Tetrahydroindazoles as Interleukin-2 Inducible T-Cell Kinase Inhibitors. Part II. Second-Generation Analogues with Enhanced Potency, Selectivity, and Pharmacodynamic Modulation in Vivo

Asymmetric Transfer Hydrogenation of gem-Difluorocyclopropenyl Ketones: The Synthesis and Functionalization of Enantioenriched cis gem-Difluorocyclopropyl Ketones

The asymmetric transfer hydrogenation of gem-difluorocyclopropenyl ketones, catalyzed by a Noyori-Ikariya ruthenium complex, was developed to access substituted optically enriched cis-disubstituted gem-difluorocyclopropyl ketones, and the value of these latter building blocks was illustrated by the synthesis of heterocycles fused to the difluorocyclopropyl moiety.

Conformational Selectivity of ITK Inhibitors: Insights from Molecular Dynamics Simulations

Interleukin-2-inducible T-cell kinase (ITK) regulates the response to T-cell receptor signaling and is a drug target for inflammatory and immunological diseases. Molecules that bind preferentially to the active form of ITK have low selectivity between kinases, whereas those that bind preferentially to the inactive form have high selectivity for ITK. Therefore, computational methods to predict the conformational selectivity of compounds are required to design highly selective ITK inhibitors. In this study, we performed absolute binding free-energy perturbation (ABFEP) simulations for 11 compounds on both active and inactive forms of ITK, and the calculated binding free energies were compared with experimental data. The conformational selectivity of 10 of the 11 compounds was correctly predicted using ABFEP. To investigate the mechanism underlying the stabilization of the active and inactive structures by the compounds, we performed extensive, conventional molecular dynamics simulations, which revealed that the compound-induced stabilization of the P-loop and linkage of conformational changes in L489, V419, F501, and M410 upon compound binding were critical factors. A guideline for designing inactive-form binders is proposed based on these key structural factors. The ABFEP and the created guidelines are expected to facilitate the discovery of highly selective ITK inhibitors.

Discovery of potent and selective HPK1 inhibitors based on the 2,4-disubstituted pyrimidine scaffold with immune modulatory properties for ameliorating T cell exhaustion

Hematopoietic progenitor kinase 1 (HPK1), a member of the mitogen-activated protein kinase (MAP4K) family, is a serine/threonine (SER/THR) kinase and has been demonstrated as a negative regulator of T cell receptor signaling. Targeting HPK1 has been considered as an attractive therapeutic strategy for immune-oncology. Here, we describe the discovery and structure-activity relationship (SAR) of potent HPK1 inhibitors based on the 2,4-disubstituted pyrimidine scaffold. Systematically SAR exploration afforded the desired compound HMC-H8 (F1) with potent HPK1 inhibition (IC50 = 1.11 nM) and highly selectivity profile. Compound HMC-H8 also exhibited robust inhibition of p-SLP 76 (IC50 = 283.0 nM) and promotion IL-2 release (EC50 = 157.08 nM), and INF-γ production in a dose-dependent manner in vitro assays. Strikingly, HMC-H8 shown effective immune reversal response in immunesuppressive condition. Moreover, Compound HMC-H8 displayed acceptable metabolic stability (T1/2 = 56.87 min), along with low CYP450 inhibition in human liver microsomes and good oral bioavailability (F = 15.05%) in rat. Furthermore, HMC-H8 was found to modulate the expression of c-Myc in Western blotting experiments. Taken together, this study provides new potent HPK1 inhibitors for further anticancer drug discovery based on immuno-oncology.

Evaluation of Substituted Pyrazole-Based Kinase Inhibitors in One Decade (2011-2020): Current Status and Future Prospects

Pyrazole has been recognized as a pharmacologically important privileged scaffold whose derivatives produce almost all types of pharmacological activities and have attracted much attention in the last decades. Of the various pyrazole derivatives reported as potential therapeutic agents, this article focuses on pyrazole-based kinase inhibitors. Pyrazole-possessing kinase inhibitors play a crucial role in various disease areas, especially in many cancer types such as lymphoma, breast cancer, melanoma, cervical cancer, and others in addition to inflammation and neurodegenerative disorders. In this article, we reviewed the structural and biological characteristics of the pyrazole derivatives recently reported as kinase inhibitors and classified them according to their target kinases in a chronological order. We reviewed the reports including pyrazole derivatives as kinase inhibitors published during the past decade (2011-2020).

Total synthesis of (+)-ent-vetiverianine a via Lewis acid-mediated cyclization

We describe the first total synthesis of (+)-ent-vetiverianine A, which exhibits a 5/6/6-fused tricyclic structure, with the longest linear sequence of 14 steps, and in 12% overall yield.

