Process for preparing an activin receptor-like kinase inhibitor

Abstract

The present disclosure provides a method for preparing a compound represented by formula (I). The method includes reacting a first starting material represented by formula (II) and a second starting material represented by formula (III) in a reaction mixture under Negishi conditions to form a compound of formula (I). R is an amine protecting group, Y is Cl, Br, or I, and Z is triflate, Cl, Br, or I. TIFF2022550451000020.tif2948TIFF2022550451000021.tif4524TIFF2022550451000022.tif3835

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims the priority of U.S. Provisional Patent Application No. 62 / 909,533, filed on October 2, 2019. The entire content of the aforementioned application is incorporated herein by reference.

Background Art

[0002] Activin receptor - like kinase - 2 (ALK2) is encoded by the activin A receptor, type I gene (ACVR1). ALK2 is a serine / threonine kinase in the bone morphogenetic protein (BMP) pathway (Shore et al., Nature Genetics 2006, 38:525 - 27). Inhibitors of ALK2 and mutant forms of ALK2 have the potential to treat many diseases, including fibrodysplasia ossificans progressiva (FOP), for example, heterotopic ossification (HO) induced by extensive surgical procedures, trauma (such as head injury or blast injury), prolonged immobilization, or severe burns, diffuse intrinsic pontine glioma (DIPG), a rare form of brain cancer, and anemia associated with chronic inflammatory diseases, infectious diseases, or neoplastic diseases.

[0003] U.S. Patent No. 10,233,186, the entire teachings of which are incorporated herein by reference, discloses potent and selective inhibitors of ALK2 and mutant forms of ALK2. Also, in U.S. Patent No. 10,233,186, as an important intermediate in the synthesis of many disclosed ALK2 inhibitors, compound 1

[0004]

Chemical Formula

[0005] is disclosed. U.S. Patent No. 10,233,186 is as shown below,

[0006]

Chemical Formula

[0007] A Suzuki reaction for the preparation of intermediates such as compound 1 is disclosed, which involves the coupling of a pyrrolo-pyridazine intermediate with a piperidinyl-pyridine compound. Summary of the Invention [Means for solving the problem]

[0008] It has now been observed that the Suzuki coupling of 6-pyrrolo-pyridazine and (bis(pinacolato)diboron piperidinyl-pyridine) to prepare compound 1 results in a complex purity profile, but the formation of by-products in the corresponding Negishi coupling is greatly reduced (Example 5). The Negishi coupling has the further advantages of requiring smaller amounts of the expensive 6-pyrrolo-pyridazine starting material, only one isolation step, and using less expensive reagents (ZnCl2 and i-propylmagnesium chloride). In addition, based on small-scale reactions, it is expected that if the Negishi coupling is employed to prepare compound 1 on an industrial scale, it will give a significantly higher yield than the Suzuki coupling. Based on these results, a new and improved synthesis of the key intermediate compound 1 is disclosed.

[0009] In one embodiment, the present disclosure provides a compound of formula (I):

[0010] [ka]

[0011] The present invention provides a method for preparing a compound represented by: The method comprises reacting in a reaction mixture with a compound of formula (II):

[0012] [ka]

[0013] a first starting material represented by and formula (III):

[0014]

Chem.

[0015] reacting a second starting material represented by under Negishi conditions to form a compound of formula (I). R is an amine protecting group, Y is Cl, Br, or I, and Z is Cl, Br, I, or triflate (preferably Br). Amine protecting groups are known in the art and are disclosed, for example, in T.W. Greene and P.G.M. Wuts "Protective Groups in Organic Synthesis" John Wiley & Sons, Inc., New York 1999. The protecting group may be added or removed using methods known in the art. Examples of amine protecting groups include (9-fluorenylmethyl carbamate), Cbz (benzyl carbamate), Boc (t-butyl carbamate), acetamide, benzyl, tosyl (p-toluenesulfonamide). In one embodiment, the amine protecting group is Boc.

[0016] Another embodiment of the present disclosure is a compound represented by formula (II), (II-A), or (II-B):

[0017]

Chem.

[0018] (wherein Y, X, and X 2 are independently Cl, Br, or I). In one embodiment, Y is Cl or I. The compounds represented by formula (II), (II-A), and (II-B) are intermediates in the disclosed Negishi reaction as described in more detail below.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

DETAILED DESCRIPTION OF THE INVENTION

[0020] The present disclosure provides an improved method for preparing Compound 1 in good yield and high purity via the Negishi reaction (also referred to herein as "Negishi coupling").

