Methods and compounds for synthesis of AAK1 inhibitors

Abstract

Disclosed herein are methods of synthesizing (S)-1-((2 ', 6-bis (difluoromethyl)-[2, 4'-bipyridyl]-5-yl) oxy)-2, 4-dimethylpent-2-amine and salts thereof, as well as compounds useful therein.

Description

Technical Field

[0001] The present invention relates to a method for preparing (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridyl]-5-yl)oxy)-2,4-dimethylpentan-2-amine and its salt forms, and synthetic intermediates useful therein. Background Art

[0002] Adaptor-associated kinase 1 (AAK1) is a member of the Ark1 / Prk1 family of serine / threonine kinases. AAK1 mRNA exists in two splice forms, referred to as the short splice form and the long splice form. The long form is predominant and is highly expressed in the brain and heart (Henderson and Conner, 2001). Mol. Biol. Cell. 2007, 18, 2698-2706). AAK1 is enriched in synaptosomal preparations and colocalizes with endocytic structures in cultured cells. AAK1 regulates clathrin-coated endocytosis, a process important in synaptic vesicle recycling and receptor-mediated endocytosis. AAK1 is associated with the AP2 complex, which links receptor cargo to the clathrin coat. Clathrin binding to AAK1 stimulates AAK1 kinase activity (Conner et al., Traffic 2003, 4, 885-890; Jackson et al., J. Cell. Biol. AAK1 phosphorylates the mu-2 subunit of AP-2, promoting the binding of mu-2 to the tyrosine-containing sorting motif on the cargo receptor (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 phosphorylation can enhance the efficiency of internalization (Motely et al., Mol. Biol. Cell. 2006, 17, 5298-5308).

[0003] AAK1 has been identified as an inhibitor of Neuregulin-1 / ErbB4 signaling in PC12 cells. Loss of AAK1 expression by RNA interference-mediated gene silencing or treatment with the kinase inhibitor K252a (which inhibits AAK1 kinase activity) results in enhanced Neuregulin-1-induced neurite outgrowth. 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 schizophrenia susceptibility genes (Buonanno, Brain Res. Bull.2010, 83, 122-131). SNPs in these two genes are associated with multiple schizophrenia endophenotypes (Greenwood et al., Am. J. Psychiatry Neuregulin 1 and ErbB4 KO mouse models have shown schizophrenia-related morphological changes and behavioral phenotypes (Jaaro-Peled et al., Schizophrenia Bulletin 2010, 36,301-313; Wen et al., Proc. Natl. Acad. Sci. USA. 2010, 107, 1211-1216). In addition, single nucleotide polymorphisms in the introns of the AAK1 gene 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 useful in treating schizophrenia, cognitive deficits in schizophrenia, Parkinson's disease, neuropathic pain, bipolar disorder, and Alzheimer's disease.

[0004] 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 a phosphorylation site mutant of Mu2 (an AAK1 substrate) all resulted in reduced HCV virion assembly. Furthermore, the same treatments were shown to inhibit HCV entry, suggesting that AAK1 inhibitors can disrupt two host-dependent stages of the viral life cycle (Neveu et al., 2011). PLoS Pathog. 2012, 8, 1-16; Neveu et al., J. Virol. Published online February 4, 2015). AAK1 inhibitors may also be useful against HIV and HBV (see, e.g., Boge et al., J. Biol. Chem. 1998, 273, 15773-15778).

[0005] Many AAK1 inhibitors have been disclosed in the literature, and some have been suggested to be useful for treating neuropathic pain. See, e.g., Hartz, RA et al., J. Med. Chem. , 2021 Aug 12;64(15):11090-11128. However, to evaluate the full potential of any drug, human clinical trials are necessary.

[0006] A specific AAK1 inhibitor, (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridyl]-5-yl)oxy)-2,4-dimethylpentan-2-amine, has been prepared on a small laboratory scale. See, e.g., U.S. Pat. No. 9,902,722. Unfortunately, synthetic methods available in laboratory settings are rarely suitable for large-scale manufacture of pharmaceutically acceptable materials. For example, the production of potentially harmful reaction byproducts needs to be minimized, and the use of toxic solvents and reagents is preferably avoided. In addition, reaction conditions that are feasible on a gram scale are often inefficient or even dangerous when scaled up. Therefore, there is a need for synthetic methods that can be used to prepare commercially useful quantities of pharmaceutically acceptable (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridyl]-5-yl)oxy)-2,4-dimethylpentan-2-amine. Summary of the invention

[0007] The present application relates to the preparation of compound (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridyl]-5-yl)oxy)-2,4-dimethylpentan-2-amine (Compound J):

[0008]

[0009] Compound J is an inhibitor of adaptor-associated kinase 1 (AAK1) and is believed to be useful in treating diseases and conditions including pain.

