HK40112924A - Methods and compounds useful in the synthesis of an aak1 inhibitor - Google Patents

Description

Methods and compounds for synthesizing AAK1 inhibitors

Technical Field

This application relates to methods for preparing (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridin]-5-yl)oxy)-2,4-dimethylpentane-2-amine and its salt forms, as well as useful synthetic intermediates therein.

Background Technology

Adaptor-associated kinase 1 (AAK1) is a member of the serine/threonine kinase family Ark1/Prk1. AAK1 mRNA exists in two spliced forms, called the short spliced form and the long spliced form. The long form is dominant and highly expressed in the brain and heart (Henderson and Conner, Mol. Biol. Cell. 2007, 18, 2698-2706). AAK1 is enriched in synaptosome formulations and co-localizes with endocytic structures in cultured cells. AAK1 regulates clathrin-coated endocytosis, a process crucial in synaptic vesicle circulation and receptor-mediated endocytosis. AAK1 is associated with the AP2 complex, which binds receptor cargo to the clathrin shell. Clathrin binding to AAK1 stimulates AAK1 kinase activity (Conner et al., Traffic 2003, 4, 885-890; Jackson et al., J. Cell. Biol. 2003, 163, 231-236). AAK1 phosphorylates the mu-2 subunit of AP-2, promoting the binding of mu-2 to tyrosine-containing sorting motifs on cargo receptors (Ricotta et al., J. Cell Bio. 2002, 156, 791-795; Conner and Schmid, J. Cell Bio. 2002, 156, 921-929). Mu2 phosphorylation is not required for receptor uptake, but it can enhance the efficiency of internalization (Motely et al., Mol. Biol. Cell. 2006, 17, 5298-5308).

AAK1 has been identified as an inhibitor of Neuregulin-1/ErbB4 signaling in PC12 cells. Loss of AAK1 expression mediated by RNA interference or treatment with the kinase inhibitor K252a (which inhibits AAK1 kinase activity) leads to enhanced neuroregulatory protein-1-induced neurite growth. These treatments result in increased ErbB4 expression and accumulation of ErbB4 in or near the plasma membrane (Kuai et al., Chemistry and Biology 2011, 18, 891-906). NRG1 and ErbB4 are putative susceptibility genes for schizophrenia (Buonanno, Brain Res. Bull. 2010, 83, 122-131). SNPs in these two genes are associated with multiple schizophrenic endophenotypes (Greenwood et al., Am. J. Psychiatry 2011, 168, 930-946). Neuroregulatory protein 1 (NRP1) and ErbB4 KO mouse models have exhibited morphological changes and behavioral phenotypes associated with schizophrenia (Jaaro-Peled et al., Schizophrenia Bulletin 2010, 36, 301-313; Wen et al., Proc. Natl. Acad. Sci. USA. 2010, 107, 1211-1216). Furthermore, single nucleotide polymorphisms (SNPs) in AAK1 gene introns are associated with the age of onset of Parkinson's disease (Latourelle et al., BMC Med. Genet. 2009, 10, 98). These results suggest that inhibiting AAK1 activity may be beneficial in the treatment of schizophrenia, cognitive deficits in schizophrenia, Parkinson's disease, neuropathic pain, bipolar disorder, and Alzheimer's disease.

Furthermore, studies using Huh-7.5 cells have demonstrated the potential use of AAK1 kinase inhibitors in the treatment of hepatitis C (HCV) infection. Reduction of AAK1 protein using RNA interference-mediated gene silencing, treatment with the kinase inhibitor sunitinib (a potent AAK1 inhibitor), and overexpression of mutants at the Mu2 (AAK1 substrate) phosphorylation site all resulted in reduced HCV virion assembly. Moreover, the same treatments were shown to inhibit HCV entry, suggesting that AAK1 inhibitors can disrupt two host-dependent phases of the viral life cycle (Neveu et al., PLoS Pathog. 2012, 8, 1-16; Neveu et al., J. Virol. Published online February 4, 2015). AAK1 inhibitors have also been used against HIV and HBV (see, e.g., Boge et al., J. Biol. Chem. 1998, 273, 15773-15778).

Numerous AAK1 inhibitors have been published in the literature, and some have been proposed for the treatment of neuropathic pain. See, for example, Hartz, RA et al., J. Med. Chem. , Aug 12, 2021;64(15):11090-11128. However, human clinical trials are essential to assess the full potential of any drug.

Specific AAK1 inhibitors, such as (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridin]-5-yl)oxy)-2,4-dimethylpentane-2-amine, have been prepared on small laboratory scales. See, for example, U.S. Patent No. 9,902,722. Unfortunately, few synthetic methods available in laboratory settings are suitable for large-scale production of pharmaceutically acceptable materials. For example, there is a need to minimize the generation of potentially harmful reaction byproducts, and it is best to avoid the use of toxic solvents and reagents. Furthermore, reaction conditions feasible on a gram-scale are often inefficient or even hazardous when scaled up. Therefore, there is a need for synthetic methods that can be used to prepare commercially useful quantities of pharmaceutically acceptable amounts of (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridin]-5-yl)oxy)-2,4-dimethylpentane-2-amine.

Summary of the Invention

This application relates to the preparation of compound (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridin]-5-yl)oxy)-2,4-dimethylpentan-2-amine (compound J):

The method of its salt. Compound J is an inhibitor of adaptor-associated kinase 1 (AAK1) and is believed to be useful in treating diseases and conditions including pain.

In one embodiment, the present invention covers a method for preparing (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridin]-5-yl)oxy)-2,4-dimethylpentane-2-amine (compound J):

The method includes causing compound H under conditions sufficient to form compound J:

With compound D:

Or its salts come into contact with an alkali.

In one embodiment, compound H is formed by subjecting compound Q to conditions sufficient to form compound H:

Prepared by contact with a fluorinating agent. (This invention covers the crystalline form of compound Q. The specific crystalline form has a melting point of approximately 150°C.)

In one embodiment, compound Q is formed by subjecting compound P to conditions sufficient to form compound Q:

It is prepared by contacting with acid.

In one embodiment, compound P is formed by subjecting compound L to conditions sufficient to form compound P:

With compound N:

Prepared by contact.

In one embodiment, compound Q is formed by subjecting compound L4 to conditions sufficient to form compound Q:

It is prepared by contacting with acid.

In one embodiment, compound L4 is formed by subjecting compound L3 to conditions sufficient to form compound L4:

With compound L1:

It is prepared by contacting a catalyst and a base.

This invention also covers a method for preparing compound K:

The method includes making compound S under conditions sufficient to form compound K:

Contact with phosphoric acid in a solvent.

In one embodiment, compound S is formed by subjecting compound J to conditions sufficient to form compound S:

It is prepared by contacting hydrochloric acid in a solvent.

This invention also covers the synthetic intermediate 6-bromo-2-(dimethoxymethyl)-3-fluoropyridine (compound L1):

.

This invention also covers 2-(dimethoxymethyl)-4-(4,4,5,5-tetramethyl-1,3,2-dioxacyclopentaborane-2-yl)pyridine (compound L3):

.

This invention also covers 2',6-bis(dimethoxymethyl)-5-fluoro-2,4'-bipyridine (compound L4):

And its salt.

