Design and evaluation of 3,6-di(hetero)aryl imidazo[1,2-a]pyrazines as inhibitors of checkpoint and other kinases.

A range of 3,6-di(hetero)arylimidazo[1,2-a]pyrazine ATP-competitive inhibitors of CHK1 were developed by scaffold hopping from a weakly active screening hit. Efficient synthetic routes for parallel synthesis were developed to prepare analogues with improved potency and ligand efficiency against CHK1. Kinase profiling showed that the imidazo[1,2-a]pyrazines could inhibit other kinases, including CHK2 and ABL, with equivalent or better potency depending on the pendant substitution. These 3,6-di(hetero)aryl imidazo[1,2-a]pyrazines appear to represent a general kinase inhibitor scaffold.

Current Status in the Discovery of Covalent Janus Kinase 3 (JAK3) Inhibitors.

The search for inhibitors of the Janus kinase family (JAK1, JAK2, JAK3 and TYK2) has been ongoing for several decades and has resulted in a number of JAK inhibitors being approved for use in patients, such as tofacitinib for the treatment of autoimmune diseases such as Rheumatoid Arthritis (RA). Although initially thought to be a JAK3 selective inhibitor, tofacitinib was subsequently found to possess significant activity to inhibit JAK1 and JAK2 which has contributed to some adverse side effects. A selective JAK3 inhibitor should only have an effect within the immune system since JAK3 is solely expressed in lymphoid tissue; this makes JAK3 a target of interest in the search for treatments of autoimmune diseases. A method to obtain selectivity for JAK3 over the other JAK family members, which has attracted more scientific attention recently, is the targeting of the active site cysteine residue, unique in JAK3 within the JAK family, with compounds containing electrophilic warheads which can form a covalent bond with the nucleophilic thiol of the cysteine residue. This review encompasses the historical search for a covalent JAK3 inhibitor and the most recently published research which hasn't been reviewed to date. The most important compounds from the publications reviewed the activity and selectivity of these compounds together with some of the more important biological results are condensed in to an easily digested form that should prove useful for those interested in the field.

Structure-guided evolution of potent and selective CHK1 inhibitors through scaffold morphing.

Pyrazolopyridine inhibitors with low micromolar potency for CHK1 and good selectivity against CHK2 were previously identified by fragment-based screening. The optimization of the pyrazolopyridines to a series of potent and CHK1-selective isoquinolines demonstrates how fragment-growing and scaffold morphing strategies arising from a structure-based understanding of CHK1 inhibitor binding can be combined to successfully progress fragment-derived hit matter to compounds with activity in vivo. The challenges of improving CHK1 potency and selectivity, addressing synthetic tractability, and achieving novelty in the crowded kinase inhibitor chemical space were tackled by multiple scaffold morphing steps, which progressed through tricyclic pyrimido[2,3-b]azaindoles to N-(pyrazin-2-yl)pyrimidin-4-amines and ultimately to imidazo[4,5-c]pyridines and isoquinolines. A potent and highly selective isoquinoline CHK1 inhibitor (SAR-020106) was identified, which potentiated the efficacies of irinotecan and gemcitabine in SW620 human colon carcinoma xenografts in nude mice.