[0010] In one embodiment, the present invention encompasses a method for preparing (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridyl]-5-yl)oxy)-2,4-dimethylpentan-2-amine (Compound J):

[0011]

[0012] A method comprising reacting compound H under conditions sufficient to form compound J:

[0013]

[0014] With compound D:

[0015]

[0016] or a salt thereof in the presence of a base.

[0017] In one embodiment, compound H is prepared by reacting compound Q under conditions sufficient to form compound H:

[0018]

[0019] Prepared by contacting with a fluorinating agent. (The present invention encompasses a crystalline form of compound Q. The melting point of the specific crystalline form is about 150°C.)

[0020] In one embodiment, compound Q is prepared by reacting compound P under conditions sufficient to form compound Q:

[0021]

[0022] Prepared by contact with an acid.

[0023] In one embodiment, compound P is prepared by reacting compound L under conditions sufficient to form compound P:

[0024]

[0025] With compound N:

[0026]

[0027] Prepared by contact.

[0028] In one embodiment, compound Q is prepared by reacting compound L4:

[0029]

[0030] Prepared by contact with an acid.

[0031] In one embodiment, compound L4 is prepared by reacting compound L3:

[0032]

[0033] With compound L1:

[0034]

[0035] It is prepared by contacting in the presence of a catalyst and a base.

[0036] The present invention also covers a method for preparing compound K:

[0037]

[0038] A method comprising reacting a compound S under conditions sufficient to form a compound K:

[0039]

[0040] Contact with phosphoric acid in a solvent.

[0041] In one embodiment, compound S is prepared by reacting compound J under conditions sufficient to form compound S:

[0042]

[0043] Prepared by contacting with hydrochloric acid in a solvent.

[0044] The present invention also encompasses the synthesis of the intermediate 6-bromo-2-(dimethoxymethyl)-3-fluoropyridine (Compound L1):

[0045] .

[0046] The present invention also encompasses 2-(dimethoxymethyl)-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pyridine (Compound L3):

[0047] .

[0048] The present invention also encompasses 2',6-bis(dimethoxymethyl)-5-fluoro-2,4'-bipyridine (Compound L4):

[0049]

[0050] and its salts.

[0051] The present invention also encompasses the compound 5-fluoro-[2,4'-bipyridine]-2',6-dicarbaldehyde (Compound Q):

[0052] .

[0053] The present invention also encompasses (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridyl]-5-yl)oxy)-2,4-dimethylpentan-2-amine (Compound J):

[0054]

[0055] A crystalline pharmaceutically acceptable salt.

[0056] The present invention also encompasses a method for determining (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridyl]-5-yl)oxy)-2,4-dimethylpentan-2-amine (Compound J):

[0057]

[0058] or a pharmaceutically acceptable salt thereof, comprising testing the sample for the presence of one or more compounds listed in Table 1.

[0059] The present invention also encompasses a compound comprising (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridyl]-5-yl)oxy)-2,4-dimethylpentan-2-amine (Compound J):

[0060]

[0061] or a pharmaceutically acceptable salt thereof, the composition comprising less than 0.01% by weight of one or more compounds listed in Table 1 below. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 A representative X-ray powder diffraction (XRPD) pattern of crystalline solid Form I of ((S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridinyl]-5-yl)oxy)-2,4-dimethylpentan-2-ammonium dihydrogen phosphate (Compound K) is provided. The spectrum was obtained using a Bruker X-ray diffractometer with a LYNXEYE detector (copper Kα radiation).

[0063] Figure 2 A representative differential scanning calorimetry (DSC) thermogram of a crystalline solid form of Compound K is provided. The thermogram was obtained using a TA Instruments DSC Q2000 instrument and a sealed gold crucible filled under ambient conditions. Two scans were performed. After melting was complete in the first scan, the sample was rapidly cooled to -50°C at a rate of approximately -40 K / min, and then the second scan was recorded. In both scans, the heating rate was 10 K / min. DETAILED DESCRIPTION

[0064] The present invention relates to a synthetic intermediate and a method for preparing (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridyl]-5-yl)oxy)-2,4-dimethylpentan-2-amine (Compound J):

[0065]

[0066] The invention relates to a method for synthesizing a pharmaceutically acceptable salt thereof, which is sufficient in quantity (e.g., greater than 1 kg, 5 kg, or 10 kg) to produce a dosage form suitable for human clinical trials and subsequent commercialization. The method of the invention minimizes the formation of harmful impurities while maximizing the synthesis yield.

[0067] The specific method of the present invention is used to prepare ((S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridyl]-5-yl)oxy)-2,4-dimethylpentan-2-ammonium dihydrogen phosphate (Compound K):

[0068]

[0069] and its crystalline solid form. The specific crystalline form of this salt is referred to herein as Form I, and its XRPD spectrum is Figure 1 The spectra shown in are substantially the same, with diffraction 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. When used herein to refer to XPRD peaks, the term "about" means ± 0.2 degrees 2-θ.