This invention also covers compound 5-fluoro-[2,4'-bipyridine]-2',6-dicarboxaldehyde (compound Q):

.

This invention also covers (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridin]-5-yl)oxy)-2,4-dimethylpentane-2-amine (compound J):

A pharmaceutically acceptable crystalline salt.

This invention also covers a determined (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridin]-5-yl)oxy)-2,4-dimethylpentan-2-amine (compound J):

A method for determining the purity of a sample of its pharmaceutically acceptable salts, comprising testing the presence of one or more compounds listed in Table 1 in the sample.

This invention also covers a compound comprising (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridin]-5-yl)oxy)-2,4-dimethylpentan-2-amine (compound J):

Or a pharmaceutically acceptable salt thereof, said composition comprising less than 0.01% by weight of one or more compounds listed in Table 1 below.

Attached Figure Description

Figure 1 shows a representative X-ray powder diffraction (XRPD) pattern of ((S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridin]-5-yl)oxy)-2,4-dimethylpentan-2-ammonium dihydrogen phosphate (compound K) in its crystalline solid form I. The spectra were obtained using a Bruker X-ray diffractometer equipped with a LYNXEYE detector (copper Kα radiation).

Figure 2 provides a representative differential scanning calorimetry (DSC) thermal analysis plot of the crystalline solid form of compound K. The thermal analysis plot was obtained using a TA Instruments DSC Q2000 instrument and a sealed gold crucible filled under ambient conditions. Two scans were performed. In the first scan, after melting, the sample was rapidly cooled to -50°C at a rate of approximately -40 K/min, and then the second scan was recorded. The heating rate was 10 K/min in both scans.

Detailed Implementation

This invention relates to synthetic intermediates and to preparation of (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridin]-5-yl)oxy)-2,4-dimethylpentan-2-amine (compound J):

The invention provides a method for synthesizing pharmaceutically acceptable salts, which are sufficient in quantity (e.g., greater than 1 kg, 5 kg, or 10 kg) to manufacture dosage forms suitable for human clinical trials and subsequent commercialization. The method of the invention minimizes the formation of harmful impurities while maximizing synthetic yield.

The specific method of this invention is used to prepare ((S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridin]-5-yl)oxy)-2,4-dimethylpentan-2-ammonium dihydrogen phosphate (compound K):

And its crystalline solid form. The specific crystalline form of this salt is referred to herein as Form I, whose XRPD spectrum is substantially the same as that shown in Figure 1, with diffraction peaks at one or more of approximately 4.81, 5.99, 7.44, 7.89, 11.66, 14.85, 15.77, 19.19, 20.86, 21.65, 23.96, 24.48, or 24.73 degrees 2-θ. When used herein to refer to XPRD peaks, the term “approximately” means ±0.2 degrees 2-θ.

The melting point of crystalline form I of compound K is approximately 184 °C (see Figure 2), as determined by differential scanning calorimetry (DSC) (melting endothermic). When referring to temperature, the terms "substantially" and "approximately" mean ±2 °C.

The crystalline form I of compound K is the most stable form of this salt found: after storage at 40°C and 75% relative humidity for up to four weeks, its form, morphology, and purity remained unchanged. Furthermore, although the melting point of form I is lower than that of the hydrochloride salt of compound J (a form with a melting point of approximately 247°C), the phosphate showed no signs of associated degradation. Instead, form I was observed to melt and recrystallize into another metastable form with a melting point of approximately 172.5°C. The water solubility of form I (26.8 mg/mL at 25°C) further facilitates its large-scale production and purification. In contrast, the water solubility of the hydrochloride salt of compound J was measured at 25°C to be 2.9 mg/mL.

One embodiment of the present invention that can be used to prepare form I is shown below:

Here, compound K is prepared by contacting compound J with phosphoric acid in a solvent under conditions sufficient to form compound K. Examples of solvents include water, methanol, ethanol, n-butanol, isopropanol, isobutanol, tert-butanol, methyl tert-butyl ether, ethyl acetate, isopropyl acetate, THF, and 2-methyl THF, and mixtures thereof. The specific solvent is isopropanol.

In some embodiments, compound J is contacted with phosphoric acid at a temperature of about 0°C to about 100°C or about 50°C to about 60°C. (When referring to reaction conditions, unless otherwise specified, the term "about" when referring to temperature is interpreted as ±10°C.) In some embodiments, compound J is contacted with phosphoric acid for about 0.5 hours to about 24 hours or about 2 hours to about 16 hours. (When referring to reaction conditions, unless otherwise specified, the term "about" when referring to time is interpreted as ±5%. For example, "about 2 hours" is equivalent to 2 hours ± 6 minutes.) In some embodiments, about 0.8 to about 1.2 molar equivalents (e.g., about 1 molar equivalent) of phosphoric acid are used relative to compound J. (Unless otherwise specified, when referring to molar equivalents or concentration, the term "about" is interpreted as ±5%.) In some embodiments, the concentration of compound J in the solvent is about 2% to about 25%.

In one embodiment of the present invention, compound K is prepared from compound S, as shown below:

In this method, compound S is neutralized with a base under conditions sufficient to form compound J, and compound J is then contacted with phosphoric acid under conditions sufficient to form compound K. Suitable bases for neutralization include NaOH, KOH, _{Na₂CO₃ ,} and _K₂CO₃ . _A preferred base is sodium hydroxide.

Neutralization of compound S with a base can typically be carried out in solvents such as water, water/MTBE, water/THF, and water/2-MeTHF (preferably water/MTBE), and at a temperature of about 0°C to about 60°C (e.g., about 20°C to about 40°C). In some embodiments, neutralization takes place for about 0.5 hours to about 24 hours (e.g., about 1 hour to about 2 hours). In some embodiments, about 0.8 to about 5 molar equivalents of base are used relative to compound S. In some embodiments, the concentration of compound S in the solvent is about 2% to about 25%.

In the second step described above, the exposure of compound J to phosphoric acid is typically carried out in a solvent, such as water, methanol, ethanol, n-butanol, isopropanol, isobutanol, tert-butanol, methyl tert-butyl ether, ethyl acetate, isopropyl acetate, THF, and 2-methylTHF, or mixtures thereof. Isopropanol is a preferred solvent.

In some embodiments, compound J is exposed to phosphoric acid at a temperature of about 0°C to about 100°C (e.g., about 50°C to about 60°C). In some embodiments, compound J is exposed to phosphoric acid for about 0.5 hours to about 24 hours (e.g., about 7 hours to about 14 hours). In some embodiments, in step 2, about 0.8 to about 1.2 molar equivalents of phosphoric acid are used relative to compound J. In some embodiments, the concentration of compound J in the solvent is about 2% to about 25%.

Compound S can be prepared as follows:

In one embodiment, compound S is prepared by exposing compound J to hydrochloric acid in a solvent under conditions sufficient to form compound S. In some embodiments, the solvent is water, IPA, a water/IPA mixture, MeOH, MeOH/water, EtOH, EtOH/water, n-BuOH, or n-BuOH/water. A preferred solvent is isopropanol.

Compound J is exposed to hydrochloric acid at a temperature of about 0°C to about 60°C (e.g., about 50°C to about 60°C) for about 0.5 hours to about 24 hours (e.g., about 4 hours to about 8 hours). Typically, about 0.8 to about 1.2 molar equivalents of hydrochloric acid are used relative to compound J. In some embodiments, the concentration of compound J in the solvent is about 2% to about 25%.

