(−)-Lomaiviticin A (<b>1</b>) is a <i>C</i><sub>2</sub>-symmetric cytotoxin
that contains two diazofluorene
functional groups and which induces double-strand breaks (DSBs) in
DNA. Evidence suggests DNA cleavage is initiated by hydrogen atom
abstraction from the deoxyribose backbone. Here we demonstrate the
formation of the vinyl radicals <b>1·</b> and <b>2·</b> from <b>1</b> by 1,7-addition of thiols to the diazofluorenes.
These radicals can affect hydrogen atom abstraction from methanol
and acetone. The first addition of thiol to <b>1</b> proceeds
at a much greater rate than the second. The diazosulfide <b>5</b> formed en route to <b>1·</b> has been detected at −50
°C and undergoes decomposition to <b>1·</b> with a
half-life of 110 min at −20 °C under air. These data,
which constitute the first direct evidence for the generation of <b>1·</b> and <b>2·</b> from <b>1</b>, provide
insights into the mechanism of DNA cleavage by <b>1</b>