[0021] The Negishi reaction is a transition metal-catalyzed cross-coupling reaction. This reaction couples an organic halide or triflate with an organozinc compound, thereby forming a carbon-carbon bond (c-c) during the process. The transition metal catalyst is usually palladium or nickel. In the case of palladium, the catalyst species is, for example, Pd(0) in the form of Pd(X 1 )2, where X 1 is a phosphine ligand. Alternatively, Pd(0) is in situ, for example, Pd in the form of Pd(X 1 )2Cl2 +2It can be generated from a species. Exemplary phosphine ligands include 1,1'-bis(di-tert-butylphosphino)ferrocene (dtbpf), 1,1'-bis(di-tert-butylphosphino)ferrocene (dcypf), 1,1'-bis(diphenylphosphino)ferrocene (dppf), 2-di-tert-butylphosphino-2',4',6'-triisopropylbiphenyl (t-BuXPhos), [2-(di-1-adamantylphosphino)-2',4',6'-triisopropyl-3,6-dimethoxybiphenyl][2-(2'-amino-1,1'-biphenyl)]palladium(II) methanesulfonate (AdBrettPhos), 2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl (SPhos), (2-dicyclohexylphosphino-2',6'-diisopropoxy-1,1'-biphenyl)[2-(2'-amino-1,1'-biphenyl)]palladium(II) methanesulfonate (RuPhos), [2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl] (XPhos), [(2-dicyclohexylphosphino-3,6-dimethoxy-2',4',6'-triisopropyl-1,1'-biphenyl)-2-(2'-amino-1,1'-biphenyl)]palladium(II) methanesulfonate (BrettPhos), [(2-{bis[3,5-bis(trifluoromethyl)phenyl]phosphine}-3,6-dimethoxy-2',4',6'-triisopropyl-1,1'-biphenyl)-2-(2'-amino-1,1'-biphenyl)]palladium(II) methanesulfonate (JackiePhos), [(2-di-tert-butylphosphino-3,6-dimethoxy-2',4',6'-triisopropyl-1,1'-biphenyl)-2-(2'-amino-1,1'-biphenyl)]palladium(II) methanesulfonate (t-BuBrettPhos), mesyl(2-(di-tert-butylphosphino)-1,1'-binaphthyl)[2-(2'-amino-1,1'-biphenyl)]palladium (TrixiePhos), (2-biphenyl)di-tert-butylphosphine, (2-biphenylyl)di-tert-butylphosphine (JohnPhos), 2'-(di-tert-butylphosphino)-N,N-dimethylbiphenyl-2-amine (t-BuDavePhos), 2-di-tert-butylphosphino-2'-methylbiphenyl (t-BuMePhos), chloro(2-dicyclohexylphosphino-1,1'-biphenyl)[2-(2'-amino-1,1'-biphenyl)]palladium(II) (CyJohnPhos), 2-dicyclohexylphosphino-2'-(N,N-dimethylamino)biphenyl (DavePhos), 2-dicyclohexylphosphino-2'-methylbiphenyl (MePhos), 2-dicyclohexylphosphino-2'-(N,N-dimethylamino)biphenyl (PhDavePhos), 2-dicyclohexylphosphino-2'-methoxy-4',6'-di-tert-butylbiphenyl (VPhos), 2-[(tert-butyl)phenylphosphino]-2',6'-bis(N,N-dimethylamino)biphenyl (PhCPhos), [(2-dicyclohexylphosphino-2',6'-bis(N,N-dimethylamino)-1,1'-biphenyl)-2-(2'-amino-1,1'-biphenyl)]palladium(II) methanesulfonate (CPhos), methanesulfonate[2-diethylphosphino-2',6'-bis(dimethylamino)-1,1-biphenyl](2'-amino-1,1'-biphenyl-2-yl)palladium(II) (EtCPhos), 2-di(tert-butyl)phosphino-2',4',6'-triisopropyl-3-methoxy-6-methylbiphenyl (RockPhos), di-1-adamantyl(4''-butyl-2'',3'',5'',6''-tetrafluoro-2',4',6'-triisopropyl-2-methoxy-metha-terphenyl)phosphine (AlPhos), and 2-(t-butylphenylphosphino)-2',6'-dimethylamino-1,1'-biphenyl ((t-Bu)PhCPhos) are included.,

[0022] Exemplary palladium catalysts include Pd(dppe)2 (bis[1,2-bis(diphenylphosphino)ethane]palladium(0)), Pd(dba)2 (bis(dibenzylideneacetone)palladium(0)), CX-11 (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene(1,4-naphthoquinone)palladium(0) dimer), CX-12 (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene(1,4-naphthoquinone)palladium(0) dimer), Pd(t-Bu3P)2 (bis(tri-tert-butylphosphine)palladium(0)), Pd(PCy3)2 (bis(tricyclohexylphosphine)palladium(0)), Pd(PPh3)4 (tetrakis(triphenylphosphine)palladium(0)), Pd2(dba)3 (tris(dibenzylideneacetone)dipalladium(0)), Pd(OAc)2 (palladium(II) acetate), PdCl2(PPh3)2 (dichlorobis(triphenylphosphine)palladium(II)), PdCl2(Amphos)2 (bis(di-tert-butyl(4-dimethylaminophenyl)phosphine)dichloropalladium(II)), Pd(MeCN)2Cl2 (bis(acetonitrile)dichloropalladium(II)), PdCl2(P(o-Tol)3)2 (dichlorobis(tri-o-tolylphosphine)palladium(II)), Pd(dppf)Cl2 (1,1’-bis(diphenylphosphino)ferrocene]dichloropalladium(II)), Pd(MeCN)4(BF4)2 (tetrakis(acetonitrile)palladium(II) tetrafluoroborate), Pd-PEPPSI-IPent (dichloro[1,3-bis(2,6-di-3-pentylphenyl)imidazol-2-ylidene](3-chloropyridyl)palladium(II)), Pd-PEPPSI-IPr ([1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene](3-chloropyridyl)palladium(II) dichloride), and Pd-PEPPSI-SIPr ((1,3-bis(2,6-diisopropylphenyl)imidazolidene)(3-chloropyridyl)palladium(II) dichloride).