One embodiment of the present invention covers a method for preparing compound J as shown below:

Here, compound J is prepared by neutralizing compound D-benzoate with a base under conditions sufficient to form compound D, wherein compound D is contacted with compound H in the presence of a base under conditions sufficient to form compound J. Compound D does not need to be separated.

Suitable solvents for these reactions include THF, 2-methylTHF, 1,4-dioxane, MTBE, DME, diethylene glycol dimethyl ether, tert-butanol, and tert-amyl alcohol. Specifically, THF is used. The base used in both steps can be added at the beginning of the first step. Examples of suitable bases include potassium tert-butoxide, sodium tert-butoxide, potassium tert-amyloxide, sodium tert-amyloxide, sodium hexamethyldisilamide, potassium hexamethyldisilamide, lithium diisopropylamide, n-butyllithium, sec-butyllithium, and tert-butyllithium. Specifically, potassium tert-butoxide is used.

In some embodiments of the invention, the neutralization of compound D-benzoate is carried out at a temperature of about -50°C to about 50°C (e.g., about 15°C to about 25°C) for about 0.5 hours to about 24 hours (e.g., about 3 hours to about 5 hours). In some embodiments, compound H is contacted with compound D in the presence of a base at a temperature of about -50°C to about 50°C (e.g., about 0°C to about 25°C) for about 2 hours to about 5 hours.

The base is used in an amount of about 1.8 to about 3 molar equivalents (e.g., about 2.5 to 3 molar equivalents) relative to compound H, and the D-benzoate of the compound is used in an amount of about 1 to about 1.5 molar equivalents (e.g., about 1.2 molar equivalents) relative to compound H.

The compound D-benzoate can be prepared as follows:

Compound B is contacted with a reducing agent under conditions sufficient to form compound D, and compound D is contacted with benzoic acid under conditions sufficient to form compound D-benzoate.

Examples of reducing agents include _NaBH4 / _BF3 ^· _Et2O , _NaBH4 / _I2 , NaBH4/TMSCl, _NaBH4 / _H2SO4 , _NaBH4 / _MsOH , _NaBH4 /TsOH, NaBH4/HCl, _NaBH4 /AlCl3, _CDI / _NaBH4 , _{BH3 THF} complex, _BH3 dimethyl sulfide complex, diborane, _LiAlH4 , and Li/ _AlCl3 /t-BuOH. In some embodiments of the invention, the reducing agent is _NaBH4 / _{BF3 · Et2O} ^. The amount of reducing agent relative to compound B can be from about 0.5 to about 4 molar equivalents (e.g., about 2 molar equivalents).

The reduction of compound B is typically carried out in solvents such as THF, 2-Me-THF, THF, 2-methylTHF, 1,4-dioxane, MTBE, DME, and diethylene glycol dimethyl ether, or mixtures thereof. THF is a preferred solvent. In some embodiments, the concentration of compound B in the solvent is from about 2% to about 25%. The reduction can be carried out at a temperature of from about -50°C to about 50°C (e.g., from about 0°C to about 25°C) for about 0.5 hours to about 24 hours (e.g., from about 5 hours to about 8 hours).

According to the method described above, compound D is contacted with benzoic acid in solvents such as MTBE, MTBE/heptane, THF, THF/heptane, EtOAc, EtOAc/heptane, IPAc, IPAc/heptane, EtOH, EtOH/heptane, IPA, IPA/heptane, toluene, and acetonitrile. MTBE is a preferred solvent. In some embodiments of the invention, this reaction is carried out at a temperature of about 0°C to about 60°C (e.g., about 45°C to about 50°C) for about 1 to 2 hours. In some embodiments, about 0.8 to about 1.5 molar equivalents (e.g., about 1.1 molar equivalents) of benzoic acid are used relative to compound D. In some embodiments, the concentration of compound D in the solvent is about 2% to about 25%.

Another intermediate used for the large-scale synthesis of compound J and its pharmaceutically acceptable salt is compound H, which can be prepared as follows:

In this method, compound H is prepared by contacting compound Q with a fluorinating agent under conditions sufficient to form compound H. Examples of fluorinating agents include _SF4 , _PhSF3 , _R2NSF3 (DAST, Morph-DAST), dialkylamide difluorosulfonium tetrafluoroborate ([ _R2N = _SF2 ] (XtalFluor-E, XtalFluor-M) _{BF4 )} , Deoxo-Fluor (BAST), Selectfluor, and 4-tert-butyl-2,6-dimethylphenyl trifluoride. A preferred fluorinating agent is DAST. Depending on the specific agent used, about 1 to about 5 molar equivalents (e.g., about 3.5) of the fluorinating agent are used relative to compound Q.

Preferably, compound Q is contacted with a fluorinating agent in a solvent such as dichloromethane, chloroform, _CCl4 , and toluene. Dichloromethane is a preferred solvent. The concentration of compound Q in the solvent can vary from about 2% to about 25%. The reaction typically occurs at a temperature of about -20°C to about 60°C (e.g., about 0°C to about 25°C) and lasts for about 1 hour to about 100 hours (e.g., about 24 hours to about 30 hours).

Compound Q can be prepared from compound L4, as shown below:

In this method, compound Q is prepared by contacting compound L4 or its salt (e.g., L4-phosphate) with an acid under conditions sufficient to form compound Q. Examples of suitable acids include HCl, HBr, HI, _H₂SO₄ , _H₃PO₄ , _HNO₃ , _MsOH , TsOH, and _HBF₄ . _The preferred acid is hydrochloric acid.

The reaction with the acid is preferably carried out in a solvent such as water or DMSO/water (preferably water) and at a temperature of about 0°C to about 100°C (e.g., about 55°C to about 60°C). This reaction typically proceeds for about 1 hour to about 24 hours (e.g., two hours). The concentration of compound L4 can be varied to optimize the yield and can be, for example, about 2% to about 25%. In some embodiments of the invention, about 1 to about 10 molar equivalents (e.g., 5 molar equivalents) of acid are used relative to compound L4.

The salt of the specific compound L4 that can be used is L4-phosphate, which can be prepared as follows:

In this method, compound L4 is contacted with phosphoric acid under conditions sufficient to prepare compound L4-phosphate. The reaction can be carried out in solvents such as MeOH, EtOH, IPA, EtOAc, IPAc, MTBE, THF, 2-Me-THF, toluene, heptane, or mixtures thereof. A preferred solvent system is toluene/methanol/heptane.

The reaction is typically carried out at a temperature of about 0°C to about 60°C (e.g., about 15°C to about 45°C) for about 1 hour to about 24 hours (e.g., about 10 hours to about 12 hours). In some embodiments of the invention, about 1 to about 2 (e.g., about 1.6) molar equivalents of phosphoric acid are used relative to compound L4. The concentration of compound L4 in the solvent can range from about 2% to about 25%.

Compound L4 can be prepared using the following method:

Here, compound L2 is contacted with a palladium catalyst, a base, a ligand, and a boron reagent under conditions sufficient to form compound L3, and said compound L3 is contacted with compound L1 in the presence of a catalyst and a base under conditions sufficient to form compound L4.