The preparation and properties of 1,1-difluorocyclopropane derivatives

Recently, the functionalization of organic molecules with fluorine substituents has grown rapidly due to its applications in such fields as medicine, agriculture or materials sciences. The aim of this article is to review the importance of 1,1-difluorocyclopropane derivatives in synthesis. It will examine the role of the fluorine substituents in both ring-forming and ring-opening reactions, as well as methods for obtaining difluorocyclopropanes as single enantiomers. Several examples are provided to highlight the biological importance of this class of compounds.

Small-Molecule Kinase Inhibitors for the Treatment of Nononcologic Diseases

Great successes have been achieved in developing small-molecule kinase inhibitors as anticancer therapeutic agents. However, kinase deregulation plays essential roles not only in cancer but also in almost all major disease areas. Accumulating evidence has revealed that kinases are promising drug targets for different diseases, including cancer, autoimmune diseases, inflammatory diseases, cardiovascular diseases, central nervous system disorders, viral infections, and malaria. Indeed, the first small-molecule kinase inhibitor for treatment of a nononcologic disease was approved in 2011 by the U.S. FDA. To date, 10 such inhibitors have been approved, and more are in clinical trials for applications other than cancer. This Perspective discusses a number of kinases and their small-molecule inhibitors for the treatment of diseases in nononcologic therapeutic fields. The opportunities and challenges in developing such inhibitors are also highlighted.

Scalable Preparation of 4,4-Disubstituted Six-Membered Cyclic Sulfones

We provide an account of synthetic strategies aimed at the efficient preparation of 4-amino-4-methyltetrahydro-2H-thiopyran 1,1-dioxide (3), an important cyclic sulfone building block for medicinal chemistry. A practical and scalable protocol has been developed that readily gives access to the title compound from commercially available and inexpensive starting materials. In addition, this novel approach has enabled the synthesis of various related 4,4-disubstituted cyclic sulfone derivatives that serve as valuable structural motifs for drug discovery.

Design, synthesis and structure-activity relationship of indolylindazoles as potent and selective covalent inhibitors of interleukin-2 inducible T-cell kinase (ITK)

Interleukin-2 inducible T-cell kinase (ITK), a member of the Tec family of tyrosine kinases, plays an important role in T cell signaling downstream of the T-cell receptor (TCR). Herein we report the discovery of a series of indolylindazole based covalent ITK inhibitors with nanomolar inhibitory potency against ITK, good kinase selectivity and potent inhibition of the phosphorylation of PLCγ1 and ERK1/2 in living cells. A computational study provided insight into the interactions between inhibitors and Phe437 at the ATP binding pocket of ITK, suggesting that both edge-to-face π-π interaction and the dihedral torsion angle contribute to inhibitors' potency. Compounds 43 and 55 stood out as selective covalent inhibitors with potent cellular activity, which could be used as chemical tools for further study of ITK functions.

Discovery of 7H-pyrrolo[2,3-d]pyrimidine derivatives as selective covalent irreversible inhibitors of interleukin-2-inducible T-cell kinase (Itk)

Interleukin-2-inducible T-cell kinase (Itk) plays an important role in multiple signal transduction pathways in T and mast cells, and is a potential drug target for treating inflammatory diseases, autoimmune diseases, and T cell leukemia/lymphoma. Herein, we describe the discovery of a series of covalent Itk inhibitors based on the 7H-pyrrolo[2,3-d]pyrimidine scaffold. Placing an appropriate substitution group at a hydration site of the ATP binding pocket of Itk and using a saturated heterocyclic ring as a linker to the reactive group were crucial for selectivity. The optimized compound 9 showed potent activity against Itk, excellent selectivity for Itk over Btk and other structurally related kinases, inhibition of phospholipase C-γ1 (PLC-γ1) phosphorylation in cells, and anti-proliferative effects against multiple T leukemia/lymphoma cell lines. Compound 9 can serve as a valuable compound for further determination of functions of Itk.

A base-promoted cascade reaction of α,β-unsaturated N-tosylhydrazones with o-hydroxybenzyl alcohols: highly regioselective synthesis of N-sec-alkylpyrazoles

An efficient method for the synthesis of N-sec-alkylpyrazoles via a cascade reaction of α,β-unsaturated N-tosylhydrazones with ortho-hydroxybenzyl alcohols has been developed.

