Development of both potent and selective kinase inhibitors
is a
challenging task in modern drug discovery. The innate promiscuity
of kinase inhibitors largely results from ATP-mimetic binding to the
kinase hinge region. We present a novel class of substituted 7,8-dichloro-1-oxo-β-carbolines
based on the distinct structural features of the alkaloid bauerine
C whose kinase inhibitory activity does not rely on canonical ATP-mimetic hinge interactions. Intriguingly, cocrystal structures revealed
an unexpected inverted binding mode and the presence of halogen bonds
with kinase backbone residues. The compounds exhibit excellent selectivity
over a comprehensive panel of human protein kinases while inhibiting
selected kinases such as the oncogenic PIM1 at low nanomolar concentrations.
Together, our biochemical and structural data suggest that this scaffold
may serve as a valuable template for the design and development of
specific inhibitors of various kinases including the PIM family of
kinases, CLKs, DAPK3 (ZIPK), BMP2K (BIKE), and others.