WO2018017983A1

WO2018017983A1 - Compounds useful for treating disorders related to ret

Info

Publication number: WO2018017983A1
Application number: PCT/US2017/043340
Authority: WO
Inventors: Jason D. Brubaker; Timothy Guzi; Kevin J. Wilson; Lucian V. Dipietro; Yulian Zhang; Douglas Wilson; Paul E. Fleming
Original assignee: Blueprint Medicines Corporation
Priority date: 2016-07-22
Filing date: 2017-07-21
Publication date: 2018-01-25
Also published as: US20180022732A1; US10227329B2

Abstract

Described herein are compounds of formula (I) that inhibit wild- type RET and its resistant mutants, pharmaceutical compositions including such compounds, and methods of using such compounds and compositions.

Description

COMPOUNDS USEFUL FOR TREATING DISORDERS RELATED TO RET

[0001] This disclosure relates to inhibitors of RET that are active against wild-type RET and its resistant mutants.

CLAIM OF PRIORITY

[0002] This application claims priority from U.S. Provisional Application No.

62/365,724, filed July 22, 2016, which is incorporated herein in its entirety. SEQUENCE LISTING

[0003] The instant application contains a Sequence Listing which has been filed electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on July 21, 2017, is named 14320_0019-00304_SL.txt and is 32,357 bytes in size.

BACKGROUND

[0004] RET is a receptor tyrosine kinase that activates multiple downstream pathways involved in cell proliferation and survival. RET fusions are implicated in several cancers including papillary thyroid carcinoma and non-small cell lung cancer. A genomics analysis on the landscape of kinase fusions identified RET fusions in breast and colon cancer patient samples, providing therapeutic rationale for the use of RET inhibitors in multiple patient subpopulations.

[0005] The identification of RET fusions as drivers in some cancers prompted the use of approved multi-kinase inhibitors with RET inhibitory activity to treat patients whose tumors express a RET fusion protein. However, these drugs cannot always be dosed at the levels required to sufficiently inhibit RET due to toxicities that result from inhibition of targets other than RET. Further, one of the greatest challenges in treating cancer is the ability of tumor cells to become resistant to therapy. Kinase reactivation via mutation is a common mechanism of resistance. When resistance occurs, the patient’s treatment options are often very limited, and the cancer progresses, unchecked, in most instances. There is thus a need for compounds that inhibit RET, as well as its resistant mutants.

SUMMARY

[0006] In one aspect, the disclosure features a compound of Formula (I) or a pharmaceutically acceptable salt thereof, wherein:

or a pharmaceutically acceptable salt thereof, wherein: ring A is an aryl or heteroaryl ring;

each of X¹ and X² is independently selected from N and C(R⁶); Z is

, -CD(R⁵)-, or -CH(R⁵)-, wherein“1” represents a point of attachment to N(R⁸); and“2” represents a point of attachment to ring A; each R¹ and each R⁷ is independently selected from C₁-C₆ alkyl, C₂-C₆ alkenyl, C₂-C₆ alkynyl, C₁-C₆ alkoxy, halo, C₁-C₆ heteroalkyl, cycloalkyl, aryl, heteroaryl, aryloxy, aralkyl, heterocyclyl,

heterocyclylalkyl, nitro, cyano, -C(O)R^c, -OC(O)R^c, -C(O)OR^d, -(C₁-C₆ alkylene)- C(O)R^c, -SR^d, -S(O)₂R^c, -S(O)₂-N(R^d)(R^d)_, -(C₁-C₆ alkylene)-S(O)₂R^c, -(C₁-C₆ alkylene)-S(O)₂-N(R^d)(R^d)_, -N(R^d)(R^d), -C(O)-N(R^d)(R^d), -N(R^d)-C(O)R^c, -N(R^d)- C(O)OR^c, -(C₁-C₆ alkylene)-N(R^d)-C(O)R^c, -N(R^d)S(O)₂R^c, and -P(O)(R^c)(R^c); wherein each of alkyl, alkenyl, alkynyl, alkoxy, heteroalkyl, cycloalkyl, aryl, heteroaryl, aryloxy, aralkyl, heterocyclyl, and heterocyclylalkyl is independently substituted with 0-5 occurrences of R^a; or two R¹ or two R⁷ are taken together with the carbon atoms to which they are attached form a cycloalkyl or heterocyclyl ring independently substituted with 0-5 occurrences of R^b;

each of R², R³ if present, and R⁴ is independently selected from hydrogen, C₁-C₆ alkyl, C₁-C₆ alkoxy, halo, hydroxyl, cyano, C₁-C₆ heteroalkyl, and -N(R^d)(R^d); wherein each of alkyl, alkoxy, and heteroalkyl is optionally and independently substituted with 0-5 occurrences of R^a;

each of R⁵ and R⁸ is independently selected from hydrogen, deuterium, C₁-C₆ alkyl, and C₁-C₆ heteroalkyl; wherein each alkyl and heteroalkyl is optionally and independently substituted with 0-5 occurrences of R^a; each R⁶ is independently selected from hydrogen, C₁-C₆ alkyl, C₁-C₆ alkoxy, halo, cyano, C₁-C₆ heteroalkyl, and -N(R^d)(R^d); wherein each alkyl, alkoxy, and heteroalkyl is optionally and independently substituted with 0-5 occurrences of R^a;

each R^a and each R^b is independently selected from C₁-C₆ alkyl, halo, hydroxyl, C₁-C₆ heteroalkyl, C₁-C₆ alkoxy, cycloalkyl, heterocyclyl, or cyano, wherein each of alkyl, heteroalkyl, alkoxy, cycloalkyl and heterocyclyl is independently substituted with 0-5 occurrences of R’;

each R’ is independently selected from C₁-C₆ alkyl, C₁-C₆ heteroalkyl, halo, hydroxyl, cycloalkyl or cyano; or two R^’ together with the atom(s) to which they are attached form a cycloalkyl or heterocyclyl ring; each R^c is independently selected from hydrogen, hydroxyl, halo, thiol, C₁-C₆ alkyl, C₁-C₆ thioalkyl, C₁-C₆ alkoxy, C₁-C₆ heteroalkyl, cycloalkyl, cycloalkylalkyl, heteroarylalkyl, heterocyclyl, and heterocyclylalkyl, wherein each of alkyl, thioalkyl, alkoxy, heteroalkyl, cycloalkyl, cycloalkylalkyl, heteroarylalkyl, heterocyclyl, and heterocyclylalkyl is independently substituted with 0- 5 occurrences of R^a, or two R^c together with the atom(s) to which they are attached form a cycloalkyl or heterocyclyl ring independently substituted with 0-5 occurrences of R^b; each R^d is independently selected from hydrogen, C₁-C₆ alkyl, C₁-C₆ heteroalkyl, cycloalkyl, cycloalkylalkyl, heteroarylalkyl, heterocyclyl, and heterocyclylalkyl, wherein each of alkyl, heteroalkyl, cycloalkyl, cycloalkylalkyl, heteroarylalkyl, heterocyclyl, and heterocyclylalkyl is independently substituted with 0-5 occurrences of R^a, or two R^d together with the atom(s) to which they are attached form a cycloalkyl or heterocyclyl ring independently substituted with 0-5 occurrences of R^b; m is 0, 1, or 2; and n is 0, 1, 2, or 3.

[0007] In some embodiments, the compound has the structural formula (Ia):

or a pharmaceutically acceptable salt thereof, wherein R¹ is halo, C₁-C₄ alkyl, C₃-C₆ cycloalkyl, or C₁-C₆ alkoxy; and R¹ is substituted with 0-3 occurrences of R^a.

[0008] In some embodiments, R¹ is fluoro, -CH_3, -CH₂CH_3, -CHF_{2 ,} -OCH₃, or cyclopropyl.

[0009] In some embodiments, R² is selected from hydrogen, -C₁-C₄ alkyl, C₁-C₆ alkoxy, hydroxyl, and halo; wherein -C₁-C₄ alkyl or C₁-C₆ alkoxy is optionally substituted (e.g., with 0-3 occurrences of R^a, e.g., cyano, halo). In some embodiments, R² is selected from hydrogen, -C₁-C₄ alkyl, C₁-C₆ alkoxy, hydroxyl, and fluoro. In some embodiments, R² is hydrogen, fluoro, -CH_3, -CH₂CH_3, -CH₂OH, -CH₂CN, - OCH₂CF₃, -OCH₂CH₂, or OMe.

[0010] In some embodiments, R³ if present is hydrogen.

[0011] In some embodiments, R⁴ is selected from hydrogen, hydroxyl, halo, cyano, C₁-C₄ alkyl and O-C₁-C₄ alkyl, wherein each alkyl portion of R⁴ is substituted with 0-3 occurrences of R^a. In some embodiments, R⁴ is selected from hydrogen, fluoro, cyano, hydroxyl, -CH₃, -CH₂CN, -CH₂CH₃, -CH₂CH₂OCH₃, -OCH₃, -OCH₂CF₃,

and -OCH₂CH₃. In some embodiments, R⁴ is selected from hydrogen, hydroxyl, and -OCH₃.

[0012] In some embodiments, Z is selected from

, -CH₂-, and -CH(C₁- C₄ alkyl)-, wherein the C₁-C₄ alk l is substituted with 0-3 occurrences of R^a. In some

embodiments, Z is selected from , -CH₂-, and -CH(CH₃)-.

[0013] In some embodiments, each R⁶ is independently selected from hydrogen, halo, cyano, and C₁-C₄ alkyl substituted with 0-3 occurrences of R^a. In some embodiments, each R⁶ is independently selected from hydrogen, fluoro, cyano, -CH₂F and -CH₃.

[0014] In some embodiments, R⁸ is selected from hydrogen and -CH₃.

[0015] In some embodiments, ring A is selected from phenyl and a 6-membered monocyclic heteroaryl comprising at least one nitrogen ring atom. In some embodiments, ring A is selected from:

embodiments, ring A is selected from

; n is 1; R⁷ is selected from 1H-pyrazol-1-yl, azetidin-1-yl, and pyrrolidin-1-yl; and R⁷ is substituted with 0-3 occurrences of R^b.

[0016] In some embodiments, R⁷ is selected from 3-fluoroazetidin-1-yl, 3,3- difluoropyrrolidin-1-yl, 3-fluoropyrrolidin-1-yl, 3-difluoromethyl-1H-pyrazol-1-yl, 4- fluoro-1H-pyrazol-1-yl, 4-chloro-1H-pyrazol-1-yl, 3-difluoromethyl-1H-pyrazol-1-yl, 4-difluoromethyl-1H-pyrazol-1-yl, 4-cyclopropyl-1H-pyrazol-1-yl, 4-fluoro-1H- pyrazol-1-yl, 3,5-bis(difluoromethyl)-1H-pyrazolyl, 3-methyl-1H-pyrazol-1-yl, 4- methyl-1H-pyrazol-1-yl, 3,5-dimethyl-1H-pyrazol-1-yl, and pyrazol-1-yl. In some embodiments, R⁷ is 4-cyclopropyl-1H-pyrazol-1-yl, 4-fluoro-1H-pyrazol-1-yl, or pyrazol-1-yl.

[0017] In some embodiments, ring A is phenyl; n is 0 or 1; and R⁷ if present is -O-C₁-C₄ alkyl.

[0018] In some embodiments, n is 0, or n is 1 and R⁷ is selected from -OCH₃ and -OCH₂CH₃.

[0019] In another aspect, the disclosure features a compound of Formula (II) or a pharmaceutically acceptable salt thereof, wherein:

or a pharmaceutically acceptable salt thereof, wherein: X¹ is selected from N and C(R¹³); each Y¹ and Y² is independently selected from N and CH, wherein no more than one of Y¹ and Y² is N; Q is selected from N, CH and CH₂; R¹¹ is C₁-C₄ alkyl; R¹² is selected from hydrogen and C₁- C₄ alkyl; R¹³ if present is selected from hydrogen, cyano and halo; R¹⁴ is selected from hydrogen, halo, cyano, hydroxyl, C₁-C₄ alkyl and C₁-C₄ alkoxy; R¹⁵ is selected from hydrogen and C₁-C₄ alkyl; R¹⁶ is selected from hydrogen, and C₁-C₄ alkyl optionally substituted with 1 or more independently selected halo; R¹⁷ is selected from hydrogen and C₁-C₄ alkyl; each of R^18a and R^19a if present and R^18b and R^19b is independently selected from hydrogen, halo, C₁-C₄ alkyl optionally substituted with one or more halo, and C₃-C₆ cycloalkyl; p is 0 or 1; and each represents a single or a double bond.

[0020] In some embodiments, R11 is -CH3; R12 is selected from hydrogen and -CH3; R13 if present is selected from hydrogen, cyano and fluoro; R14 is selected from hydrogen, fluoro, cyano, hydroxyl, -CH3, -CH2CH3, -OCH3, and -OCH2CH3; R15 is selected from hydrogen and -CH3; R16 is selected from hydrogen, -CH3 and -CHF2; R17 is selected from hydrogen and -CH3; each of R18a and R19a if present is independently selected from hydrogen and fluoro, wherein at least one of R18a or R19a is hydrogen; each of R18b and R19b is independently selected from hydrogen,

fluoro, chloro, -CH3, -CHF2, and cyclopropyl, wherein at least one of R18b or R19b is hydrogen; and each is the same.

[0021] In some embodiments, p is 1.

[0022] In some embodiments, R¹⁴ is selected from hydrogen, fluoro, cyano, hydroxyl, and -OCH_3.

[0023] In another aspect, the disclosure features a compound of Formula (III) or a pharmaceutically acceptable salt thereof, wherein:

or a pharmaceutically acceptable salt thereof, wherein: X¹ is selected from N and CH;

Z’ is selected from

or -CH(R²⁸)-, wherein“1” represents a point of attachment to N(R²⁶); and“2” represents a point of attachment to ring B; ring B is selected from phenyl, pyridinyl, 1H-pyrazolyl, and pyrazinyl; R²¹ is selected from C₃-C₆ cycloalkyl and C₁-C₄ alkyl; R²² is selected from hydrogen and C₁-C₄ alkyl; R²³ is selected from hydrogen and cyano; R²⁴ is selected from hydrogen, hydroxy and halo; R²⁵ is selected from hydrogen, halo, hydroxy, C₁-C₄ alkoxy, -C₁-C₄ alkyl, -C₁-C₄ alkyl-O-C₁-C₄ alkyl, wherein each C₁-C₄ alkyl is optionally substituted with 1 or more substituents independently selected from halo and cyano; R²⁶ is selected from hydrogen and C₁-C₄ alkyl; R²⁷, if present, is independently selected from 1H-pyrazolyl, pyridinyl, and C₁-C₄ alkoxy, wherein the 1H-pyrazol-1-yl is optionally substituted with up to 2 substituents independently selected from C₁-C₄ alkyl and halo; R²⁸ is selected from hydrogen and C₁-C₄ alkyl; and o is 0 or 1.

[0024] In some embodiments, Z’ is selected from

, -CH₂,

or -CH(CH₃)-; the portion of the molecule represented by

is selected from

; R²¹ is selected from -CH₃ and cyclopropyl;

R²² is selected from hydrogen and -CH₃; R²³ is selected from hydrogen and cyano; R²⁴ is selected from hydrogen, hydroxy and fluoro; R²⁵ is selected from hydrogen, fluoro, hydroxy, -OCH₃, -OCH₂CF₃, -CH₂CH₂OCH₃, -CH₃, -CH₂CH₃, and -CH₂CN; R²⁶ is selected from hydrogen and -CH₃; and R³⁷ is selected from

hydrogen, -OCH₃, -OCH₂CH₃, 1H-pyrazol-1-yl, 4-fluoro-1H-pyrazol-1-yl, 3,5- dimethyl-1H-pyrazol-1-yl, and pyridin-2-yl.

[0025] In some embodiments, Z’ is -CH₂ or -CH(CH₃)-;

[0026] In another aspect, the disclosure features a pharmaceutical composition comprising a compound as described herein; and a pharmaceutically acceptable carrier.

[0027] In another aspect, the disclosure features a method for inhibiting RET activity in a cell or in a patient, comprising the step of contacting the cell or administering to the patient a compound as described herein or a pharmaceutical composition as described herein. In some embodiments, the cell or patient has, or has been identified as having, a RET alteration, e.g., a RET mutation, e.g., a fusion or point mutation. In some embodiments, the patient comprises a RET-altered cell, cancer, gene, or gene product.

[0028] In another aspect, the disclosure features a method for treating a subject suffering from a condition mediated by aberrant RET activity, comprising administering to the subject a therapeutically effective amount of a compound as described herein or a pharmaceutical composition as described herein. In some embodiments, the subject has or has been identified as having (e.g., wherein a cancer cell in the subject has or has been identified as having) a RET alteration, e.g., a RET mutation, e.g., a fusion or point mutation. In some embodiments, a cell, cancer, gene, or gene product from the subject

is or has been identified as being RET-altered. In some embodiments, the subject has or has been identified as having (e.g., a cancer cell in the subject has or has been identified as having) a RET alteration, e.g., a RET mutation, e.g., a fusion or point mutation.

[0029] In some embodiments, the condition mediated by aberrant RET activity is a condition mediated by any RET activity that is not normal e.g., any activity due to a RET-altered gene or gene product, which affects the amount or activity of the gene or gene product as compared to the normal or wild-type gene. In some embodiments, the condition mediated by aberrant RET activity is a familial or sporadic cancer, e.g., a solid tumor such as thyroid, lung, breast, or pancreatic. In some embodiments, the condition mediated by aberrant RET activity is irritable bowel syndrome (IBS). In some embodiments, the aberrant RET activity promotes the condition, such that inhibition of RET ameliorates at least one symptom of the condition. In some embodiments, the aberrant RET activity comprises increased RET activity or expression level, gain of function mutation, and/or constitutive activation of RET. In some embodiments, the aberrant RET activity corresponds to aberrant amounts of RET, e.g., aberrant nucleic acid or protein amounts.

[0030] In another aspect, the disclosure features a method for treating a subject who has developed resistance to a treatment for a condition mediated by aberrant RET activity, comprising administering to the subject a therapeutically effective amount of a compound as described herein or a pharmaceutical composition as described herein. In some embodiments, the subject has developed resistance to a wild-type RET inhibitor. In some embodiments, the cancer treatment to which the subject is resistant is a wild- type RET inhibitor that is active against the wild-type RET, but less active, e.g., much less active, against one or more mutated forms of RET. In some embodiments, the wild-type RET inhibitor is selected from ponatinib, cabozanitib, and vandetanib.

[0031] In another aspect, the present disclosure provides a use of a compound or pharmaceutical composition described herein, e.g., a compound of structural Formula (I), (Ia), (II), or (III) described herein (e.g., a compound in Table 1) or a

pharmaceutically acceptable salt or composition thereof, in the manufacture of a medicament for inhibiting RET activity in a cell or in a subject. In some embodiments, the cell or subject has, or has been identified as having, a RET alteration, e.g., a RET

mutation, e.g., a fusion or point mutation. In some embodiments, a cell, cancer, gene, or gene product from the subject is or has been identified as being RET-altered.

[0032] In another aspect, the present disclosure provides a use of a compound or pharmaceutical composition described herein, e.g., a compound of structural Formula (I), (Ia), (II), or (III) described herein (e.g., a compound in Table 1) or a

pharmaceutically acceptable salt or composition thereof, in the manufacture of a medicament for treating a subject suffering from a condition mediated by aberrant RET activity. In some embodiments, the subject has, or has been identified as having (e.g., wherein a cancer cell in the subject has, or has been identified as having) a RET alteration, e.g., a RET mutation, e.g., a fusion or point mutation. In some embodiments, a cell, cancer, gene, or gene product from the subject is or has been identified as being RET-altered.

[0033] In another aspect, the present disclosure provides a use of a compound or pharmaceutical composition described herein, e.g., a compound of structural Formula (I), (Ia), (II), or (III) described herein (e.g., a compound in Table 1) or a

pharmaceutically acceptable salt or composition thereof, in the manufacture of a medicament for treating a subject who has developed resistance to a cancer treatment.

[0034] In another aspect, the present disclosure provides a method of preventing development of one or more RET-altered cell, cancer, gene, or gene product, in a cell or in a patient, comprising the step of contacting the cell or administering to the patient a compound according to structural Formula (I), (Ia), (II), or (III).