Crystal structure of 3,6,6-trimethyl-4-oxo-1-(pyridin-2-yl)-4,5,6,7-tetra-hydro-1H-indazol-7-aminium chloride and its monohydrate

The title compounds, C15H19N4O+·Cl- and C15H19N4O+·Cl-·H2O, obtained in attempts to synthesize metal complexes using tetra-hydro-indazole as a ligand, were characterized by NMR, IR and X-ray diffraction techniques. The partially saturated ring in the tetra-hydro-indazole core adopts a sofa conformation. An intra-molecular N-H⋯N hydrogen bond formed by the protonated amino group and the N atom of the pyridyl substituent is found in the first structure. In the hydro-chloride, the organic moieties are linked by two N-H⋯Cl- hydrogen bonds, forming a C(4) graph-set. In the hydrate crystal, a Cl- anion and a water mol-ecule assemble the moieties into infinite bands showing hydrogen-bond patterns with graph sets C(6), R64(12) and R42(8). Organic moieties form π-π stacked supra-molecular structures running along the b axis in both structures.

A greener and efficient access to substituted four- and six-membered sulfur-bearing heterocycles

The regioselective functionalization of four- and six-membered cyclic sulfones was investigated using a lithiation/functionalization strategy.

Partially Saturated Bicyclic Heteroaromatics as an sp(3) -Enriched Fragment Collection

Fragment‐based lead generation has proven to be an effective means of identifying high‐quality lead compounds for drug discovery programs. However, the fragment screening sets often used are principally comprised of sp²‐rich aromatic compounds, which limits the structural (and hence biological) diversity of the library. Herein, we describe strategies for the synthesis of a series of partially saturated bicyclic heteroaromatic scaffolds with enhanced sp³ character. Subsequent derivatization led to a fragment collection featuring regio‐ and stereo‐controlled introduction of substituents on the saturated ring system, often with formation of new stereocenters.

The "Cyclopropyl Fragment" is a Versatile Player that Frequently Appears in Preclinical/Clinical Drug Molecules

Recently, there has been an increasing use of the cyclopropyl ring in drug development to transition drug candidates from the preclinical to clinical stage. Important features of the cyclopropane ring are, the (1) coplanarity of the three carbon atoms, (2) relatively shorter (1.51 Å) C-C bonds, (3) enhanced π-character of C-C bonds, and (4) C-H bonds are shorter and stronger than those in alkanes. The present review will focus on the contributions that a cyclopropyl ring makes to the properties of drugs containing it. Consequently, the cyclopropyl ring addresses multiple roadblocks that can occur during drug discovery such as (a) enhancing potency, (b) reducing off-target effects,

Fragment Molecular Orbital Method Applied to Lead Optimization of Novel Interleukin-2 Inducible T-Cell Kinase (ITK) Inhibitors

Inhibition of inducible T-cell kinase (ITK), a nonreceptor tyrosine kinase, may represent a novel treatment for allergic asthma. In our previous reports, we described the discovery of sulfonylpyridine (SAP), benzothiazole (BZT), indazole (IND), and tetrahydroindazole (THI) series as novel ITK inhibitors and how computational tools such as dihedral scans and docking were used to support this process. X-ray crystallography and modeling were applied to provide essential insight into ITK-ligand interactions. However, "visual inspection" traditionally used for the rationalization of protein-ligand affinity cannot always explain the full complexity of the molecular interactions. The fragment molecular orbital (FMO) quantum-mechanical (QM) method provides a complete list of the interactions formed between the ligand and protein that are often omitted from traditional structure-based descriptions. FMO methodology was successfully used as part of a rational structure-based drug design effort to improve the ITK potency of high-throughput screening hits, ultimately delivering ligands with potency in the subnanomolar range.

Inhibition of the kinase ITK in a mouse model of asthma reduces cell death and fails to inhibit the inflammatory response

Interleukin-2 (IL-2)-inducible T cell kinase (ITK) mediates T cell receptor (TCR) signaling primarily to stimulate the production of cytokines, such as IL-4, IL-5, and IL-13, from T helper 2 (TH2) cells. Compared to wild-type mice, ITK knockout mice are resistant to asthma and exhibit reduced lung inflammation and decreased amounts of TH2-type cytokines in the bronchoalveolar lavage fluid. We found that a small-molecule selective inhibitor of ITK blocked TCR-mediated signaling in cultured TH2 cells, including the tyrosine phosphorylation of phospholipase C-γ1 (PLC-γ1) and the secretion of IL-2 and TH2-type cytokines. Unexpectedly, inhibition of the kinase activity of ITK during or after antigen rechallenge in an ovalbumin-induced mouse model of asthma failed to reduce airway hyperresponsiveness and inflammation. Rather, in mice, pharmacological inhibition of ITK resulted in T cell hyperplasia and the increased production of TH2-type cytokines. Thus, our studies predict that inhibition of the kinase activity of ITK may not be therapeutic in patients with asthma.