The preparation of compound L3 is typically carried out in solvents such as THF, 2-MeTHF, 1,4-dioxane, DME, MTBE, _Et₂O , or ACN. In some embodiments, the solvent is 2-MeTHF. Examples of palladium catalysts that can be used to prepare compound L3 include Pd(OAc) _₂ , _PdCl₂ (dppf), Pd( _PPh₃ ) _₄ , _PdCl₂ ( _PPh₃ ) _₂ , and _Pd₂ (dba) _₃ . _Pd₂ (dba) _₃ is a preferred catalyst. Bases used to form compound L3 include NaOAc, KOAc, _NaHCO₃ , _KHCO₃ , _{Na₂CO₃ , K₂CO₃} , _{K₂HPO₄ ,} and _K₃PO₄ . KOAc is a preferred base. Suitable ligands include _PCy₃ , SPhos, and _{Xphos .} Xphos is a preferred ligand. Boron reagents that can be used in the reaction include tetrahydrodiboron, PinBH _, and _Pin₂B₂ . The preferred boron reagent is _{Pin₂B₂ .}

In some embodiments of the invention, compound L2 is contacted with a palladium catalyst, a base, a ligand, and a boron reagent at a temperature of about 0°C to about 100°C (e.g., about 70°C to about 80°C) for about 0.5 hours to about 48 hours (e.g., about 16 hours to about 24 hours). In some embodiments, about 0.8 to about 2 (e.g., 1) molar equivalents of the boron reagent are used relative to compound L2. In some embodiments, the concentration of compound L2 in the solvent is about 2% to about 25%.

The next step in the reaction described above (wherein compound L3 reacts with compound L1) is typically carried out in a solvent such as water, THF, 2-MeTHF, 1,4-dioxane, DME, MTBE, _Et₂O , and mixtures thereof. A preferred solvent is water/2-MeTHF. The concentration of compound L1 can range from about 2% to about 25%, but as with all reactions disclosed herein, these figures can be varied using methods well known to those skilled in the art to maximize product yield and minimize cost.

Examples of bases _that can be used to form compound L4 include _Na₂CO₃ , _K₂CO₃ , _Na₃PO₄ , _K₃PO₄ , _{NaOH ,} and _KOH . _A preferred base is sodium carbonate ( _Na₂CO₃ ). Depending on the base, about 1 to 2 molar equivalents (e.g., 2 molar equivalents) of the base are used relative to compound L2. This step is carried out at a temperature of about 20°C to about 100°C (e.g., about 70°C to about 80°C) for about 1 hour to about 48 hours (e.g., about 16 hours to about 24 hours). About 1 to 2 molar equivalents (e.g., 1 molar equivalent) of compound L1 are used relative to compound L2.

The synthetic intermediate compound L2 can be prepared as follows:

In this method, compound SM3 is contacted with trimethoxymethane in the presence of an acid under conditions sufficient to form compound _L2 . Examples of suitable acids include _H₂SO₄ , MsOH, _TsOH , _H₃PO₄ , _HNO₃ , HCl, and HBr. Hydrochloric acid is preferred.

The reactions described above are typically carried out in solvents such as 1,4-dioxane, DME, _Et₂O , THF, 2-Me-THF, toluene, DCM, MTBE, ACN, and methanol. Methanol is the preferred solvent. The temperature range for carrying out this reaction is from about 0°C to about 80°C (e.g., from about 60°C to about 65°C), and the duration of the reaction is from about 0.5 hours to about 48 hours (e.g., from about 6 hours to about 10 hours).

In some embodiments of the invention, about 0.01 to about 1 molar equivalent (e.g., about 0.2 molar equivalents) of an acid is used relative to SM3, and about 1 to about 4 molar equivalents (e.g., about 2 molar equivalents) of trimethoxymethane is used relative to SM3. The concentration of SM3 in the solvent can range from about 2% to about 30%.

Compound L2 can also be prepared as shown below using similar reaction conditions to those described above (although using more trimethoxymethane):

The synthetic intermediate compound L1 can be prepared as follows:

In this method, compound L1 is prepared by contacting compound SM2 with trimethoxymethane in the presence of an acid under conditions sufficient to form acetal compound _L1 . Examples of suitable acids include _H₂SO₄ , MsOH, TsOH, _H₃PO₄ , _{HNO₃ ,} HCl, and HBr. Hydrochloric acid is preferred.

This reaction is preferably carried out in solvents such as 1,4-dioxane, DME, _Et₂O , THF, 2-Me-THF, toluene, DCM, MTBE, ACN, and methanol. Methanol is the preferred solvent.

In some embodiments of the invention, SM2 and trimethoxymethane are contacted in the presence of an acid at a temperature of about 0°C to about 80°C (e.g., about 60°C to about 65°C) for about 0.5 hours to about 48 hours (e.g., about 3 hours to about 6 hours). The acid is typically used in an amount of about 0.01 to about 1 molar equivalent (e.g., about 0.05 molar equivalents) relative to SM2. The trimethoxymethane is typically used in an amount of about 1 to about 4 molar equivalents (e.g., about 2 molar equivalents) relative to SM2. In some embodiments, the concentration of SM2 in the solvent is about 2% to about 30%.

In one embodiment of the present invention, compounds J, K, and S are prepared as shown in Scheme 1:

Option 1

In this method, compound J or a pharmaceutically acceptable salt thereof is prepared by: a) contacting compound L3 with compound L1 in the presence of a catalyst and a base under conditions sufficient to form compound L4; b) contacting compound L4 or a salt thereof with an acid under conditions sufficient to form compound Q; c) contacting compound Q with a fluorinating agent under conditions sufficient to form compound H; and d) contacting compound H with compound D in the presence of a base under conditions sufficient to form said compound J.

Compound S is prepared by a process that includes exposing compound J in a solvent to hydrochloric acid.

Compound K is prepared by a process comprising: a) neutralizing compound S with a base under conditions sufficient to form compound J; and b) exposing the resulting compound J to phosphoric acid in a solvent under conditions sufficient to form compound K.

In one specific embodiment of the invention, compound K is prepared by a process comprising: a) contacting compound L3 with compound L1 in the presence of a catalyst and a base under conditions sufficient to form compound L4; b) contacting compound L4 with an acid under conditions sufficient to form compound Q; c) contacting compound Q with a fluorinating agent under conditions sufficient to form compound H; d) contacting compound H with compound D in the presence of a base under conditions sufficient to form compound J; e) contacting compound J with hydrochloric acid in a solvent under conditions sufficient to form compound S; f) neutralizing compound S with a base under conditions sufficient to form compound J; and g) exposing the resulting compound J to phosphoric acid in a solvent under conditions sufficient to form compound K.

In another embodiment, compound K is prepared by a process comprising: a) contacting compound L3 with compound L1 in the presence of a catalyst and a base under conditions sufficient to form compound L4; b) contacting L4 with an acid under conditions sufficient to form compound Q; c) contacting compound Q with a fluorinating agent under conditions sufficient to form compound H; d) contacting compound H with compound D in the presence of a base under conditions sufficient to form compound J; and e) exposing the resulting compound J to phosphoric acid in a solvent under conditions sufficient to form said compound K.