[0070] The melting point of the crystalline form I of compound K is about 184°C (see Figure 2 ), as determined by differential scanning calorimetry (DSC) (melting endotherm). When referring to temperature, the terms "substantially" and "about" mean ± 2°C.

[0071] Crystalline Form I of Compound K is the most stable form of this salt found: after storage for up to four weeks at 40°C and 75% relative humidity, the form itself, morphology and purity did not change. In addition, although the melting point of Form I is lower than that of the hydrochloride salt of Compound J (which is a form of it with a melting point of about 247°C), the phosphate salt does not show signs of concomitant degradation. Instead, Form I was observed to melt and recrystallize into another metastable form with a melting point of about 172.5°C. The aqueous solubility of Form I (26.8 mg / mL at 25°C) further facilitates its large-scale manufacturing and purification. In comparison, the aqueous solubility of the hydrochloride salt of Compound J was measured at 25°C at 2.9 mg / mL.

[0072] One embodiment of the present invention that can be used to prepare Form I is shown below:

[0073]

[0074] 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. A specific solvent is isopropanol.

[0075] 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, the term "about" may be interpreted as ±10°C when used to refer to temperature, unless otherwise stated.) 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, the term "about" may be interpreted as ±5% when referring to time, unless otherwise stated. For example, "about 2 hours" is the same as 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 is used relative to Compound J. (Unless otherwise stated, the term "about" may be interpreted as ±5% when referring to molar equivalents or concentrations.) In some embodiments, the concentration of Compound J in the solvent is about 2% to about 25%.

[0076] In one embodiment of the present invention, compound K is prepared from compound S as follows:

[0077]

[0078] In this method, compound S is neutralized with a base under conditions sufficient to form compound J, and compound J is contacted with phosphoric acid under conditions sufficient to form compound K. Suitable bases for neutralization include NaOH, KOH, Na2CO3, and K2CO3. The preferred base is sodium hydroxide.

[0079] The neutralization of compound S with a base can generally be carried out in a solvent such as water, water / MTBE, water / THF, and water / 2-MeTHF (a preferred solvent is 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, the neutralization is carried out 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%.

[0080] The exposure of compound J to phosphoric acid in the second step shown above is usually 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-methyl THF, or a mixture thereof. The preferred solvent is isopropanol.

[0081] In some embodiments, the exposure of Compound J to phosphoric acid is carried out at a temperature of about 0°C to about 100°C (e.g., about 50°C to about 60°C). In some embodiments, the exposure of Compound J to phosphoric acid is carried out 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%.

[0082] Compound S can be prepared as follows:

[0083]

[0084] 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. The preferred solvent is isopropanol.

[0085] 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). About 0.8 to about 1.2 molar equivalents of hydrochloric acid are generally used relative to Compound J. In some embodiments, the concentration of Compound J in the solvent is about 2% to about 25%.

[0086] One embodiment of the present invention encompasses a method for preparing Compound J as shown below:

[0087]

[0088] Here, Compound J is prepared by neutralizing Compound D-benzoate with a base under conditions sufficient to form Compound D, which is contacted with Compound H in the presence of a base under conditions sufficient to form Compound J. Compound D need not be isolated.

[0089] Suitable solvents for these reactions include THF, 2-methyl THF, 1,4-dioxane, MTBE, DME, diglyme, tert-butyl alcohol and tert-amyl alcohol. The specific solvent is THF. The base used in the two steps can be added at the beginning of the first step. Examples of suitable bases include potassium tert-butoxide, sodium tert-butoxide, potassium tert-amyl alcohol, sodium tert-amyl alcohol, sodium hexamethyldisilazide, potassium hexamethyldisilazide, lithium diisopropylamide, n-butyl lithium, sec-butyl lithium and tert-butyl lithium. The specific base is potassium tert-butoxide.

[0090] In some embodiments of the present invention, the neutralization of the 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.

[0091] About 1.8 to about 3 molar equivalents (e.g., about 2.5 to 3 molar equivalents) of the base are used relative to Compound H, and about 1 to about 1.5 molar equivalents (e.g., about 1.2 molar equivalents) of Compound D-benzoate are used relative to Compound H.

[0092] The compound D-benzoate can be prepared as follows:

[0093]

[0094] wherein 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.

[0095] Examples of reducing agents include NaBH4 / BF3 . In some embodiments of the present invention, the reducing agent is NaBH4 / BF3. . Et2O. The amount of the reducing agent may be about 0.5 to about 4 molar equivalents relative to compound B (eg, about 2 molar equivalents).

[0096] The reduction of compound B is usually carried out in a solvent such as THF, 2-Me-THF, THF, 2-methyl THF, 1,4-dioxane, MTBE, DME and diglyme or a mixture thereof. A preferred solvent is THF. In some embodiments, the concentration of compound B in the solvent is about 2% to about 25%. The reduction can be carried out at a temperature of about -50°C to about 50°C (e.g., about 0°C to about 25°C) for about 0.5 hours to about 24 hours (e.g., about 5 hours to about 8 hours).

