Synthesis and Evaluation of 4‑Hydroxycoumarin Imines as Inhibitors of Class II Myosins

Inhibitors
of muscle myosin ATPases are needed to treat conditions
that could be improved by promoting muscle relaxation. The lead compound
for this study ((3-(N-butylethanimidoyl)­ethyl)-4-hydroxy-2H-chromen-2-one; BHC) was previously discovered to inhibit
skeletal myosin II. BHC and 34 analogues were synthesized to explore
structure–activity relationships. The properties of analogues,
including solubility, stability, and toxicity, suggest that the BHC
scaffold may be useful for developing therapeutics. Inhibition of
actin-activated ATPase activity of fast skeletal and cardiac muscle
myosin II, inhibition of skeletal muscle contractility ex
vivo, and slowing of in vitro actin-sliding
velocity were measured. Several analogues with aromatic side arms
showed improved potency (half-maximal inhibitory concentration (IC50) <1 μM) and selectivity (≥12-fold) for skeletal
myosin versus cardiac myosin compared to BHC. Several
analogues blocked neurotransmission, suggesting that they are selective
for nonmuscle myosin II over skeletal myosin. Competition and molecular
docking studies suggest that BHC and blebbistatin bind to the same
site on myosin.