Sydnone Cycloaddition Route to Pyrazole-Based Analogs of Combretastatin A4

The combretastatins
are an important class of tubulin-binding agents.
Of this family, a number of compounds are potent tumor vascular disrupting
agents (VDAs) and have shown promise in the clinic for cancer therapy.
We have developed a modular synthetic route to combretastatin analogs
based on a pyrazole core through highly regioselective alkyne cycloaddition
reactions of sydnones. These compounds show modest to high potency
against human umbilical vein endothelial cell proliferation. Moreover,
evidence is presented that these novel VDAs have the same mode of
action as CA4P and bind reversibly to β-tubulin, believed to
be a key feature in avoiding toxicity. The most active compound from
in vitro studies was taken forward
to an in vivo model and instigated an increase in tumor cell necrosis.