Novel inhibitors of RANKL-induced osteoclastogenesis: Design, synthesis, and biological evaluation of 6-(2,4-difluorophenyl)-3-phenyl-2H-benzo[e][1,3]oxazine-2,4(3H)-diones

A series of novel 6-(2,4-difluorophenyl)-3-phenyl-2H-benzo[e][1,3]oxazine-2,4(3H)-dione derivatives were synthesized and evaluated for their inhibitory effects on osteoclast activities by using TRAP-staining assay. Among the tested compounds, 3d and 3h exhibited more potent osteoclast-inhibitory activities than the lead compound NDMC503 (a ring-fused structure of NDMC101), as reported in our previous study. Both 3d and 3h exhibited two-fold increase in activity compared to NDMC503. In addition, our biological results indicated that 3d and 3h could suppress RANKL-induced osteoclastogenesis-related marker genes, such as NFATc1, c-fos, TRAP, and cathepsin K. Notably, 3d could significantly attenuate the bone-resorbing activity of osteoclasts in the pit formation assay. Thus, this study might provide a new class of lead structures that warrant further development as potential anti-resorptive agents.