ZNL0325, a Pyrazolopyrimidine-Based Covalent Probe, Demonstrates an Alternative Binding Mode for Kinases

The
pyrazolopyrimidine (PP) heterocycle is a versatile and widely
deployed core scaffold for the development of kinase inhibitors. Typically,
a 4-amino-substituted pyrazolopyrimidine binds in the ATP-binding
pocket in a conformation analogous to the 6-aminopurine of ATP. Here,
we report the discovery of ZNL0325 which exhibits a flipped binding
mode where the C3 position is oriented toward the ribose binding pocket.
ZNL0325 and its analogues feature an acrylamide side chain at the
C3 position which is capable of forming a covalent bond with multiple
kinases that possess a cysteine at the αD-1 position including
BTK, EGFR, BLK, and JAK3. These findings suggest that the ability
to form a covalent bond can override the preferred noncovalent binding
conformation of the heterocyclic core and provides an opportunity
to create structurally distinct covalent kinase inhibitors.