Discovery of bicyclo[3,3,1]non-2-ene as a novel skeleton for HIF-1 inhibitors

Bicyclo[3,3,1]non-2-ene was used as a novel three-dimensional skeleton for the design and synthesis of hypoxia-inducible factor (HIF)-1 inhibitors. Among the compounds synthesized, compound 4b was found to be a potent inhibitor of HIF-1α protein accumulation under hypoxia and inhibited HIF-1α transcriptional activity in HeLa (human cervical carcinoma) cells (half maximal inhibitory concentration [IC50] = 3.0 μM). The inhibition of HIF-1α accumulation induced by compound 4b was attenuated by treating the cells with MG132, a proteasome inhibitor, in a concentration-dependent manner, indicating that the compound 4b induces oxygen-independent proteasomal degradation of HIF-1α.