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.