[0023] Alternatively, the palladium catalyst is selected from Pd(MeCN)2Cl2, Pd[P(o-Tol)3]2Cl2, PdCl2(Amphos)2, and Pd(dba)2. In another alternative, the palladium catalyst is Pd2(dba)3 / P(R 1 )3, Pd(PPh3)4, Pd(PPh3)2Cl2, Pd(MeCN)2Cl2, Pd[P(o-Tol)3]2Cl2, PdCl2(Amphos)2, Pd(PtBu3)2, Pd(dppf)Cl2, Pd(dba)2, Pd2(dba)3, and Pd(XPhos) (wherein each R 1 is C1-C6 alkyl, C3-C6 cycloalkyl, benzyl, or phenyl, and benzyl or phenyl is each optionally and independently substituted with one or more groups selected from halogen, C1-C3 alkyl, and C1-C3 alkoxy). In another alternative, the palladium catalyst is Pd2(dba)3. In yet another alternative, the palladium catalyst is PdP(tBu)3.

[0024] In another embodiment, the palladium catalyst can be combined with a phosphine ligand. For example, the palladium catalyst is Pd2(dba) combined with P(tBu)3.

[0025] In the case of nickel, the catalyst species is Ni(0), and Ni(0) can be generated in situ from Ni +2 species such as NiCl2. Exemplary nickel catalysts include Ni(acac)2, Ni(cod)2, Ni(PCy3)2Cl2, NiBr2, NiI2, Ni(OAc)2, Ni(OTf)2, Ni(BF4)2, NiCl2(PPh3)2.

[0026] The organic halide or organic triflate in the Negishi reaction may be an alkenyl, aryl, allyl, alkynyl, or propargyl halide or triflate, and the organozinc compound is R-Zn-X (wherein X is chloride, bromide, or iodide, and R is an alkenyl, aryl, allyl, alkyl, benzyl, homoallyl, or homopropargyl group). The conditions for carrying out the Negishi reaction are, for example, described in Recent Developments in Negishi Cross-Coupling Reactions Diana Haas, Jeffrey M. Hammann, Robert Greiner, Paul Knochel *ACS Catal. 2016, V6(3) pp. 1540 - 1552; Mild Negishi Cross-Coupling Reactions Catalyzed by Acenaphthoimidazolylidene Palladium Complexes at Low Catalyst Loadings Z. Liu, N. Dong, M. Xu, Z. Sun, T. Tu, J. Org. Chem., 2013, 78, 7436 - 7444; An Extremely Active Catalyst for the Negishi Cross-Coupling Reaction J. E. Milne, S. L. Buchwald, J. Am. Chem. Soc., 2004, 126, 13028 - 13032; One-Pot Negishi Cross-Coupling Reactions of In Situ Generated Zinc Reagents with Aryl Chlorides, Bromides, and Triflates S. Sase, M. Jaric, A. Metzger, V. Malakhov, P. Knochel, J. Org. Chem., 2008, 73, 7380 - 7382; Efficient Negishi Coupling Reactions of Aryl Chlorides Catalyzed by Binuclear and Mononuclear Nickel-N-Heterocyclic Carbene Complexes Z. Xi, Y. Zhou, W. Chen, J. Org. Chem., 2008, 73, 8497 - 8501; Cross-Coupling of Aryltrimethylammonium Iodides with Arylzinc Reagents Catalyzed by Amido Pincer Nickel Complexes X.-Q. Zhang, Z.-X. Wang, J. Org. Chem., 2012, 77, 3658 - 3663; Efficient Cross-Coupling of Aryl Chlorides with Arylzinc Reagents Catalyzed by Amido Pincer Complexes of Nickel L.Wang, Z.-X. Wang, Org. Lett., 2007, 9, 4335 - 4338; Highly Regio- and Stereoselective Synthesis of (Z)-Trisubstituted Alkenes via Propyne Bromoboration and Tandem Pd-Catalyzed Cross-Coupling C. Wang, T. Tobrman, Z. Xu, E.-i. Negishi, Org. Lett., 2009, 11, 4092 - 4095; Highly Regioselective Synthesis of Trisubstituted Allenes via Lithiation of 1-Aryl-3-alkylpropadiene, Subsequent Transmetalation, and Pd-Catalyzed Negishi Coupling Reaction J. Zhao, Y. Liu, S. Ma, Org. Lett., 2008, 10, 1521 - 1523; High Temperature Metalation of Functionalized Aromatics and Heteroaromatics using (tmp)2Zn·2MgCl2·2LiCl and Microwave Irradiation S. Wunderlich, P. Knochel, Org. Lett., 2008, 10, 4705 - 4707; A Mild Negishi Cross-Coupling of 2-Heterocyclic Organozinc Reagents and Aryl Chlorides M. R. Luzung, J. S. Patel, J. Yin, J. Org. Chem., 2010, 75, 8330 - 8332; Synthesis of Substituted Cyclopropanecarboxylates via Room Temperature Palladium-Catalyzed α-Arylation of Reformatsky Reagents S. N. Greszler, G. T. Halvorsen, E. A. Voight, Org. Lett., 2017, 19, 2490 - 2493; and Enantioselective, Palladium-Catalyzed α-Arylation of N-Boc-pyrrolidine by K.R. Campos, A. Klapars, J.H. Waldman, P.G. Dormer, C.-Y. Chen, J. Am. Chem. Soc., 2006, 128, 3538 - 3539.

