Phenothiazinium–fluoroquinolone drug conjugates

Synthesis and antibacterial screening of a homologous series of 3-dialkylaminophenothiazinium-7-norfloxacin conjugates was carried out alongside a corresponding series of symmetrical methylene blue derivatives. The norfloxacin conjugates maintained typical methylene blue derivative photoproperties, such as long wavelength absorption, but produced no measurable singlet oxygen in the standard assay and provided no significant increase in the magnitude of photoantibacterial action, this being similar to the methylene blue homologues, although both the conjugates and homologues were considerably more active than methylene blue itself both against Staphylococcus aureus and Escherichia coli. DNA binding via intercalation was considerably greater for the series of norfloxacin conjugates than for the methylene blue homologues.