This invention covers methods for ensuring that the final active pharmaceutical ingredient has a purity suitable for administration to human patients. To this end, potential impurities including those shown in Table 1 below were synthesized and characterized by ^1H NMR and mass spectrometry.

Table 1

The compounds in Table 1 were observed at various stages of the laboratory-scale development work that led to the methods of the present invention.

This invention includes a method for testing the purity of compound J or a pharmaceutically acceptable salt thereof by testing for the presence of one or more compounds listed in Table 1. Preferred methods include testing for the presence of one or more compounds using mass spectrometry and/or HPLC.

5.1 Examples

Various embodiments of the invention can be understood by considering the examples provided below. In these embodiments, all temperatures are described in degrees Celsius and all parts and percentages are by weight unless otherwise stated. Reagents are available from commercial suppliers and can be used without further purification unless otherwise stated. (Reagents can also be prepared according to standard literature procedures known to those skilled in the art.)

Unless otherwise stated, all reactions are carried out at ambient temperature (or room temperature). Reactions are typically measured by HPLC, and termination is determined based on the consumption of the starting material.

Compound structure and purity were confirmed by one or more of the following methods: proton nuclear magnetic resonance ( ^¹H NMR) spectroscopy, ^¹³C NMR spectroscopy, mass spectrometry, infrared spectroscopy, melting point, X-ray crystallography, LC-MS, and/or HPLC. Chemical shifts were reported in parts per million (ppm, δ) at the low field of a distance standard (e.g., an internal standard such as TMS). Alternatively, ^¹H NMR chemical shifts were referenced to the signal of residual protons in deuterated solvents known in the art. Peak multiplicity was specified as follows: s, singlet; d, doublet; dd, twin doublet; t, triplet; dt, twin triplet; q, quartet; br, broadened; and m, multiplet. Coupling constants were expressed in Hertz (Hz). Mass spectrometry (MS) data were acquired using a mass spectrometer with APCI or ESI ionization.

5.1.1 Synthesis of 6-bromo-2-(dimethoxymethyl)-3-fluoropyridine (compound L1)

A solution of HCl/MeOH (10 mL 3.9 M solution, 0.05 equivalents) was added to a mixture of SM2 (158.5 g, 777 mmol, 1 equivalent), MeOH (1585 mL, 10V), and trimethoxymethane (166 g, 15.6 mol, 2.0 equivalents). The resulting mixture was aged at 60–65 °C (reflux) until the reaction was complete (3–6 hours), then cooled to 10–20 °C. The mixture was concentrated to 2–3V below 50 °C and diluted with 2-Me-THF (10V), followed by quenching with 10% _K₂CO₃ ( _3V ). The organic layer was separated and concentrated to 1–2V below 50 °C. The solution was rinsed with 2-Me-THF (5V) and then diluted with more 2-Me-THF (5V) to give a solution of compound L1 in 2-Me-THF (845.2 g, 99% purity, 21.7% determination, 94.4% solution yield). LC-MS: m/z 250, 252, 220, 218 (M-OMe) ^1H NMR (400 MHz, chloroform-d) δ 7.38 (dd, J = 3.5, 8.6 Hz, 1H), 7.17–7.30 (m, 1H), 5.37–5.48 (m, 1H), 3.39 (s, 6H).

5.1.2 Synthesis of 4-chloro-2-(dimethoxymethyl)pyridine (compound L2)

Add HCl/MeOH (42.3 mL 3.9 M solution, 0.20 equivalents) to a mixture of SM3 (117.3 g, 819.5 mmol, 1 equivalent), MeOH (1160 mL, 10V), and trimethoxymethane (174 g, 1.64 mol, 2.0 equivalents). Heat the mixture to 60–65 °C (reflux) until the reaction is complete (6–10 h), then cool to 10–20 °C. After concentrating to 3–5V and diluting with 2-Me- _THF (10V), quench the reaction with 10% _K₂CO₃ (3V, pH 8–9). The organic layer was separated and concentrated to 1–2 V, rinsed with 2-Me-THF (5 V x 2), and then diluted with 2-Me-THF (5 V) to give a solution of compound L2 in 2-Me-THF (588.5 g, 99.18% HPLC purity, 22.3% determination, 85.3% solution yield). ^¹H NMR (400 MHz, chloroform-d) δ 8.42–8.57 (m, 1H), 7.56 (d, J = 2.0 Hz, 1H), 7.25 (dd, J = 2.1, 5.3 Hz, 1H), 5.28–5.39 (m, 1H), 3.38 (s, 6H). LC-MS m/z 187, 156 (M-OMe).

5.1.3 Synthesis of 2',6-bis(dimethoxymethyl)-5-fluoro-2,4'-bipyridine phosphate (compound L4-phosphate)

Preparation of L3: A mixture of compound L2 in 2-Me-THF (95.5 g, 1.00 equivalent, 5-6 V), 2-Me-THF (10 V), Pin _{2B 2} (1.05 equivalent), KOAc (3.0 equivalent), and Xphos (0.02 equivalent) was degassed by jet injection with N _2. Pd ₂ (dba) ₃ (0.01 equivalent) was added, and the mixture was again degassed by jet injection with N _2. The reaction mixture was heated to 70-80 °C and stirred until the borosilicate of L2 was complete (16-24 h) to produce L3, which was used directly in the next Suzuki coupling step.

L4 was prepared via Suzuki coupling of L3 and L1: After cooling to 15–25 °C, a solution of compound L1 in 2-Me-THF (0.96 equivalents, 5–6 V), _Na₂CO₃ (2.0 equivalents solid), and _H₂O (5 V) were _added sequentially. After degassing with _N₂ jet, the reaction mixture was aged at 70–80 °C until Suzuki coupling was complete (16–24 h). After cooling to 15–25 °C, the reaction mixture was filtered through a diatomaceous earth mat (0.5 X) and the filter cake was washed with 2-Me-THF (1–2 V). The organic layer in the filtrate was separated, concentrated to 1–2 V, diluted with toluene (10 V), and washed twice with L-cysteine/NaOH (pH > 10) (5 X, L-cysteine/NaOH/ _H₂O ratio: 1/0.5/9). The organic layer was then washed with _H₂O (5X) and concentrated to 5V to obtain a toluene solution of the free base L4 in toluene. An analytical sample of the free base L4 was obtained by crystallization in heptane/MTBE. ¹ HNMR (400 MHz, chloroform-d) δ 8.66-8.77 (m, 1H), 8.06 (d, J =1.22 Hz, 1H), 7.94 (dd, J = 1.77, 5.20 Hz, 1H), 7.86 (dd, J = 3.55, 8.56 Hz, 1H), 7.51-7.60 (m, 1H), 5.63 (s, 1H), 5.44-5.48 (m, 1H), 3.54-3.60 (m, 6H), 3.43-3.49 (m, 6H); mp 41.8℃ (DSC peak); XRPD 2θ: 6.70, 7.61, 9.67, 13.56, 13.77, 13.99, 15.36, 19.36, 20.71, 21.81, 23.10, 26.96, 27.72, 28.02, 29.36, 31.88, 32.04, 39.09.