[0035] In another aspect, the present disclosure provides a method of treating a patient suffering from cancer comprising administering to the patient a compound described herein (e.g., a compound having a lower IC₅₀ for RET than for KDR, a compound having a similar IC₅₀ for wild-type RET compared to mutant RET, and/or a compound of structural Formula (I), (Ia), (II), or (III) described herein (e.g., a compound in Table 1)), or a pharmaceutical composition comprising the compound, wherein the subject has a RET-altered cell, cancer, gene, or gene product that is responsive to the compound. In some embodiments, the disclosure provides a method of treating cancer in a patient, said method comprising administering an effective amount

of a compound described herein to a patient having a RET-altered cell, cancer, gene, or gene product that is responsive to the compound.

[0036] In another aspect, the present disclosure provides a method of treating a subject suffering from cancer comprising the steps of:

a. receiving information related to a RET sequence, e.g., information related to a RET-altered gene or gene product, e.g., having a RET fusion or point mutation; and

b. administering to the subject a compound described herein (e.g., a compound having a lower IC₅₀ for RET than for KDR, a compound having a similar IC₅₀ for wild-type RET compared to mutant RET, and/or a compound of structural Formula (I), (Ia), (II), or (III) described herein (e.g., a compound in Table 1)), or a pharmaceutical composition comprising the compound, if the information indicates a RET-altered cell, cancer, gene, or gene product.

[0037] In some embodiments, the subject is administered a cancer treatment other than a compound of structural Formula (I), (Ia), (II), or (III) if the information indicates that the subject has a wild-type RET sequence. In some embodiments, the cancer treatment is a wild-type RET inhibitor.

[0038] In another aspect, the present disclosure provides a method of treating cancer in a subject, said method comprising:

a. obtaining a biological sample (e.g., a tumor biopsy) from a human subject;

b. detecting whether a RET-altered cell, cancer, gene, or gene product, e.g., having a fusion or point mutation, is present in the biological sample;

c. identifying the subject as responsive to a compound described herein (e.g., a compound having a lower IC₅₀ for RET than for KDR, a compound having a similar IC₅₀ for wild-type RET compared to mutant RET, and/or a compound of structural Formula (I), (Ia), (II), or (III) described herein (e.g., a compound in Table 1)) when the presence of the RET-altered cell, cancer, gene, or gene product in the biological sample is detected; and

d. administering an effective amount of the compound to the subject.

[0039] In another aspect, the present disclosure provides a method of treating cancer in a subject, said method comprising:

a. determining if, having determined if, or receiving information that the subject has a RET-altered cell, cancer, gene, or gene product, e.g., having a fusion or point mutation;

b. identifying the subject as responsive to a compound described herein (e.g., a compound having a lower IC₅₀ for RET than for KDR, a compound having a similar IC₅₀ for wild-type RET compared to mutant RET, and/or a compound of structural Formula (I), (Ia), (II), or (III) described herein (e.g., a compound in Table 1)) when the subject has a RET-altered cell, cancer, gene, or gene product; and

c. administering an effective amount of the compound to the subject. [0040] In another aspect, the present disclosure provides a method of diagnosing cancer in a subject, said method comprising:

a. obtaining a biological sample (e.g., a tumor biopsy) from a human subject;

c. diagnosing the subject with cancer when the presence of the RET-altered cell, cancer, gene, or gene product in the biological sample is detected.

[0041] In another aspect, the present disclosure provides a method of predicting the efficacy of a compound described herein (a compound having a lower IC₅₀ for RET than for KDR, a compound having a similar IC₅₀ for wild-type RET compared to mutant RET, and/or a compound of structural Formula (I), (Ia), (II), or (III) described herein (e.g., a compound in Table 1)) in a treatment of cancer in a subject comprising the step of:

determining if, having determined if, or receiving information that the subject has a RET-altered cell, cancer, gene, or gene product, e.g., having a mutation, e.g., a fusion or point mutation, e.g., by a method selected from hybridization-based methods, amplification-based methods, microarray analysis, flow cytometry analysis, DNA

sequencing, next-generation sequencing (NGS), primer extension, PCR, in situ hybridization, dot blot, and Southern blot;

wherein said determining if, having determined if, or receiving information is predictive of efficacy of the compound in the treatment.

[0042] In some embodiments of any of the methods and uses herein, the method further comprises administering to the subject a compound described herein (e.g., a compound having a lower IC₅₀ for RET than for KDR, a compound having a similar IC₅₀ for wild-type RET compared to mutant RET, and/or a compound of structural Formula (I), (Ia), (II), or (III) described herein (e.g., a compound in Table 1)), e.g., responsive to a determination or diagnosis made by a method described herein.

[0043] In some embodiments of any of the methods and uses herein, the RET-altered cell, cancer, gene, or gene product comprises a fusion mutation, e.g., CCDC6-RET or KIF5B-RET or a fusion of Table 3. In some embodiments, the RET-altered cell, cancer, gene, or gene product comprises a point mutation of amino acid position 634, 918, or 804 of RET, or a point mutation at a position listed in Table 4, e.g., a point mutation specified in Table 4. In some embodiments, the RET-altered cell, cancer, gene, or gene product comprises a point mutation at amino acid 634, 918, or 804, 806, 810, 865, 870, 891, e.g., is selected from RET C634W, M918T, V804L, V804E, V804M, V804L, V806C, Y806C, Y806S, Y806N, Y806H, G810R, G810S, L865V, L870F, and S891A. In some embodiments, the RET alteration is located at least partially within, or is located wholly within one or more of: the N-terminal extracellular domain (e.g., within one or more cadherin-like repeats and/or the cysteine-rich region), the transmembrane domain, or the tyrosine kinase domain (e.g., within one or more of the ATP binding site or proton acceptor site). In some embodiments, the RET fusion further comprises a point mutation, e.g., KIF5B-RET (V804L) or KIF5B-RET (V804M).

[0044] In some embodiments of any of the methods and uses herein, the subject suffers from a cancer selected from colorectal cancer, lung cancer (e.g., a lung adenocarcinoma, e.g., NSCLC), thyroid cancer (e.g., medullary thyroid cancer), or leukemia. In some embodiments, the subject suffers from a cancer listed herein, e.g., in Table 3.

[0045] In some embodiments, the cancer is wild-type RET.

[0046] In some embodiments, the cancer is lung cancer, e.g., a lung adenocarcinoma, and the RET-altered cell, cancer, gene, or gene product comprises a CCDC6-RET fusion. In some embodiments, the cancer is lung adenocarcinoma and the RET-altered cell, cancer, gene, or gene product comprises a KIF5B-RET fusion. In some

embodiments, the cancer is lung adenocarcinoma and the RET-altered cell, cancer, gene, or gene product comprises KIF5B-RET (V804L). In some embodiments, the lung adenocarcinoma is NSCLC.

[0047] In some embodiments, the cancer is thyroid cancer, e.g., medullary thyroid cancer, and the RET-altered cell, cancer, gene, or gene product comprises a C634W mutation.

[0048] In some embodiments, the cancer is leukemia and the RET-altered cell, cancer, gene, or gene product comprises a KIF5B-RET fusion.

[0049] In some embodiments, the cancer is thyroid cancer and the RET-altered cell, cancer, gene, or gene product comprises a M918T mutation. In some embodiments, the cancer is medullary thyroid cancer and the RET-altered cell, cancer, gene, or gene product comprises a M918T mutation.

[0050] In some embodiments, the cancer is leukemia and the RET-altered cell, cancer, gene, or gene product comprises comprises KIF5B-RET (V804L) or KIF5B- RET (V804M) fusion.

[0051] In some embodiments, the cancer is thyroid cancer and the RET-altered cell, cancer, gene, or gene product comprises comprises a CCDC6-RET fusion. In some embodiments, the cancer is colorectal cancer and the RET-altered cell, cancer, gene, or gene product comprises CCDC6-RET fusion. In some embodiments, the cancer is colorectal cancer and the RET-altered cell, cancer, gene, or gene product comprises CCDC6-RET (V804M) fusion.

[0052] In some embodiments of any of the methods and uses herein, the compound or pharmaceutical composition has a lower IC₅₀ for RET than for KDR, e.g., has a KDR/RET IC₅₀ ratio of at least 3x, 4x, 5x, 10x, 20x, 50x, or 100x, and optionally up to 50x or 100x. In some embodiments, the compound or pharmaceutical composition has a KDR/RET IC₅₀ ratio of between 3x-4x, 4x-5x, 5x-10x, 10x-20x, 20x-50x, or 50x- 100x. In some embodiments, the compound or pharmaceutical composition has a

similar IC₅₀ for wild-type RET compared to mutant RET (e.g., for V804L RET or V804E RET), e.g., has a wild-type/mutant IC₅₀ ratio of no more than 3x, 2x, 1.5x, 1x, or 0.5x, e.g., of between 3x and 0.5x.

[0053] In some embodiments of any of the methods and uses herein, the subject does not develop a RET-altered cell, cancer, gene, or gene product for at least 1, 2, 3, 6, 9, 12, 24, or 36 months after initiation of administration of the compound. In some embodiments, the compound is administered as a first line therapy. In some

embodiments, the compound is administered to a treatment-naïve subject. In some embodiments, the compound is not administered in combination with another kinase inhibitor. In some embodiments, the compound is not administered in combination with another RET inhibitor. For example, the compound can be administered as a monotherapy or in combination with one or other agents which are not kinase inhibitors, e.g., not RET inhibitors.

[0054] In some embodiments of any of the methods and uses herein, the compound is administered at an amount sufficient to reach at least 70%, 80%, 90%, or 95% inhibition of RET in vivo.

EMBODIMENTS OF THE DISCLOSURE

Definitions

[0055] As used herein, the terms a“patient,”“subject,”“individual,” and“host” refer to either a human or a non-human animal suffering from or suspected of suffering from a disease or disorder associated with aberrant RET expression (i.e., increased RET activity caused by signaling through RET) or biological activity.

[0056] “Treat” and“treating” such a disease or disorder refers to ameliorating at least one symptom of the disease or disorder. These terms, when used in connection with a condition such as a cancer, refer to one or more of: impeding growth of the cancer, causing the cancer to shrink by weight or volume, extending the expected survival time of the patient, inhibiting tumor growth, reducing tumor mass, reducing size or number of metastatic lesions, inhibiting the development of new metastatic

lesions, prolonging survival, prolonging progression- free survival, prolonging time to progression, and/or enhancing quality of life.

[0057] The term“preventing” when used in relation to a condition or disease such as cancer, refers to a reduction in the frequency of, or delay in the onset of, symptoms of the condition or disease. Thus, prevention of cancer includes, for example, reducing the number of detectable cancerous growths in a population of patients receiving a prophylactic treatment relative to an untreated control population, and/or delaying the appearance of detectable cancerous growths in a treated population versus an untreated control population, e.g., by a statistically and/or clinically significant amount.

[0058] The term“therapeutic effect” refers to a beneficial local or systemic effect in animals, particularly mammals, and more particularly humans, caused by administration of a compound or composition of the disclosure. The phrase“therapeutically-effective amount” means that amount of a compound or composition of the disclosure that is effective to treat a disease or condition caused by over expression of RET or aberrant RET biological activity at a reasonable benefit/risk ratio. The therapeutically effective amount of such substance will vary depending upon the subject and disease or condition being treated, the weight and age of the subject, the severity of the disease condition, the manner of administration and the like, which can readily be determined by one of skill in the art.

[0059] As used herein,“developing resistance” means that when a drug is first administered to the patient, the patient’s symptoms improve, whether measured by decrease in tumor volume, a decrease in the number of new lesions, or some other means that a physician uses to judge disease progression; however, those symptoms stop improving, or even worsen at some point. At that time, the patient is said to have developed resistance to the drug.

[0060] “Alteration” as used herein, of a gene or gene product (e.g., the RET gene or gene product) refers to the presence of a mutation or mutations within the gene or gene product, e.g., a mutation, which of the gene or gene product, as compared to the normal or wild-type gene. The alteration can be in amount, structure, and/or activity in a cancer tissue or cancer cell, as compared to its amount, structure, and/or activity, in a normal or healthy tissue or cell (e.g., a control), and is associated with a disease or condition, such

as cancer. For example, an alteration which is associated with cancer, or predictive of responsiveness to an anti-cancer therapeutic, can have an altered nucleotide sequence (e.g., a mutation), amino acid sequence, chromosomal translocation, intra-chromosomal inversion, copy number, expression level, protein level, protein activity, or methylation status, in a cancer tissue or cancer cell, as compared to a normal, healthy tissue or cell. Exemplary mutations include, but are not limited to, point mutations (e.g., silent, missense, or nonsense), deletions, insertions, inversions, linking mutations,

duplications, translocations, inter- and intra-chromosomal rearrangements. Mutations can be present in the coding or non-coding region of the gene, e.g., a 3’ UTR or 5’ UTR.

[0061] A subject having“altered RET” refers to a subject comprising a RET alteration, e.g., in one or more of their cancer cells.

[0062] A“RET-altered” cell, cancer, gene, or gene product refers to a cell, cancer, gene, or gene product comprising a RET alteration as described herein.

[0063] “Aliphatic group” means a straight-chain, branched-chain, or cyclic hydrocarbon group and includes saturated and unsaturated groups, such as an alkyl group, an alkenyl group, and an alkynyl group.

[0064] “Alkylene” refers to a divalent radical of an alkyl group, e.g., -CH₂-, - CH₂CH₂-, and -CH₂CH₂CH₂-.

[0065] “Alkenyl” means an aliphatic group containing at least one double bond.

[0066] “Alkoxyl” or“alkoxy” means an alkyl group having an oxygen radical attached thereto. Representative alkoxyl groups include methoxy, ethoxy, propyloxy, tert-butoxy and the like. The term“haloalkoxy” refers to an alkoxy in which one or more hydrogen atoms are replaced by halo, and includes alkoxy moieties in which all hydrogens have been replaced by halo (e.g., perfluoroalkoxy).

[0067] “Alkyl” refers to a monovalent radical of a saturated straight or branched hydrocarbon, such as a straight or branched group of 1-12, 1-10, or 1-6 carbon atoms, referred to herein as C₁-C₁₂ alkyl, C₁-C₁₀ alkyl, and C₁-C₆ alkyl, respectively.

Exemplary alkyl groups include, but are not limited to, methyl, ethyl, propyl, isopropyl, 2-methyl-1-propyl, 2-methyl-2-propyl, 2-methyl-1-butyl, 3-methyl-1-butyl,

2-methyl-3-butyl, 2,2-dimethyl-1-propyl, 2-methyl-1-pentyl, 3-methyl-1-pentyl, 4-methyl-1-pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl,

2,2-dimethyl-1-butyl, 3,3-dimethyl-1-butyl, 2-ethyl-1-butyl, butyl, isobutyl, t-butyl, pentyl, isopentyl, neopentyl, hexyl, heptyl, octyl, etc.

[0068] “Alkenylene" refers to an alkenyl group having two connecting points. For example,“ethenylene” represents the group -CH=CH-. Alkenylene groups can also be in an unsubstituted form or substituted form with one or more substituents.

[0069] “Alkynyl” refers to a straight or branched hydrocarbon chain containing 2-12 carbon atoms and characterized in having one or more triple bonds. Examples of alkynyl groups include, but are not limited to, ethynyl, propargyl, and 3-hexynyl. One of the triple bond carbons may optionally be the point of attachment of the alkynyl substituent.

[0070] “Alkynylene” refers to an alkynyl having two connecting points. For example,“ethynylene” represents the group -C≡C-. Alkynylene groups can also be in an unsubstituted form or substituted form with one or more substituents.

[0071] “Hydroxyalkylene” or“hydroxyalkyl” refers to an alkylene or alkyl moiety in which an alkylene or alkyl hydrogen atom is replaced by a hydroxyl group.

Hydroxyalkylene or hydroxyalkyl includes groups in which more than one hydrogen atom has been replaced by a hydroxyl group.

[0072] “Aromatic ring system” is art-recognized and refers to a monocyclic, bicyclic or polycyclic hydrocarbon ring system, wherein at least one ring is aromatic.

[0073] “Aryl” refers to a monovalent radical of an aromatic ring system.

Representative aryl groups include fully aromatic ring systems, such as phenyl, naphthyl, and anthracenyl, and ring systems where an aromatic carbon ring is fused to one or more non-aromatic carbon rings, such as indanyl, phthalimidyl, naphthimidyl, or tetrahydronaphthyl, and the like.

[0074] “Arylalkyl” or“aralkyl” refers to an alkyl moiety in which an alkyl hydrogen atom is replaced by an aryl group. Aralkyl includes groups in which more than one hydrogen atom has been replaced by an aryl group. Examples of“arylalkyl” or

“aralkyl” include benzyl, 2-phenylethyl, 3-phenylpropyl, 9-fluorenyl, benzhydryl, and trityl groups.

[0075] “Aryloxy” refers to -O-(aryl), wherein the aryl moiety is as defined herein.

[0076] “Halo” refers to a radical of any halogen, e.g., -F, -Cl, -Br, or -I.

[0077] “Haloalkyl” and“haloalkoxy” refers to alkyl and alkoxy structures that are substituted with one or more halo groups or with combinations thereof. For example, the terms“fluoroalkyl” and“fluoroalkoxy” include haloalkyl and haloalkoxy groups, respectively, in which the halo is fluorine.“Haloalkylene” refers to a divalent alkyl, e.g., -CH₂-, -CH₂CH₂-, and -CH₂CH₂CH₂-, in which one or more hydrogen atoms are replaced by halo, and includes alkyl moieties in which all hydrogens have been replaced by halo.

[0078] “Heteroalkyl” refers to an optionally substituted alkyl, which has one or more skeletal chain atoms selected from an atom other than carbon, e.g., oxygen, nitrogen, sulfur, phosphorus or combinations thereof. A numerical range may be given, e.g. C₁-C₆ heteroalkyl which refers to the number of carbons in the chain, which in this example includes 1 to 6 carbon atoms. For example, a–CH₂OCH₂CH₃ radical is referred to as a“C₃” heteroalkyl. Connection to the rest of the molecule may be through either a heteroatom or a carbon in the heteroalkyl chain.“Heteroalkylene” refers to a divalent optionally substituted alkyl, which has one or more skeletal chain atoms selected from an atom other than carbon, e.g., oxygen, nitrogen, sulfur, phosphorus or combinations thereof.

[0079] “Carbocyclic ring system” refers to a monocyclic, bicyclic or polycyclic hydrocarbon ring system, wherein each ring is either completely saturated or contains one or more units of unsaturation, but where no ring is aromatic.

[0080] “Carbocyclyl” refers to a monovalent radical of a carbocyclic ring system. Representative carbocyclyl groups include cycloalkyl groups (e.g., cyclobutyl, cyclopentyl, cyclohexyl and the like), and cycloalkenyl groups (e.g., cyclopentenyl, cyclohexenyl, cyclopentadienyl, and the like).

[0081] “Cycloalkyl” refers to a cyclic, bicyclic, tricyclic, or polycyclic non-aromatic hydrocarbon groups having 3 to 12 carbons. Any substitutable ring atom can be

substituted (e.g., by one or more substituents). The cycloalkyl groups can contain fused or spiro rings. Fused rings are rings that share a common carbon atom. Examples of cycloalkyl moieties include, but are not limited to, cyclopropyl, cyclohexyl,

methylcyclohexyl, adamantyl, and norbornyl.

[0082] “Cycloalkylalkyl” refers to a–(cycloalkyl)-alkyl radical where cycloalkyl and alkyl are as disclosed herein. The“cycloalkylalkyl” is bonded to the parent molecular structure through the alkyl group.

[0083] “Heteroaromatic ring system” is art-recognized and refers to monocyclic, bicyclic or polycyclic ring system wherein at least one ring is both aromatic and comprises at least one heteroatom (e.g., N, O or S); and wherein no other rings are heterocyclyl (as defined below). In certain instances, a ring which is aromatic and comprises a heteroatom contains 1, 2, 3, or 4 ring heteroatoms in such ring.

