Diastereomeric bactericidal effect of Ru(phenanthroline)(2)dipyridophenazine

Metal susceptibility assays and spot plating were used to investigate the antimicrobial activity of enantiopure [Ru(phen)(2)dppz](2+) (phen =1,10‐phenanthroline and dppz = dipyrido[3,2‐a:2´,3´‐c]phenazine) and [μ‐bidppz(phen)(4)Ru(2)](4) (+) (bidppz =11,11´‐bis(dipyrido[3,2‐a:2´,3´‐c]phenazinyl)), on Gram‐negative Escherichia coli and Gram‐positive Bacillus subtilis as bacterial models. The minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) were determined for both complexes: while [μ‐bidppz(phen)(4)Ru(2)](4) (+) only showed a bactericidal effect at the highest concentrations tested, the antimicrobial activity of [Ru(phen)(2)dppz](2+) against B. subtilis was comparable to that of tetracyline. In addition, the Δ‐enantiomer of [Ru(phen)(2)dppz](2+) showed a 2‐fold higher bacteriostatic and bactericidal effect compared to the Λ‐enantiomer. This was in accordance with the enantiomers relative binding affinity for DNA, thus strongly indicating DNA binding as the mode of action.