[0097] According to the method shown above, compound D is contacted with benzoic acid in a solvent such as MTBE, MTBE / heptane, THF, THF / heptane, EtOAc, EtOAc / heptane, IPAc, IPAc / heptane, EtOH, EtOH / heptane, IPA, IPA / heptane, toluene and acetonitrile. Preferred solvent is MTBE. In some embodiments of the present invention, this reaction is carried out at a temperature of about 0 ° C to about 60 ° C (for example, about 45 ° C to about 50 ° C) for about 1 to 2 hours. In some embodiments, relative to compound D, benzoic acid of about 0.8 to about 1.5 molar equivalents (for example, about 1.1 molar equivalents) is used. In some embodiments, the concentration of compound D in the solvent is about 2% to about 25%.

[0098] Another intermediate for large-scale synthesis of Compound J and its pharmaceutically acceptable salts is Compound H, which can be prepared as follows:

[0099]

[0100] 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), dialkylamido difluorosulfonium tetrafluoroborate ([R2N=SF2] (XtalFluor-E, XtalFluor-M) BF4), Deoxo-Fluor (BAST), Selectfluor and 4-tert-butyl-2,6-dimethylphenyl sulfur 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.

[0101] Preferably compound Q is contacted with a fluorinating agent in a solvent such as dichloromethane, chloroform, CCl4 and toluene. A preferred solvent is dichloromethane. The concentration of compound Q in the solvent can vary between about 2% and about 25%. The reaction usually occurs at a temperature of about -20°C to about 60°C (for example, about 0°C to about 25°C), and continues for about 1 hour to about 100 hours (for example, about 24 hours to about 30 hours).

[0102] Compound Q can be prepared from compound L4 as follows:

[0103]

[0104] In this method, compound Q is prepared by contacting compound L4 or a salt thereof (e.g., phosphate 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. A preferred acid is hydrochloric acid.

[0105] The reaction with acid is preferably carried out in a solvent such as water or DMSO / water (preferred solvent is water) and at a temperature of about 0°C to about 100°C (e.g., about 55°C to about 60°C). This reaction is generally carried out for about 1 hour to about 24 hours (e.g., two hours). The concentration of compound L4 can be changed to optimize the yield, and can be, for example, about 2% to about 25%. In some embodiments of the present invention, relative to compound L4, an acid of about 1 to about 10 molar equivalents (e.g., 5 molar equivalents) is used.

[0106] A particularly useful salt of compound L4 is L4-phosphate, which can be prepared as follows:

[0107]

[0108] 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 a solvent such as MeOH, EtOH, IPA, EtOAc, IPAc, MTBE, THF, 2-Me-THF, toluene, heptane or a mixture thereof. A preferred solvent system is toluene / methanol / heptane.

[0109] The reaction is generally 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 present 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 may range from about 2% to about 25%.

[0110] Compound L4 can be prepared using the following method:

[0111]

[0112] Here, compound L2 is contacted with a palladium catalyst, a base, a ligand, and a boron reagent under conditions sufficient to form compound L3, which is contacted with compound L1 in the presence of a catalyst and a base under conditions sufficient to form compound L4.

[0113] The preparation of compound L3 is generally carried out in a solvent 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. A preferred catalyst is Pd2(dba)3. Bases used to form compound L3 include NaOAc, KOAc, NaHCO3, KHCO3, Na2CO3, K2CO3, K2HPO4 and K3PO4. A preferred base is KOAc. Suitable ligands include PCy3, SPhos and Xphos. A preferred ligand is Xphos. Boron reagents available in the reaction include tetrahydrodiboron, PinBH and Pin2B2. A preferred boron reagent is Pin2B 2。

[0114] In some embodiments of the present 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%.

[0115] The next step of the reaction shown above, wherein compound L3 is reacted 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. The preferred solvent is water / 2-MeTHF. The concentration of compound L1 may range from about 2% to about 25%, but as with the conditions of all reactions disclosed herein, these numbers may be varied using methods well known to those skilled in the art to maximize product yield and minimize cost.

[0116] Examples of alkalis that can be used to form compound L4 include Na2CO3, K2CO3, Na3PO4, K3PO4, NaOH and KOH. A preferred alkali is sodium carbonate (Na2CO3). Depending on the alkali, about 1 to 2 molar equivalents (e.g., 2 molar equivalents) of alkali 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). Relative to compound L2, about 1 to about 2 molar equivalents (e.g., 1 equivalent) of compound L1 are used.

[0117] The synthetic intermediate compound L2 can be prepared as follows:

[0118]

[0119] 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. The preferred acid is hydrochloric acid.