Preparation of L4 phosphate: A solution _of 85% _H3PO4 (based on 1.6 equivalents of free base of compound L4) in MeOH (1-2V) was added to a toluene solution of L4 over 2 hours to obtain a suspension. The suspension was concentrated to 3V below 45°C, and n-heptane (10V) was added over 2 hours. The mixture was concentrated to 10V below 45°C, and the batch temperature was adjusted to 15-25°C. After stirring for 6-8 hours, the mixture was filtered, and the filter cake was washed with n-heptane (1-2V). The wet cake was dried under reduced pressure with slight _N2 purging at 40°C to give 190.5 g of L4-phosphate (93.2% yield). ¹ H NMR (400 MHz, DMSO-d ₆ ) δ 8.63-8.72 (m, 1H), 8.24 (dd, J = 3.6, 8.7 Hz, 1H), 8.11 (d, J =1.1 Hz, 1H), 8.01 (dd, J = 1.8, 5.2 Hz, 1H), 7.92 (dd, J = 8.7, 9.9 Hz, 1H), 5.58 (s, 1H), 5.36 (s, 1H), 3.43 (s, 6H), 3.35 (s, 6H). LC-MS: [M+H] ⁺ 323.2; mp. 124.2℃ (DSC peak); 21.55, 22.12, 23.09, 23.39, 23.73, 25.61, 26.25,27.48, 27.73, 28.26, 29.55, 30.35, 31.10, 31.82, 34.13, 34.68, 36.04, 39.48.

5.1.4 Synthesis of 5-fluoro-[2,4'-bipyridine]-2',6-dicarboxaldehyde (compound Q)

A mixture of compound L4-phosphate (177 g, 111 g L4 free base = 1.0X), 1N HCl (1110 mL, 10V), and toluene (555 mL, 5V) was stirred at 15–25 °C for 0.5–1.0 h. The organic phase was separated, and the aqueous layer was stirred at 55–60 °C for 2 h. The mixture was then slowly concentrated (3 h) at 55–60 °C under reduced pressure (-0.08 to -0.085 MPa) to remove the generated MeOH, and then cooled to 30–40 ° _C . DCM (777V) was loaded, and the pH of the mixture was adjusted to 5–7 with 15% _Na₂CO₃ (3.5–4.5X). The layers were separated, and the aqueous layer was extracted with DCM (2V). The combined organic layers were washed with _H₂O (5V) and filtered through a _Na₂SO₄ pad ( _1X ). The filter pads were rinsed with DCM (2V) and the combined filtrate was concentrated to 8-10V. The reactor walls were spray-washed with 2V DCM, and then n-heptane (8-10V) was added over 2.0-5.0 hours. The mixture was concentrated to 10-12V at atmospheric pressure and below 60°C (with ≤40% residual DCM in the supernatant). The suspension was aged at 30-40°C for 1.0-2.0 hours, then at 5-10°C for 6-8 hours, and filtered. The filter cake was washed with 1:4 DCM/n-heptane (1-2V) and dried under reduced pressure at 40-50°C to give 80.19 g of compound Q (98% yield). LC-MS: [M+H] ⁺ 231; [M+H+H ₂ O] ⁺ 249; ¹ H NMR (400 MHz, chloroform-d) δ 10.27 (s, 1H), 10.18 (s, 1H), 8.91-9.00(m, 1H), 8.51-8.59 (m, 1H), 8.24-8.31 (m, 1H), 8.17 (dd, J = 3.5, 8.7 Hz, 1H), 7.77 (t, J = 9.0 Hz, 1H); mp. 150℃ (DSC peak).

5.1.5 Synthesis of 2',6-bis(difluoromethyl)-5-fluoro-2,4'-bipyridine (compound H)

The solution of compound Q (30.0 g, 1.00X) and _Et3N (0.044X) in anhydrous DCM (KF ≤ 0.02%, 20X) was cooled to 0–5 °C. DAST (3.50X) was slowly added at 0–10 °C, and the mixture was then aged at 20–25 °C until the reaction was complete (approximately 24 hours). The reaction mixture was quenched in 15% _K2CO3 (28X) at 0–20 ° _C for two hours and aged at 20–25 °C for 0.5 hours. The organic layer was separated, cooled to 10–20 °C, and treated with 1 M HCl (9.9–11.1X) at 10–25 °C for 0.5–1 hour. After standing for 0.5 hours, the mixture was filtered through a diatomaceous earth mat (approximately 0.5X), followed by a small wash with DCM (2.0–3.0X). The filtrate was allowed to stand, and the organic layer was separated, washed with _H₂O (10X), and filtered through a silica gel pad (approximately 1.5X). The silica gel pad was washed with DCM (5.0X – 6.0X, three times) until the purity of compound H in the filtrate fraction decreased to <90%. The combined filtrates were concentrated to approximately 2-3V at below 30°C, and then co-distilled with isopropanol at 50°C until the residual DCM was <5.0% (total IPA used was 6-7X), resulting in a final volume of 3-4V. The distillation residue was aged at 55-60°C for 0.5 hours, cooled to 35-40°C, and aged for another 0.5 hours. Water (9.0-10.0X) was slowly added at 33-40°C (1-3 hours), and the mixture was stirred for 0.5 hours. After aging at 15-20°C, the suspension was filtered, and the filter cake was washed sequentially with IPA/ _H₂O (1:4, wt/wt, 1X) and _H₂O (2X). The wet cake was dried under reduced pressure at 40-45°C until KF < 0.3% and residual IPA < 0.1% (18-24 hours) to give 30.15 g of compound H (82% yield). Melting point (mp) 75°C (DSC peak). LC-MS: [M+H] ⁺ 275.2; ¹ H NMR (400 MHz, chloroform-d) δ 8.71-8.89 (m, 1H), 8.22 (s, 1H), 7.91-8.12 (m, 2H), 7.71 (t, J = 8.9 Hz, 1H), 7.00 (s, 1H), 6.87(s, 1H), 6.82-7.05 (m, 1H), 6.59 (s, 1H), 6.73 (s, 1H).

5.1.6 Synthesis of (S)-2-amino-2,4-dimethylpentane-1-ol benzoate (compound D-benzoate)

_BF3 · _Et2O (200 g, 2.0 equivalent) was slowly added to a mixture of _NaBH4 (53 g, 2.0 equivalent) and THF (1.0 L) at 0–10 °C. The reaction mixture was heated to 15 °C, and then (S)-(α)-methylleucine (100 g, 1.0 equivalent) was added over 1 hour at < 25 °C. The mixture was aged at 20–25 °C for 5–8 hours, and then slowly quenched in 10% NaOH aqueous solution (750 mL) at 25–30 °C. The organic layer was separated, washed with 15% NaCl aqueous solution (200 mL), and then diluted with n-heptane (300 mL). 2N HCl (approximately 300 mL) was added to the mixture until the pH reached 1–2. The organic layer was separated and extracted with 1N HCl (300 mL). The combined aqueous layers were alkalized with 30% NaOH (approximately 500 mL) until pH >13, and then extracted with MTBE (500 mL x 3). The combined organic extracts were dried over anhydrous _Na₂SO₄ (100-200 g ₎ , filtered, concentrated to approximately 200 mL, and then rinsed with MTBE (200-500 mL) until the water content in the concentrate was <0.5%. A solution of amino alcohol D was then slowly (for 5 hours) added to a solution of benzoic acid (93 g, 1.1 equivalents) in MTBE (500 mL) at 45-50 °C. After stirring for 1 hour, the mixture was slowly (for 5-8 hours) cooled to 20-25 °C and aged for 5-8 hours to obtain a suspension. The suspension was filtered, the filter cake was washed with 1/1 MTBE/n-heptane (150 mL), and dried under reduced pressure at 40-50 °C to give compound D-benzoate in 92% yield. mp. 125.4℃ (DSC peak); ^¹H NMR (400 MHz, methanol- _d⁴ ) δ 7.88–7.99 (m, 2H), 7.27–7.46 (m, 3H), 3.45–3.62 (m, 2H), 1.69–1.87 (m, 1H), 1.56–1.66 (m, 1H), 1.44–1.54 (m, 1H), 1.29 (s, 3H), 1.00 (d, J = 6.60 Hz, 6H); XRPD 2θ: 6.67, 6.83, 12.84, 13.37, 15.16, 16.95, 17.83, 19.90, 20.32, 21.23, 22.28, 23.70, 24.09, 24.42, 26.24, 26.91, 27.49, 30.60, 32.64, 33.98, 34.98, 35.13.