[0027] Aryl zinc can be prepared using zinc metal such as ZnCl2 or ZnBr2 under mild reaction conditions via Grignard or organolithium intermediates. For example, Recent Developments in Negishi Cross-Coupling Reactions by Diana Haas, Jeffrey M. Hammann, Robert Greiner, Paul Knochel *ACS Catal. 2016, V6(3) pp. 1540 - 1552. Giovannini R, Knochel P (1998). "Ni(II)-Catalyzed Cross-Coupling between Polyfunctional Arylzinc Derivatives and Primary Alkyl Iodides". Journal of the American Chemical Society. 120(43):11186 - 11187. doi:10.1021 / ja982520o. See Jie Jack Li, Chapter 3 - Applications of Palladium Chemistry to the Total Synthesis of Naturally Occurring of Indole Alkaloids in "Alkaloids: Chemical and Biological Perspectives" 14:437 - 503 (1999). In some cases, organozinc compounds can be prepared directly by reacting with ZnCl2. (S.P. Nolan and O. Navarro, 11.01 - C - C Bond Formation by Cross - coupling in "Comprehensive Organometallic Chemistry III" 11:1 - 37 (2007).

[0028] The term "under Negishi conditions" means transition - metal - catalyzed cross - coupling, which is a carbon - carbon bond - forming reaction between an organic halide and an organozinc compound. "Under Negishi conditions" also includes the formation of organozinc compounds, such as by the reaction of zinc halide with a Grignard or organolithium intermediate.

[0029] In one aspect, i) the first starting material has the formula (II - B):

[0030]

Chemical formula

[0031] It is converted into an organozinc intermediate represented by this. This organozinc intermediate reacts with a second starting material in the presence of a palladium catalyst to form a compound of formula (I). X is Cl, Br, or I. Alternatively, X in the organozinc intermediate (formula (II-B)) is Cl and Y in the second starting material (formula II) is Br. Suitable solvents for this reaction include ether solvents such as tetrahydrofuran, methyltetrahydrofuran, anisole, and mixtures thereof. The organozinc intermediate often reacts with the second starting material without isolating the organozinc intermediate.

[0032] In one embodiment, a solution of an alkoxide or amine base in an ether solvent is mixed with the organozinc intermediate prior to reaction with the second starting material. Adding this base to the reaction mixture has the advantage of reducing by-product formation. Examples of suitable bases include potassium tert-butoxide (KOtBu), morpholine, piperazine, benzylpiperazine, NH3, NH4Cl, and hexamethyldisilazane. KOtBu is commonly used. In one embodiment, the equivalent of the base relative to the first starting material is between 0.5 and 3.0. In one embodiment, the equivalent of the base relative to the first starting material is between 1.5 and 3.0. Methyltetrahydrofuran is a commonly used ether solvent.

[0033] In yet another embodiment, the reaction of the organozinc intermediate with the second starting material is carried out in the presence of an aprotic polar solvent such as N-methyl-2-pyrrolidinone, dimethylformamide, or dimethyl sulfoxide. N-methyl-2-pyrrolidinone is commonly used. In one embodiment, between 0.05 and 1.5 times the amount or mL of the aprotic polar solvent per gram of the starting material is used.

[0034] In another embodiment, the reaction mixture containing the reaction product of the organozinc intermediate and the second starting material is extracted with a basic aqueous solution of N-acetyl-L-cysteine after the formation of the compound of formula (I). The concentration of the N-acetyl-L-cysteine solution is usually less than 1 g per 5 mL of water. "Extraction" of the reaction mixture refers to directly washing the reaction mixture with the N-acetyl-L-cysteine solution to form an aqueous phase and an organic phase. Next, the organic phase containing Compound 1 is separated from the aqueous phase. Alternatively, "extraction" refers to quenching the reaction mixture with an aqueous solution to form an aqueous phase and an organic phase. Next, the organic phase containing Compound 1 is separated from the aqueous phase and then extracted with the N-acetyl-L-cysteine solution. The N-acetyl-L-cysteine solution extraction has the advantage of reducing the residual palladium in the final reaction product (Compound 1).