[0120] The reaction shown above is usually carried out in a solvent such as 1,4-dioxane, DME, Et2O, THF, 2-Me-THF, toluene, DCM, MTBE, ACN, methanol. The preferred solvent is methanol. The temperature range for carrying out this reaction can be from about 0°C to about 80°C (e.g., from about 60°C to about 65°C), and the duration range can be from about 0.5 hour to about 48 hours (e.g., from about 6 to about 10 hours).

[0121] In some embodiments of the present invention, about 0.01 to about 1 molar equivalent (e.g., about 0.2 molar equivalent) of 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 may range from about 2% to about 30%.

[0122] Compound L2 can also be prepared as shown below using similar reaction conditions to those described above (although using more trimethoxymethane):

[0123]

[0124] The synthetic intermediate compound L1 can be prepared as follows:

[0125]

[0126] In this method, compound L1 is prepared by contacting compound SM2 with trimethoxymethane in the presence of an acid under conditions sufficient to form the acetal compound L1. Examples of suitable acids include H2SO4, MsOH, TsOH, H3PO4, HNO3, HCl and HBr. The preferred acid is hydrochloric acid.

[0127] 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. The preferred solvent is methanol.

[0128] In some embodiments of the present invention, SM2 is contacted with trimethoxymethane 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). Relative to SM2, about 0.01 to about 1 molar equivalent (e.g., about 0.05 molar equivalent) of acid is typically used. Relative to SM2, about 1 to about 4 molar equivalents (e.g., about 2 molar equivalents) of trimethoxymethane are typically used. In some embodiments, the concentration of SM2 in the solvent is about 2% to about 30%.

[0129] In one embodiment of the present invention, compounds J, K and S are prepared as shown in Scheme 1:

[0130] Solution 1

[0131]

[0132] In this method, compound J or a pharmaceutically acceptable salt thereof is prepared by the following process: 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 its salt 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.

[0133] Compound S is prepared by a process comprising exposing Compound J to hydrochloric acid in a solvent.

[0134] 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.

[0135] In a 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.

[0136] 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; e) exposing the resulting compound J to phosphoric acid in a solvent under conditions sufficient to form compound K.

[0137] The present invention encompasses 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 1 The products were characterized by H NMR and mass spectrometry.

[0138] Table 1

[0139]

[0140] The compounds in Table 1 were observed at various stages of bench-scale development work leading to the method of the present invention.

[0141] The present invention includes a method of 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.

[0142] 5.1 Example

[0143] Various embodiments of the present invention may be understood by considering the examples provided below. In these examples, all temperatures are set forth in degrees Celsius and all parts and percentages are by weight unless otherwise stated. Reagents may be purchased from commercial suppliers and used without further purification unless otherwise stated. (Reagents may also be prepared according to standard literature procedures known to those skilled in the art.)

[0144] Unless otherwise stated, reactions were performed at ambient temperature (or room temperature). Reactions were typically monitored by HPLC and terminated as judged by consumption of starting material.

[0145] The structure and purity of the compounds were confirmed by one or more of the following methods: proton nuclear magnetic resonance ( 1 H NMR) spectroscopy, 13 C NMR spectroscopy, mass spectrometry, infrared spectroscopy, melting point, X-ray crystallography, LC-MS and / or HPLC. Chemical shifts are reported in parts per million (ppm, δ) downfield from a standard (e.g., an internal standard such as TMS). Alternatively,1 H NMR chemical shifts are referenced to the signals of residual protons in deuterated solvents as known in the art. Peak multiplicities are designated as follows: s, singlet; d, doublet; dd, double of doublets; t, triplet; dt, double of triplets; q, quartet; br, broadened; and m, multiplet. Coupling constants are in Hertz (Hz). Mass spectrometry (MS) data were acquired using a mass spectrometer with APCI or ESI ionization.

[0146] 5.1.1 Synthesis of 6-bromo-2-(dimethoxymethyl)-3-fluoropyridine (Compound L1)

[0147]

[0148] HCl / MeOH solution (10 mL 3.9 M solution, 0.05 eq) was charged into a mixture of SM2 (158.5 g, 777 mmol, 1 eq), MeOH (1585 mL, 10V) and trimethoxymethane (166 g, 15.6 mol, 2.0 eq). The resulting mixture was aged at 60-65°C (reflux) until the reaction was complete (3-6 hours) and then cooled to 10-20°C. After being concentrated to 2-3V below 50°C and diluted with 2-Me-THF (10V), the reaction was quenched with 10% KCO (3V). The organic layer was separated and concentrated to 1-2V below 50°C. This 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% assay, 94.4% solution yield). LC-MS: m / z 250, 252, 220, 218 (M-OMe) 1 H 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).