[0084] “Heteroaryl” refers to a monovalent radical of a heteroaromatic ring system. Representative heteroaryl groups include ring systems where (i) each ring comprises a heteroatom and is aromatic, e.g., imidazolyl, oxazolyl, thiazolyl, triazolyl, pyrrolyl, furanyl, thiophenyl pyrazolyl, pyridinyl, pyrazinyl, pyridazinyl, pyrimidinyl, indolizinyl, purinyl, naphthyridinyl, and pteridinyl; (ii) each ring is aromatic or carbocyclyl, at least one aromatic ring comprises a heteroatom and at least one other ring is a hydrocarbon ring or e.g., indolyl, isoindolyl, benzothienyl, benzofuranyl, dibenzofuranyl, indazolyl, benzimidazolyl, benzthiazolyl, quinolyl, isoquinolyl, cinnolinyl, phthalazinyl, quinazolinyl, quinoxalinyl, carbazolyl, acridinyl, phenazinyl, phenothiazinyl, phenoxazinyl, pyrido[2,3-b]-1,4-oxazin-3-(4H)-one,

5,6,7,8-tetrahydroquinolinyl and 5,6,7,8-tetrahydroisoquinolinyl; and (iii) each ring is aromatic or carbocyclyl, and at least one aromatic ring shares a bridgehead heteroatom with another aromatic ring, e.g., 4H-quinolizinyl.

[0085] “Heterocyclic ring system” refers to monocyclic, bicyclic and polycyclic ring systems where at least one ring is saturated or partially unsaturated (but not aromatic) and comprises at least one heteroatom. A heterocyclic ring system can be attached to its pendant group at any heteroatom or carbon atom that results in a stable structure and any of the ring atoms can be optionally substituted.

[0086] “Heterocyclyl” refers to a monovalent radical of a heterocyclic ring system. Representative heterocyclyls include ring systems in which (i) every ring is

non-aromatic and at least one ring comprises a heteroatom, e.g., tetrahydrofuranyl, tetrahydropyranyl, tetrahydrothienyl, pyrrolidinyl, pyrrolidonyl, piperidinyl, pyrrolinyl, decahydroquinolinyl, oxazolidinyl, piperazinyl, dioxanyl, dioxolanyl, diazepinyl, oxazepinyl, thiazepinyl, morpholinyl, and quinuclidinyl; (ii) at least one ring is non-aromatic and comprises a heteroatom and at least one other ring is an aromatic carbon ring, e.g., 1,2,3,4-tetrahydroquinolinyl, 1,2,3,4-tetrahydroisoquinolinyl; and (iii) at least one ring is non-aromatic and comprises a heteroatom and at least one other ring is aromatic and comprises a heteroatom, e.g., 3,4-dihydro-1H-pyrano[4,3-c]pyridine, and 1,2,3,4-tetrahydro-2,6-naphthyridine. In some embodiments, heterocyclyl can include:

, wherein the point of attachment to the base structure can be through any of the atoms on the heterocyclyl, e.g., through a carbon atom or a nitrogen atom of the heterocyclyl.

[0087] “Heterocyclylalkyl” refers to an alkyl group substituted with a heterocyclyl group. The“heterocyclylalkyl” is bonded to the parent molecular structure through the alkyl group.

[0088] “Cyano” refers to a–CN radical.

[0089] “Nitro” refers to–NO₂.

[0090] “Hydroxy” or“hydroxyl” refers to–OH.

[0091] “Hydroxyalkylene” refers to a divalent alkyl, e.g., -CH₂-, -CH₂CH₂-, and - CH₂CH₂CH₂-, in which one or more hydrogen atoms are replaced by a hydroxy, and includes alkyl moieties in which all hydrogens have been replaced by hydroxy.

[0092] “Substituted”, whether preceded by the term“optionally” or not, means that one or more hydrogens of the designated moiety are replaced with a suitable substituent.

Unless otherwise indicated, an“optionally substituted” group may have a suitable substituent at each substitutable position of the group, and when more than one position in any given structure may be substituted with more than one substituent selected from a specified group, the substituent may be either the same or different at each position. Combinations of substituents envisioned under this disclosure are preferably those that result in the formation of stable or chemically feasible compounds. The term“stable”, as used herein, refers to compounds that are not substantially altered when subjected to conditions to allow for their production, detection, and, in certain embodiments, their recovery, purification, and use for one or more of the purposes disclosed herein.

[0093] As used herein, the definition of each expression, e.g., alkyl, m, n, etc., when it occurs more than once in any structure, is intended to be independent of its definition elsewhere in the same structure.

[0094] Certain compounds of the present disclosure may exist in particular geometric or stereoisomeric forms. The present disclosure contemplates all such compounds, including cis- and trans-isomers, R- and S-enantiomers, diastereomers, (D)-isomers, (L)-isomers, the racemic mixtures thereof, and other mixtures thereof, as falling within the scope of the disclosure. Additional asymmetric carbon atoms may be present in a substituent such as an alkyl group. All such isomers, as well as mixtures thereof, are intended to be included in this disclosure.

[0095] If, for instance, a particular enantiomer of compound of the present disclosure is desired, it may be prepared by asymmetric synthesis, or by derivation with a chiral auxiliary, where the resulting diastereomeric mixture is separated and the auxiliary group cleaved to provide the pure desired enantiomers. Alternatively, where the molecule contains a basic functional group, such as amino, or an acidic functional group, such as carboxyl, diastereomeric salts are formed with an appropriate

optically-active acid or base, followed by resolution of the diastereomers thus formed by fractional crystallization or chromatographic means well known in the art, and subsequent recovery of the pure enantiomers.

[0096] Unless otherwise indicated when a disclosed compound is named or depicted by a structure without specifying the stereochemistry and has one or more chiral centers,

it is understood to represent all possible stereoisomers of the compound, as well as enantiomeric mixtures thereof.

[0097] The“enantiomeric excess” or“% enantiomeric excess” of a composition can be calculated using the equation shown below. In the example shown below a composition contains 90% of one enantiomer, e.g., the S enantiomer, and 10% of the other enantiomer, i.e., the R enantiomer.

ee = (90-10)/100 = 80%.

Thus, a composition containing 90% of one enantiomer and 10% of the other enantiomer is said to have an enantiomeric excess of 80%.

[0098] The compounds or compositions described herein may contain an

enantiomeric excess of at least 50%, 75%, 90%, 95%, or 99% of one form of the compound, e.g., the S-enantiomer. In other words such compounds or compositions contain an enantiomeric excess of the S enantiomer over the R enantiomer.

[0099] The compounds described herein may also contain unnatural proportions of atomic isotopes at one or more of the atoms that constitute such compounds. For example, the compounds may be radiolabeled with radioactive isotopes, such as for example deuterium (²H), tritium (³H), carbon-13 (¹³C), or carbon-14 (¹⁴C). All isotopic variations of the compounds disclosed herein, whether radioactive or not, are intended to be encompassed within the scope of the present disclosure. In addition, all tautomeric forms of the compounds described herein are intended to be within the scope of the disclosure.

[00100] The compound can be useful as the free base or as a salt. Representative salts include the hydrobromide, hydrochloride, sulfate, bisulfate, phosphate, nitrate, acetate, valerate, oleate, palmitate, stearate, laurate, benzoate, lactate, phosphate, tosylate, citrate, maleate, fumarate, succinate, tartrate, napthylate, mesylate, glucoheptonate, lactobionate, and laurylsulphonate salts and the like. (See, for example, Berge et al. (1977)“Pharmaceutical Salts”, J. Pharm. Sci.66:1-19.) Compounds

[00101] In one aspect, the disclosure features a compound of Formula (I) or a pharmaceutically acceptable salt thereof, wherein:

ring A is an aryl or heteroaryl ring;

each of X¹ and X² is independently selected from N and C(R⁶); Z is

each of R⁵ and R⁸ is independently selected from hydrogen, deuterium, C₁-C₆ alkyl, and C₁-C₆ heteroalkyl; wherein each alkyl and heteroalkyl is optionally and independently substituted with 0-5 occurrences of R^a; each R⁶ is independently selected from hydrogen, C₁-C₆ alkyl, C₁-C₆ alkoxy, halo, cyano, C₁-C₆ heteroalkyl, and -N(R^d)(R^d);

wherein each alkyl, alkoxy, and heteroalkyl is optionally and independently substituted with 0-5 occurrences of R^a;

[00102] In some embodiments, the compound has the structural formula (Ia):

[00103] In some embodiments, R1 is fluoro, -CH3, -CH2CH3, -CHF2 , -OCH3, or cyclopropyl.

[00104] In some embodiments, R² is selected from hydrogen, -C₁-C₄ alkyl, C₁-C₆ alkoxy, hydroxyl, and halo; wherein -C₁-C₄ alkyl or C₁-C₆ alkoxy is optionally substituted (e.g., with 0-3 occurrences of R^a, e.g., cyano, halo). In some embodiments, R² is selected from hydrogen, -C₁-C₄ alkyl, C₁-C₆ alkoxy, hydroxyl, and fluoro. In some embodiments, R² is hydrogen, fluoro, -CH_3, -CH₂CH_3, -CH₂OH, -CH₂CN, - OCH₂CF₃, -OCH₂CH₂, or OMe.

[00105] In some embodiments, R³ if present is hydrogen.

[00106] In some embodiments, R⁴ is selected from hydrogen, hydroxyl, halo, cyano, C₁-C₄ alkyl and O-C₁-C₄ alkyl, wherein each alkyl portion of R⁴ is substituted with 0-3 occurrences of R^a. In some embodiments, R⁴ is selected from hydrogen, fluoro, cyano, hydroxyl, -CH₃, -CH₂CN, -CH₂CH₃, -CH₂CH₂OCH₃, -OCH₃, -OCH₂CF₃,

[00107] In some embodiments, Z is selected from

embodiments, Z is selected from , -CH₂-, and -CH(CH₃)-. [00108] In some embodiments, each R⁶ is independently selected from hydrogen, halo, cyano, and C₁-C₄ alkyl substituted with 0-3 occurrences of R^a. In some embodiments, each R⁶ is independently selected from hydrogen, fluoro, cyano, -CH₂F and -CH₃.

[00109] In some embodiments, R⁸ is selected from hydrogen and -CH₃.

[00110] In some embodiments, ring A is selected from phenyl and a 6-membered monocyclic heteroaryl comprising at least one nitrogen ring atom. In some

embodiments, ring A is selected from:

embodiments, ring A is selected from and

[00111] In some embodiments, R⁷ is selected from 3-fluoroazetidin-1-yl, 3,3- difluoropyrrolidin-1-yl, 3-fluoropyrrolidin-1-yl, 3-difluoromethyl-1H-pyrazol-1-yl, 4- fluoro-1H-pyrazol-1-yl, 4-chloro-1H-pyrazol-1-yl, 3-difluoromethyl-1H-pyrazol-1-yl, 4-difluoromethyl-1H-pyrazol-1-yl, 4-cyclopropyl-1H-pyrazol-1-yl, 4-fluoro-1H- pyrazol-1-yl, 3,5-bis(difluoromethyl)-1H-pyrazolyl, 3-methyl-1H-pyrazol-1-yl, 4- methyl-1H-pyrazol-1-yl, 3,5-dimethyl-1H-pyrazol-1-yl, and pyrazol-1-yl. In some embodiments, R⁷ is 4-cyclopropyl-1H-pyrazol-1-yl, 4-fluoro-1H-pyrazol-1-yl, or pyrazol-1-yl.

[00112] In some embodiments, ring A is phenyl; n is 0 or 1; and R⁷ if present is -O-C₁-C₄ alkyl.

[00113] In some embodiments, n is 0, or n is 1 and R⁷ is selected from -OCH₃

[00114] In another aspect, the disclosure features a compound of Formula (II) or a pharmaceutically acceptable salt thereof, wherein:

[00115] In some embodiments, R¹¹ is -CH₃; R¹² is selected from hydrogen and -CH₃; R¹³ if present is selected from hydrogen, cyano and fluoro; R¹⁴ is selected from hydrogen, fluoro, cyano, hydroxyl, -CH₃, -CH₂CH₃, -OCH₃, and -OCH₂CH₃; R¹⁵ is selected from hydrogen and -CH₃; R¹⁶ is selected from hydrogen, -CH₃ and -CHF₂; R¹⁷ is selected from hydrogen and -CH₃; each of R^18a and R^19a if present is independently selected from hydrogen and fluoro, wherein at least one of R^18a or R^19a is hydrogen; each of R^18b and R^19b is independently selected from hydrogen, fluoro,

chloro, -CH₃, -CHF₂, and cyclopropyl, wherein at least one of R^18b or R^19b is hydrogen; and each is the same.

[00116] In some embodiments, p is 1.

[00117] In some embodiments, R¹⁴ is selected from hydrogen, fluoro, cyano, hydroxyl, and -OCH_3.

[00118] In another aspect, the disclosure features a compound of Formula (III) or a pharmaceutically acceptable salt thereof, wherein:

Z’ is selected from

[00119] In some embodiments, Z’ is selected from , -CH₂,

or -CH(CH₃)-;

the portion of the molecule represented by

is selected from

; R²¹ is selected

from -CH₃ and cyclopropyl;

[00120] In some embodiments, Z’ is -CH₂ or -CH(CH₃)-. [00121] Table 1 below shows the structures of exemplary compounds of the disclosure.

Table 1. Exemplary Compounds

[00122] Pharmaceutically acceptable salts of these compounds are also contemplated for the uses described herein.

[00123] "Pharmaceutically acceptable salt" refers to any salt of a compound of the disclosure which retains its biological properties and which is not toxic or otherwise undesirable for pharmaceutical use. Pharmaceutically acceptable salts may be derived from a variety of organic and inorganic counter-ions well known in the art and include. Such salts include: (1) acid addition salts formed with organic or inorganic acids such as hydrochloric, hydrobromic, sulfuric, nitric, phosphoric, sulfamic, acetic, trifluoroacetic, trichloroacetic, propionic, hexanoic, cyclopentylpropionic, glycolic, glutaric, pyruvic, lactic, malonic, succinic, sorbic, ascorbic, malic, maleic, fumaric, tartaric, citric, benzoic, 3-(4-hydroxybenzoyl)benzoic, picric, cinnamic, mandelic, phthalic, lauric, methanesulfonic, ethanesulfonic, 1 ,2-ethane-disulfonic, 2-hydroxyethanesulfonic, benzenesulfonic, 4-chlorobenzenesulfonic, 2-naphthalenesulfonic, 4-toluenesulfonic, camphoric, camphorsulfonic, 4-methylbicyclo[2.2.2]-oct-2-ene-1-carboxylic, glucoheptonic, 3-phenylpropionic, trimethylacetic, tert-butylacetic, lauryl sulfuric, gluconic, benzoic, glutamic, hydroxynaphthoic, salicylic, stearic, cyclohexylsulfamic, quinic, muconic acid and the like acids; or (2) salts formed when an acidic proton present in the parent compound either (a) is replaced by a metal ion, e.g., an alkali metal ion, an alkaline earth ion or an aluminum ion, or alkali metal or alkaline earth metal hydroxides, such as sodium, potassium, calcium, magnesium, aluminum, lithium, zinc, and barium hydroxide, ammonia or (b) coordinates with an organic base, such as aliphatic, alicyclic, or aromatic organic amines, such as ammonia, methylamine, dimethylamine, diethylamine, picoline, ethanolamine, diethanolamine, triethanolamine, ethylenediamine, lysine, arginine, ornithine, choline, N,N'-dibenzylethylene-diamine, chloroprocaine, diethanolamine, procaine, N-benzylphenethylamine, N- methylglucamine piperazine, tris(hydroxymethyl)-aminomethane,

tetramethylammonium hydroxide, and the like. Pharmaceutically acceptable salts further include, by way of example only, sodium, potassium, calcium, magnesium, ammonium, tetraalkylammonium and the like, and when the compound contains a basic functionality, salts of non-toxic organic or inorganic acids, such as hydrochloride, hydrobromide, tartrate, mesylate, besylate, acetate, maleate, oxalate and the like.

Pharmaceutical Compositions

[00124] Pharmaceutical compositions of the disclosure comprise one or more compounds of the disclosure and one or more physiologically or pharmaceutically acceptable carrier. The term“pharmaceutically acceptable carrier” refers to a pharmaceutically-acceptable material, composition or vehicle, such as a liquid or solid filler, diluent, excipient, solvent or encapsulating material, involved in carrying or transporting any subject composition or component thereof. Each carrier must be “acceptable” in the sense of being compatible with the subject composition and its components and not injurious to the patient. Some examples of materials which may serve as pharmaceutically acceptable carriers include: (1) sugars, such as lactose, glucose and sucrose; (2) starches, such as corn starch and potato starch; (3) cellulose, and its derivatives, such as sodium carboxymethyl cellulose, ethyl cellulose and cellulose acetate; (4) powdered tragacanth; (5) malt; (6) gelatin; (7) talc; (8) excipients, such as cocoa butter and suppository waxes; (9) oils, such as peanut oil, cottonseed oil, safflower oil, sesame oil, olive oil, corn oil and soybean oil; (10) glycols, such as propylene glycol; (11) polyols, such as glycerin, sorbitol, mannitol and polyethylene glycol; (12) esters, such as ethyl oleate and ethyl laurate; (13) agar; (14) buffering agents, such as magnesium hydroxide and aluminum hydroxide; (15) alginic acid; (16) pyrogen-free water; (17) isotonic saline; (18) Ringer’s solution; (19) ethyl alcohol; (20) phosphate buffer solutions; and (21) other non-toxic compatible substances employed in pharmaceutical formulations.

[00125] The compositions of the disclosure may be administered orally, parenterally, by inhalation spray, topically, rectally, nasally, buccally, vaginally or via an implanted reservoir. The term "parenteral" as used herein includes subcutaneous, intravenous, intramuscular, intra-articular, intra-synovial, intrasternal, intrathecal, intrahepatic, intralesional and intracranial injection or infusion techniques. In some embodiments, the compositions of the disclosure are administered orally, intraperitoneally or intravenously. Sterile injectable forms of the compositions of this disclosure may be aqueous or oleaginous suspension. These suspensions may be formulated according to techniques known in the art using suitable dispersing or wetting agents and suspending agents. The sterile injectable preparation may also be a sterile injectable solution or suspension in a non-toxic parenterally acceptable diluent or solvent, for example as a

solution in 1,3-butanediol. Among the acceptable vehicles and solvents that may be employed are water, Ringer's solution and isotonic sodium chloride solution. In addition, sterile, fixed oils are conventionally employed as a solvent or suspending medium.

[00126] For this purpose, any bland fixed oil may be employed including synthetic mono- or di-glycerides. Fatty acids, such as oleic acid and its glyceride derivatives are useful in the preparation of injectables, as are natural pharmaceutically-acceptable oils, such as olive oil or castor oil, especially in their polyoxyethylated versions. These oil solutions or suspensions may also contain a long-chain alcohol diluent or dispersant, such as carboxymethyl cellulose or similar dispersing agents that are commonly used in the formulation of pharmaceutically acceptable dosage forms including emulsions and suspensions. Other commonly used surfactants, such as Tween, Spans and other emulsifying agents or bioavailability enhancers which are commonly used in the manufacture of pharmaceutically acceptable solid, liquid, or other dosage forms may also be used for the purposes of formulation.

[00127] The pharmaceutically acceptable compositions of this disclosure may be orally administered in any orally acceptable dosage form including, but not limited to, capsules, tablets, aqueous suspensions or solutions. In the case of tablets for oral use, carriers commonly used include lactose and corn starch. Lubricating agents, such as magnesium stearate, are also typically added. For oral administration in a capsule form, useful diluents include lactose and dried cornstarch. When aqueous suspensions are required for oral use, the active ingredient is combined with emulsifying and suspending agents. If desired, certain sweetening, flavoring or coloring agents may also be added.

[00128] Alternatively, the pharmaceutically acceptable compositions of this disclosure may be administered in the form of suppositories for rectal administration. These can be prepared by mixing the agent with a suitable non-irritating excipient that is solid at room temperature but liquid at rectal temperature and therefore will melt in the rectum to release the drug. Such materials include cocoa butter, beeswax and polyethylene glycols.

[00129] The pharmaceutically acceptable compositions of this disclosure may also be administered topically, especially when the target of treatment includes areas or organs

readily accessible by topical application, including diseases of the eye, the skin, or the lower intestinal tract. Suitable topical formulations are readily prepared for each of these areas or organs. Topical application for the lower intestinal tract can be effected in a rectal suppository formulation (see above) or in a suitable enema formulation. Topically-transdermal patches may also be used.