[0035] In another embodiment, the organozinc intermediate is obtained by reacting the first starting material with a Grignard reagent R’MgX 2 to form an organometallic intermediate represented by formula (II-A):

[0036]

Chemical formula

[0037] This organometallic intermediate then reacts with ZnX2 to form the organozinc intermediate. R’ is C1-C6 alkyl, C1-C6 alkenyl, C1-C6 alkynyl, phenyl, benzyl, or monocyclic heteroaryl, and phenyl, benzyl, or heteroaryl is each optionally and independently substituted with one or more groups selected from halogen, C1-C3 alkyl, and C1-C3 alkoxy groups, and X 2 is Cl, Br, or I. In one embodiment, the Grignard reagent is isopropylmagnesium chloride (i-PrMgCl). Conveniently, the organometallic intermediate reacts with ZnX2 without isolating the organometallic intermediate.

[0038] The reaction of the first starting material with a Grignard reagent can be carried out in an ether solvent. One commonly used ether solvent is tetrahydrofuran. In one embodiment, the reaction of the first starting material with a Grignard reagent is carried out in a mixture containing anisole and an ether solvent. Using anisole in this reaction mixture has the advantage of reducing by-products. In one embodiment, the reaction of the first starting material with a Grignard reagent is carried out in a mixture containing an aromatic solvent such as benzene, toluene, xylene, and mixtures thereof.

[0039] Specific conditions for preparing Compound 1 by the method of the present disclosure are provided in Examples 1 and 5. Compound 1 can be readily converted to an ALK-2 inhibitor by first removing the amine protecting group and then carbamoylating the resulting free amine to the desired ALK-2 inhibitor. Appropriate conditions for these two conversions are disclosed in U.S. Patent No. 10,233,186. Specific conditions for the removal of the Boc protecting group are provided in Example 2 below, and those for carbamoylation are provided in Example 3.

[0040] The following examples are intended to be illustrative and are not intended to limit the scope of the present disclosure in any way.

Examples

[0041] Example 1 Preparation of tert-butyl 4-(6-(5-(4-ethoxy-1-isopropylpiperidin-4-yl)pyridin-2-yl)pyrrolo[1,2-b]pyridazin-4-yl)piperazine-1-carboxylate

[0042]

Chemical formula

[0043] 1.1 Preparation of 2-bromo-5-(4-ethoxy-1-isopropylpiperidin-4-yl)pyridine (Compound 2) Compound 2 was prepared from the starting materials 1-isopropylpiperidin-4-one and 2-bromo-5-iodopyridine via the synthetic route as shown in the above scheme. It was also commercially available from Acceledev. 1.2 Preparation of tert-butyl 4-(6-bromopyrrolo[1,2-b]pyridazin-4-yl)piperazine-1-carboxylate (Compound 3) A mixture of 6-bromopyrrolo[1,2-b]pyridazin-4-ol (5.5 kg, 25.8 mol) and triethylamine (3.1 kg, 1.2 equiv) in acetonitrile (27 L, 4.9-fold amount) is stirred at -10 °C. To this mixture, trifluoromethanesulfonic anhydride (7.1 kg, 0.98 equiv) is added together with a rinse solution of additional acetonitrile (2 L, 0.36-fold amount). The reaction solution is stirred until the reaction is complete, and at the completion of the reaction, trimethylsilyl chloride (0.3 kg, 0.1 equiv) is added. Next, to this mixture, triethylamine (3.7 kg, 1.3 equiv) and N-Boc-piperazine (5.5 kg, 1.2 equiv) are added together with a rinse solution of additional acetonitrile (2 L, 0.36-fold amount). The reaction solution is heated to 65 - 75 °C until the reaction is complete. The reaction mixture is concentrated at 45 - 55 °C, diluted with water, and then cooled to 15 - 25 °C to crystallize the product. The product is filtered and washed with isopropanol (2 × 11 L, 2 × 2-fold amount) to obtain 7.0 kg (yield 72.4%). 1.3 Preparation of tert-butyl 4-(6-(5-(4-ethoxy-1-isopropylpiperidin-4-yl)pyridin-2-yl)pyrrolo[1,2-b]pyridazin-4-yl)piperazine-1-carboxylate (Compound 1) 2-Bromo-5-(4-ethoxy-1-isopropylpiperidin-4-yl)pyridine (Compound 2, 5.9 kg, prepared as disclosed in US10233186) was dissolved in anisole (24 L). The resulting solution was heated to 90 - 100 °C and partially distilled to reduce the water content. The remaining reaction solution was cooled to 45 - 55 °C, and isopropylmagnesium chloride (20% in tetrahydrofuran, 9.6 kg) was added. Once the completion of the conversion was confirmed, a solution of zinc chloride (25% in methyltetrahydrofuran, 10.7 kg) was added while heating was continued. Next, potassium tert-butoxide (25% in methyltetrahydrofuran, 17.6 kg), Pd2(dba)3 (18 g), and tert-Bu3P·HBF4 (23 g) were added to the resulting organozinc (Intermediate 1) solution. Further, N-methyl-2-pyrrolidone (0.6 L) was added, followed by tert-butyl 4-(6-bromopyrrolo[1,2-b]pyridazin-4-yl)piperazine-1-carboxylate (Compound 3, prepared as disclosed in US10233186) as a solution in tetrahydrofuran (6.0 kg of Compound 3 in 9 L of tetrahydrofuran). Heating was continued until the conversion to Compound 1 was complete.