[0149] 5.1.2 Synthesis of 4-chloro-2-(dimethoxymethyl)pyridine (Compound L2)

[0150]

[0151] HCl / MeOH (42.3 mL 3.9 M solution, 0.20 eq) was charged into a mixture of SM3 (117.3 g, 819.5 mmol, 1 eq), MeOH (1160 mL, 10 V) and trimethoxymethane (174 g, 1.64 mol, 2.0 eq). The mixture was heated to 60-65 ° C (reflux) until the reaction was complete (6-10 hours) and then cooled to 10-20 ° C. After concentrating to 3-5 V and diluting with 2-Me-THF (10 V), the reaction was quenched with 10% K CO (3 V, pH 8-9). The organic layer was separated and concentrated to 1-2 V, rinsed with 2-Me-THF (5 V x 2), 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% assay, 85.3% solution yield). 1 H 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, 5.3Hz, 1H), 5.28-5.39 (m, 1H), 3.38 (s, 6H). LC-MS m / z 187, 156 (M-OMe).

[0152] 5.1.3 Synthesis of 2',6-bis(dimethoxymethyl)-5-fluoro-2,4'-bipyridyl phosphate (Compound L4-phosphate)

[0153]

[0154] Preparation of L3: A mixture of compound L2 in 2-Me-THF (95.5 g, 1.00 eq., 5-6 V), 2-Me-THF (10 V), Pin2B2 (1.05 eq.), KOAc (3.0 eq.) and Xphos (0.02 eq.) was degassed by sparging with N2. Pd2(dba)3 (0.01 eq.) was added, and the mixture was degassed again by sparging with N2. The reaction mixture was heated to 70-80 °C and stirred until the borylation of L2 was complete (16-24 hours) to produce L3, which was directly used in the next Suzuki coupling step.

[0155] Preparation of L4 via Suzuki coupling of L3 and L1: After cooling to 15-25°C, a solution of compound L1 in 2-Me-THF (0.96 eq., 5-6V), Na2CO3 (2.0 eq. solid) and H2O (5V) were added in sequence. After degassing by sparging with N2, the reaction mixture was aged at 70-80°C until the Suzuki coupling was complete (16-24 hours). After cooling to 15-25°C, the reaction mixture was filtered through a diatomaceous earth pad (0.5X) and the filter cake was rinsed with 2-Me-THF (1-2V). The organic layer in the filtrate was separated, concentrated to 1-2V, diluted with toluene (10V) and washed twice with L-cysteine / NaOH (pH>10) (5X, ratio of L-cysteine / NaOH / H2O: 1 / 0.5 / 9). The organic layer was then washed with H2O (5X) and concentrated to 5V to give a toluene solution of compound L4 free base in toluene. An analytical sample of L4 free base 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.

[0156] Preparation of L4 phosphate: A solution of 85% H3PO4 (based on 1.6 equivalents of compound L4 free base) in MeOH (1-2V) was added to the toluene solution of the above L4 within 2 hours to obtain a suspension. The suspension was concentrated to 3V below 45°C, and n-heptane (10V) was added within 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 rinsed with n-heptane (1-2V). The wet cake was purged and dried with slight N2 at 40°C under reduced pressure to obtain 190.5 g L4-phosphate (93.2% yield).1 H NMR (400 MHz, DMSO-d6) 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] + 17.73, 28.26, 29.55, 30.35, 31.10, 31.82, 34.13, 34.68, 36.04, 39.48.

[0157] 5.1.4 Synthesis of 5-fluoro-[2,4'-bipyridine]-2',6-dicarbaldehyde (Compound Q)

[0158]

[0159] The mixture of compound L4-phosphate (177 g, 111 g L4 free alkali = 1.0X), 1N HCl (1110 mL, 10V) and toluene (555 mL, 5V) was stirred at 15-25°C for 0.5-1.0 hour. Separate the organic phase and stir the water layer at 55-60°C for 2 hours. The mixture is slowly (3 hours) concentrated to remove the MeOH produced at 55-60°C under reduced pressure (-0.08 to -0.085 Mpa), and then cooled to 30-40°C. DCM (777V) is loaded and the pH of the mixture is adjusted to 5-7 with 15% NaCO (3.5-4.5X). Separate the layers and extract the water layer with DCM (2V). The organic layer combined is washed with H o (5V) and filtered through Na sO pad (1X). The filter pad was rinsed with DCM (2V) and the combined filtrate was concentrated to 8-10V. The reactor wall was sprayed with 2VDCM, and then n-heptane (8-10V) was loaded in 2.0-5.0 hours. The mixture was concentrated to 10-12V (DCM≤40% remaining in the supernatant) below 60°C under normal atmospheric pressure. The suspension was aged for 1.0-2.0 hours at 30-40°C, aged for 6-8 hours at 5-10°C, 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 obtain 80.19 g of compound Q (98% yield). LC-MS: [M+H] + 231; [M+H+H2O] + 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°C (DSC peak).