5.1.7 Synthesis of (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridin]-5-yl)oxy)-2,4-dimethylpentane-2-amine hydrochloride (compound S)

Solid t-BuOK (based on compound H, 2.5-3.0 equivalents) was added in portions to a mixture of compound D-benzoate (based on compound H, 1.2 equivalents) and THF (10.5-11.6X) at 15-20°C. The mixture was heated to 20-25°C and stirred for 3-5 hours, then cooled to 0-5°C. A solution of compound H (1.00X) in THF (3.6-4.5X) was slowly added (approximately 1 hour) while keeping the batch temperature below 20°C. The reaction mixture was aged at 20-25°C until the reaction was complete (1-3 hours). MTBE (6X) was added, and the mixture was cooled to 10-15°C. _H₂O (9.0-11.0X) was slowly added (1-3 hours) while keeping the batch temperature below 25°C. The layers were separated, and the aqueous layer was extracted with MTBE (2.2X). The combined organic layers were concentrated to 2-3V under reduced pressure at temperatures below 30°C. Free base compound J: ^¹H NMR (400 MHz, DMSO- _d⁶ ) δ 8.70–8.84 (m, 1H), 8.40 (d, J = 8.8 Hz, 1H), 8.33 (s, 1H), 8.22 (br d, J = 5.0 Hz, 1H), 7.81 (d, J = 8.8 Hz, 1H), 7.17–7.41 (m, 1H), 6.89–7.13 (m, 1H), 3.82–3.95 (m, 2H), 1.74–1.88 (m, 1H), 1.55 (br s, 2H), 1.33–1.46 (m, 2H), 1.12 (s, 3H), 0.93 (t, J = 7.1 Hz). (Hz, 6H). After exchanging the solvent for IPA to 2-3V by co-distillation (6.0-6.5X), more IPA (3.8-4.2X) is added, and the mixture is heated to 50-60°C. A solution of 35% HCl (0.44-0.47X) in IPA (1.3-1.5X) is slowly added (about 1 hour) while maintaining the batch at 50-60°C. The resulting suspension is aged at 50-60°C for 1.0-2.0 hours, cooled to 20-30°C over 2.0-4.0 hours, stirred at 20-30°C for 1.0-2.0 hours, and then filtered. The filter cake is washed with MTBE (3.5-4.0X) and dried under reduced pressure at 40-50°C for 16-24 hours to give compound S. LC-MS m/z 386.1; mp. 246.4°C (DSC peak), ¹ H NMR (400 MHz, DMSO-d6) δ8.81 (d, J = 5.3 Hz, 1H), 8.51 (br s, 2H), 8.45 (d, J = 8.9 Hz, 1H), 8.34 (s,1H), 8.24 (d, J = 5.1 Hz, 1H), 7.91 (d, J = 8.9 Hz, 1H), 7.56-7.87 (m, 1H), 6.90-7.23 (m, 1H), 4.29 (s, 2H), 1.72-1.91 (m, 2H), 1.54-1.72 (m, 1H), 1.42(s, 3H), 0.86-1.00 (m, 6H).

5.1.8 Synthesis of (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridin]-5-yl)oxy)-2,4-dimethylpentan-2-amine phosphate (compound K)

A mixture of compound S (9.5 kg, 1.0X), MTBE (76.0 kg, 8.0X), and water (50.0 kg, 5.3X) was treated with a 20% aqueous solution of NaOH (0.95 kg NaOH solid in 4.0 kg water) at 35–40 °C until all solids dissolved (2.0–5.0 h). The reaction mixture was cooled to 20–25 °C and stirred for 1.0–2.0 h. The organic layer was separated, washed with water (46.5 kg, 4.9X), and concentrated to approximately 25 L (2–3X) under reduced pressure at ≤30 °C. The solvent was exchanged for IPA (79.0 kg IPA, 8.3X) by co-distillation under reduced pressure at ≤50 °C, resulting in a final volume of 29–38 L (3–4X). The distillation residue was then diluted with IPA (60 kg) and heated to 50–60 °C. A solution of _H₃PO₄ (2.8 _kg , 0.29X) in IPA (5.0 kg, 0.53X) was added over 2.0–4.0 hours. More IPA (22.0 kg, 2.3X) was added, and the batch was stirred at 50–60 °C for 2.0–4.0 hours. The batch was cooled to 15–20 °C over 2.0–4.0 hours, and then stirred at 15–20 °C for 1.0–2.0 hours. The resulting suspension was filtered, and the filter cake was washed sequentially with IPA (27.0 kg, 2.84X) and MTBE (31 kg, 3.3X). The wet cake was dried under reduced pressure at 45–55 °C for 17–24 hours to give compound K. The salt ratio of compound J to phosphate in compound K was determined to be 1:1 (using two separate HPLC methods with UV and IC detectors, respectively). The purity of compound K was 98.7–99.9% by HPLC. The crystallinity of compound K was confirmed by XRPD and further supported by DSC. ¹ H NMR (400 MHz, DMSO-d ₆ ) δ 8.78 (d, J = 5.1 Hz, 1H), 8.41(d, J = 8.8 Hz, 1H), 8.31 (s, 1H), 8.21 (d, J = 5.1 Hz, 1H), 7.88 (brd, H),7.47 (t, J _HCF = 54 Hz, 1H), 7.04 (t, J _HCF = 54 Hz, 1H), 4.03-4.29 (m, 2H), 1.72-1.87 (m, 1H), 1.60-1.69 (m, 1H), 1.49-1.59 (m, 1H), 1.33 (s, 3H), 0.92(d, J = 6.6, 3H), 0.87 (d, J = 6.6, 3H); ¹³ C NMR (100 MHz, DMSO-d6) δ 21.62,22.74, 24.61, 24.82, 44.69 54.57, 72.80, 110.53 (t, J _CF = 237 Hz), 113.84 (t,J _CF = 238 Hz), 116.68, 122.19, 125.03, 140.07 (t, J _CF = 22 Hz), 144.13,145.98, 150.52, 152.80 (t, J _CF = 25 Hz), 153.51. XRPD: 4.80, 5.99, 7.43, 7.88, 9.57, 11.58, 14.84, 15.21, 15.75, 17.91, 18.83, 19.17, 20.41, 20.84, 21.67, 23.23, 23.95, 24.41, 24.72, 25.27, 26.37, 30.14.

