Fe(II)-induced decomposition of 1,2,4-trioxolanes (ozonides) 1 and 2 is studied in detail. The inner-sphere electron transfer reduction, which is sensitive to steric effects, is proposed to be a reasonable mechanism for the peroxide decomposition, i.e., the selective generation of one of the two possible Fe(III)-complexed oxy radicals. The fate of the oxy radical species is revealed in detail by using 18O-tracer studies in the reduction of 18O-labeled ozonides 1a and 2a, in which the ethereal oxygens are labeled by 18O atom (18O, 77%) and also by the reduction in the presence of H2 18O (18O, 10%). The results of the 18O-tracer studies are consistent with the regioselective generation of the Fe(III)-complexed oxy radical species.

Our focus was to develop an anti-angiogenic drug possessing the inhibitory activity of urokinase-type plasminogen activator (u-PA) production. During preliminary screening, the effects of 13 ozonides on the inhibition of u-PA production in human fibrosarcoma HT-1080 cells and on the inhibition of angiogenesis on chicken embryonic chorioallantoic membranes were determined. Of the ozonides tested, 9 inhibited in vitro u-PA production of HT-1080 cells and 7 of these 9 exhibited strong anti-angiogenic activity. Interestingly, 6 of the 13 ozonides also inhibited cathepsin B activity. 1-Phenyl-1, 4-epoxy-1H,4H-naphtho[1,8-de][1, 2]dioxepin (ANO-2) potently inhibited cathepsin B (IC 50 ‫؍‬ 0.47 M) as well as u-PA production. Consequently, ANO-2 was selected for further study. ANO-2 inhibited tube formation by human umbilical vein endothelial cells cultured on Matrigel while exhibiting no cytotoxicity. Additionally, in vivo administration of ANO-2 inhibited angiogenesis induced by mouse Sarcoma-180 cells tested using the mouse dorsal air sac assay. Moreover, ANO-2 also suppressed primary tumor growth and reduced the number of pulmonary metastases caused by Lewis lung carcinoma cells in mice. These in vitro and in vivo activities indicate that ANO-2 has considerable potential as a new and potent anti-angiogenic drug that inhibits both u-PA production and enzymatic activity of cathepsins, indicating that ANO-2 may be a multifunctional inhibitor of angiogenesis.