[0160] 5.1.5 Synthesis of 2',6-bis(difluoromethyl)-5-fluoro-2,4'-bipyridine (Compound H)

[0161]

[0162] Compound Q (30.0 g, 1.00X) and EtN (0.044X) in anhydrous DCM (KF≤0.02%, 20X) solution 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 put into 15% KCO (28X) at 0-20°C for two hours, and aged for 0.5 hour at 20-25°C. 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 hour, the mixture was filtered through a diatomaceous earth pad (approximately 0.5X), followed by a small amount of flushing 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 pad (about 1.5X). The silica pad was washed with DCM (5.0X – 6.0X, three times) until the purity of compound H in the filtrate fraction was reduced to <90%. The combined filtrate was concentrated to about 2-3V below 30°C and then co-distilled with isopropanol at 50°C until residual DCM < 5.0% (a total of 6-7X IPA used), with 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 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 with IPA / H2O (1:4, weight / weight, 1X), then H2O (2X). The wet cake was dried at 40-45°C under reduced pressure 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).

[0163] 5.1.6 Synthesis of (S)-2-amino-2,4-dimethylpentan-1-ol benzoate (Compound D-benzoate)

[0164]

[0165] BF3.Et2O (200 g, 2.0 equivalents) was slowly added to a mixture of NaBH4 (53 g, 2.0 equivalents) in 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 equivalents) was added at < 25 ° C within 1 hour. The mixture was aged for 5-8 hours at 20-25 ° C, and then slowly quenched in a 10% NaOH aqueous solution (750 mL) at 25-30 ° C. The organic layer was separated, washed with a 15% NaCl aqueous solution (200 mL), and then diluted with n-heptane (300 mL). 2N HCl (about 300 mL) was added to the mixture until the pH reached 1-2. The organic layer was separated and extracted with 1 N HCl (300 mL). The combined aqueous layer was basified with 30% NaOH (about 500 mL) until pH>13, then extracted with MTBE (500 mL x 3). The combined organic extracts were dried over anhydrous Na2SO4 (100-200 g), filtered, concentrated to about 200 mL, and then rinsed with MTBE (200-500 mL) until the moisture content in the concentrate was <0.5%. The solution of amino alcohol D was then slowly (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 (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 obtain compound D-benzoate with a yield of 92%. 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.

[0166] 5.1.7 Synthesis of (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridyl]-5-yl)oxy)-2,4-dimethylpentan-2-amine hydrochloride (Compound S)

[0167]

[0168] Solid t-BuOK (2.5-3.0 equivalents based on compound H) was charged in batches to a mixture of compound D-benzoate (1.2 equivalents based on compound H) and THF (10.5-11.6X) at 15-20°C. The mixture was warmed to 20-25°C, stirred for 3-5 hours, and then cooled to 0-5°C. A solution of compound H (1.00X) in THF (3.6-4.5X) was added slowly (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 added slowly (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 2-3 V under reduced pressure at below 30 °C. Free base Compound J: 1H NMR (400 MHz, DMSO-d6) δ8.70-8.84 (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, 6H). After the solvent was exchanged to IPA to 2-3V by co-distillation (6.0-6.5X), more IPA (3.8-4.2X) was added and the mixture was heated to 50-60°C. A solution of 35% HCl (0.44-0.47X) in IPA (1.3-1.5X) was added slowly (about 1 hour) while keeping the batch at 50-60°C. The resulting suspension was 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 was washed with MTBE (3.5-4.0X) and dried at 40-50°C under reduced pressure 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).

[0169] 5.1.8 Synthesis of (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridyl]-5-yl)oxy)-2,4-dimethylpentan-2-amine phosphate (Compound K)

[0170]

[0171] A mixture of compound S (9.5 kg, 1.0X), MTBE (76.0 kg, 8.0X), water (50.0 kg, 5.3X) was treated with 20% NaOH aqueous solution (0.95 kg NaOH solid in 4.0 kg water) at 35-40°C until all solids dissolved (2.0-5.0 hours). The reaction mixture was cooled to 20-25°C and stirred for 1.0-2.0 hours. The organic layer was separated, washed with water (46.5 kg, 4.9X), and concentrated to about 25 L (2-3X) under reduced pressure at ≤30°C. Solvent was exchanged to IPA (79.0 kg IPA, 8.3X) by co-distillation at ≤50°C under reduced pressure, and the final volume was 29-38 L (3-4X), and 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 with IPA (27.0 kg, 2.84X) and MTBE (31 kg, 3.3X) successively. The wet cake was dried under reduced pressure at 45-55°C for 17-24 hours to obtain compound K. The salt ratio between compound J and phosphoric acid in compound K was determined to be 1:1 (two separate HPLC methods using UV and IC detectors, respectively). The purity of compound K was 98.7-99.9 area % by HPLC. The crystallinity of Compound K was confirmed by XRPD and further supported by DSC. 1 H NMR (400 MHz, DMSO-d6) 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 H-C-F = 54 Hz, 1H), 7.04 (t, J H-C-F= 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 C-F = 237 Hz), 113.84 (t,J C-F = 238 Hz), 116.68, 122.19, 125.03, 140.07 (t, J C-F = 22 Hz), 144.13,145.98, 150.52, 152.80 (t, J C-F = 25 Hz), 153.51. 20.84,21.67, 23.23, 23.95, 24.41, 24.72, 25.27, 26.37, 30.14.

