3-Amino-benzo[d]isoxazoles as Novel Multitargeted Inhibitors of Receptor Tyrosine Kinases

A series of benzoisoxazoles and benzoisothiazoles have been synthesized and evaluated as inhibitors of receptor tyrosine kinases (RTKs). Structure–activity relationship studies led to the identification of 3-amino benzo[d]isoxazoles, incorporating a N,N′-diphenyl urea moiety at the 4-position that potently inhibited both the vascular endothelial growth factor receptor (VEGFR) and platelet-derived growth factor receptor families of RTKs. Within this series, orally bioavailable compounds possessing promising pharmacokinetic profiles were identified, and a number of compounds demonstrated in vivo efficacy in models of VEGF-stimulated vascular permeability and tumor growth. In particular, compound 50 exhibited an ED50 of 2.0 mg/kg in the VEGF-stimulated uterine edema model and 81% inhibition in the human fibrosarcoma (HT1080) tumor growth model when given orally at a dose of 10 mg/kg/day.