[00130] For topical applications, the pharmaceutically acceptable compositions may be formulated in a suitable ointment containing the active component suspended or dissolved in one or more carriers. Carriers for topical administration of the compounds of this disclosure include, but are not limited to, mineral oil, liquid petrolatum, white petrolatum, propylene glycol, polyoxyethylene, polyoxypropylene compound, emulsifying wax and water. Alternatively, the pharmaceutically acceptable

compositions can be formulated in a suitable lotion or cream containing the active components suspended or dissolved in one or more pharmaceutically acceptable carriers. Suitable carriers include, but are not limited to, mineral oil, sorbitan monostearate, polysorbate 60, cetyl esters wax, cetearyl alcohol, 2-octyldodecanol, benzyl alcohol and water.

[00131] The pharmaceutically acceptable compositions of this disclosure may also be administered by nasal aerosol or inhalation. Such compositions are prepared according to techniques well-known in the art of pharmaceutical formulation and may be prepared as solutions in saline, employing benzyl alcohol or other suitable preservatives, absorption promoters to enhance bioavailability, fluorocarbons, and/or other conventional solubilizing or dispersing agents.

[00132] The amount of the compounds of the present disclosure that may be combined with the carrier materials to produce a composition in a single dosage form will vary depending upon the host treated, the particular mode of administration.

Preferably, the compositions should be formulated so that a dosage of between 0.01-100 mg/kg body weight/day of the inhibitor can be administered to a patient receiving these compositions.

Dosages

[00133] Toxicity and therapeutic efficacy of compounds of the disclosure, including pharmaceutically acceptable salts and deuterated variants, can be determined by standard pharmaceutical procedures in cell cultures or experimental animals. The LD₅₀ is the dose lethal to 50% of the population. The ED₅₀ is the dose therapeutically effective in 50% of the population. The dose ratio between toxic and therapeutic effects (LD₅₀/ ED₅₀) is the therapeutic index. Compounds that exhibit large therapeutic indexes are preferred. While compounds that exhibit toxic side effects may be used, care should be taken to design a delivery system that targets such compounds to the site of affected tissue in order to minimize potential damage to uninfected cells and, thereby, reduce side effects.

[00134] Data obtained from the cell culture assays and animal studies can be used in formulating a range of dosage for use in humans. The dosage of such compounds may lie within a range of circulating concentrations that include the ED₅₀ with little or no toxicity. The dosage may vary within this range depending upon the dosage form employed and the route of administration utilized. For any compound, the

therapeutically effective dose can be estimated initially from cell culture assays. A dose may be formulated in animal models to achieve a circulating plasma concentration range that includes the IC₅₀ (i.e., the concentration of the test compound that achieves a half-maximal inhibition of symptoms) as determined in cell culture. Such information can be used to more accurately determine useful doses in humans. Levels in plasma may be measured, for example, by high performance liquid chromatography.

[00135] It should also be understood that a specific dosage and treatment regimen for any particular patient will depend upon a variety of factors, including the activity of the specific compound employed, the age, body weight, general health, sex, diet, time of administration, rate of excretion, drug combination, and the judgment of the treating physician and the severity of the particular disease being treated. The amount of a compound of the present disclosure in the composition will also depend upon the particular compound in the composition.

Treatment

[00136] In an aspect, the disclosure features a method for inhibiting RET activity in a cell or in a patient, comprising the step of contacting the cell or administering to the patient a compound as described herein or a pharmaceutical composition as described herein.

[00137] In another aspect, the disclosure features a method for treating a subject suffering from a condition mediated by aberrant RET activity, comprising administering to the subject a therapeutically effective amount of a compound as described herein or a pharmaceutical composition as described herein.

[00138] In another aspect, the disclosure features a method for treating a subject who has developed resistance to a treatment for a condition mediated by aberrant RET activity, comprising administering to the subject a therapeutically effective amount of a compound as described herein or a pharmaceutical composition as described herein.

[00139] RET fusions have been implicated in several types of cancers. Generally, these RET fusions have a RET kinase domain that is the same as in wild-type RET; therefore, as used herein, any RET protein with the same kinase domain as wild-type RET will be referred to as“wild-type RET” unless noted otherwise. Mutations can occur at least in the RET extracellular and kinase domains. Mutations can occur in the RET kinase domain, leading to resistant mutants of RET.

[00140] The activity of exemplary compounds that are approved or in development for RET-related conditions is shown below. As shown, the compounds are active against the wild-type RET, but are much less active against the mutated forms (“wild- type RET inhibitors”).

Table 2.

[00141] The disclosure provides compounds that inhibit both wild-type RET and resistant mutants of RET. In addition, the compounds of the disclosure can be selective for wild-type RET, over other kinases, thus leading to reduced toxicities associated with inhibiting other kinases. In one aspect, compounds of the disclosure are selective for RET over KDR. In one aspect, compounds of the disclosure do not cause adverse effects such as hypertension, arterial thrombosis, and hemorrhage.

[00142] In addition, the disclosure provides inhibitors of mutant RET. Mutations can be predicted using structural biology and computational analyses, as well as by examining codon sequences in which a sequence change gives rise to a codon for a different amino acid. Using such methods, resistant mutants for RET are predicted to have point mutations at the 804 gatekeeper residue in the RET protein and/or at residues at or near the gatekeeper residue. In some embodiments, the mutation may be at one or more of the 804, 806, 810, 865, 870, 891, and 918 residues. Specific examples of RET resistant mutants include: V804L, V804M, V804E, Y806C, Y806S, Y806H, Y806N, G810R, G810S, L865V, L870F, S891A and M918T mutants.

[00143] Mutations occurring from administration of a particular inhibitor (e.g., a known RET wild-type inhibitor) can be determined experimentally by exposing cells to a mutation-promoting agent, such as ENU. The cells are washed, then plated with increasing concentrations (2-100X proliferation IC₅₀) of the compound of choice. The wells with cellular outgrowth are then collected after 3-4 weeks. The RET kinase domain is then sequenced to identify resistance mutations (i.e., altered forms of the RET protein that retain enzymatic activity). Resistance can be confirmed by exposing these cells with the compound of choice. Resistant mutants that have been identified experimentally include the V804L, V804E, V804M, and Y806H mutants. In some embodiments, the mutation is a substitution of cysteine (C609, C611, C618, C620, C630, and C634) in the RET extracellular domain for any other amino acid. In some embodiments, the RET cysteine variants (affecting C609, C611, C618, and C620) are the“Janus mutations.” In some embodiments, RET mutations include: RET C634W, RET M918T, V804L, V804E, V804M, V804L, Y806C, Y806S, Y806N, Y806H, G810R, G810S, L865V, L870F, and S891A mutants.

[00144] Because of their activity against wild-type RET and mutant RET, the compounds described herein can be used to treat a patient with a condition associated

with aberrant RET activity. The compounds described herein can provide treatments for irritable bowel syndrome (IBS), proliferative diseases, and any other conditions related to aberrant RET activity. The compounds can be used to treat irritable bowel syndrome. The compounds can be used to treat various cancers. In some embodiments, the cancer is selected from papillary thyroid carcinoma (PTC), medullary thyroid cancer (MTC), pheochromocytoma (PC), pancreatic ductal adenocarcinoma, multiple endocrine neoplasia (MEN2A and MEN2B), metastatic breast cancer, testicular cancer, small cell lung cancer, non-small cell lung cancer, chronic myelomonocytic leukemia, colorectal cancer, ovarian cancer, and cancers of the salivary gland. In some

embodiments, the cancer is a solid tumor. In some embodiments, the condition associated with aberrant RET activity is a thyroid cancer (e.g., papillary thyroid carcinoma, thyroid adenocarcinoma, or MTC, e.g., familial MTC), lung cancer (e.g., lung adenocarcinoma, small-cell lung carcinoma, or non-small cell lung carcinoma), breast cancer (e.g., estrogen receptor-positive tumors and endocrine-resistant tumors e.g., resistant to oestrogen modulators such as tamoxifen, agents that block oestrogen biosynthesis such as aromatase inhibitors, and oestrogen receptor antagonists such as fulvestrant), pancreatic cancer (e.g., carcinoma of the pancreas or pancreatic ductal carcinoma), haematopoietic cancer, e.g., a leukemia (e.g., chronic myelomonocytic leukemia or acute myeloid leukemia), colon cancer (e.g., colon carcinoma), melanoma (e.g., cutaneous or desmoplastic malignant melanomas), prostate cancer, renal cancer (e.g., renal cell carcinoma), and head and neck tumors, neuroblastoma, ganglioneuroma (e.g., ganglioneuroma of the mouth or gut), colon cancer (e.g., sporadic colon cancers), MEN2A (multiple endocrine neoplasia type 2A), or MEN2B (multiple endocrine neoplasia type 2B). In one aspect, the MEN2A is characterized by MTC and includes adrenal tumor pheochromocytoma. Substitutions of cysteines in RET are found in subjects with MEN2A and also frequent in FMTC. RET extracellular domain exon 8 mutations, such as G533C) or the RET intracellular domain (residues E768, L790, Y791, V804, and S891) are associated with FMTC or MEN2A. Substitutions in the RET kinase domain, Met918 to Thr (M918T) or A883F are found in subjects with MEN2B. RET M918T and RET A883F are also found in sporadic MTC.

[00145] The compounds can also be used to treat a patient who has developed resistance to a wild-type RET inhibitor, or a patient with a particular RET mutant. The

method includes the step of administering a compound or composition of the disclosure that is active against one or more RET resistant mutants. In certain embodiments, the RET resistant mutant is selected from V804L, V804M, V804E, Y806C, Y806S, Y806N, Y806H, G810R, G810S, L865V, L870F, S891A and M918T. By“active” is meant that a compound has an IC₅₀ of less than 1 µM, 500 nM, 250 nM, 100 nM, 75 nM, 50 nM, 25 nM, 10 nM, or 5 nM when measured in a biochemical assay, against at least one resistant mutant.

[00146] In some embodiments, the cancer is a solid tumor. In some embodiments, the condition associated with aberrant RET activity is a thyroid cancer (e.g., papillary thyroid carcinoma, thyroid adenocarcinoma, or MTC, e.g., familial MTC), lung cancer (e.g., lung adenocarcinoma, small-cell lung carcinoma, or non-small cell lung carcinoma), breast cancer (e.g., estrogen receptor-positive tumors and endocrine- resistant tumors e.g., resistant to oestrogen modulators such as tamoxifen, agents that block oestrogen biosynthesis such as aromatase inhibitors, and oestrogen receptor antagonists such as fulvestrant), pancreatic cancer (e.g., carcinoma of the pancreas or pancreatic ductal carcinoma), haematopoietic cancer, e.g., a leukemia (e.g., chronic myelomonocytic leukemia or acute myeloid leukemia), colon cancer (e.g., colon carcinoma), melanoma (e.g., cutaneous or desmoplastic malignant melanomas), prostate cancer, renal cancer (e.g., renal cell carcinoma), and head and neck tumors,

neuroblastoma, ganglioneuroma (e.g., ganglioneuroma of the mouth or gut), colon cancer (e.g., sporadic colon cancers), MEN2A (multiple endocrine neoplasia type 2A), or MEN2B (multiple endocrine neoplasia type 2B). In one aspect, the MEN2A is characterized by MTC and includes adrenal tumor pheochromocytoma. Substitutions of cysteines in RET are found in subjects with MEN2A and also frequent in FMTC. RET extracellular domain exon 8 mutations, such as G533C) or the RET intracellular domain (residues E768, L790, Y791, V804, and S891) are associated with FMTC or MEN2A. Substitutions in the RET kinase domain, Met918 to Thr (M918T) or A883F are found in subjects with MEN2B. RET M918T and RET A883F are also found in sporadic MTC.

[00147] The compounds may also be used to treat a subject having a RET-altered cell, cancer, gene, or gene product. The RET alteration may be, e.g., a point mutation, insertion, deletion, amplification, or fusion, or a combination thereof.

[00148] The compounds may also be used to treat a subject having a RET-altered cell, cancer, gene, or gene product comprising a RET alteration described in Table 3 or Table 4 herein. In some embodiments, the subject has a fusion between RET and a RET fusion partner listed in Table 3, e.g., comprises a fusion protein that comprises RET or a fragment thereof and a protein of Table 3 or fragment thereof. In some embodiments, the fusion partner is N-terminal or C-terminal of RET. In some embodiments, the subject has an alteration at a position in RET that is described in Table 4. In some embodiments, a subset of the subject’s cells, e.g., a subset of the subject’s tumor cells, comprise the RET alteration. In some embodiments, a subset of the subject’s cells, e.g., a subset of the subject’s tumor cells, are RET-altered. In some embodiments, the subject has a cancer listed in Table 3, e.g., the subject has both a RET mutation and a cancer listed in Table 3.

Table 3. RET fusions

Table 4. RET mutations

[00149] RET has two primary protein and mRNA isoforms, named RET51 and RET9. In some embodiments, RET has a sequence of isoform RET51 (SEQ ID NO: 1). The kinase domain corresponds to amino acids 724-1016 of SEQ ID NO: 1.

[00150] In some embodiments, RET has a sequence of isoform RET9 (SEQ ID NO: 2).

[00151] In some embodiments, RET51 is encoded by a nucleic acid having the sequence of SEQ ID NO: 3.

[00152] In some embodiments, RET9 is encoded by a nucleic acid having the sequence of SEQ ID NO: 4.

[00153] The compounds and compositions described herein can be administered alone or in combination with other compounds, including other RET-modulating compounds, or other therapeutic agents. In some embodiments, the compound or composition of the disclosure may be administered in combination with one or more compounds selected from cabozantinib (COMETRIQ), vandetanib (CALPRESA), sorafenib (NEXAVAR), sunitinib (SUTENT), regorafenib (STAVARGA), ponatinib (ICLUSIG), bevacizumab (AVASTIN), crizotinib (XALKORI), or gefitinib (IRESSA). The compound or composition of the disclosure may be administered simultaneously or sequentially with the other therapeutic agent by the same of different routes of administration. The compound of the disclosure may be included in a single formulation with the other therapeutic agent or in separate formulations.

Synthesis

[00154] Compounds of the disclosure, including salts and N -oxides thereof, can be prepared using known organic synthesis techniques and can be synthesized according to any of numerous possible synthetic routes, such as those in the Schemes below. The

reactions for preparing compounds of the disclosure can be carried out in suitable solvents which can be readily selected by one of skill in the art of organic synthesis. Suitable solvents can be substantially non-reactive with the starting materials

(reactants), the intermediates, or products at the temperatures at which the reactions are carried out, e.g., temperatures which can range from the solvent’s freezing temperature to the solvent’s boiling temperature. A given reaction can be carried out in one solvent or a mixture of more than one solvent. Depending on the particular reaction step, suitable solvents for a particular reaction step can be selected by the skilled artisan.

[00155] Preparation of compounds of the disclosure can involve the protection and deprotection of various chemical groups. The need for protection and deprotection, and the selection of appropriate protecting groups, can be readily determined by one skilled in the art. The chemistry of protecting groups can be found, for example, in Wuts and Greene, Protective Groups in Organic Synthesis, 4th ed., John Wiley & Sons: New Jersey, (2006), which is incorporated herein by reference in its entirety.

[00156] Reactions can be monitored according to any suitable method known in the art. For example, product formation can be monitored by spectroscopic means, such as nuclear magnetic resonance (NMR) spectroscopy (e.g., ¹H or ¹³C), infrared (IR) spectroscopy, spectrophotometry (e.g., UV-visible), mass spectrometry (MS), or by chromatographic methods such as high performance liquid chromatography (HPLC) or thin layer chromatography (TLC).Analytical instruments and methods for compound characterization:

[00157] LC-MS: Unless otherwise indicated, all liquid chromatography-mass spectrometry (LC-MS) data (sample analyzed for purity and identity) were obtained with an Agilent model-1260 LC system using an Agilent model 6120 mass spectrometer utilizing ES-API ionization fitted with an Agilent Poroshel 120 (EC-C18, 2.7um particle size, 3.0 x 50mm dimensions) reverse-phase column at 22.4 degrees Celsius. The mobile phase consisted of a mixture of solvent 0.1% formic acid in water and 0.1% formic acid in acetonitrile. A constant gradient from 95% aqueous/5% organic to 5% aqueous/95% organic mobile phase over the course of 4 minutes was utilized. The flow rate was constant at 1mL/min.

[00158] Prep LC-MS: Preparative HPLC was performed on a Shimadzu Discovery VP® Preparative system fitted with a Luna 5u C18(2) 100A, AXIA packed, 250 x 21.2 mm reverse-phase column at 22.4 degrees Celsius. The mobile phase consisted of a mixture of solvent 0.1% formic acid in water and 0.1% formic acid in acetonitrile. A constant gradient from 95% aqueous/5% organic to 5% aqueous/95% organic mobile phase over the course of 25 minutes was utilized. The flow rate was constant at 20 mL/min. Reactions carried out in a microwave were done so in a Biotage Initiator microwave unit.

[00159] Silica gel chromatography: Silica gel chromatography was performed on either a Teledyne Isco CombiFlash® Rf unit or a Biotage® Isolera Four unit.

[00160] Proton NMR: Unless otherwise indicated, all ¹H NMR spectra were obtained with a Varian 400MHz Unity Inova 400 MHz NMR instrument (acquisition time = 3.5 seconds with a 1 second delay; 16 to 64 scans). Where characterized, all protons were reported in DMSO-d6 solvent as parts-per million (ppm) with respect to residual DMSO (2.50 ppm). EXAMPLES

[00161] The following examples are intended to be illustrative, and are not meant in any way to be limiting.

[00162] The below Synthetic Protocols and specific synthesis examples are meant to provide general guidance in connection with preparing the compounds of the disclosure. One skilled in the art would understand that the preparations shown in the Synthetic Protocols and specific examples can be modified or optimized using general knowledge of organic chemistry to prepare various compounds of the disclosure.

[00163] In general, the compounds of this disclosure were prepared using one of the following five Synthetic Protocols.

Synthetic Protocol 1:

[00164] A heteroaryl dihalide can be coupled to an amino pyrazole under nucleophilic aromatic substitution reaction conditions using a base such as diisopropylethylamine (DIPEA) or triethylamine (TEA) in a polar solvent to provide the bicyclic ring system. The bicyclic heteroaryl halide can then undergo an SnAr reaction with an amino ester or amino acid intermediate to give a tricyclic ring system. The amino ester or amino acid intermediates are either commercially available or prepared as described in“Synthesis of Heterocycle Intermediates”. When an amino acid is used, the tricyclic acid product can then be coupled to a variety amines under amide coupling reaction conditions to give the final product examples. The amines are either commercially available, or could be prepared as described below under the heading“Synthesis of Amine Intermediates”. Alternatively, if an amino ester was used in the SnAr reaction, the tricyclic ester is hydrolyzed under basic, acidic, or other conditions to give the tricyclic acid

intermediate. The tricyclic acid intermediate can be coupled to an amine as described above to then give the final compound.

Synthetic Protocol 2:

[00165] A heteroaryl dihalide can be coupled to an amino ester (either commercially available or prepared as described in“Synthesis of Heterocycle Intermediates”) under SnAr conditions, using a base such as DIPEA, TEA, Cs₂CO₃, CsF, Na₂CO₃, or other bases. The resulting bicyclic heteroaryl halide can then be coupled with an amino pyrazole under nucleophilic aromatic substitution reaction conditions or palladium mediated coupling conditions. The tricyclic ester can then be hydrolyzed under basic, acidic, or other conditions to give a tricyclic acid intermediate. The final compound examples are then prepared by an amide coupling reaction with the tricyclic acid and an amine. The amines could be commercially available, or could be prepared as described below under the heading“Synthesis of Amine Intermediates”.

Synthetic Protocol 3:

[00166] An N-protected amino acid intermediate can be coupled to an amine using amide coupling reaction conditions. The protected amino acid intermediate starting material used above could be commercially available, or prepared as described in “Synthesis of Heterocycle Intermediates” below. The protecting group can be benzyl, tert-butoxycarbonyl, or others. The amines used in the amide coupling are either commercially available, or could be prepared as described below under the heading “Synthesis of Amine Intermediates”. The protecting group is then removed under typical deprotection conditions to give an amino amide intermediate. The amino amide intermediate is then coupled to a bicyclic heteroaryl halide under SnAr conditions, using a base such as DIPEA, TEA, Cs₂CO₃, CsF, Na₂CO₃, or other bases, to give the final compound. In some instances, a palladium mediated coupling reaction could be used instead of a SnAr reaction.

