueous solution may be adjusted to a basic pH (e.g., 0.9 ...8 to 14) by adding a basic aqueous solution and extracting with an organic solvent, such as methylene chloride, dichloroethane, or 2-methyltetrahydrofuran, or a mixture thereof, wherein the PMEC is in the organic solvent. In some cases, the organic solvent comprises methylene chloride. The PMEC in the organic solvent can be subjected to solvent exchange from the organic extraction solvent to methyl t-butyl ether (MTBE) and reacted with phosphoric acid to form the phosphate salt. In some specific formulations, piperazine is suspended in 4.0 volumes (V) of water at 20 ± 5 °C. Methyl chloroformate (1 equivalent) is added over the course of 1 hour, maintaining the batch temperature below 20 °C. The reaction is stirred at 20 ± 5 °C for 1 hour. One or more methylene chloride extractions are performed, discarding the methylene chloride layer each time. The aqueous layer is treated with a 10 M aqueous NaOH solution (0.8 equivalents) to adjust the pH to between 9.5 and 10.3. NaCl (1.47 equivalents) is added to the aqueous layer, and methylene chloride washes (2 x 4V) are performed. The methylene chloride layers are combined and distilled to 2.5V. Methyl butyl ether (MTBE) (8V or 4.5V) is added, and the solution is concentrated to 2.5V. MTBE (3.5V or 4.5V) is added, and the solution is concentrated to 2.5V. MTBE (3.5V) is added again, and the mixture is filtered with polishing. The filtered solution was heated to 45 ± 5 °C (e.g., 40 to 50 °C) and an 85% phosphoric acid solution (0.5 equivalent) in MTBE (1.5 V or 3.5 V) was added over 3 hours while maintaining a batch temperature of 45 ± 5 °C (e.g., 40 to 50 °C). The suspension was cooled to 20 ± 5 °C over 2 hours and agitated for 1 hour at 20 ± 5 °C. The suspension was filtered and the resulting cake was washed with MTBE (2 V) and dried (e.g., by nitrogen and vacuum for 24 h).The PMEC phosphate hydrate yield is 48.5%, with 100% of the % LC area, an assay of 64.6% by weight, a water content of 4.2% by weight by Karl Fischer titration, residual MTBE at 0.44% by weight and 0.2% of the % residual piperazine area by GC. Process for manufacturing PIPN from FNT: FNT can be brominated to form FNB, which in turn can be reacted with PMEC phosphate hydrate to form PIPN (see, for example, the top of Scheme 2). FNT can be brominated to form FNB by reaction with NBS and benzoyl chloride in acetic acid at a temperature of 70–95 °C. The FNB can optionally be extracted with toluene and / or washed with an aqueous basic solution to remove impurities. Alternatively, FNT can be brominated to form FNB by reaction with sodium bromate and sodium bisulfite in isopropyl acetate and water. The FNB formed by reaction with sodium bromate and sodium bisulfite can optionally be washed with an aqueous solution of sodium thiosulfate and / or an aqueous solution of sodium chloride to remove impurities.FNB, regardless of how it is formed from FNT, can optionally be treated with diethylphosphite and a trialalkylamine (e.g., triethylamine or diisopropylethylamine) at a temperature of 30 to 65 °C to reduce unwanted dibrominated impurities. FNB, regardless of how it is formed from FNT, can be blended with a trialalkylamine base (e.g., triethylamine or diisopropylethylamine) and PMEC phosphate hydrate to form PIPN. PIPN can be further converted to the hydrochloride salt form by blending with hydrochloric acid and can be further isolated. In some specific embodiments, 2-fluoro-3-nitrotoluene (3.0 kg, 1 equiv.) is charged into a reactor followed by benzoyl peroxide (0.03 equiv.) and N-bromosuccinimide (0.56 equiv.). Acetic acid (3 V) is charged into the reactor and the batch is heated to 83 °C. After 1.5 h, a suspension of NBS (0.56 equiv.) in acetic acid (1 V) is charged into the reactor. After an additional 1.5 h, a second suspension of NBS (0.56 equiv.) in acetic acid (1 V) is charged into the reactor. After a further 5 h, a solution of H3PO3 (0.1 equiv.) in acetic acid (0.1 V) is charged into the reactor, and the batch is stirred for 30 minutes and then cooled to 20 °C. Water (5.5 V) and toluene (8 V) are charged into the reactor, and the batch is vigorously stirred for 30 minutes. Stirring is then stopped, and the layers are allowed to separate. The lower aqueous layer is discarded. A solution is charged into the reactor. of NaOH (1.7 equiv.) in water (7 V) while maintaining a batch temperature below 30 °C. The batch is vigorously stirred for 30 minutes. Stirring is stopped and The batch is filtered into a clean reactor and the layers are allowed to separate. The lower aqueous layer is discarded. N,N-diisopropylethylamine (0.53 equiv.) is charged into the reactor, followed by methanol (0.23 V), and the batch is heated to 40 °C. A solution of diethylphosphite (0.46 equiv.) in methanol (0.23 V) is charged into the reactor, and the batch is stirred for 3 h. The batch is then cooled to 20 °C. To a solution of 1 equiv. of 2-fluoro-3-nitrophenylmethylbromide in toluene (9 V), prepared by radical bromination of 2-fluoro-3-nitrotoluene, 2.3 equiv. of diisopropylethylamine is added at 20 °C. A solution of 1.05 equiv. PMEC phosphate hydrate was added dropwise to methanol (2.6 V). After stirring for 1-3 hours, water (5 V) was added and the layers were separated. The organic phase was washed twice with saturated aqueous NH4Cl (5 V) and then once with saturated aqueous NaHCCh (5 V).After polishing filtration, the toluene layer is diluted with isopropanol (90.7 V) and water (0.5 V). The solution is heated to 55 °C and concentrated HCl (0.15 V) is added for 30 minutes. The solution is then seeded with PIPN-HCCl (3 mol%) and held at 55 °C for 15 minutes. Additional concentrated HC1 (0.62 V) was added over 4 hours. The solution was held at 55 °C for 15 minutes and cooled to 20 °C in > 1 hour. The solution was stirred for 30 minutes and filtered. The crystals were washed twice with IPA (5.6 V). The cake was dried under vacuum and nitrogen to yield PIPN-HC1 (yield 82%, 98.6 wt%, 99.6 LCAP). In other specific embodiments, 2-fluoro-3-nitrotoluene (3.0 kg, 1 equiv.) is charged into a reactor followed by benzoyl peroxide (0.03 equiv.) and N-bromosuccinimide (NBS, 0.1 equiv.). Acetic acid (2 V) is charged into the reactor and the mixture is heated to 83 °C. The reaction mixture is stirred for 1.5 h, then a suspension of NBS (0.4 equiv.) in acetic acid (0.9 V) is added. The reaction mixture is stirred for another 1.5 h and a second suspension of NBS (0.4 equiv.) in acetic acid (0.9 V) is added. The reaction mixture is stirred for another 1.5 h and a second suspension of NBS (0.8 equiv.) in acetic acid (1.6 V) is added. Acetic acid (1.0 equiv.) is added and the reaction mixture is stirred for 1.5 minutes. A solution of phosphorous acid (H3PO3, 0.1 equiv.) in acetic acid (0.1 V) is then charged into the reactor. The mixture is stirred for 60 minutes and cooled to 20 °C. Water (5.5 V) and toluene (8 V) are added to the vessel and the two-phase mixture is stirred vigorously for 30 minutes.The stirring is stopped and the layers are allowed to separate. The aqueous layer is discarded. A solution of sodium hydroxide (1.7 equiv.) in water (7 V) is charged while maintaining the temperature below 30 °C. The two-phase mixture is stirred vigorously for 30 minutes. Stirring is stopped, and the layers are allowed to separate. The two-phase mixture is filtered, and the aqueous layer is discarded. The reaction mixture is transferred to a separate clean vessel, the original vessel is rinsed with toluene (1.2 V), and the rinse volume is added to the reaction mixture. The organic layer is charged with diisopropylethylamine (0.53 equiv.) and methanol (0.23 V), and the mixture is heated to 40 °C. A solution of diethylphosphite (0.46 equiv.) in methanol (0.23 V) is charged, and the reaction mixture is stirred for 3 h. The mixture is then cooled to 20 °C. To the FNB solution in toluene, prepared by radical bromination of 2-fluoro-3-nitrotoluene (FNT), diisopropylethylamine (2.3 equiv.) and toluene (1 V) are added.The FNB solution is added to a solution of methanol (1.8 V) and PMEC phosphate hydrate (1.05 equivalents). The original container holding the FNB solution is rinsed with methanol (0.8 V), and the rinse water is added to the reaction mixture. The reaction mixture is stirred for 4 hours at 25 °C, and water (5 V) is added while maintaining the batch temperature below 30 °C. The two-phase mixture is stirred for 30 minutes, and the layers separate. The organic phase is washed twice with 3 M aqueous ammonium chloride (5 V) and once with 1 M aqueous sodium bicarbonate (5 V). The reaction mixture is transferred to a separate clean container, the original container is rinsed with toluene (IV), and the rinse water is added to the reaction mixture. After polishing filtration, isopropanol (9.7 V) and water (0.6 V) are added to the organic solution. The solution is heated to 55 °C and 32 wt% aqueous hydrochloric acid (0.25 equivalents) is added for 30 minutes.The solution is stirred at 55 °C for 15 minutes and seeded with a suspension of PIPN (hydrochloride salt, 0.045 equivalents) in isopropanol (0.2 V). The suspension is stirred at 55 °C for 30 minutes. An additional 32% aqueous hydrochloric acid (1.0 equivalent) is added over 4 hours. The solution is stirred at 55 °C for 30 minutes and cooled to 20 °C over 2 hours. The suspension is stirred for 30 minutes and filtered. The product cake is washed twice with isopropanol (5.6 V). The product cake is filter-dried to yield PIPN at 82% yield with an assay of 98.6% by weight and 99.6% LC area. In some specific formulations, 2-fluoro-3-nitrotoluene (5.1 g) is dissolved in isopropyl acetate (30 mL), and a solution of sodium bromate (14.9 g) in water (50 mL) is added. The mixture is cooled to 10 °C. A solution of sodium bisulfite (10.3 g) in water (100 mL) is added over 20 minutes. The resulting mixture is heated to 80 °C for 3 h. The reaction vessel is exposed to visible light. The contents are cooled to 20 °C, and the phases are separated. The organic phase is washed sequentially with 10% aqueous sodium thiosulfate and saturated aqueous sodium chloride. 1-(Bromomethyl)-2-fluoro-3-nitrobenzene (FNB) is obtained in an assay yield of 74%, with an assay yield of 11% of the dibromide product. Manufacture of APYR: 5-amino-2-methylpyridine (APYR) is commercially available as a feedstock, however, it contains various amounts of the hydrochloride salt (3-5 wt %) and is provided as a dark brown or black material. In addition, it may contain multiple possibly genotoxic impurities, such as depicted in Scheme 5. Consequently, to use APYR as a commercial API starting material with high and constant purity, a purification protocol for APYR or a synthesis process to prepare APYR is convenient. Scheme 5 Nitropyridlne (NPYR) In silico mutagenicity hydroxyl amine Fe / HCI Through these Intermediates: hydrazine intermediate , azo intermediate In silico mutagenicity In silico mutagenicity In silico mutagenicity Aminopyridine (APYR) Commercially available A method is provided for purifying APYR by washing an isopropyl acetate solution of APYR with up to 10 wt% of the corresponding hydrochloride salt with aqueous sodium hydroxide and then mixing the organic phase with carbon. APYR can be crystallized