Modes of methyleneoxy bridging and their effect on tetrahydronaphthalene lignan cytotoxicity.

Dioxatricyclodecane, oxabicyclooctane, and benzodihydropyran derivatives of alpha-conidendrin (ACON), podophyllotoxin (PT), and sikkimotoxin (SK) were prepared to learn which methyleneoxy bridging modes and arene and aryl substituents coincided with high cytotoxicity. PT-derived dioxatricyclodecane 14 showed in vitro activity at 10(-8) M. SK analogue 12 was less active, and ACON analogue 11 was inactive at 10(-4) M. In vivo intraperitoneal and subcutaneous activities of 14 were observed. In vitro cytotoxicities were higher for oxabicyclooctanes when hydroxymethyl group and methyleneoxy bridge were cis, as in deoxypicropodophyllin analog20, rather than trans, as in PT analogue 5. Acetylation of the hydroxymethyl group of 20 lowered activities, whereas acetylation of 5 increased or lowered activities. Reduction of the hydroxymethyl group of 5 to a methyl group increased cytotoxicities. Molecular dynamics indicated the THN scaffold of benzodihydropyrans was conformationally mobile, but scaffolds of oxabicyclooctanes and dioxatricyclodecanes were immobile. Each of three PT-benzodihydropyrans was less active than its oxabicyclooctane counterpart.