Synthetic Protocol 4:

[00167] An N-protected amino acid intermediate can be coupled to an amine using amide coupling reaction conditions. The protected amino acid intermediate starting material used above could be commercially available, or prepared as described in “Synthesis of Heterocycle Intermediates” below. The protecting group can be benzyl, tert-butoxycarbonyl, or others. The amines used in the amide coupling are either commercially available, or could be prepared as described below under the heading “Synthesis of Amine Intermediates”. The protecting group is then removed under typical deprotection conditions to give an amino amide intermediate. The amino amide intermediate is then coupled to a heteroaryl dihalide under SnAr conditions, using a base such as DIPEA, TEA, Cs₂CO₃, CsF, Na₂CO₃, or other bases, to give a heteroaryl halide. The heteroaryl halide is then coupled to an amino pyrazole intermediate under SnAr or palladium mediated coupling conditions to give the final compound.

Synthetic Protocol 5:

[00168] An amino acid intermediate can be coupled to a heteroaryl dihalide under SnAr conditions using DIPEA, TEA, Cs₂CO₃, CsF, Na₂CO₃, or other bases. The resulting acid intermediate can then be coupled to an amine using amide coupling reaction conditions. The amines used in the amide coupling are either commercially available, or could be prepared as described below under the heading“Synthesis of Amine Intermediates”. The amide product, which contains a heteroaryl halide group, is then coupled to an aminopyrazole intermediate under palladium mediated coupling conditions to give the final compound.

[00169] Example 1. Synthesis of Compound 161

[00170] Step 1: Synthesis of 2-chloro-6-methyl-N-(5-methyl-1H-pyrazol-3- yl)pyrimidin-4-amine

[00171] A suspension of 2,4-dichloro-6-methyl-pyrimidine (120.00 g, 736.2 mmol, 1.00 eq) , 5-methyl-1H-pyrazol-3-amine (78.65 g, 0.81 mol, 1.10 eq) and DIPEA (142.72 g, 1.10 mol, 1.50 eq) in DMSO (400 mL) was heated at 60 °C for 16 hrs. TLC (PE/EA, 5:1, 1:1) showed the reaction was complete. The reaction mixture was cooled to 30 °C and poured into ice-water (800 mL). The resulting mixture was extracted with MTBE (800 mL x 10). The combined organic layers were washed with water (400 mL x 3), brine (400 mL x 3) and dried over Na₂SO₄. After filtration, the filtrate was concentrated under reduced pressure and the residue was recrystallized from DCM (10 mL/g) to afford 2-chloro-6-methyl-N-(5-methyl-1H-pyrazol-3-yl)pyrimidin-4-amine (105.60 g, 472.14 mmol, 64%) as a yellow solid. The structure was confirmed by LC- MS and NMR.

[00172] Step 2: Synthesis of 4-methoxy-1-(4-methyl-6-((5-methyl-1H-pyrazol-3- yl)amino)pyrimidin-2-yl)piperidine-4-carboxylic acid

[00173] A mixture of 4-methoxypiperidine-4-carboxylic acid (214 mg, 1.34 mmol), 2- chloro-6-methyl-N-(5-methyl-1H-pyrazol-3-yl)pyrimidin-4-amine (300 mg, 1.34 mmol) and DIPEA (520 mg, 4.02 mmol) in 2-propanol (3 mL) was heated to 150 °C in a microwave reactor. The reaction mixture was stirred for 50 min, and then was cooled to ambient temperature. The reaction mixture was concentrated and the residue was purified by column chromatography on silica gel (gradient elution, 0 to 10% methanol- DCM) to give 4-methoxy-1-(4-methyl-6-((5-methyl-1H-pyrazol-3-yl)amino)pyrimidin- 2-yl)piperidine-4-carboxylic acid (435 mg, 94%). MS (ES+) C₁₆H₂₂N6O₃ requires: 346, found: 347 [M+H]⁺.

[00174] Step 3: Synthesis of N-((6-(1H-pyrazol-1-yl)pyridin-3-yl)methyl)-4- methoxy-1-(4-methyl-6-((5-methyl-1H-pyrazol-3-yl)amino)pyrimidin-2- yl)piperidine-4-carboxamide

[00175] HBTU (220 mg, 0.577 mmol) was added to a mixture of 4-methoxy-1-(4- methyl-6-((5-methyl-1H-pyrazol-3-yl)amino)pyrimidin-2-yl)piperidine-4-carboxylic acid (100 mg, 0.289 mmol), (6-(1H-pyrazol-1-yl)pyridin-3-yl)methanamine (50 mg, 0.289 mmol) and DIPEA (112 mg, 0.866 mmol) in DMF (3.0 mL) at ambient temperature. The reaction mixture was stirred for 16 h, and then was partitioned between dichloromethane and water. The dichloromethane layer was washed with saturated aqueous sodium chloride solution, dried over sodium sulfate, filtered, and concentrated. The residue was purified by column chromatography on silica gel (gradient elution, 0 to 10% methanol-DCM) to give the title compound (35 mg, 24%) as a white solid.

[00176] Example 2. Synthesis of Compound 166

[00177] Step 1: Synthesis of methyl 3-ethyl-1-(4-methyl-6-((5-methyl-1H-pyrazol- 3-yl)amino)pyrimidin-2-yl)azetidine-3-carboxylate

[00178] A solution of methyl 3-ethylazetidine-3-carboxylate (50 mg, 0.40 mmol), 2- chloro-6-methyl-N-(5-methyl-1H-pyrazol-3-yl)pyrimidin-4-amine (78 mg, 0.40 mmol) and DIPEA (150 mg, 1.20 mmol) in isoamyl alcohol (0.5 mL) was stirred at 150 °C for 5 h. The reaction mixture was then cooled to ambient temperature and concentrate to give a residue (85 mg) which was used in the next step without further purification. Step 2: Synthesis of 3-ethyl-1-(4-methyl-6-((5-methyl-1H-pyrazol-3- yl)amino)pyrimidin-2-yl)azetidine-3-carboxylic acid

[00179] LiOH (380 mg, 9.00 mmol) was added to a solution of methyl 3-ethyl-1-(4- methyl-6-((5-methyl-1H-pyrazol-3-yl)amino)pyrimidin-2-yl)azetidine-3-carboxylate (600 mg, 1.80 mmol) in methanol (4 mL), THF (4 mL) and water (4 mL) at ambient temperature. The reaction mixture was stirred for 4 h, and then was concentrated. The residue was dissolved in DMSO and purified by reverse-phase HPLC (ACN/H2O gradient elution with 0.1% TFA) to give 3-ethyl-1-(4-methyl-6-((5-methyl-1H-pyrazol- 3-yl)amino)pyrimidin-2-yl)azetidine-3-carboxylic acid (550 mg).

[00180] Step 3: Synthesis of (S)-3-ethyl-N-(1-(6-(4-fluoro-1H-pyrazol-1- yl)pyridin-3-yl)ethyl)-1-(4-methyl-6-((5-methyl-1H-pyrazol-3-yl)amino)pyrimidin- 2-yl)azetidine-3-carboxamide

[00181] A mixture of 3-ethyl-1-(4-methyl-6-((5-methyl-1H-pyrazol-3- yl)amino)pyrimidin-2-yl)azetidine-3-carboxylic acid (67 mg, 0.21 mmol), (S)-1-(6-(4- fluoro-1H-pyrazol-1-yl)pyridin-3-yl)ethanamine hydrochloride (51 mg, 0.21 mmol), HBTU (80 mg, 0.21 mmol) and NMM (64 mg, 0.63 mmol) in DMF (2 mL) was stirred at 25 °C for 1 h. The solution was purified by preparative HPLC to give the title product (71 mg, 66%) as a white solid.

[00182] Example 3. Synthesis of Compound 107

[00183] Step 1: Synthesis of methyl 1-(6-bromo-4-methylpyridin-2-yl)-3- methylazetidine-3-carboxylate

[00184] A mixture of 2-bromo-6-fluoro-4-methylpyridine (500 mg, 2.63 mmol), methyl 3-methylazetidine-3-carboxylate (480 mg, 2.63 mmol), Na₂CO3 (840 mg, 7.89 mmol), and isoamyl alcohol (0.5 mL) was heated to 140 °C for 8 h. The reaction mixture was then cooled to ambient temperature, and methanol (15 mL) was added. The mixture was filtered, and the filtrate was concentrated to give methyl 1-(6-bromo-4- methylpyridin-2-yl)-3-methylazetidine-3-carboxylate (700 mg) which was used in the next step without further purification.

[00185] Step 2: Synthesis of methyl 3-methyl-1-(4-methyl-6-((5-methyl-1H- pyrazol-3-yl)amino)pyridin-2-yl)azetidine-3-carboxylate

[00186] A mixture of methyl 1-(6-bromo-4-methylpyridin-2-yl)-3- methylazetidine-3-carboxylate (400 mg, 1.27 mmol), 5-methyl-1H-pyrazol-3-amine (119 mg, 1.52 mmol), Pd₂(dba)₃ (116 mg, 0.127 mmol), Xantphos (147 mg, 0.254 mmol) and KOAc (373 mg, 3.810 mmol) in 1,4-dioxane (15 mL) under nitrogen was stirred at 100 °C for 8 h. The mixture was cooled to ambient temperature and partitioned between ethyl acetate and water. The organic layer was washed with saturated aqueous sodium chloride solution, and the washed solution was dried over sodium sulfate. The dried solution was filtered, and the filtrate was concentrated to afford methyl 3-methyl- 1-(4-methyl-6-((5-methyl-1H-pyrazol-3-yl)amino)pyridin-2-yl)azetidine-3-carboxylate (700 mg), which was used in the next step without further purification.

[00187] Steps 3-4: Synthesis of N-((6-(1H-pyrazol-1-yl)pyridin-3-yl)methyl)-3- methyl-1-(4-methyl-6-((5-methyl-1H-pyrazol-3-yl)amino)pyridin-2-yl)azetidine-3- carboxamide

[00188] The title compound was prepared from of methyl 3-methyl-1-(4-methyl-6- ((5-methyl-1H-pyrazol-3-yl)amino)pyridin-2-yl)azetidine-3-carboxylate using the same

two-step procedure (hydrolysis and amide coupling) as in Synthetic Protocol 1 to give a white solid.

[00189] Example 4. Synthesis of Compound 136

[00190] Step 1: Synthesis of N-((6-(1H-pyrazol-1-yl)pyridin-3-yl)methyl)-1- benzyl-4-hydroxypiperidine-4-carboxamide

[00191] A mixture of 1-benzyl-4-hydroxypiperidine-4-carboxylic acid (436 mg, 1.85 mmol), (6-(1H-pyrazol-1-yl)pyridin-3-yl)methanamine (0.323 g, 1.85 mmol), HATU (1.05 g, 2.78 mmol) and DIPEA (717 mg, 5.56 mmol) in DMF (20 mL) was stirred at ambient temperature for 16 h. The reaction mixture was then partitioned between ethyl acetate and water. The layers were separated, and the aqueous layer was further extracted with ethyl acetate. The organic layers were combined, and the combined layers were washed sequentially with water, brine, and then dried over sodium sulfate. The dried solution was filtered, and the filtrate was concentrated. The residue was purified by flash column chromatography on silica gel (gradient elution, 0 to 10% methanol-DCM to give N-((6-(1H-pyrazol-1-yl)pyridin-3-yl)methyl)-1-benzyl-4- hydroxypiperidine-4-carboxamide (218 mg, yield 30%) as a yellow solid. MS (ES+) C₂₂H₂₅N₅O₂ requires: 391, found 392 [M+H]⁺.

[00192] Step 2: Synthesis of N-((6-(1H-pyrazol-1-yl)pyridin-3-yl)methyl)-4- hydroxypiperidine-4-carboxamide

[00193] To a solution of N-((6-(1H-pyrazol-1-yl)pyridin-3-yl)methyl)-1-benzyl-4- hydroxypiperidine-4-carboxamide (200 mg, 0.510 mmol) in MeOH (5 mL) was added Pd/C (1-% by weight, 100 mg) under N₂. The resulting suspension was evacuated and refilled with hydrogen three times and stirred at ambient temperature for 16 h under hydrogen. The reaction mixture was then filtered through celite, and the filtrate was concentrated to give N-((6-(1H-pyrazol-1-yl)pyridin-3-yl)methyl)-4-hydroxypiperidine- 4-carboxamide (150 mg), which was used in the next step without purification. MS (ES+) C₁₆H₂₀N₄O₂ requires: 300, found: 301 [M+H]⁺.

[00194] Step 3: Synthesis of N-((6-(1H-pyrazol-1-yl)pyridin-3-yl)methyl)-4- hydroxy-1-(4-methyl-6-(3-methyl-1H-pyrazol-5-ylamino)pyrimidin-2- yl)piperidine-4-carboxamide

[00195] A mixture of N-((6-(1H-pyrazol-1-yl)pyridin-3-yl)methyl)-4- hydroxypiperidine-4-carboxamide (100 mg, 0.33 mmol), 2-chloro-6-methyl-N-(3- methyl-1H-pyrazol-5-yl)pyrimidin-4-amine (70 mg, 0.33 mmol) and K₂CO₃ (96 mg , 0.70 mmol) in DMF (10 mL) was heated to 80 °C for 16 h. The mixture was slowly poured into ice water and extracted with ethyl acetate (3x). The combined organic layers were washed sequentially with water, brine, and then dried over sodium sulfate. The dried solution was filtered, and the filtrate was concentrated. The residue was purified by flash column chromatography on silica gel (gradient elution, 0 to 10% methanol- DCM to afford the title compound (100 mg, yield 62%) as a yellow solid.

[00196] Example 5. Synthesis of Compound 160

[00197] Step 1: Synthesis of tert-butyl 4-((6-(1H-pyrazol-1-yl)pyridin-3- yl)methylcarbamoyl)-4-methoxypiperidine-1-carboxylate

[00198] To a solution of 1-(tert-butoxycarbonyl)-4-methoxypiperidine-4-carboxylic acid (200 mg, 0.771 mmol), (6-(1H-pyrazol-1-yl)pyridin-3-yl)methanamine (148 mg, 0.848 mmol) and DIPEA (298 mg, 2.31 mmol) in THF (10 mL) was added HATU (293 mg, 0.770 mmol) at ambient temperature. The solution was stirred at ambient temperature for 18 h, and then was concentrated. The residue was purified by flash column chromatography on silica gel (gradient elution, 0 to 10% methanol-DCM) to give tert-butyl 4-((6-(1H-pyrazol-1-yl)pyridin-3-yl)methylcarbamoyl)-4- methoxypiperidine-1-carboxylate (300 mg, yield 94%) as a yellow oil. MS (ES+) C₂₁H₂₉N₅O₄ requires: 415 found: 416 [M+H]⁺.

[00199] Step 2: Synthesis of N-((6-(1H-pyrazol-1-yl)pyridin-3-yl)methyl)-4- methoxypiperidine-4-carboxamide hydrochloride

[00200] To a solution of tert-butyl 4-(((6-(1H-pyrazol-1-yl)pyridin-3- yl)methyl)carbamoyl)-4-methoxypiperidine-1-carboxylate (340 mg, 0.818 mmol) in dioxane (5 mL) was added HCl (4 M in dioxane, 5 mL) at ambient temperature. The solution was stirred at ambient temperature for 18 h, and was then concentrated to give N-((6-(1H-pyrazol-1-yl)pyridin-3-yl)methyl)-4-methoxypiperidine-4-carboxamide hydrochloride (250 mg) as a white solid that was used without further purification. MS (ES+) C₁₆H₂₂ClN₅O₂ requires: 351 found: 316 [M+H]⁺.

[00201] Step 3: Synthesis N-((6-(1H-pyrazol-1-yl)pyridin-3-yl)methyl)-1-(6- bromo-4-methylpyridin-2-yl)-4-methoxypiperidine-4-carboxamide

[00202] A mixture of N-((6-(1H-pyrazol-1-yl)pyridin-3-yl)methyl)-4- methoxypiperidine-4-carboxamide hydrochloride (280 mg, crude), 2-bromo-6-fluoro-4- methylpyridine (181 mg, 0.96 mmol) and DIPEA (373 mg, 2.88 mmol) in IPA (20 mL) was stirred at 100 °C for 60 h. The reaction mixture was then cooled to ambient temperature and concentrated. The residue was purified by flash column

chromatography on silica gel (isocratic elution, 1:15 methanol-DCM) to give the N-((6- (1H-pyrazol-1-yl)pyridin-3-yl)methyl)-1-(6-bromo-4-methylpyridin-2-yl)-4- methoxypiperidine-4-carboxamide (180 mg, yield 47%) as a yellow solid. MS (ES+) C₂₂H₂₅BrN₆O₂ requires: 484, 486 found: 485, 487 [M+H]⁺.

[00203] Step 4: Synthesis N-((6-(1H-pyrazol-1-yl)pyridin-3-yl)methyl)-4- methoxy-1-(4-methyl-6-(3-methyl-1H-pyrazol-5-ylamino)pyridin-2-yl)piperidine-4- carboxamide

[00204] A mixture of N-((6-(1H-pyrazol-1-yl)pyridin-3-yl)methyl)-1-(6-bromo-4- methylpyridin-2-yl)-4-methoxypiperidine-4-carboxamide (80 mg, 0.164 mmol), 3- methyl-1H-pyrazol-5-amine (47.7 mg, 0.492 mmol), Pd₂(dba)₃ (30 mg, 0.033 mmol), t- Bu-XPhos (27.8 mg, 0.0656 mmol) and KOAc (64.1 mg, 0.655 mmol) in toluene (2 mL) was stirred at 120 °C under microwave irradiation for 2 h. The reaction mixture

was then cooled to ambient temperature, filtered, and concentrated. The residue was purified by flash column chromatography on silica gel (isocratic elution, 1:30 methanol- DCM). The compound was then further purified by reverse-phase HPLC (ACN/H2O gradient elution with 0.1% TFA) to give the title compound (30 mg, yield 37%) as a tan solid.

[00205] Example 6. Synthesis of Compound 194

[00206] Step 1: Synthesis of 1-(6-bromo-4-methylpyridin-2-yl)-3-ethoxyazetidine- 3-carboxylic acid

[00207] A mixture of 2-bromo-6-fluoro-4-methylpyridine (493 mg, 2.59 mmol), 3- ethoxyazetidine-3-carboxylic acid hydrochloride (471 mg, 2.59 mmol), DIPEA (3.17 mL, 18.2 mmol), in ethanol (4.30 mL) was heated to 100 °C for 18 h. The reaction mixture was then concentrated and used in the next step without any further

purification. MS (ES+)

requires: 314 found: 315 [M+H]⁺.

[00208] Step 2: Synthesis of (S)-1-(6-bromo-4-methylpyridin-2-yl)-3-ethoxy-N-(1- (6-(4-fluoro-1H-pyrazol-1-yl)pyridin-3-yl)ethyl)azetidine-3-carboxamide

[00209] HATU (855 mg, 2.25 mmol) was added to a mixture of 1-(6-bromo-4- methylpyridin-2-yl)-3-ethoxyazetidine-3-carboxylic acid (590 mg, 1.88 mmol), (S)-1-

(6-(4-fluoro-1H-pyrazol-1-yl)pyridin-3-yl)ethanamine hydrochloride (550 mg, 2.27 mmol), and DIPEA (1.96 mL, 11.3 mmol) in DMF (4.7 mL) at 20 °C. The reaction mixture was stirred for 5 min, and then was treated with aqueous sodium hydroxide solution (5 M, 20 mL). After stirring for an additional 20 min, the mixture was filtered, and the solid was purified by flash-column chromatography on silica gel (gradient elution, 0 to 10% methanol-DCM) to give (S)-1-(6-bromo-4-methylpyridin-2-yl)-3- ethoxy-N-(1-(6-(4-fluoro-1H-pyrazol-1-yl)pyridin-3-yl)ethyl)azetidine-3-carboxamide (980 mg, 100%) as a yellow solid. MS (ES+) C₂₂H₂₄BrFN₆O₂ requires: 502 found: 3503 [M+H]⁺.