from isopropyl acetate and heptane, optionally after azeotropic drying of the organic phase and filtration with polishing. The process for purifying APYR is illustrated in Scheme 6. The purification of APYR involves the conversion of the APYR hydrochloride salt to the free base of APYR and the simultaneous removal of inorganic material by using a basic aqueous sodium hydroxide wash of an APYR isopropyl acetate solution. After carbon treatment (e.g., mixing with carbon and filtering the slurry or recirculating an isopropyl acetate solution through carbon capsules), the solution comprising APYR is azeotropically dried and filtered by polishing. The clear isopropyl acetate solution is concentrated, and the APYR is crystallized by the addition of heptane. APYR is isolated in >99% of the LC area and an assay of >99% by weight. Scheme 6 APYR Hydrochloride -3-5% by weight Dark color Me i. Aqueous NaOH IPAc ii. Carbon treatment iii. Azeotropic drying iv. Polishing filtration .Me IPAc aminopyridine solution Clear solution V. Concentrate seed at 50 °C v. Heptane Crystallization from her. Aqueous NaOH IPAc li. Treatment with charcoal NPYR Up to 5 % hydrochloride Dark color .Me ,Me IPAc / Heptane APYR APISM >99 % LC area >99 % by weight yield 90 % Reaction mixture IPAc iii. IPAc / H2 / Pd-C iv. Catalyst filtration v. Concentrate seed at 50 °C vi. Heptane ,Me APYR APISM \___________ High purity Crystallization from aminopyridine IPAc IPAc / Heptane yield 85 % >99 % LC area >99 wt % In some specific embodiments, a crude 5-amino-2-methylpyridine (APYR) solution in isopropyl acetate (IPAc) (15 volumes) is washed with 1 N aqueous NaOH (1.0 volume) and circulated through carbon capsules until the solution color control (COS) (COS 20) is met. The solution is azeotropically dried by concentration to approximately 6 volumes, and isopropyl acetate (8 volumes) is added. The mixture is then polished and filtered into a separate vessel. The original vessel is rinsed with isopropyl acetate (1.0 volume), and the rinse volume is added to the reaction mixture. The solution is then concentrated, for example, by distillation under reduced pressure, and the product is crystallized from isopropyl acetate and heptane (1:4, 10 volumes). In some cases, the solution is concentrated to 3 volumes at 60 °C and seeded with purified APYR (1% mol).The suspension is stirred for 30 minutes, cooled to 20 °C for 3 hours, and stirred for 1 hour. Heptane (8 volumes) is added over the course of 3 hours to complete crystallization. The suspension is stirred for 1 hour, filtered, and the product cake is washed using heptane (2 x 3 volumes). The purified APYR is isolated by filtration, dried, and obtained in a 90% yield with >99% LC area. APYR from NPYR: In some cases, APYR is synthesized from NPYR, as detailed in Scheme 6. NPYR is hydrogenated in the presence of a palladium catalyst to form crude APYR, which can be crystallized from isopropyl acetate and heptane. The hydrogenation of NPYR to generate crude APYR is carried out after a basic aqueous wash and carbon treatment. The carbon treatment comprises mixing the slurry with carbon and filtering it, or recirculating an isopropyl acetate solution through carbon capsules. The APYR solution is azeotropically dried and filtered by polishing. APYR is crystallized from isopropyl acetate and heptane. In some cases, NPYR is purified before hydrogenation by washing with isopropyl acetate and aqueous sodium hydroxide and by performing a treatment of charcoal (mix with charcoal and then filter the charcoal). In some specific embodiments, a 15 V isopropyl acetate solution of 2-methyl-5-nitropyridine (NPYR) is washed with a 2 V aqueous 1 N NaOH solution and 2 V water. The solution is optionally circulated through carbon