Synthesis and SAR of new pyrrolo[2,1-f][1,2,4]triazines as potent p38 alpha MAP kinase inhibitors

Reactions of 3-amino-1,2,4-triazine with coupling reagents and electrophiles

Analogs of a new heterocyclic system were obtained from the reactions of 3-amino-1,2,4-triazine with coupling reagents such as boronic acids, and terminal alkynes in the presence of a palladium catalyst. Other reactions such as amination of the triazine at position 5, followed by electrophilic reactions with phenyl isocyanates and benzoyl chlorides, were performed to form new monoureido and benzoylated compounds.

Synthetic strategies for pyrrolo[2,1-f][1,2,4]triazine: the parent moiety of antiviral drug remdesivir

This review summarizes diverse synthetic protocols for the preparation of pyrrolo[2,1-f][1,2,4]triazine derivatives, covering literature sources from the past two decades. For effective representation, the synthetic methods toward the title compound are classified into six distinct categories: 1) synthesis from pyrrole derivatives, 2) synthesis via bromohydrazone, 3) synthesis via formation of triazinium dicyanomethylide, 4) multistep synthesis, 5) transition metal mediated synthesis, and 6) rearrangement of pyrrolooxadiazines. A brief outline of all optimized schemes is provided with relevant examples.

Fragment-based identification and optimization of a class of potent pyrrolo[2,1-f][1,2,4]triazine MAP4K4 inhibitors

MAP4K4 has been shown to regulate key cellular processes that are tied to disease pathogenesis. In an effort to generate small molecule MAP4K4 inhibitors, a fragment-based screen was carried out and a pyrrolotriazine fragment with excellent ligand efficiency was identified. Further modification of this fragment guided by X-ray crystal structures and molecular modeling led to the discovery of a series of promising compounds with good structural diversity and physicochemical properties. These compounds exhibited single digit nanomolar potency and compounds 35 and 44 achieved good in vivo exposure.

Rosiglitazone inhibits TGF-β 1 induced activation of human Tenon fibroblasts via p38 signal pathway

Purpose

Transdifferentiation of human Tenon fibroblasts to myofibroblasts and subsequent deposition of extracellular matrix is a key step in the scarring after glaucoma filtration surgery. The p38 signaling pathway plays an important role in cell proliferation and differentiation, and its upstream regulators and downstream molecules are widely distributed in the eye. We aimed to investigate the role of p38 in the activation of Tenon fibroblasts and that of the anti-fibrotic mechanism of rosiglitazone in the modulation of the p38 signaling pathway.

Methods

Cultured Tenon fibroblasts were stimulated with transforming growth factor (TGF)-β1. Activation of p38 was examined by western blot analysis. Rosiglitazone and blocking of the p38 signaling pathway by SB203580 were used to antagonize stimulation by TGF-β1. Fibroblast motility was examined by wound closure assay; alpha-smooth muscle actin, connective tissue growth factor, and collagen type I were determined by qPCR and western blot. Expression and localization of alpha-smooth muscle actin were determined by immunofluorescence staining.

Results

Phosphorylated p38 was upregulated in fibroblasts stimulated with TGF-β1, and this effect was substantially inhibited by rosiglitazone. Proliferation and migration of fibroblasts were suppressed by rosiglitazone and SB203580. Expression of alpha-smooth muscle actin, connective tissue growth factor, and collagen type I were decreased at the mRNA and protein levels by rosiglitazone and SB203580. However, the inhibitory effect of SB203580 on transcription and protein expression was weaker than that of rosiglitazone. Similar phenomena were found on immunofluorescence microscopy of alpha-smooth muscle actin.

Conclusions

The p38 signaling pathway mediates the TGF-β1-induced transdifferentiation of human Tenon fibroblasts to myofibroblasts. Rosiglitazone can exert anti-fibrotic activity by interfering with the TGF-β/p38 signaling pathway and might be useful for modulating scar formation after glaucoma filtration surgery.

X-ray structure of p38α bound to TAK-715: comparison with three classic inhibitors

The p38α mitogen-activated protein kinase regulates the synthesis of pro-inflammatory cytokines in response to stimulation by a diverse set of stress signals. Various different chemotypes and clinical candidates that inhibit p38α function have been reported over the years. In this publication, the novel structure of p38α cocrystallized with the clinical candidate TAK-715 is reported. Owing to the impact of crystallization conditions on the conformation of protein kinases (and in particular p38α), the structures of complexes of p38α with SB-203580, SCIO-469 and VX-745 have also been determined to enable in-depth comparison of ligand-induced protein conformations. The impact of experimental conditions on p38α-inhibitor complex structures, most importantly soaking versus cocrystallization, is discussed. Analysis of the structures and quantification of the protein-ligand interactions couples ligand-induced protein conformations to the number of interactions and to inhibitor selectivity against the human kinome. This shows that for the design of novel kinase inhibitors, selectivity is best obtained through maximization of the number of interactions throughout the ATP pocket and the exploitation of specific features in the active site.

Druggability Assessment of Allosteric Proteins by Dynamics Simulations in the Presence of Probe Molecules

Druggability assessment of a target protein has emerged in recent years as an important concept in hit-to-lead optimization. A reliable and physically relevant measure of druggability would allow informed decisions on the risk of investing in a particular target. Here, we define “druggability” as a quantitative estimate of binding sites and affinities for a potential drug acting on a specific protein target. In the present study, we describe a new methodology that successfully predicts the druggability and maximal binding affinity for a series of challenging targets, including those that function through allosteric mechanisms. Two distinguishing features of the methodology are (i) simulation of the binding dynamics of a diversity of probe molecules selected on the basis of an analysis of approved drugs and (ii) identification of druggable sites and estimation of corresponding binding affinities on the basis of an evaluation of the geometry and energetics of bound probe clusters. The use of the methodology for a variety of targets such as murine double mutant-2, protein tyrosine phosphatase 1B (PTP1B), lymphocyte function-associated antigen 1, vertebrate kinesin-5 (Eg5), and p38 mitogen-activated protein kinase provides examples for which the method correctly captures the location and binding affinities of known drugs. It also provides insights into novel druggable sites and the target’s structural changes that would accommodate, if not promote and stabilize, drug binding. Notably, the ability to identify high affinity spots even in challenging cases such as PTP1B or Eg5 shows promise as a rational tool for assessing the druggability of protein targets and identifying allosteric or novel sites for drug binding.