[0044] Example 2 Preparation of 6-(5-(4-ethoxy-1-isopropylpiperidin-4-yl)pyridin-2-yl)-4-(piperazin-1-yl)pyrrolo[1,2-b]pyridazine (Compound 4)

[0045]

Chem.

[0046] Compound 1 prepared as described in Example 1 was used without purification or isolation from its reaction mixture. The reaction mixture was diluted with tetrahydrofuran (8.8 kg), and 33% hydrochloric acid (21 kg) in water (36 kg) was added. The acidic aqueous mixture containing the product was washed with methyltetrahydrofuran (31 kg) and then with isopropyl acetate (2 x 11 kg). Next, this aqueous solution was diluted with isopropyl acetate (53 kg) and basified with ammonia (25%, 33 kg). The organic phase was separated and washed with acetylcysteine (3 x 26 kg) and water (2 x 18 kg). The organic solution was spread, heptane (41.7 kg) was added to crystallize the product, and then the product was isolated by filtration to obtain approximately 3.6 kg of Compound 4 after drying.

[0047] Example 3 Preparation of an ALK-2 inhibitor from Compound 4

[0048] [Chemical formula]

[0049] 1,1-Carbonyldiimidazole (1.51 kg), isopropyl acetate (6.4 kg), and alcohol R-OH (e.g., 1.1 equivalents relative to 1,1-carbonyldiimidazole) were added to the reaction vessel. This reaction solution was stirred at 20 - 30 °C for 30 minutes until the reaction was complete. This reaction solution was heated to 30 - 40 °C, filtered, and the filter was washed with isopropyl acetate (7.7 kg). Ammonia (25%, 3.2 kg) was added to this diluted mixture, and compound 4 (3.5 kg) was added. This reaction solution was heated to 50 - 60 °C and distilled under reduced pressure. This mixture was further diluted with isopropyl acetate (6.1 kg) to confirm the completion of the reaction. At this point, the reaction mixture was diluted and stirred with water (3.5 kg) and isopropyl acetate (36.9 kg). This mixture was allowed to stand to separate the organic phase. This organic solution was further washed with water (5 × 7 kg). After the final separation, the organic phase was diluted with isopropyl acetate (7.7 kg) and distilled under reduced pressure at 50 - 60 °C to reduce the water content. Next, the organic solvent may be removed to isolate the ALK-2 inhibitor.

[0050] Example 4 N-acetylcysteine is significantly more effective than potassium carbonate and 2,4,6-trimercapto-1,3,5-triazine (TMT) in omitting palladium from the reactants of Example 1. To 1.15 equivalents of 2-bromo-5-(4-ethoxy-1-isopropylpiperidin-4-yl)pyridine (Compound 2), 6-fold amount of toluene was added and the mixture was heated to a jacket temperature (JT) of 145 °C (the equivalents and fold amounts are all relative to Compound 3, 1 equivalent being 30.4 g. The fold amount is 1 mL / 1 gram of the reference substance, which is Compound 3 in this case). At an internal temperature (IT) of 112 - 121 °C, 4-fold amount of toluene was distilled off. At IT of 45 °C, a total of 1.37 equivalents of isopropylmagnesium chloride (2 M in tetrahydrofuran) was added until the reaction was complete. At that point, 1.20 equivalents of ZnCl2 (2 M in tetrahydrofuran) was added at 45 °C and the mixture was stirred at JT of 80 °C for 14 hours. At IT of 45 °C, 0.1-fold amount of N-methyl-2-pyrrolidinone, 1 mol% Pd2(dba)3, and 4 mol% tBu3P·HBF4 were added. A solution of 1.0 equivalent of Compound 3 (30.4 g) in 2.5-fold amount of methyltetrahydrofuran (MeTHF) was added over 30 minutes at IT of 45 °C. After 1 hour, 0.15 equivalent of Compound 3 in 0.4-fold amount of tetrahydrofuran was added additionally. This mixture was stirred at IT of 45 °C for 2 hours, transferred to another reaction vessel, rinsed with 1.6-fold amount of MeTHF, and then added to a solution of 4.1 equivalents of K2CO3 in 25-fold amount of water over 10 minutes at 24 °C. Next, 0.43-fold amount of 30%-w / w NaOH was added, the aqueous phase was separated, and the organic phase was divided into three portions. Each divided organic phase was washed with 2 × 1.6-fold amount of either (i) potassium carbonate, (ii) 2,4,6-trimercapto-1,3,5-triazine (TMT), or (iii) N-acetylcysteine. Next, 3.3-fold amount of water and 0.95-fold amount of 2 M HCl were added and the organic phase was separated. Subsequently, 0.30-fold amount of 30%-w / w NaOH and Norit CGP super (about 0.5 g) were added. The mixture was stirred at IT of 45 °C for 2 hours, filtered, and washed with 0.33-fold amount of MeTHF. This organic phase was washed with 2 × 1-fold amount of water. Boc2O (0.08-fold amount, 2 M) was added and the mixture was stirred at 24 °C for 15 minutes. While adding n-heptane (3 × 1.6-fold amount), MeTHF was distilled off at JT of 80 - 120 °C. The brown slurry was cooled to 0 °C, stirred for 15 minutes, filtered, and washed with 2 × 0.7-fold amount of n-heptane (re-slurry washing).

