A structureâactivity relationship (SAR) guided design of novel tubulin polymerization inhibitors has resulted in a series of benzo[b]furans with exceptional potency toward cancer cells and activated endothelial cells. The potency of early lead compounds has been substantially improved through the synergistic effect of introducing a conformational bias and additional hydrogen bond donor to the pharmacophore. Screening of a focused library of potent tubulin polymerization inhibitors for selectivity against cancer cells and activated endothelial cells over quiescent endothelial cells has afforded 7-hydroxy-6-methoxy-2-methyl-3-(3,4,5-trimethoxybenzoyl)benzo[b]furan (BNC105, 8) as a potent and selective antiproliferative. Because of poor solubility, 8is administered as its disodium phosphate ester prodrug 9(BNC105P), which is rapidly cleaved in vivo to return the active 8. 9exhibits both superior vascular disrupting and tumor growth inhibitory properties compared with the benchmark agent combretastatin A-4 disodium phosphate 5(CA4P). [ABSTRACT FROM AUTHOR]