capsules until the solution color control (COS) (COS 20) is met. NPYR is hydrogenated with 4.5 bar of hydrogen, for example, at 70 psi / 50–60 °C (e.g., 55 °C) in the presence of 5% Pd / C (on BASF commercially available Escat™ 1421 activated carbon, loaded at 1.5 wt%) for approximately 1 hour. The reaction mixture is filtered and azeotropically dried by concentrating to approximately 7 V, adding 8 V of isopropyl acetate, and filtering with polishing. The solution is concentrated to 3 V under reduced pressure at 60 °C. The product is crystallized from isopropyl acetate and heptane (1:4) optionally by seeding with pure APYR (1 mol %) and / or optionally by cooling to 20 °C.The product is optionally filtered and washed using heptane (2 x 3 V). APYR is isolated at a 75% yield with >99% LC area. PCAR Fabrication: In the process described above for preparing omecamtiv mecarbil dihydrochloride hydrate, N-methylpyrrolidone (NMP) is used as a cosolvent in the PCAR preparation. However, NMP is difficult to remove from the product cake, requiring washing with 30 volumes of acetonitrile to reduce its level in the cake below 5000 ppm. Additionally, NMP is a potentially hazardous solvent listed under the REACH protocol, regulated by the European Union, which was adopted to enhance the protection of human health and the environment from chemical risks. It has been found that, by using purified APYR prepared as described above, APYR hydrochloride levels in isolated crystallized PCAR can be easily maintained below 1% of the LC area without the use of NMP (see Scheme 7).This was not the case with unpurified APYR since 1 to 2% of the LC area of ​​APYR hydrochloride was found in isolated PCAR prepared without NMP from this starting material and constitutes a surprising discovery. Therefore, a method for preparing PCAR by mixing APYR and phenyl chloroformate in acetonitrile and in the absence of NMP is provided herein. The reaction can take place at 15 to 30 °C for 1 to 15 hours. The method can utilize APYR that has been purified as highlighted above—for example, by removing the hydrochloride salt from APYR and its dark color. APYR can be prepared from NPYR as described above. PCAR can be formed as its hydrochloride salt. PCAR can be crystallized, for example, as the hydrochloride salt. In some specific embodiments, a solution of 5-amino-2-methylpyridine (APYR) in ACN (15 volumes) is reacted with phenyl chloroformate (1.05 equivalents) for 3 hours at 20 ± 5 °C while the product crystallizes from the reaction mixture. The product slurry is filtered, and the cake is dried in a filter / dryer. PCAR is isolated in a 97% yield, with HPLC purity > 99%, 0.3% APYR, and 0.25% R-urea. In some cases, acetonitrile (14 volumes) is added to the purified APYR, and the mixture is stirred for 30 minutes. The mixture is then filtered with polishing into a separate vessel. The original vessel is rinsed with acetonitrile (1.0 volume), and the rinse volume is added to the reaction mixture. Phenyl chloroformate (1.05 equiv.) is added over the course of 5 hours at 20 °C in the presence of PCAR seeds (0.01 equiv.). The mixture is stirred for an additional 2 hours.The product is isolated by filtration and the cake is washed with acetonitrile (2x2 volumes) . The cake is dried in filter / dryer. PCAR is isolated at a yield of 97% with > 99 % of the LC area of ​​PCAR and 0.3 % of the LC area of ​​residual APYR. Scheme 7 Aminopyridine (APYR) Purified Phenyl carbamate+HCI (PCAR) Crystalline GMP intermediate yield 95 % Phenyl chloroformate Acetonitrile Stage 3 GMP Reactive crystallization Impurity of APYR 0.2-0.8 % area of ​​LC PIPA Manufacturing: The solvent used during the hydrogenation of PIPN to provide PIPA in the previous process for preparing omecamtiv mecarbil