[00210] Step 3: Synthesis of (S)-3-ethoxy-N-(1-(6-(4-fluoro-1H-pyrazol-1- yl)pyridin-3-yl)ethyl)-1-(4-methyl-6-((5-methyl-1H-pyrazol-3-yl)amino)pyridin-2- yl)azetidine-3-carboxamide

[00211] A mixture of (S)-1-(6-bromo-4-methylpyridin-2-yl)-3-ethoxy-N-(1-(6-(4- fluoro-1H-pyrazol-1-yl)pyridin-3-yl)ethyl)azetidine-3-carboxamide (432 mg, 0.824 mmol), 3-methyl-1H-pyrazol-5-amine (280 mg, 2.88 mmol), Pd₂(dba)₃ (38 mg, 0.041 mmol), t-Bu-XPhos (70 mg, 0.17 mmol) and sodium tert-butoxide (317 mg, 3.30 mmol) in toluene (2.7 mL) was stirred at 115 °C for 15 min. The reaction mixture was then cooled to ambient temperature, loaded onto silica gel, and purified by flash column chromatography on silica gel (gradient elution, 0 to 10% methanol-DCM) to give the title compound (94 mg, 21%) as a light-pink solid.

[00212] Example 7. Synthesis of Heterocycle Intermediates

A. Ethyl 3-methoxy-2-methylazetidine-3-carboxylate

[00213] Step 1: Synthesis of 1-(tert-butoxycarbonyl)-3-methoxy-2- methylazetidine-3-carboxylic acid

[00214] To a mixture of tert-butyl 2-methyl-3-oxoazetidine-1-carboxylate (360 mg, 1.94 mmol), bromoform (1.36 mL) in methanol (8 mL) was added potassium hydroxide (872 mg, 15.6 mmol) at 0 °C. The cooling bath was removed, and the reaction mixture was stirred at 20 °C for 16 h. The residue was then concentrated to afford 1-(tert- butoxycarbonyl)-3-methoxy-2-methylazetidine-3-carboxylic acid (500 mg, crude) as white solid which was used in the next step without further purification.

[00215] Step 2: Synthesis of 1-(tert-butyl) 3-ethyl 3-methoxy-2-methylazetidine- 1,3-dicarboxylate

[00216] To a mixture of afford 1-(tert-butoxycarbonyl)-3-methoxy-2-methylazetidine- 3-carboxylic acid (500 mg, crude, 1.94 mmol) in DMF (5 mL) was added iodoethane (0.400 mL) in one portion at 0°C under nitrogen. The mixture was stirred at 25 °C for 16 h. The reaction mixture was partitioned between water (20 mL) and EtOAc (30 mL). The organic phase was separated, washed with water (20 mL), dried over sodium sulfate, filtered, and concentrated. The residue was purified by column chromatography on silica gel (gradient elution, 5 to 20% ethyl acetate-petroleum ether) to afford 1-(tert- butyl) 3-ethyl 3-methoxy-2-methylazetidine-1,3-dicarboxylate (300 mg) as yellow oil.

[00217] Step 3: Synthesis of ethyl 3-methoxy-2-methylazetidine-3-carboxylate

[00218] To a solution of 1-(tert-butyl) 3-ethyl 3-methoxy-2-methylazetidine-1,3- dicarboxylate (300 mg, 1.10 mmol) in CHCl₃ (10 mL) was added TMSI (440 mg, 2.20

mmol). The mixture was stirred at 25 °C for 1 h. The reaction mixture was then concentrated to give a yellow oil which was used directly in the synthetic protocols 1 or 2 as a heterocycle intermediate.

B. Ethyl 3-hydroxypiperidine-4-carboxylate

Step 1: Synthesis of ethyl 1-benzyl-3-hydroxypiperidine-4-carboxylate

[00219] Ethyl 1-benzyl-3-oxopiperidine-4-carboxylate hydrochloride (1.06 g, 3.56 mmol) in MeOH (18 mL) was treated with sodium borohydride (0.457 g, 12.1 mmol) at 20 °C. The reaction mixture was stirred for 20 min, and then additional sodium borohydride (0.220 g, 5.82 mmol) was added. After stirring for 20 min, a third portion of sodium borohydride (0.054 g, 1.4 mmol) was added, and the resulting mixture stirred for an additional 20 min. Water was then added to the reaction mixture, and the MeOH removed in vacuo. The aqueous mixture was extracted with ethyl acetate (3x), and the combined organic extracts were washed with brine. The washed organic layer was dried over sodium sulfate, filtered and concentrated in vacuo to give a mixture of ethyl and methyl 1-benzyl-3-hydroxypiperidine-4-carboxylate (0.67 g). Ethyl ester: MS (ES+) C₁₅H₂₁NO₃ requires: 263, found: 264 [M + H]⁺. Methyl ester: MS (ES+) C₁₄H₂₉NO₃ requires: 249, found: 250 [M + H]⁺.

[00220] Step 2: Synthesis of Ethyl 3-hydroxypiperidine-4-carboxylate

[00221] A mixture of ethyl and methyl 1-benzyl-3-hydroxypiperidine-4-carboxylate (0.667 g) and Pd(OH)₂/C (50 mg, 0.071 mmol) were stirred in MeOH (15 mL) under a balloon of H₂ at 20 °C for 18 hours. The reaction mixture was filtered through celite, rinsing with methanol, and the filtrate was concentrated to give a mixture of ethyl and methyl 3-hydroxypiperidine-4-carboxylate (0.405 g) as a pale yellow gum. The crude product was used directly in synthetic protocols 1 or 2 as a heterocycle intermediate.

[00222] Example 8. Synthesis of Amine Intermediates

(S)-1-(6-(4-fluoro-1H-pyrazol-1-yl)pyridin-3-yl)ethan-1-amine

[00223] Step 1: 1-(6-(4-fluoro-1H-pyrazol-1-yl)pyridin-3-yl)ethan-1-one

[00224] 4-Fluoro-1H-pyrazole (4.73 g, 55 mmol) and potassium carbonate (17.27 g, 125 mmol) were combined and stirred in N,N-dimethylformamide (41.7 mL) for 10 minutes in an open sealed tube before addition of 2-bromo-5-acetylpyridine (10 g, 50 mmol). The reaction tube was sealed and stirred 20 hours at 100°C. The reaction mixture was then cooled to room temperature and poured into water (~700 mL). The mixture was sonicated and stirred for 20 minutes. A beige solid was isolated by filtration, washed with small amounts of water, and dried to yield 1-(6-(4-fluoro-1H- pyrazol-1-yl)pyridin-3-yl)ethan-1-one (9.81 g, 96% yield). MS: M+1 = 206.0.

[00225] Step 2: (R)-N-((S)-1-(6-(4-fluoro-1H-pyrazol-1-yl)pyridin-3-yl)ethyl)-2- methylpropane-2-sulfinamide

[00226] To a stirred room temperature solution of 1-(6-(4-fluoro-1H-pyrazol-1- yl)pyridin-3-yl)ethan-1-one (9.806 g, 47.8 mmol) in THF (96 mL) was added (R)-(-)-t- Butylsulfinamide (5.79 g, 47.8 mmol) followed by titanium (IV) ethoxide (21.8 g, 96 mmol). The solution was stirred at 75°C on an oil bath for 15 hours. The reaction solution was cooled to room temperature and then to -78°C (external temperature) before the next step. To the -78°C solution was added dropwise over nearly 55 minutes L-Selectride (143 mL of 1N in THF, 143 mmol). During addition, some bubbling was observed. The reaction was then stirred after the addition was completed for 15 minutes at -78°C before warming to room temperature. LC-MS of sample taken during removal from cold bath showed reaction was completed. The reaction was cooled to -50°C and

quenched slowly with methanol (~ 10 mL), then poured into water (600 mL) and stirred. An off-white precipitate was removed by filtration, with ethyl acetate used for washes. The filtrate was diluted with ethyl acetate (800 mL), the layers were separated, and the organic layer was dried over sodium sulfate, filtered, and concentrated down. The crude was purified by silica gel chromatography to yield (R)-N-((S)-1-(6-(4-fluoro-1H- pyrazol-1-yl)pyridin-3-yl)ethyl)-2-methylpropane-2-sulfinamide (10.5 g, 99% purity, 70.3% yield) as a light yellow solid. MS: M+1 = 311.1.

[00227] Step 3: (S)-1-(6-(4-fluoro-1H-pyrazol-1-yl)pyridin-3-yl)ethan-1-amine

[00228] A solution of (R)-N-((S)-1-(6-(4-fluoro-1H-pyrazol-1-yl)pyridin-3-yl)ethyl)- 2-methylpropane-2-sulfinamide (10.53 g, 33.9 mmol)) in methanol (79 mmol) and 4N HCl/dioxane (85 mL, 339 mmol) was stirred 2.5 hours. LC-MS showed reaction was completed. The reaction solution was poured into diethyl ether (300 mL). A sticky solid was formed. The mixture was treated with ethyl acetate (200 mL) and sonicated. The solvents were decanted, and the sticky solid was treated with more ethyl acetate (~ 200 mL), sonicated and stirred. The bulk of the sticky solid was converted to a suspension. A light yellow solid was isolated by filtration, washed with smaller amounts of ethyl acetate, and dried to yield (S)-1-(6-(4-fluoro-1H-pyrazol-1-yl)pyridin-3-yl)ethan-1- amine (7.419 g, 78% yield). LC-MS confirmed desired product in high purity. MS: M+1 = 207.1.

(S)-1-(5-(4-fluoro-1H-pyrazol-1-yl)pyrazin-2-yl)ethan-1-amine

[00229] Step 1: 1-(5-(4-fluoro-1H-pyrazol-1-yl)pyrazin-2-yl)ethan-1-one

[00230] Sodium hydride (60 wt.%, 276 mg, 6.90 mmol) was added to a mixture of 1- (5-chloropyrazin-2-yl)ethanone (800 mg, 5.11 mmol) and 4-Fluoro-1H-pyrazole (484 mg, 5.62 mmol) in N,N-dimethylformamide (6.0 mL) at ambient temperature for 10

minutes. The reaction mixture was then poured into water (70 mL) and was sonicated and stirred for 20 minutes. A dark red solid was isolated by filtration, washed with small amounts of water, and dried to 1-(5-(4-fluoro-1H-pyrazol-1-yl)pyrazin-2-yl)ethan-1-one (919 mg, 95% yield). MS: M+1 = 207.

[00231] Step 2: (R)-N-((S)-1-(5-(4-fluoro-1H-pyrazol-1-yl)pyrazin-2-yl)ethyl)-2- methylpropane-2-sulfinamide

[00232] To a stirred room temperature solution of 1-(5-(4-fluoro-1H-pyrazol-1- yl)pyrazin-2-yl)ethan-1-one (4.67 g, 22.7 mmol) in THF (45 mL) was added (R)-(-)-t- Butylsulfinamide (2.75 g, 22.7 mmol) followed by titanium (IV) ethoxide (10.3 g, 45.3 mmol). The solution was stirred at 75°C on an oil bath for 20 hours. The reaction solution was cooled to room temperature and then to -78°C before the next step. To the -78°C solution was added dropwise over 50 minutes L-Selectride (50.1 mL of 1 N in THF, 50.1 mmol). During addition, some bubbling was observed. The reaction was then stirred after the addition was completed for 15 minutes at -78°C before warming to room temperature. LC-MS of sample taken during removal from cold bath showed reaction was completed. The reaction was cooled to -60°C and quenched slowly with methanol (1 mL), then poured into water (100 mL) and stirred. The mixture was filtered and the solids were washed further with ethyl acetate. The filtrate was diluted with ethyl acetate, the layers were separated, and the organic layer was dried over sodium sulfate. The dried solution was filtered, and the filtrate was concentrated. The residue was purified by flash-column chromatography (gradient elution, 0 to 100% ethyl acetate- dichloromethane) to give (R)-N-((S)-1-(5-(4-fluoro-1H-pyrazol-1-yl)pyrazin-2- yl)ethyl)-2-methylpropane-2-sulfinamide (1.04 g, 14%) as a brown solid. MS: M+1 = 312. ¹H NMR (400 MHz, DMSO-d6) δ 9.12 (d, J = 1.4 Hz, 1H), 8.73 (d, J = 4.5 Hz, 1H), 8.59 (d, J = 1.4 Hz, 1H), 8.03 (d, J = 4.1 Hz, 1H),

5.69 (d, J = 5.7 Hz, 1H), 4.62 (p, J = 6.8 Hz, 3H), 1.57 (d, J = 6.9 Hz, 3H), 1.12 (s, 9H).

[00233] Step 3: (S)-1-(5-(4-fluoro-1H-pyrazol-1-yl)pyrazin-2-yl)ethan-1-amine

[00234] A solution of (R)-N-((S)-1-(5-(4-fluoro-1H-pyrazol-1-yl)pyrazin-2-yl)ethyl)- 2-methylpropane-2-sulfinamide (1.04 g, 3.34 mmol) in methanol (7.8 mL) and 4N HCl/dioxane (8.34 mL, 33.4 mmol) was stirred for 1.5 h at ambient temperature. The reaction mixture was poured into diethyl ether (100 mL). A light beige solid was

isolated by filtration to afford (S)-1-(5-(4-fluoro-1H-pyrazol-1-yl)pyrazin-2-yl)ethan-1- amine (689 mg, 85% yield). MS: M+1 = 208.

(5-(4-fluoro-1H-pyrazol-1-yl)pyrazin-2-yl)methanamine

[00235] Step 1: 5-(4-fluoro-1H-pyrazol-1-yl)pyrazine-2-carbonitrile

[00236] To a solution of 5-chloropyrazine-2-carbonitrile (280 mg, 2.0 mmol) in DMF was added 4-fluoro-1H-pyrazole (170 mg, 2.0 mmol), and potassium acetate (395 mg, 4.0 mmol). The mixture was stirred at the 100°C for 4 hours. The reaction mixture was cooled to 20°C, poured into brine (25 mL), and extracted with ethyl acetate. The organic layer was dried over sodium sulfate, concentrated and purified by column chromatography (hexane: ethyl acetate = 5:1) to give 5-(4-fluoro-1H-pyrazol-1- yl)pyrazine-2-carbonitrile (310 mg, Yield 82%). The structure was confirmed by LC-MS.

[00237] Step 2: (5-(4-fluoro-1H-pyrazol-1-yl)pyrazin-2-yl)methanamine

[00238] A mixture of 5-(4-fluoro-1H-pyrazol-1-yl)pyrazine-2-carbonitrile (190 mg, 1.0 mmol) and NiCl₂ (12 mg, 0.1 mmol) in MeOH (5 mL) was added NaBH₄ (380 mg, 10 mmol) at 0 °C. The mixture was stirred at 0 °C for 2 hours, quenched with aqueous NH₄Cl and purified by HPLC to give (5-(4-fluoro-1H-pyrazol-1-yl)pyrazin-2- yl)methanamine (160 mg, Yield 82%). The structure was confirmed by LC-MS.

(6-(4-fluoro-1H-pyrazol-1-yl)pyridazin-3-yl)methanamine

[00239] Step 1: Synthesis of tert-butyl ((6-chloropyridazin-3-yl)methyl)carbamate

[00240] To a solution of (6-chloropyridazin-3-yl)methanamine (300 mg, 2.0 mmol) in a mixture of THF (9 mL) and water (9 mL), was added NaHCO₃ (200 mg, 2.4 mmol) and (Boc)₂O (570 mg, 2.6 mmol). The mixture was stirred at 20 °C for 2 h, and then the reaction mixture was concentrated to remove the THF. The water was extracted with DCM (2x), and the combined organic layers were dried over sodium sulfate, filtered, and concentrated to give The organic solvent was dried with anhydrous Na₂SO₄, concentrated by reduce pressure to give tert-butyl ((6-chloropyridazin-3- yl)methyl)carbamate (460 mg).

[00241] Step 2: Synthesis tert-butyl ((6-(4-fluoro-1H-pyrazol-1-yl)pyridazin-3- yl)methyl)carbamate

[00242] A mixture of tert-butyl ((6-chloropyridazin-3-yl)methyl)carbamate (300 mg, 1.2 mmol), 4-fluoro-1H-pyrazole (106 mg, 1.2 mmol) and Cs₂CO₃ (1.2 g, 3.6 mmol) in ACN (20 ml) was stirred at 80 °C for 6 h. The reaction mixture was then filtered, and the filtrate was concentrated to give tert-butyl ((6-(4-fluoro-1H-pyrazol-1-yl)pyridazin- 3-yl)methyl)carbamate (246 mg, Purity: 80%), which was used in the next step without further purification.

[00243] Step 3: Synthesis (6-(4-fluoro-1H-pyrazol-1-yl)pyridazin-3- yl)methanamine

[00244] A solution of tert-butyl ((6-(4-fluoro-1H-pyrazol-1-yl)pyridazin-3- yl)methyl)carbamate (246 mg, 0.9 mmol) in HCl (4.0 M in dioxane, 10 mL) was stirred

at 20 °C for 2 h. The reaction mixture was then concentrated to give the title compound (162 mg, Purity: 80%), which was used without further purification. MS (ES+)

C₈H₈FN₅ requires: 193, found: 194 [M + H]⁺.

(6-(3,5-dimethyl-1H-pyrazol-1-yl)pyridin-3-yl)methanamine

[00245] Step 1: 6-(3,5-Dimethyl-1H-pyrazol-1-yl)nicotinonitrile

[00246] To the solution of 6-chloronicotinonitrile (300 mg, 2.2 mmol) in DMF (10 mL), was added 3,5-dimethyl-1H-pyrazole (210 mg, 2.2 mmol ) and Cs₂CO₃ (1.4 g, 4.4 mmol). The mixture was stirred at 90°C for 16 h. Water (25 mL) was added to the reaction mixture, and the mixture was filtered. The solids were washed with water and dried under vacuum to give 6-(3,5-Dimethyl-1H-pyrazol-1-yl)nicotinonitrile (320 mg, yield 74.6%).

[00247] Step 2: tert-Butyl ((6-(3,5-dimethyl-1H-pyrazol-1-yl)pyridin-3- yl)methyl)carbamate

[00248] To 6-(3,5-Dimethyl-1H-pyrazol-1-yl)nicotinonitrile (300 mg, 1.5 mmol) in MeOH (10 mL), was added NiCl₂ (19 mg, 0.15 mmol), (Boc)₂O (654 mg, 3.0 mmol) and NaBH₄ (142 mg, 3.8 mmol). The mixture was stirred at ambient temperature for 3h. Saturated aqueous ammonium chloride solution was added and the MeOH was removed under vacuum. The aqueous suspension was then partitioned with ethyl acetate, and the layers were separated. The organic layer was washed with saturated sodium bicarbonate solution (2×50mL). The organic layer was dried with anhydrous sodium sulfate, filtered, and concentrated under vacuum to give 450 mg target compound which was used in the next step without further purification.

[00249] Step 3: 6-(3,5-Dimethyl-1H-pyrazol-1-yl)nicotinonitrile

[00250] A solution of HCl in Dioxane (4.0 M, 10 mL) was added to compound tert- Butyl ((6-(3,5-dimethyl-1H-pyrazol-1-yl)pyridin-3-yl)methyl)carbamate (450 mg). The mixture was stirred for 2h, and then was dried under reduced pressure to give the title compound (350 mg) as a light brown solid that was used without further purification.¹H NMR (400 MHz, DMSO-d6) δ 8.51 (d, J =2.1 Hz, 1H), 8.34 (s, 3H), 8.03 (dd, J = 8.5, 2.4 Hz, 1H), 7.87 (d, J = 8.5 Hz, 1H), 6.14 (s, 1H), 4.12 (q, J = 5.7 Hz, 2H), 2.59 (s, 3H), 2.21 (s, 3H).

(6-(4-chloro-1H-pyrazol-1-yl)pyridin-3-yl)methanamine

[00251] Step 1: 6-(4-Chloro-1H-pyrazol-1-yl)nicotinonitrile

[00252] To a solution of 6-chloronicotinonitrile (300 mg, 2.2 mmol) in DMF (10 mL), was added 4-chloro-1H-pyrazole (227 mg, 2.2 mmol ) and Cs₂CO₃ (1.4 g, 4.4 mmol). The mixture was stirred at 90 °C for 16 h. Water (25 mL) was added to the mixture, and the mixture was filtered. The solids were washed with water and dried under vacuum to give 6-(4-Chloro-1H-pyrazol-1-yl)nicotinonitrile (380 mg, 84%).