5.1.9 Synthesis of (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridin]-5-yl)oxy)-2,4-dimethylpentan-2-amine phosphate (compound K)

Compound K seeds (0.18 g) were added to a solution of compound J (9.14 g) in IPA (100 mL) at 50–60 °C. A solution of 85% phosphoric acid (2.87 g, 1.05 equivalent) in IPA (7 mL) was added over 2–4 hours. The suspension was aged for 2–4 hours, then cooled to 15–20 °C and aged for 1–2 hours over the same period. The suspension was filtered, and the filter cake was washed with IPA (20 mL), followed by washing with MTBE (44 mL). The wet cake was dried under reduced pressure at 45–55 °C for 17–24 hours to give 11.3 g of compound K, 98% yield.

Seed formation of compound K: IPA (1.0 mL) was added to compound J (50.08 mg, 0.134 mmol, 1.0 equivalent) to form a clear solution at ambient temperature, followed by the addition of phosphoric acid (0.156 mL, 1 M in IPA, 0.156 mmol, 1.20 equivalent). The mixture was stirred for 6 hours to obtain a suspension, which was then aged at 60 °C for 30 min. After cooling to room temperature, heptane (0.5 mL) was added, and the resulting mixture was stirred for 1 hour. The resulting suspension was filtered, and the filter cake was washed with MTBE (0.5 mL) and dried overnight under reduced pressure at 45–48 °C to obtain seeds of compound K (59.28 mg, 94.4% yield).

The salt ratio, purity, XRPD, DSC, and TGA data were essentially the same as those obtained for compound K in Example 2.

Each reference cited in this article (e.g., patents, patent applications, and publications) is incorporated herein in its entirety by way of citation.

Claims (41)

1. A method for preparing (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridin]-5-yl)oxy)-2,4-dimethylpentan-2-amine (compound J): The method includes causing compound H under conditions sufficient to form compound J: With compound D: Or its salts come into contact with an alkali. 2. The method of claim 1, wherein the base is an alkoxide. 3. The method of claim 2, wherein the alkoxide is potassium tert-butoxide. 4. The method according to any one of claims 1 to 3, wherein compound H is formed by subjecting compound Q to conditions sufficient to form compound H: It is prepared by contacting a fluorinating agent. 5. The method of claim 4, wherein the fluorinating agent is DAST. 6. The method of claim 4 or 5, wherein compound Q is formed by subjecting compound P to conditions sufficient to form compound Q: It is prepared by contacting with acid. 7. The method of claim 6, wherein the acid is hydrochloric acid. 8. The method of claim 6 or 7, wherein compound P is formed by subjecting compound L to conditions sufficient to form compound P: With compound N: Prepared by contact. 9. The method of claim 4 or 5, wherein compound Q is formed by subjecting compound L4 to conditions sufficient to form compound Q: It is prepared by contacting with acid. 10. The method of claim 9, wherein the acid is hydrochloric acid. 11. The method of claim 9 or 10, wherein compound L4 is formed by subjecting compound L3 to conditions sufficient to form compound L4: With compound L1: It is prepared by contacting a catalyst, ligand, and base. 12. The method of claim 11, wherein the catalyst is Pd2(dba)2. 13. The method of claim 11 or 12, wherein the ligand is Xphos. 14. The method according to any one of claims 11 to 13, wherein the base is sodium carbonate. 15. The method of any one of claims 1 to 14, wherein the salt of said compound D is a benzoate. 16. The method of claim 13, wherein the solvent is isopropanol. 17. A method for preparing compound K: The method includes making compound S (e.g., in MTBE): Compound J is obtained by contacting with an aqueous solution of NaOH; and compound J is contacted with an acid (e.g., phosphoric acid or hydrochloric acid) in a solvent under conditions sufficient to form compound K. 18. The method of claim 17, wherein compound S is formed by subjecting compound J to conditions sufficient to form compound S: It is prepared by contacting hydrochloric acid in a solvent. 19. The method of claim 18, wherein the solvent is isopropanol. 20. The method of claim 18, wherein compound J is prepared according to any one of claims 1 to 16. 21. A compound, which is 6-bromo-2-(dimethoxymethyl)-3-fluoropyridine (compound L1): . 22. A compound, which is 2-(dimethoxymethyl)-4-(4,4,5,5-tetramethyl-1,3,2-dioxaneborane-2-yl)pyridine (compound L3): . 23. A compound, which is 2',6-bis(dimethoxymethyl)-5-fluoro-2,4'-bipyridine (compound L4): Or its salt. 24. The compound of claim 23, wherein it is a hydrochloride, phosphate or maleate. 25. The compound of claim 24, wherein it is a crystalline 2',6-bis(dimethoxymethyl)-5-fluoro-2,4'-bipyridine phosphate with a melting point of about 125°C. 26. The compound of claim 25, having an XRPD spectrum containing peaks at one or more of about 6.70, 7.61, 9.67, 13.56, 13.77, 13.99, 15.36, 19.36, 20.71, 21.81, 23.10, 26.96, 27.72, 28.02, 29.36, 31.88, 32.04, 39.09 degrees 2θ. 27. A compound, which is 5-fluoro-[2,4'-bipyridine]-2',6-dicarboxaldehyde (compound Q): . 28. A crystalline form of the compound as claimed in claim 27, having a melting point of about 150°C. 29. A compound, which is (S)-2-amino-2,4-dimethylpentane-1-ol benzoate (compound D-benzoate): . 30. A crystalline form of the compound as described in claim 29. 31. A compound, which is 2',6-bis(difluoromethyl)-5-fluoro-2,4'-bipyridine (compound H): . 32. A crystalline form of the compound as described in claim 31. 33. A (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridin]-5-yl)oxy)-2,4-dimethylpentane-2-amine (compound J): A pharmaceutically acceptable crystalline salt. 34. The pharmaceutically acceptable crystalline salt of claim 33, wherein it is a hydrochloride salt. 35. The hydrochloride salt of claim 34, wherein the melting point is 247°C (decomposes). 36. The hydrochloride of claim 34, having an XRPD spectrum containing peaks at one or more of about 9.2, 11.7, 13.9, 18.7, 22.2, 25.0 or 26.8 degrees 2θ. 37. The pharmaceutically acceptable crystalline salt of claim 33, wherein the crystalline salt is a phosphate. 38. The phosphate of claim 37, having a melting point of about 184°C. 39. The phosphate of claim 38, having an XPRD spectrum containing peaks at one or more of about 4.81, 5.99, 7.44, 7.89, 11.66, 14.85, 15.77, 19.19, 20.86, 21.65, 23.96, 24.48, or 24.73 degrees 2-θ. 40. A known (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridin]-5-yl)oxy)-2,4-dimethylpentane-2-amine (compound J): A method for determining the purity of a sample of a pharmaceutically acceptable salt thereof, comprising testing the presence of one or more compounds listed in Table 1 in the sample. 41. A compound containing (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridin]-5-yl)oxy)-2,4-dimethylpentane-2-amine (compound J): Or a pharmaceutically acceptable salt thereof, said composition comprising less than 0.01% by weight of one or more compounds listed in Table 1.