dihydrochloride hydrate was isopropyl acetate. The hydrogenation reaction proceeded successfully in this solvent; however, evaporative crystallization (solvent distillation during product crystallization) was necessary due to the high solubility of PIPA in isopropyl acetate:heptane mixtures in ratios above 5:95. It was necessary to reduce the high levels of isopropyl acetate used by distillation after seeding the product solution, which led to product contamination and a lack of process robustness.For the process described herein, isopropyl acetate was replaced with toluene, which eliminated all the problems highlighted above, given that the toluene:heptane ratio to be achieved immediately before filtration is 30:70, thus eliminating evaporative crystallization. Furthermore, ethanol was used as a cosolvent during the hydrogenation reaction to increase the solubility of PIPA and ensure the miscibility of the byproduct in water. Finally, aqueous sodium bicarbonate was replaced with aqueous sodium hydroxide to operate the PIPN free-basis conversion for the commercial process, limiting the volumes of aqueous wash solution and eliminating gas release. The process for preparing PIPA from PIPN as described herein is presented in Scheme 8. Scheme 8 Piperazine Nltro+HCl (PH»N) Yo. ) Toluene / NaOH (aq.) ii. ) Hj / Pd-crToluene / Ethanol - iii. ) Heptane Stage 4 GMP Piperazine aniline (PIPA) Crystalline GMP Intermediate 90% yield Therefore, a method for synthesizing PIPA is provided herein, comprising mixing PIPN (which may comprise PIPN hydrochloride salt), an aqueous solution of an inorganic base, and toluene to form a PIPN-free base solution. The inorganic base may be sodium bicarbonate or sodium hydroxide, for example. In some embodiments, the inorganic base comprises sodium hydroxide. The PIPN-free base solution is then hydrogenated in the presence of a palladium catalyst in toluene and an alcohol solvent to form crude PIPA. The alcohol solvent may comprise ethanol or isopropanol. PIPA is then crystallized from a heptane-toluene solvent mixture. In some specific modalities, a mixture of 1 equivalent of PIPN-HC1 and toluene (4 V) are added to 1 M aqueous NaOH (3.3 V) at °C. Stirring is continued for 1 hour before phase separation. The organic layer is washed twice with a mixture of water (2.4 V) and saturated brine (0.6 V), then distilled to 3.8 V. The solution is filtered, the reactor is rinsed with toluene (1 V), and the rinse solution is filtered before combining the organic layers. Pd / C (0.7 wt%) is added to the toluene layer, and the heterogeneous mixture is loaded into a hydrogenation vessel. Ethanol (IV) is added to the mixture. Hydrogenation is carried out at 20 °C at 60 psig of hydrogen. After the reaction is complete, the mixture is filtered and rinsed with toluene (1 V). The mixture is distilled at 2.4 V, seeded with 1 mol% PIPA in heptane (0.1 V) at 35 °C and then cooled to 20 °C. The addition of heptane (5.6 V) is completed in 3 hours.The mixture is filtered and dried under vacuum and nitrogen to provide PIPA (yield 90%, L 97.0% by weight, L 98.0 LCAP).

Claims

1. A process for preparing omecamtiv mecarbil dihydrochloride hydrate characterized in that it comprises (a) mixing methyl 4-(3-amino-2-fluorobenzyl)piperazine-1-carboxylate FORMULA 1 (PIPA), phenyl (6-methylpyridin-3-yl)carbamate FORMULA 2 (PCAR), and a trialalkylamine in acetonitrile and tetrahydrofuran to form a crude omecamtiv mecarbil solution; (b) isolating the omecamtiv mecarbil free base from the crude omecamtiv mecarbil solution; and (c) mixing the isolated omecamtiv mecarbil free base with 2 to 3 molar equivalents of hydrochloric acid in isopropanol and water to form omecamtiv mecarbil dihydrochloride hydrate FORMULA 3. 24 Claims follow