Dramatic improvements in viral inactivation with brominated psoralens, naphthalenes and anthracenes

Amino or polyamino derivatives of naphthalene (N-H), anthracene (A-H) and 8-alkoxypsoralen (PSR-H) were prepared along with their monobrominated analogs (N-Br, A-Br and PSR-Br). The ammonium salts of these compounds are all water soluble and bind strongly to calf thymus DNA and to lambda phage, a double-helical DNA, protein-coated virus. Binding of the sensitizer to DNA occurs, presumably by a mixture of hydrophobic, intercalative and electrostatic interactions. Relative binding constants to calf thymus DNA and to lambda phage were measured by the ethidium bromide fluorescence quenching assay. In general the brominated analogs bind more tightly to calf thymus DNA and to the virus than to the nonhalogenated analogs. It is demonstrated that the brominated aromatics are much more effective at inactivating lambda phage upon photoactivation (lambda approximately 310 or 350 nm) than are their nonbrominated analogs. At identical sensitizer concentrations (by weight) and light flux N-Br, A-Br, and PSR-Br produce 5-6 more logs of viral inactivation than their nonbrominated counterparts (N-H, A-H and PSR-H, respectively). The bromine effect may originate from light-induced electron transfer and subsequent cleavage of the C-Br bond of the sensitizer radical anion bonds to form aryl radicals. Singlet oxygen cannot be responsible for the viral inactivation because the brominated sensitizers are equally effective in the presence and absence of oxygen. Dithiothreitol does not protect lambda phage from light-induced inactivation by the brominated sensitizer thereby demonstrating that the photogenerated reactive intermediates responsible for the effect are complexed to the virus and are not generated free in solution.