Pyrazolylpyrimidinamines Decorated via Petasis Reaction as Small-Molecule Activators of the RNA-Degrading Ribonuclease IRE1α

The multicomponent Petasis boron-Mannich reaction (PR) enables the generation of functionalized amines that are of biological interest. Here, we demonstrated that a series of pyrazolylpyrimidinamines decorated via PR are new small-molecule activators of the dual kinase and ribonuclease RNA-degrading protein inositol-requiring enzyme 1α (IRE1α), which is an essential effector in the unfolded protein response associated with many human diseases. Compound SH4 was identified via a FRET assay and showed potent activity in activating the IRE1α ribonuclease (RNase) activity, inducing increased XBP1 mRNA splicing, and inducing Bloc1s1 mRNA degradation. Based on a binding mode analysis, the following series of PR-decorated functionalized amines was further probed as IRE1α RNase activators. One PR-derived compound, AK177, showed nanomolar activating potency in biochemical assays but minimal activities in cellular evaluations. Overall, we present here a series of pyrazolylpyrimidinamines as new small-molecule activators of the IRE1α RNase activity, which served as the first examples of applying PR in accessing bioactive compounds targeting the kinase domain of a ribonuclease involved in mRNA cleavage and splicing.