Heme-regulated inhibitor kinase (HRI), an eukaryotic translation initiation factor 2 alpha (eIF2α) kinase, plays critical roles in cell proliferation, differentiation, and adaptation to cytoplasmic stress. HRI is also a critical modifier of hemoglobin disorders such as β-thalassemia. We previously identified N,N′-diarylureas as potent activators of HRI suitable for studying biology of this important kinase. To expand the repertoire of chemotypes that activate HRI we screened a ~1,900 member N,N′-disubstituted urea library in the surrogate eIF2α phosphorylation assay identifying N-aryl,N′-cyclohexylphenoxyurea as a promising scaffold. We validated hit compounds as a bona-fide HRI activators in secondary assays and explored contributions of substitutions on the N-aryl and N′-cyclohexylphenoxy groups to their activity by studying focused libraries of complementing analogs. We tested these N-aryl,N′-cyclohexylphenoxyureas in the surrogate eIF2α phosphorylation and cell proliferation assays, demonstrating significantly improved bioactivities and specificities. We consider these compounds to represent lead candidates for the development of potent and specific HRI activators.

HRI plays critical roles in proliferation and maturation of red blood‐cell precursors, responding to cytoplasmic stress and adaptation to hemoglobin disorders. N,N′‐diarylureas are potent activators of the heme‐regulated inhibitor kinase (HRI), an eIF2‐alpha kinase. We hypothesized that other substituted ureas with potentially more favorable activity and physic‐chemical properties would also activate HRI. Initially, we screened a ~2000 member library containing a diverse array of substituted ureas in the surrogate assay for eIF2‐alpha phosphorylation. We identified di‐substituted aryl‐cyclohexylarylurea as an active scaffold. We explored contributions of substituted aryl and cyclohexylaryl groups to the activity of this scaffold by assembly of a focused library and follow‐up synthesis. We tested N‐aryl, N′‐cyclohexylarylureas in the surrogate assay for eIF2‐alpha phosphorylation and cell proliferation assays, demonstrating significantly improved bioactivities. A random group of these compounds was further characterized in secondary assays for activity and specificity. These agents may become leads for the development of potent, non‐toxic, and target specific anti‐cancer agents.