seco-Cyclothialidines:  New Concise Synthesis, Inhibitory Activity toward Bacterial and Human DNA Topoisomerases, and Antibacterial Properties

seco-Cyclothialidines are a promising class of bacterial DNA gyrase B subunit inhibitors. A new seco-cyclothialidine derivative containing a dioxazine moiety, BAY 50-7952, was synthesized through a new concise pathway. One key step of the synthesis is the straightforward formation of the 2-aminothiazole derivative of S-tritylcysteine. In biological tests, BAY 50-7952 and other known seco-cyclothialidines exhibited high and selective activity toward bacterial DNA gyrase and toward Gram-positive bacteria. The dioxazine moiety and other similar groups were found to be important for the ability of the seco-cyclothialidines to penetrate bacterial membranes. The opposite enantiomer ((S)-form) of BAY 50-7952 was also synthesized, and neither significant target activity nor in vitro antibacterial activity were found, suggesting a highly selective fit of the (R)-form. Despite promising in vitro activity, only poor activity was found in the murine infection model.