Virtual screening filters for the design of type II p38 MAP kinase inhibitors: a fragment based library generation approach

In this work, we introduce the development and application of a three-step scoring and filtering procedure for the design of type II p38 MAP kinase leads using allosteric fragments extracted from virtual screening hits. The design of the virtual screening filters is based on a thorough evaluation of docking methods, DFG-loop conformation, binding interactions and chemotype specificity of the 138 p38 MAP kinase inhibitors from Protein Data Bank bound to DFG-in and DFG-out conformations using Glide, GOLD and CDOCKER. A 40 ns molecular dynamics simulation with the apo, type I with DFG-in and type II with DFG-out forms was carried out to delineate the effects of structural variations on inhibitor binding. The designed docking-score and sub-structure filters were first tested on a dataset of 249 potent p38 MAP kinase inhibitors from seven diverse series and 18,842 kinase inhibitors from PDB, to gauge their capacity to discriminate between kinase and non-kinase inhibitors and likewise to selectively filter-in target-specific inhibitors. The designed filters were then applied in the virtual screening of a database of ten million (10⁷) compounds resulting in the identification of 100 hits. Based on their binding modes, 98 allosteric fragments were extracted from the hits and a fragment library was generated. New type II p38 MAP kinase leads were designed by tailoring the existing type I ATP site binders with allosteric fragments using a common urea linker. Target specific virtual screening filters can thus be easily developed for other kinases based on this strategy to retrieve target selective compounds.

P38 MAPK signaling pathway: biological functions, roles in the pathogenesis of liver fibrosis and common research methods

The activation and proliferation of hepatic stellate cells (HSC) are the key events in hepatic fibrogenesis. Now the research about the mechanisms of action of HSC-related signal transduction has become a hot topic. This article reviews the biological functions of the p38 MAPK signaling pathway and its roles in the pathogenesis of liver fibrosis and summarizes common research methods for this signaling pathway.

A novel fused 1,2,4-triazine aryl derivative as antioxidant and nonselective antagonist of adenosine A(2A) receptors in ethanol-activated liver stellate cells

It has been detected that hepatic adenosine A(2A) receptors play an active role in the pathogenesis of hepatic fibrosis and suggest a novel therapeutic target in the treatment and prevention of hepatic cirrhosis. In this paper we examined if our new triazine derivative (IMT) can inhibit ethanol-induced activation of HSCs measured as increased α-SMA, collagen synthesis and enhanced oxidative stress in rat liver stellate cells. We also investigated its influence on cytokines (TGF-β, TNF-α) synthesis, MMP-2 and TIMP-1 production and ethanol-induced intracellular signal transduction. Moreover, with using of known adenosine A(2A) receptor agonist (CGS 21680), and antagonist (SCH 58261) we examined if this triazine derivative acts on adenosine receptors. We detected a strong antagonistic action of new triazine derivative (IMT) on ethanol-induced rat liver stellate cells activation, observed as a significant decrease in α-SMA, collagen synthesis, reactive oxygen species production, TGF-β, TNF-α, MMP-2 and TIMP-1 production as well as JNK, p38MAPK, NFκB, IκB, Smad3 phosphorylation. Moreover, IMT strongly inhibited activation of stellate cells by known selective agonist of adenosine A(2A) receptor (CGS 21680). When known A(2A) receptor antagonist (SCH 58261) was used together with IMT this effect was not spectacular. Additionally, only slight enhancement of inhibition was observed when cells were pretreated both IMT with SCH 58261, hence we suppose that IMT acts as nonselective antagonist of A(2A) receptors, and, besides its antioxidant activity, also by this way inhibited ethanol-induced stellate cell activation.

Discovery of pyrrolo[2,1-f][1,2,4]triazine C6-ketones as potent, orally active p38α MAP kinase inhibitors

Pyrrolo[2,1-f][1,2,4]triazine based inhibitors of p38α have been prepared exploring functional group modifications at the C6 position. Incorporation of aryl and heteroaryl ketones at this position led to potent inhibitors with efficacy in in vivo models of acute and chronic inflammation.

Discovery of 4-(5-(cyclopropylcarbamoyl)-2-methylphenylamino)-5-methyl-N-propylpyrrolo[1,2-f][1,2,4]triazine-6-carboxamide (BMS-582949), a clinical p38α MAP kinase inhibitor for the treatment of inflammatory diseases

The discovery and characterization of 7k (BMS-582949), a highly selective p38α MAP kinase inhibitor that is currently in phase II clinical trials for the treatment of rheumatoid arthritis, is described. A key to the discovery was the rational substitution of N-cyclopropyl for N-methoxy in 1a, a previously reported clinical candidate p38α inhibitor. Unlike alkyl and other cycloalkyls, the sp(2) character of the cyclopropyl group can confer improved H-bonding characteristics to the directly substituted amide NH. Inhibitor 7k is slightly less active than 1a in the p38α enzymatic assay but displays a superior pharmacokinetic profile and, as such, was more effective in both the acute murine model of inflammation and pseudoestablished rat AA model. The binding mode of 7k with p38α was confirmed by X-ray crystallographic analysis.