[0051] The quenched reaction mixture was divided into three parts, and the palladium content measured by inductively coupled plasma mass spectrometry (ICP-MS) was as follows: standard (K2CO3): 1,400 ppm Pd, 2× extraction with TMT: 1,000 ppm Pd, 2× extraction with N-acetylcysteine: 120 ppm Pd.

[0052] Example 5 The Negishi process for preparing Compound 1 results in a product with fewer impurities compared to the corresponding Suzuki process.

[0053]

Chemical formula

[0054] To a container containing Compound 4 (1.0 g) in 2.4 mL (2.4 eq) of water and 1,4-dioxane (12.0 mL, 12 eq), 0.68 g (1.0 eq) of 2-bromo-5-(4-ethoxy-1-isopropylpiperidin-4-yl)pyridine (Compound 2), K2CO3 (0.57 g, 2.0 eq), and Pd(PPh3)4 (0.12 g, 0.05 eq) were added. The reaction solution was heated to 80 °C until the completion of the reaction was confirmed by HPLC (Figure 1).

[0055] To 3.27 g of 2-bromo-5-(4-ethoxy-1-isopropylpiperidin-4-yl)pyridine (Compound 2), 6 eq of toluene and 1.2 eq of iPrMgCl (2 M in THF) were added. The mixture was heated to 65 °C. After the reaction was completed, 1.3 eq of ZnCl2 (1.9 M in MeTHF) was added, and the reaction solution was maintained at 20 - 25 °C. At 45 °C, Compound 3 was added together with THF (3 eq) and PdP(tBu3)2 (0.1 eq), and the mixture was stirred until the completion of the reaction was confirmed by HPLC (Figure 2).

[0056] It is clear from FIGS. 1 and 2 that the preparation of Compound 1 by the method of the present disclosure is significantly more concise than the corresponding Suzuki coupling and produces far fewer impurities.

Claims

**Claim 1** A method for preparing a compound represented by formula (I): 【Chemical 1】 comprising reacting, in a reaction mixture, a first starting material represented by formula (II): [Chemical Formula 2] and a second starting material represented by formula (III): [Chemical Formula 3] under Negishi conditions to form a compound of formula (I), wherein R is an amine protecting group, Y is Cl, Br, or I, and Z is Cl, Br, I, or triflate, wherein i) the first starting material of formula (II) is reacted with a Grignard reagent R’MgX₂ to form an organometallic intermediate represented by formula (II-A): 【Chemical Formula 4】 such that the first starting material of formula (II) is converted to an organozinc intermediate of formula (II-B) [Chemical Formula 5] and the organometallic intermediate of formula (II-A) reacts with ZnX₂ to form an organozinc intermediate of formula (II-B), wherein R’ is C₁-C₆ alkyl, C₁-C₆ alkenyl, C₁-C₆ alkynyl, phenyl, benzyl, or monocyclic heteroaryl, and phenyl, benzyl, or heteroaryl is each optionally and independently substituted with one or more groups selected from halogen, C₁-C₃ alkyl, and C₁-C₃ alkoxy groups, and X₂ is Cl, Br, or I, ii) the organozinc intermediate of formula (II-B) reacts with the second starting material of formula (III) in the presence of a palladium catalyst to form a compound of formula (I) wherein X is Cl, Br, or I, a method. **Claim 2** The method according to claim 1, wherein X is Cl and Y is Br. **Claim 3** The method according to claim 1 or 2, wherein the organozinc intermediate of formula (II-B) reacts with the second starting material of formula (III) without isolating the organozinc intermediate of formula (II-B). **Claim 4** **Claim 5** The palladium catalyst is selected from Pd(X １ ), ２ and Pd(X １ ), ２ Cl ２ wherein each X １ is independently a phosphine ligand), the method according to any one of claims 1 to 3. ​ The method according to claim 4, wherein the phosphine ligand is selected from dtbpf, dcyphf, dppf, t-BuXPhos, AdBrettPhos, SPhos, RuPhos, XPhos, BrettPhos, JackiePhos, t-BuBrettPhos, TrixiePhos, JohnPhos, t-BuDavePhos, t-BuMePhos, CyJohnPhos, DavePhos, MePhos, PhDavePhos, VPhos, PhCPhos, CPhos, EtCPhos, RockPhos, AlPhos, and (t-Bu)PhCPhos.