[00253] Step 2: tert-Butyl ((6-(4-chloro-1H-pyrazol-1-yl)pyridin-3- yl)methyl)carbamate

[00254] To 6-(4-chloro-1H-pyrazol-1-yl)nicotinonitrile (350 mg, 1.7 mmol) in MeOH (10 mL), was added NiCl₂ (19 mg, 0.17 mmol), (Boc)₂O (741 mg, 3.4 mmol) and NaBH₄ (163 mg, 4.3 mmol). The mixture was stirred at ambient temperature for 3h. Saturated aqueous ammonium chloride solution was added and the MeOH was removed under vacuum. The aqueous suspension was then partitioned with ethyl acetate, and the

layers were separated. The organic layer was washed with saturated sodium bicarbonate solution (2×50mL). The organic layer was dried with anhydrous sodium sulfate, filtered, and concentrated under vacuum to give 480 mg target compound which was used in the next step without further purification.

[00255] Step 3: (6-(4-chloro-1H-pyrazol-1-yl)pyridin-3-yl)methanamine

[00256] A solution of HCl in Dioxane (4.0 M, 10 mL) was added to tert-Butyl ((6-(4- chloro-1H-pyrazol-1-yl)pyridin-3-yl)methyl)carbamate (450 mg, 1.5 mmol) at ambient temperature. The mixture was stirred for 2 h, and then was dried under reduced pressure to give the title compound (290 mg) as a light brown solid that was used without further purification. MS: M+1 = 209.

(6-(3-(difluoromethyl)-1H-pyrazol-1-yl)pyridin-3-yl)methanamine

[00257] Step 1: 6-(3-formyl-1H-pyrazol-1-yl)nicotinonitrile

[00258] To a solution of 1H-pyrazole-3-carbaldehyde (72 mg, 0.75 mmol) and 6- chloronicotinonitrile (75 mg, 0.50 mmol ) in i-PrOH (2 mL) was added Cs₂CO₃ (100 mg, 0.300 mmol). The resulting mixture was stirred at 100 °C for 2 h. The resulting mixture was then concentrated and crude was purified by flash-column chromatography on silica gel to give 6-(3-formyl-1H-pyrazol-1-yl)nicotinonitrile (1.26 g).

[00259] Step 2: 6-(3-(difluoromethyl)-1H-pyrazol-1-yl)nicotinonitrile

[00260] To a solution of 6-(3-formyl-1H-pyrazol-1-yl)nicotinonitrile (1.26 g, 6.36 mmol) in DCM (120 mL) was added DAST (16.8 mL, 127 mmol) at -78 °C. After the addition, the cooling bath was removed and the reaction mixture was stirred for 16 h. The reaction mixture was then treated with saturated aqueous sodium bicarbonate

solution, and the organic layer was separated. The organic layer was washed with water, dried over sodium sulfate, filtered, and concentrated. The residue was purified by flash- column chromatography on silica gel to give 6-(3-(difluoromethyl)-1H-pyrazol-1- yl)nicotinonitrile (745 mg).

[00261] Steps 3-4: (6-(3-(difluoromethyl)-1H-pyrazol-1-yl)pyridin-3- yl)methanamine

[00262] The title compound was prepared from 6-(3-(difluoromethyl)-1H-pyrazol-1- yl)nicotinonitrile using the same two-step procedure (reduction/protection followed by deprotection) as above. MS (ES+) C₁₀H₁₀F₂N₄ requires: 224, found: 225 [M + H]⁺.

1-(pyridin-2-yl)pyrrolidin-3-amine

[00263] Step 1: Synthesis of tert-butyl (1-(pyridin-2-yl)pyrrolidin-3-yl)carbamate

[00264] A mixture of 2-fluoropyridine (1.75 mL, 20.1 mmol), tert-butyl pyrrolidin-3- ylcarbamate (250 mg, 1.34 mmol), and DIPEA (0.23 mL, 1.3 mmol) was heated to 120 °C for 6 h. The reaction mixture was then concentrated to remove excess 2- fluoropyridine, and was then purified by flash-column chromatography on silica gel (gradient elution, 5 to 60% ethyl acetate-hexanes) to give tert-butyl (1-(pyridin-2- yl)pyrrolidin-3-yl)carbamate (180 mg, 51%) as a white solid. MS (ES+) C₁₄H₂₁N₃O₂ requires: 263, found: 264 [M + H]⁺.

[00265] Step 2: Synthesis of 1-(pyridin-2-yl)pyrrolidin-3-amine

[00266] A solution of tert-butyl (1-(pyridin-2-yl)pyrrolidin-3-yl)carbamate (180 mg, 0.684 mmol) in ethyl acetate (4 mL) was treated with HCl (4.0 M in dioxane, 3.4 mL, 14 mmol) at 20 °C. After stirring for 16 h, the reaction mixture was concentrated to give 1-(pyridin-2-yl)pyrrolidin-3-amine hydrochloride (162 mg, 100%) as an off white solid that was used without any further purification. MS (ES+) C₉H₁₃N₃ requires: 163, found: 164 [M + H]⁺.

1-(6-(1H-pyrazol-1-yl)pyridin-3-yl)-N-methylmethanamine

[00267] Step 1: Synthesis of tert-butyl ((6-(1H-pyrazol-1-yl)pyridin-3- yl)methyl)carbamate

[00268] To a solution of (6-(1H-pyrazol-1-yl)pyridin-3-yl)methanamine (1.0 g, 5.8 mmol) in DCM (20 mL) was added TEA (1.75 g, 17.3 mmol) and Boc₂O (1.9 g, 8.6 mmol) at 25 °C. The resulting mixture was stirred at 25 °C for 16 h. The reaction mixture was then partitioned between ethyl acetate and water. The organic layer was washed with brine, dried over sodium sulfate, filtered, and concentrated. The residue was purified by flash column chromatography on silica gel (gradient elution, 0-10% methanol-DCM) to give tert-butyl ((6-(1H-pyrazol-1-yl)pyridin-3-yl)methyl)carbamate (1.3 g, yield 82%) as a light yellow solid. MS (ES+) C₁₄H₁₈N₄O₂ requires: 274, found 275 [M + H]⁺.

[00269] Step 2: Synthesis of tert-butyl ((6-(1H-pyrazol-1-yl)pyridin-3- yl)methyl)(methyl)carbamate

[00270] To a solution of tert-butyl (6-(1H-pyrazol-1-yl)pyridin-3-yl)methylcarbamate (1.2 g, 4.3 mmol) in THF (30 mL) was added NaH (347 mg, 8.38 mmol, 60% dispersion in mineral oil) at 0 °C under nitrogen. The resulting mixture was stirred at 0 °C for 30 min, and then MeI (740 mg, 5.21 mmol) was added in one portion and the solution was allowed to stir at 25 °C for 3 hours. The reaction mixture was then partitioned between water and EtOAc. The organic layer was washed with brine, dried over sodium sulfate, and concentrated. The residue was purified by flash column chromatography on silica gel (gradient elution, 0-10% methanol-DCM) to give tert-butyl ((6-(1H-pyrazol-1-

yl)pyridin-3-yl)methyl)(methyl)carbamate (950 mg, yield 76%) as a white powder. MS (ES+) C₁₅H₂₀N₄O₂ requires: 288, found 233 [M + H-56]⁺.

[00271] Step 3: Synthesis of 1-(6-(1H-pyrazol-1-yl)pyridin-3-yl)-N- methylmethanamine

[00272] To a solution of tert-butyl (6-(1H-pyrazol-1-yl)pyridin-3- yl)methyl(methyl)carbamate (940 mg, 3.26 mmol) in MeOH (5 mL) was added HCl (4.0 M in dioxane, 3.0 mL) at 25 °C. The resulting mixture was stirred at 25 °C for 16 h. The reaction mixture was then concentrated, and the residue was washed with diethyl ether to give the hydrochloride salt of title compound (640 mg, yield 88%) as a white powder. MS (ES+) C₁₀H₁₂N₄ requires: 188, found: 189 [M+H]⁺.

[00273] The following amine intermediates were made according to the above procedures:

Table 5.

[00274] Example 9. Synthesis of Other Compound of the Disclosure.

[00275] The synthetic protocols depicted above were used to prepare additional compounds of the disclosure as indicated below. The NMR and LC MS data obtained for compounds disclosed herein are also shown below in Table 6.

Table 6.

[00276] Example 10. Assays.

[00277] In order to assess the activity of chemical compounds against the relevant kinase of interest, the Caliper LifeSciences electrophoretic mobility shift technology platform was used. Fluorescently labeled substrate peptide was incubated in the presence of kinase and ATP so that a reflective proportion of the peptide was phosphorylated. At the end of the reaction, the mix of phosphorylated (product) and non-phosphorylated (substrate) peptides were passed through the microfluidic system of the Caliper EZ Reader 2, under an applied potential difference. The presence of the phosphate group on the product peptide provided a difference in mass and charge between those of the substrate peptide, resulting in a separation of the substrate and product pools in the sample. As the pools pass a LEDS within the instrument, these

pools were detected and resolved as separate peaks. The ratio between these peaks therefore reflects the activity of the chemical matter at that concentration in that well, under those conditions. The two specific assays used are described in detail below.

A. RET wild type assay at KM

[00278] In each well of a 384-well plate, 7.5 nM - 10 nM of wild type RET

(ProQinase 1090-0000-1) was incubated in a total of 12.5 µL of buffer (100 mM HEPES pH 7.5, 0.015% BriJ 35, 10 mM MgCl₂, 1mM DTT) with 1 µM CSKtide (FITC-AHA-KKKKD DIYFFFG-NH2) (SEQ ID NO: 5) and 25 µM ATP at 25°C for 120 minutes in the presence or absence of a dosed concentration series of compound (1% DMSO final concentration). The reaction was stopped by the addition of 70 µL of Stop buffer (100 mM HEPES pH 7.5, 0.015% BriJ 35, 35 mM EDTA and 0.2% of Coating Reagent 3 (Caliper Lifesciences)). The plate was then read on a Caliper EZReader 2 (protocol settings: -1.7 psi, upstream voltage -500, downstream voltage - 3000, post sample sip 35s). Data was normalized to 0% and 100% inhibition controls and the IC₅₀ calculated using a 4-parameter fit in the CORE LIMS.

B. RET V804L Gatekeeper mutant assay at KM

[00279] In each well of a 384-well plate, 7.5 nM - 10 nM of mutant RET (ProQinase 1096-0000-1) was incubated in a total of 12.5 µL of buffer (100 mM HEPES pH 7.5, 0.015% BriJ 35, 10 mM MgCl2, 1mM DTT) with 1 µM CSKtide (FITC-AHA- KKKKDDIYFFFG-NH2) (SEQ ID NO: 5) and 10 µM ATP at 25°C for 120 minutes in the presence or absence of a dosed concentration series of compound (1% DMSO final concentration). The reaction was stopped by the addition of 70 µL of Stop buffer (100 mM HEPES pH 7.5, 0.015% BriJ 35, 35 mM EDTA and 0.2% of Coating Reagent 3 (Caliper Lifesciences)). The plate was then read on a Caliper EZReader 2 (protocol settings: -1.7 psi, upstream voltage -500, downstream voltage -3000, post sample sip 35s). Data was normalized to 0% and 100% inhibition controls and the IC₅₀ calculated using a 4-parameter fit in the CORE LIMS.

[00280] In the Table 7 below, the following designations are used: < 10.00 nM = A; 10.01-100.0 nM = B; >100 nM = C; and ND = not determined.

Table 7.

[00281] Example 11. Compounds disclosed herein are potent inhibitors of wild-type and mutant RET

[00282] In some embodiments, compounds according to structural Formula (I), (Ia), (II), and (III) are potent and selective inhibitors of oncogenic RET mutant and fusion proteins. Currently, there are no approved inhibitors that selectively target these disease-driving RET alterations.

1. Additional in vitro assays [00283] A compound described herein can be further tested in vitro for inhibition of other mutant RET kinases, including e.g., RET V804M and RET M918T kinases, as well as CCDC6-RET and KIF5B-RET fusion kinases. The IC₅₀ can be calculated.

2. Additional cellular assays [00284] In cellular systems, the activity of a compound of structural Formula (I), (Ia), (II), or (III) can be measured by inhibition of RET mutant or RET fusion

autophosphorylation, RET-dependent signaling, and by inhibition of RET dependent cell proliferation. More specifically, the compound can be assayed for activity in cancer cell lines endogenously expressing activated RET fusions or other mutants. Exemplary cells that can be used for these studies include patient xenografts and established cell lines. Exemplary patient xenografts include colorectal cancer patient derived xenograft, Lung adenocarcinoma patient derived xenograft, and NSCLC patient derived xenograft. Exemplary cell lines include Ba/F3-KIF5B-RET (a model for leukemia), LC2/ad cells (a model for lung cancer), MZ-CRC 1 (a model for thyroid cancer), and TT cells (a medullary thyroid cancer cell line). Exemplary RET mutations that can be used for these studies include fusions such as KIF5B-RET and CCDC6-RET; point mutations such as RET C634W, RET V804L, RET V804E, RET V804M, and RET M918T; and fusions containing point mutations such as KIF5B-RET (V804L) and KIF5B-RET (V804M). KIF5B-RET (V804L) refers to a mutant RET that comprises a fusion with KIF5B and further comprises a V804L mutation in RET (referring the amino acid numbering of wild-type RET). KIF5B-RET (V804M) refers to a mutant RET that comprises a fusion with KIF5B and further comprises a V804M mutation in RET.

2a. Autophosphorylation assays [00285] As an example of an autophosphorylation assay, in Ba/F3 models engineered to express KIF5B RET, the compound is tested for its ability to inhibit RET fusion protein signaling as measured by inhibition of RET autophosphorylation. IC₅₀ can be calculated. Wild-type RET inhibitors cabozantinib and vandetanib can be used as controls (less potent compounds than the test compound) in these cellular assays. In some embodiments, the compound of structural Formula (I), (Ia), (II), or (III) potently and selectively inhibit RET autophosphorylation.

[00286] The compound can also be tested for ability to inhibit RET

autophosphorylation in LC2/ad cells, a non-engineered NSCLC cell line that expressed a CCDC6-RET fusion (Suzuki et al, 2013 Cancer Sci.104, 896–903). For instance, immunoblot is performed for LC2/ad cells expressing the CCDC6-RET fusion protein and treated with the test compound at different concentrations; Phosphorylated

(phospho[Y1062]) and total protein levels of RET are measured.

2b. Proliferation assays [00287] In some embodiments, the compound of structural Formula (I), (Ia), (II), or (III) inhibits proliferation.

[00288] In proliferation assays, the compound can be tested for ability to inhibit KIF5B-RET dependent Ba/F3 cell growth. The IC₅₀ can be calculated.

[00289] Inhibition of RET activity with the compound can also be tested for inhibition of proliferation of the CCDC6-RET expressing cell line. Similarly, the compound can also be tested for its ability to inhibit RET pathway signaling and RET dependent proliferation in the human MTC TT and MZ-CRC 1 cell lines, driven by RET C634W or RET M918T mutations, respectively. In some embodiments, in RET-driven cell lines, the test compound inhibits RET activity and RET-driven proliferation more potently than the multi-kinase inhibitors such as cabozantinib and vandetanib.

2c. Downstream signalling assays [00290] In LC2/ad cells, a non-engineered NSCLC cell line that expressed a CCDC6- RET fusion (Suzuki et al, 2013), the compound can be tested for its ability to inhibit phosphorylation of the RET substrate Src homology domain (Shc) (Hayashi et al, 2000

Oncogene.19, 4469–4475), and downstream signaling through extracellular signal regulated kinase (ERK)1/2, including downregulation of dual specificity phosphatase 6 (DUSP6) and sprouty receptor tyrosine kinase signaling antagonist 4 (SPRY4) (Lito et al, 2013 Nat. Med.19, 1401–1409). For instance, immunoblot can be performed for LC2/ad cells expressing the CCDC6-RET fusion protein and treated with the test compound at different concentrations; phosphorylated and total levels of downstream biomarkers, e.g., phospho(Y239/Y240)-Shc and phospho(Y202/T204)-ERK1/2, are measured. In addition, to determine expression levels of downstream targets, LC2/ad cells can be treated with the compound, cabozantinib, or DMSO for 7 hours and RNA is harvested. Gene expression levels of DUSP6 and SPRY4 can be measured by qRT- PCR. In some embodiments, the compound induces a dose-dependent decrease in expression of the ERK1/2 target genes DUSP6 and SPRY4 but not the control gene glycogen synthase kinase 3 beta (GSK3B).

3. Animal models [00291] Antitumor efficacy of compounds of structural Formula (I), (Ia), (II), or (III) can be demonstrated in several RET-driven in vivo models. The Ba/F3-KIF5B-RET allograft model uses KIF5B RET fusion-dependent Ba/F3 cells. The test compound can be administered orally with an appropriate dose. Tumor size can be measured e.g., twice weekly. In some embodiments, administration of the compound results in robust and dose-dependent growth inhibition of Ba/F3-KIF5B-RET allograft tumors, e.g., in complete TGI and Mouse body weight can be measured e.g., twice-weekly during the administration. In some embodiments, the compound is well tolerated with no significant changes in animal body weight observed.

[00292] Similar assays can be performed using other animal models, including a Ba/F3-KIF5B-RET (V804L) allograft tumor model which comprises a KIF5B RET V804L fusion protein, an KIF5B-RET NSCLC allograft tumor model, an MTC cell line xenograft driven by a RET C634W mutation, and a CCDC6-RET fusion positive colorectal cancer allograft tumor model. The RET V804L mutation has been observed in rare cases of MTC and is predicted to be insensitive to cabozantinib and vandetanib in vitro and in vivo (Carlomagno et al, 2004 Biochem. Biophys. Res. Commun.

207, 1022–1028; Bentzien et al, 2013 Thyroid.23, 1569–1577). In some embodiments,

the compound causes complete TGI and regressions in a cancer that is not responsive to cabozantinib or vandetanib.

[00293] Biochemical markers can also be assayed in the treated mice. To assess direct inhibition of KIF5B-RET (V804L) fusion kinase activity in Ba/F3 KIF5B-RET (V804L) tumors, the compound can be administered orally at an appropriate dose to tumor bearing mice for several days and plasma and tumors can be collected from individual mice at appropriate time points after the last dose. Test compound concentrations in plasma can be determined by liquid chromatograph/tandem mass spectrometry (LC/MS/MS). Inhibition of KIF5B-RET (V804L) signaling in the tumor tissue can be assessed by a phosphor RET enzyme linked immunosorbent assay

(ELISA) and by immunoblotting, e.g., as described above. Quantitation of the phospho- RET signal by ELISA can measure the percent KIF5B-RET (V804L) inhibition in treated animals as compared to vehicle treated controls. Suppression of downstream RET pathway signaling can be demonstrated by inhibition of Shc phosphorylation. In some embodiments, a dose and time-dependent correlation is observed between the concentration of the test compound in mouse plasma and the level of phosphorylated KIF5B RET (V804L). In some embodiments, administration of the compound at an amount sufficient to reach at least 90% inhibition of RET in vivo leads to therapeutic efficacy, e.g., can lead to 100% tumor growth inhibition.

[00294] Example 12. Selectivity of Compounds of Structural Formulas (I), (Ia), (II), and(III)

Efficacy against wild-type and mutant RET [00295] In some embodiments, compounds according to structural Formula (I), (Ia), (II), and (III) are potent inhibitors of wild-type and mutant RET. For instance the IC₅₀ of a compound can be tested in a cell line comprising wild-type RET and in a second cell line comprising mutant RET, e.g., a point mutation or fusion.

Selectivity for RET over KDR [00296] In some embodiments, compounds according to structural Formula (I), (Ia), (II), and (III) are selective for RET over another kinase, such as KDR (also called Vascular endothelial growth factor receptor 2). KDR is a tyrosine-protein kinase that

acts as a cell-surface receptor for VEGFA, VEGFC and VEGFD. Inhibition of

KDR/VEGFR2 has been associated clinically with certain adverse effects, e.g., hypertension, arterial thrombosis, and hemorrhage, and therefore selectivity for RET over KDR is desirable.

