We present the discovery of thieno[3,2-<i>d</i>]pyrimidine <b>SGC-STK17B-1</b> (<b>11s</b>), a high-quality chemical probe for this understudied “dark” kinase. <b>11s</b> is an ATP-competitive inhibitor that showed remarkable selectivity over other kinases including the closely related STK17A. X-ray crystallography of <b>11s</b> and related thieno[3,2-<i>d</i>]pyrimidines bound to STK17B revealed a unique P-loop conformation characterized by a salt bridge between R41 and the carboxylic acid of the inhibitor.

<div>CAMKK2 is a serine/threonine kinase and an activator of AMPK whose dysregulation is linked with multiple diseases. Unfortunately, STO-609, the tool inhibitor commonly used to probe CAMKK2 signaling, has limitations. To identify promising scaffolds as starting points for the development of high-quality CAMKK2 chemical probes, we utilized a hinge-binding scaffold hopping strategy to design new CAMKK2 inhibitors. Starting from the potent but promiscuous disubstituted 7-azaindole GSK650934 (CAMKK2 IC50 = 3 nM), a total of 32 compounds, composed of single ring, 5,6-, and 6,6-fused heteroaromatic cores were synthesized. The compound set was specifically designed to probe interactions with the kinase hinge-binding residues. These compounds were evaluated in vitro in biochemical and cellular assays for CAMKK2 inhibition. Compared to GSK650394 and STO-609, thirteen of our compounds displayed similar or better CAMKK2 inhibitory potency in vitro, while compounds 13g and 45 had greatly improved selectivity for CAMKK2 across the kinome. Our systematic survey of hinge binding chemotypes identified several potent and selective inhibitors of CAMKK2 to serve as starting points for medicinal chemistry programs aimed at the identification of CAMKK2 chemical probes and clinical candidates<br></div>

We present the discovery of thieno[3,2-<i>d</i>]pyrimidine <b>SGC-STK17B-1</b> (<b>11s</b>), a high-quality chemical probe for this understudied “dark” kinase. <b>11s</b> is an ATP-competitive inhibitor that showed remarkable selectivity over other kinases including the closely related STK17A. X-ray crystallography of <b>11s</b> and related thieno[3,2-<i>d</i>]pyrimidines bound to STK17B revealed a unique P-loop conformation characterized by a salt bridge between R41 and the carboxylic acid of the inhibitor.

RIOK2 is an understudied kinase associated with a variety of human cancers including non-small cell lung cancer and glioblastoma. No potent, selective, and cell-active chemical probe currently exists for RIOK2. Such a reagent would expedite research into the biological functions of RIOK2 and validate it as a therapeutic target. Herein, we describe the synthesis of naphthyl-pyridine based compounds that have both improved cellular activity while maintaining selectivity for RIOK2.