[0172] 5.1.9 Synthesis of (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridyl]-5-yl)oxy)-2,4-dimethylpentan-2-amine phosphate (Compound K)

[0173]

[0174] 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 equivalents) in IPA (7 mL) was added within 2-4 hours. The suspension was aged for 2-4 hours, cooled to 15-20 ° C and aged for 1-2 hours within 2-4 hours. 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 obtain 11.3 g of compound K, 98% yield.

[0175] Compound K seed formation: IPA (1.0 mL) was added to compound J (50.08 mg, 0134 mmol, 1.0 eq) to form a clear solution at ambient temperature, and then phosphoric acid (0.156 mL, 1M in IPA, 0.156 mmol, 1.20 eq) was added. The mixture was stirred for 6 hours to obtain a suspension, and 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 under reduced pressure at 45-48 ° C overnight to obtain compound K seeds (59.28 mg, 94.4% yield).

[0176] The salt ratio, purity, XRPD, DSC and TGA data were essentially the same as those obtained for Compound K in Example 2.

[0177] Each reference (eg, patents, patent applications, and publications) cited herein is hereby incorporated by reference in its entirety.

Claims

1. A method for preparing (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridyl]-5-yl)oxy)-2,4-dimethylpentan-2-amine (Compound J): A method comprising reacting compound H under conditions sufficient to form compound J: With compound D: or a salt thereof in the presence of a base.

2. The process 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 of any one of claims 1 to 3, wherein compound H is prepared by reacting compound Q under conditions sufficient to form compound H: Prepared by contacting with 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 prepared by reacting compound P under conditions sufficient to form compound Q: Prepared by contact with an 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 prepared by reacting compound L under conditions sufficient to form compound P: With compound N: Prepared by contact.

9. The method of claim 4 or 5, wherein compound Q is prepared by reacting compound L4 under conditions sufficient to form compound Q: Prepared by contact with an 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 prepared by reacting compound L3 under conditions sufficient to form compound L4: With compound L1: It is prepared by contacting in the presence of a catalyst, a ligand and a 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 process of 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 compound D is a benzoate salt.

16. The method of claim 13, wherein the solvent is isopropyl alcohol.

17. A method for preparing compound K: A method comprising subjecting a compound S (e.g., in MTBE) to: contacting with aqueous NaOH to obtain Compound J; and contacting Compound J with an acid (eg, 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 prepared by reacting compound J under conditions sufficient to form compound S: Prepared by contacting with hydrochloric acid in a solvent.

19. The method of claim 18, wherein the solvent is isopropanol.

20. The process 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-dioxaborolan-2-yl)pyridine (Compound L3): 。 23. A compound, which is 2',6-bis(dimethoxymethyl)-5-fluoro-2,4'-bipyridine (Compound L4): or a salt thereof.

24. The compound of claim 23, which is a hydrochloride, a phosphate or a maleate salt.

25. The compound of claim 24, which is crystalline 2',6-bis(dimethoxymethyl)-5-fluoro-2,4'-bipyridyl phosphate having a melting point of about 125°C.

26. The compound of claim 25 having an XRPD spectrum comprising 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-dicarbaldehyde (Compound Q): 。 28. A crystalline form of the compound of claim 27 having a melting point of about 150°C.

29. A compound, which is (S)-2-amino-2,4-dimethylpentan-1-ol benzoate (Compound D-benzoate): 。 30. A crystalline form of the compound of 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 of claim 31.

33. (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridyl]-5-yl)oxy)-2,4-dimethylpentan-2-amine (Compound J): A crystalline pharmaceutically acceptable salt.

34. The crystalline pharmaceutically acceptable salt of claim 33 which is a hydrochloride salt.

35. The hydrochloride salt of claim 34 having a melting point of 247°C (decomposition).

36. The hydrochloride salt of claim 34 having an XRPD spectrum comprising 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 crystalline pharmaceutically acceptable salt of claim 33 which is a phosphate salt.

38. The phosphate salt of claim 37 having a melting point of about 184°C.

39. The phosphate salt of claim 38 having an XPRD spectrum comprising a peak 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-theta.

40. A method for determining (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridyl]-5-yl)oxy)-2,4-dimethylpentan-2-amine (Compound J): or a pharmaceutically acceptable salt thereof, comprising testing the sample for the presence of one or more compounds listed in Table 1.

41. A compound comprising (S)-1-((2',6-bis(difluoromethyl)-[2,4'-bipyridyl]-5-yl)oxy)-2,4-dimethylpentan-2-amine (Compound J): or a pharmaceutically acceptable salt thereof, the composition comprising less than 0.01% by weight of one or more compounds listed in Table 1.

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