[00297] To test selectivity, the test compound can be assayed for its ability to inhibit proliferation in parental Ba/F3 cells that do not express a RET mutation, e.g., does not express a KIF5B-RET fusion. A weak IC₅₀ in the parental cell line indicates that the test compound is selective for cell lines dependent on oncogenic RET.

[00298] The selectivity of a compound on RET versus other human kinases can be characterized by profiling binding across a panel of over 450 human kinases and disease-relevant kinase mutants. In some embodiments, the compound has a high degree of selectivity for RET and RET kinase mutants over other kinases tested. To define the binding affinity for the kinases bound by the compound in kinome screening and additional kinases of interest, the dissociation constant (Kd) can be determined.

[00299] To differentiate the compound from multi-kinase inhibitors with biochemical activity against RET, the activity of the compound against recombinant kinase insert domain receptor (KDR) (also known as vascular endothelial growth factor receptor 2 [VEGFR2]) and fibroblast growth factor receptor 1 (FGFR1) can be tested, as inhibition of these kinases is associated with dose-limiting toxicities in humans. Inhibition of KDR/VEGFR2 has been associated clinically with hypertension, arterial thrombosis, and hemorrhage, whereas inhibition of fibroblast growth factor receptors (FGFRs) is associated with hyperphosphatemia and tissue calcification (Abdel-Rahman and Fouad, 2014 Crit. Rev. Oncol. Hematol.92, 194-–207; Touat et al, 2015 Clin. Cancer Res.21, 2684–2694). In some embodiments, the compound is a more potent inhibitor of WT RET than KDR/VEGFR2 and FGFR1, respectively. In contrast, in some embodiments a multi-kinase inhibitor exhibits approximately equal or increased potency on KDR versus WT RET.

[00300] Example 13. Selective compounds prevent RET resistance mutants

[00301] The compounds herein can be tested for the propensity of a cancer to develop one or more RET mutations associated with drug resistance. For example, RET-altered cancer cells (e.g., Ba/F3 KIF5B-RET cells) can be treated with a mutagen such as ENU,

exposed to a compound herein or a control compound (e.g., for 2-3 weeks), and the cell number can be quantified. Cells with high proliferation can be subjected to DNA sequencing to detect RET mutations. In some embodiments, a compound of structural Formula (I), (Ia), (II), or (III) leads to no or fewer RET mutations than a control compound such as a multi-kinase inhibitor such as cabozantinib.

[00302] Incorporation by Reference

[00303] All publications and patents mentioned herein are hereby incorporated by reference in their entirety as if each individual publication or patent was specifically and individually indicated to be incorporated by reference.

[00304] Equivalents

[00305] Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the disclosure described herein. Such equivalents are intended to be encompassed by the following claims.

Claims

Claims: 1. A compound of Formula (I) or a pharmaceutically acceptable salt thereof,

wherein:

ring A is an aryl or heteroaryl ring;

each of X¹ and X² is independently selected from N and C(R⁶);

Z is

, -CD(R⁵)-, or -CH(R⁵)-, wherein“1” represents a point of attachment to N(R⁸); and“2” represents a point of attachment to ring A;

each R¹ and each R⁷ is independently selected from C₁-C₆ alkyl, C₂-C₆ alkenyl, C₂-C₆ alkynyl, C₁-C₆ alkoxy, halo, C₁-C₆ heteroalkyl, cycloalkyl, aryl, heteroaryl, aryloxy, aralkyl, heterocyclyl, heterocyclylalkyl, nitro, cyano, -C(O)R^c, -OC(O)R^c, - C(O)OR^d, -(C₁-C₆ alkylene)-C(O)R^c, -SR^d, -S(O)₂R^c, -S(O)₂-N(R^d)(R^d)_, -(C₁-C₆ alkylene)-S(O)₂R^c, -(C₁-C₆ alkylene)-S(O)₂-N(R^d)(R^d)_, -N(R^d)(R^d), -C(O)-N(R^d)(R^d), - N(R^d)-C(O)R^c, -N(R^d)-C(O)OR^c, -(C₁-C₆ alkylene)-N(R^d)-C(O)R^c, -N(R^d)S(O)₂R^c, and -P(O)(R^c)(R^c); wherein each of alkyl, alkenyl, alkynyl, alkoxy, heteroalkyl, cycloalkyl, aryl, heteroaryl, aryloxy, aralkyl, heterocyclyl, and heterocyclylalkyl is independently substituted with 0-5 occurrences of R^a; or two R¹ or two R⁷ are taken together with the carbon atoms to which they are attached form a cycloalkyl or heterocyclyl ring independently substituted with 0-5 occurrences of R^b;

each of R², R³ if present, and R⁴ is independently selected from hydrogen, C₁-C₆ alkyl, C₁-C₆ alkoxy, halo, hydroxyl, cyano, C₁-C₆ heteroalkyl, and -N(R^d)(R^d); wherein

each of alkyl, alkoxy, and heteroalkyl is optionally and independently substituted with 0-5 occurrences of R^a;

each of R⁵ and R⁸ is independently selected from hydrogen, deuterium, C₁-C₆ alkyl, and C₁-C₆ heteroalkyl; wherein each alkyl and heteroalkyl is optionally and independently substituted with 0-5 occurrences of R^a;

each R⁶ is independently selected from hydrogen, C₁-C₆ alkyl, C₁-C₆ alkoxy, halo, cyano, C₁-C₆ heteroalkyl, and -N(R^d)(R^d); wherein each alkyl, alkoxy, and heteroalkyl is optionally and independently substituted with 0-5 occurrences of R^a; each R^a and each R^b is independently selected from C₁-C₆ alkyl, halo, hydroxyl, C₁-C₆ heteroalkyl, C₁-C₆ alkoxy, cycloalkyl, heterocyclyl, or cyano, wherein each of alkyl, heteroalkyl, alkoxy, cycloalkyl and heterocyclyl is independently substituted with 0-5 occurrences of R’;

each R’ is independently selected from C₁-C₆ alkyl, C₁-C₆ heteroalkyl, halo, hydroxyl, cycloalkyl or cyano; or two R^’ together with the atom(s) to which they are attached form a cycloalkyl or heterocyclyl ring;

each R^c is independently selected from hydrogen, hydroxyl, halo, thiol, C₁-C₆ alkyl, C₁-C₆ thioalkyl, C₁-C₆ alkoxy, C₁-C₆ heteroalkyl, cycloalkyl, cycloalkylalkyl, heteroarylalkyl, heterocyclyl, and heterocyclylalkyl, wherein each of alkyl, thioalkyl, alkoxy, heteroalkyl, cycloalkyl, cycloalkylalkyl, heteroarylalkyl, heterocyclyl, and heterocyclylalkyl is independently substituted with 0-5 occurrences of R^a, or two R^c together with the atom(s) to which they are attached form a cycloalkyl or heterocyclyl ring independently substituted with 0-5 occurrences of R^b;

each R^d is independently selected from hydrogen, C₁-C₆ alkyl, C₁-C₆ heteroalkyl, cycloalkyl, cycloalkylalkyl, heteroarylalkyl, heterocyclyl, and

heterocyclylalkyl, wherein each of alkyl, heteroalkyl, cycloalkyl, cycloalkylalkyl, heteroarylalkyl, heterocyclyl, and heterocyclylalkyl is independently substituted with 0- 5 occurrences of R^a, or two R^d together with the atom(s) to which they are attached form a cycloalkyl or heterocyclyl ring independently substituted with 0-5 occurrences of R^b; m is 0, 1, or 2; and

n is 0, 1, 2, or 3.

2. The compound of claim 1 or a pharmaceutically acceptable salt thereof, having the structural formula (Ia):

wherein R¹ is halo, C₁-C₄ alkyl, C₃-C₆ cycloalkyl, or C₁-C₆ alkoxy; and R¹ is substituted with 0-3 occurrences of R^a.

3. The compound of claim 1 or a pharmaceutically acceptable salt thereof, wherein R¹ is fluoro, -CH_3, -CH₂CH_3, -CHF_{2 ,} -OCH₃, or cyclopropyl.

4. The compound of any one of claims 1-3 or a pharmaceutically acceptable salt thereof, wherein R² is selected from hydrogen, -C₁-C₄ alkyl, C₁-C₆ alkoxy, hydroxyl, and halo; wherein -C₁-C₄ alkyl or C₁-C₆ alkoxy is optionally substituted (e.g., with 0-3 occurrences of R^a, e.g., cyano, halo).

5. The compound of claim 4 or a pharmaceutically acceptable salt thereof, wherein R² is selected from hydrogen, -C₁-C₄ alkyl, C₁-C₆ alkoxy, hydroxyl, and fluoro.

6. The compound of claim 4 or a pharmaceutically acceptable salt thereof, wherein R² is hydrogen, fluoro, -CH_3, -CH₂CH_3, -CH₂OH, -CH₂CN, -OCH₂CF₃, -OCH₂CH₂, or OMe.

7. The compound of any one of claims 1-6 or a pharmaceutically acceptable salt thereof, wherein R³ if present is hydrogen.

8. The compound of any one of claims 1-7 or a pharmaceutically acceptable salt thereof, wherein R⁴ is selected from hydrogen, hydroxyl, halo, cyano, C₁-C₄ alkyl and O-C₁-C₄ alkyl, wherein each alkyl portion of R⁴ is substituted with 0-3

occurrences of R^a.

9. The compound of claim 8 or a pharmaceutically acceptable salt thereof, wherein R⁴ is selected from hydrogen, fluoro, cyano,

hydroxyl, -CH₃, -CH₂CN, -CH₂CH₃, -CH₂CH₂OCH₃, -OCH₃, -OCH₂CF₃, and -OCH₂CH₃.

10. The compound of claim 9 or a pharmaceutically acceptable salt thereof, wherein R⁴ is selected from hydrogen, hydroxyl, and -OCH₃.

11. The compound of any one of claims 1-10 or a pharmaceutically acceptable salt

thereof, wherein Z is selected from -CH₂-, and -CH(C₁-C₄ alkyl)-,

wherein the C₁-C₄ alkyl is substituted with 0-3 occurrences of R^a.

12. The compound of claim 11 or a pharmaceutically acceptable salt thereof,

wherein Z is selected from -CH₂-, and -CH(CH₃)-.

13. The compound of any one of claims 1-12 or a pharmaceutically acceptable salt thereof, wherein each R⁶ is independently selected from hydrogen, halo, cyano, and C₁-C₄ alkyl substituted with 0-3 occurrences of R^a.

14. The compound of claim 13 or a pharmaceutically acceptable salt thereof,

wherein each R⁶ is independently selected from hydrogen, fluoro, cyano, -CH₂F and -CH₃.

15. The compound of any one of claims 1-14 or a pharmaceutically acceptable salt thereof, wherein R⁸ is selected from hydrogen and -CH₃.

16. The compound of any one of claims 1-15 or a pharmaceutically acceptable salt thereof, wherein ring A is selected from phenyl and a 6-membered monocyclic

heteroaryl comprising at least one nitrogen ring atom.

17. The compound of claim 16 or a pharmaceutically acceptable salt thereof,

wherein ring A is selected from:

18. The compound of any one of claims 1-17 or a pharmaceutically acceptable salt thereof, wherein:

ring A is selected from

n is 1;

R⁷ is selected from 1H-pyrazol-1-yl, azetidin-1-yl, and pyrrolidin-1-yl; and R⁷ is substituted with 0-3 occurrences of R^b.

19. The compound of claim 18 or a pharmaceutically acceptable salt thereof,

wherein R⁷ is selected from 3-fluoroazetidin-1-yl, 3,3-difluoropyrrolidin-1-yl, 3- fluoropyrrolidin-1-yl, 3-difluoromethyl-1H-pyrazol-1-yl, 4-fluoro-1H-pyrazol-1-yl, 4-chloro-1H-pyrazol-1-yl, 3-difluoromethyl-1H-pyrazol-1-yl, 4-difluoromethyl-1H- pyrazol-1-yl, 4-cyclopropyl-1H-pyrazol-1-yl, 4-fluoro-1H-pyrazol-1-yl, 3,5- bis(difluoromethyl)-1H-pyrazolyl, 3-methyl-1H-pyrazol-1-yl, 4-methyl-1H-pyrazol- 1-yl, 3,5-dimethyl-1H-pyrazol-1-yl, and pyrazol-1-yl.

20. The compound of claim 19 or a pharmaceutically acceptable salt thereof,

wherein R⁷ is 4-cyclopropyl-1H-pyrazol-1-yl, 4-fluoro-1H-pyrazol-1-yl, or pyrazol- 1-yl.

21. The compound of claim 1 or a pharmaceutically acceptable salt thereof, wherein: ring A is phenyl;

n is 0 or 1; and

R⁷ if present is -O-C₁-C₄ alkyl.

22. The compound of claim 21 or a pharmaceutically acceptable salt thereof,

wherein n is 0, or n is 1 and R⁷ is selected from -OCH₃ and -OCH₂CH₃.

23. A compound having the structural formula (II):

or a pharmaceutically acceptable salt thereof, wherein:

X¹ is selected from N and C(R¹³);

each Y¹ and Y² is independently selected from N and CH, wherein no more than one of Y¹ and Y² is N;

Q is selected from N, CH and CH₂;

R¹¹ is C₁-C₄ alkyl;

R¹² is selected from hydrogen and C₁- C₄ alkyl;

R¹³ if present is selected from hydrogen, cyano and halo;

R¹⁴ is selected from hydrogen, halo, cyano, hydroxyl, C₁-C₄ alkyl and C₁-C₄ alkoxy;

R¹⁵ is selected from hydrogen and C₁-C₄ alkyl;

R¹⁶ is selected from hydrogen, and C₁-C₄ alkyl optionally substituted with 1 or more independently selected halo;

R¹⁷ is selected from hydrogen and C₁-C₄ alkyl;

each of R^18a and R^19a if present and R^18b and R^19b is independently selected from hydrogen, halo, C₁-C₄ alkyl optionally substituted with one or more halo, and C₃-C₆

cycloalkyl;

p is 0 or 1; and

each represents a single or a double bond.

24. The compound of claim 23 or a pharmaceutically acceptable salt thereof,

wherein:

R¹¹ is -CH₃;

R¹² is selected from hydrogen and -CH₃;

R¹³ if present is selected from hydrogen, cyano and fluoro;

R¹⁴ is selected from hydrogen, fluoro, cyano, hydroxyl, -CH₃, -CH₂CH₃, -OCH₃, and -OCH₂CH₃;

R¹⁵ is selected from hydrogen and -CH₃;

R¹⁶ is selected from hydrogen, -CH₃ and -CHF₂;

R¹⁷ is selected from hydrogen and -CH₃;

each of R^18a and R^19a if present is independently selected from hydrogen and fluoro, wherein at least one of R^18a or R^19a is hydrogen;

each of R^18b and R^19b is independently selected from hydrogen, fluoro, chloro, -CH₃, -CHF₂, and cyclopropyl, wherein at least one of R^18b or R^19b is hydrogen; and

each is the same.

25. The compound of claim 23 or a pharmaceutically acceptable salt thereof,

wherein p is 1.

26. The compound of claim 23 or a pharmaceutically acceptable salt thereof,

wherein R¹⁴ is selected from hydrogen, fluoro, cyano, hydroxyl, and -OCH_3.

27. A compound having structural formula III:

or a pharmaceutically acceptable salt thereof, wherein:

X¹ is selected from N and CH;

Z’ is selected from

or -CH(R²⁸)-, wherein“1” represents a point of attachment to N(R²⁶); and“2” represents a point of attachment to ring B;

ring B is selected from phenyl, pyridinyl, 1H-pyrazolyl, and pyrazinyl;

R²¹ is selected from C₃-C₆ cycloalkyl and C₁-C₄ alkyl;

R²² is selected from hydrogen and C₁-C₄ alkyl;

R²³ is selected from hydrogen and cyano;

R²⁴ is selected from hydrogen, hydroxy and halo;

R²⁵ is selected from hydrogen, halo, hydroxy, C₁-C₄ alkoxy, -C₁-C₄ alkyl, -C₁-C₄ alkyl-O-C₁-C₄ alkyl, wherein each C₁-C₄ alkyl is optionally substituted with 1 or more substituents independently selected from halo and cyano;

R²⁶ is selected from hydrogen and C₁-C₄ alkyl;

R²⁷, if present, is independently selected from 1H-pyrazolyl, pyridinyl, and C₁- C₄ alkoxy, wherein the 1H-pyrazol-1-yl is optionally substituted with up to 2 substituents independently selected from C₁-C₄ alkyl and halo;

R²⁸ is selected from hydrogen and C₁-C₄ alkyl; and

o is 0 or 1.

28. The compound of claim 27 or a pharmaceutically acceptable salt thereof,

wherein:

Z’ is selected from

, -CH₂, or -CH(CH₃)-; the portion of the molecule represented by

is selected from

R²¹ is selected from -CH₃ and cyclopropyl;

R²² is selected from hydrogen and -CH₃;

R²³ is selected from hydrogen and cyano;

R²⁴ is selected from hydrogen, hydroxy and fluoro;

R²⁵ is selected from hydrogen, fluoro,

hydroxy, -OCH₃, -OCH₂CF₃, -CH₂CH₂OCH₃, -CH₃, -CH₂CH₃, and -CH₂CN;

R²⁶ is selected from hydrogen and -CH₃; and

R³⁷ is selected from hydrogen, -OCH₃, -OCH₂CH₃, 1H-pyrazol-1-yl, 4- fluoro-1H-pyrazol-1-yl, 3,5-dimethyl-1H-pyrazol-1-yl, and pyridin-2-yl.

29. The compound of claim 27 or a pharmaceutically acceptable salt thereof,

wherein Z’ is -CH₂ or -CH(CH₃)-.

30. A pharmaceutical composition comprising a compound of any one of claims 1 to 29 or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier.

31. A method for inhibiting RET activity in a cell or in a patient, comprising the step of contacting the cell or administering to the patient a compound of any one of claims 1 to 29 or a pharmaceutically acceptable salt thereof, or a pharmaceutical composition of claim 30.

32. A method for treating a subject suffering from a condition mediated by aberrant RET activity, comprising administering to the subject a therapeutically effective amount of a compound of any one of claims 1 to 29 or a pharmaceutically

acceptable salt thereof, or a pharmaceutical composition of claim 30.

33. A method for treating a subject who has developed resistance to a treatment for a condition mediated by aberrant RET activity, comprising administering to the subject a therapeutically effective amount of a compound of any one of claims 1 to 29 or a pharmaceutically acceptable salt thereof, or a pharmaceutical composition of claim 30.

34. The method of claim 33, wherein the subject has developed resistance to a wild- type RET inhibitor.

35. A method of treating cancer in a subject, said method comprising:

a. determining if, having determined if, or receiving information that the subject has a RET-altered cell, cancer, gene, or gene product;

b. identifying the patient as responsive to a compound of any one of claims 1 to 29 when the subject has the RET-altered cell, cancer, gene, or gene product; and

c. administering an effective amount of the compound to the subject.

36. The method of claim 35, wherein the subject has a RET fusion or point

mutation.

37. A method of treating cancer in a patient, said method comprising administering an effective amount of a compound of any one of claims 1 to 29 to a patient having a RET-altered cell, cancer, gene, or gene product that is responsive to the compound.

38. A compound of any one of claims 1 to 29 or a pharmaceutical composition of claim 30 for use in inhibiting RET activity in a cell or in a patient.

39. A compound of any one of claims 1 to 29 or a pharmaceutical composition of claim 30 for use in treating a subject suffering from a condition mediated by aberrant RET activity.

40. A compound of any one of claims 1 to 29 or a pharmaceutical composition of claim 30 for use in treating a subject who has developed resistance to a cancer treatment.

41. The compound or pharmaceutical composition for the use according to claim 40, wherein the subject has developed resistance to a wild-type RET inhibitor.

42. A compound of any one of claims 1 to 29 for use in a method of treating cancer in a subject, said method comprising:

c. administering an effective amount of the compound to the subject.

43. The compound of claim 42, wherein the subject has a RET fusion or point

mutation.

44. A compound of any one of claims 1 to 29 for use in a method of treating cancer in a patient, said method comprising administering an effective amount of the compound to a patient having a RET-altered cell, cancer, gene, or gene product that is responsive to the compound.