6. The palladium catalyst is Pd(dppe) ２ (bis[1,2-bis(diphenylphosphino)ethane]palladium(0)), Pd(dba) ２ (bis(dibenzylideneacetone)palladium(0)), CX-11 (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene(1,4-naphthoquinone)palladium(0) dimer), CX-12 (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene(1,4-naphthoquinone)palladium(0) dimer), Pd(t-Bu ３ P) ２ (bis(tri-tert-butylphosphine)palladium(0)), Pd(PCy ３ ) ２ (bis(tricyclohexylphosphine)palladium(0)), Pd(PPh ３ ) ４ (tetrakis(triphenylphosphine)palladium(0)), Pd ２ (dba) ３ (tris(dibenzylideneacetone)dipalladium(0)), Pd(OAc) ２ (palladium(II) acetate), PdCl ２ (PPh ３ ) ２ (dichlorobis(triphenylphosphine)palladium(II)), PdCl ２ (Amphos) ２ (bis(di-tert-butyl(4-dimethylaminophenyl)phosphine)dichloropalladium(II)), Pd(MeCN) ２ Cl ２ (bis(acetonitrile)dichloropalladium(II)), PdCl ２ (P(o-Tol) ３ ) ２ (dichlorobis(tri-o-tolylphosphine)palladium(II)), Pd(dppf)Cl ２ (1,1'-bis(diphenylphosphino)ferrocene]dichloropalladium(II)), Pd(MeCN) ４ (BF ４ ) ２ The method according to claim 4, selected from (tetrakis(acetonitrile)palladium(II) tetrafluoroborate), Pd-PEPPSI-IPent (dichloro[1,3-bis(2,6-di-3-pentylphenyl)imidazol-2-ylidene](3-chloropyridyl)palladium(II)), Pd-PEPPSI-IPr ([1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene](3-chloropyridyl)palladium(II) dichloride), and Pd-PEPPSI-SIPr ((1,3-bis(2,6-diisopropylphenyl)imidazolidene)(3-chloropyridyl)palladium(II) dichloride).

7. The palladium catalyst is Pd(MeCN) ２ Cl ２ , Pd[P(o-Tol) ３ ２ Cl ２ , PdCl ２ (Amphos) ２ , and Pd(dba) ２ ２ , and the method according to claim 4, selected from ２ .

8. The palladium catalyst is Pd ２ (dba) ３ / P(R １ ) ３ , Pd(PPh ３ ) ４ , Pd(PPh ３ ) ２ Cl ２ , Pd(MeCN) ２ Cl ２ , Pd[P(o-Tol) ３ ２ Cl ２ , PdCl ２ (Amphos) ２ , Pd(PtBu ３ ) ２ , Pd(dppf)Cl ２ , Pd(dba) ２ , Pd ２ (dba) ３ , and Pd(XPhos) (wherein each R １ is C １ to C ６ alkyl, C ３ to C ６ cycloalkyl, benzyl, or phenyl, and benzyl or phenyl is each optionally and independently substituted with one or more groups selected from halogen, C １ to C ３ alkyl, and C １ to C ３ alkoxy), the method according to claim 4.​

9. The palladium catalyst is Pd ２ (dba) ３ The method according to claim 4, wherein the palladium catalyst is Pd(dba).

10. The palladium catalyst is PdP(tBu) ３ The method according to claim 4, wherein the palladium catalyst is PdP(tBu).

11. The method according to any one of claims 1 to 10, wherein the Grignard reagent is i-PrMgCl.

12. The organometallic intermediate of formula (II-A) reacts with ZnX without isolating the organometallic intermediate of formula (II-A). ２ The method according to any one of claims 1 to 10, wherein the reaction occurs.

13. The method according to any one of claims 1 to 12, wherein the first starting material of formula (II) reacts with the Grignard reagent in a mixture containing anisole.

14. The method according to claim 13, wherein the first starting material of formula (II) reacts with the Grignard reagent in a mixture of anisole and an ether solvent.

15. The method according to claim 14, wherein the ether solvent is tetrahydrofuran.

16. The method according to any one of claims 1 to 15, wherein the KOtBu in the ether solvent is mixed with the organozinc intermediate of formula (II-B) before the reaction with the second starting material of formula (III).

17. The method according to claim 16, wherein the organozinc intermediate of formula (II-B) is mixed with KOtBu in tetrahydrofuran.

18. The method according to claim 16 or 17, wherein the reaction between the organozinc intermediate of formula (II-B) and the second starting material of formula (III) is carried out in the presence of N-methyl-2-pyrrolidinone.

19. The method according to any one of claims 1 to 18, further comprising the step of extracting the reaction mixture with a basic aqueous solution of N-acetyl-L-cysteine after the formation of the compound of formula (I).

20. The method according to any one of claims 1 to 19, wherein R is selected from Fmoc (9-fluorenylmethyl carbamate), Cbz (benzyl carbamate), Boc (tert-butoxycarbonyl), acetamide, benzyl, and tosyl (p-toluenesulfonamide).

21. The method according to claim 20, wherein R is tert-butoxycarbonyl. **Claim 22** The method according to any one of claims 1 to 21, wherein Z is Br. **Claim 23** Compound represented by formula (II-A): 【Chemical Formula 6】 (wherein X2 is Cl, Br, or I). **Claim 24** The method according to any one of claims 1 to 12, wherein the first starting material of formula (II) reacts with a Grignard reagent in a mixture containing an aromatic solvent selected from the group consisting of benzene, toluene, and xylene.

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