Hydroxy tricyclic 1,5-naphthyridinone oxabicyclooctane-linked novel bacterial topoisomerase inhibitors as broad-spectrum antibacterial agents-SAR of RHS moiety (Part-3).

Novel bacterial topoisomerase inhibitors (NBTIs) are a new class of broad-spectrum antibacterial agents targeting bacterial Gyrase A and ParC and have potential utility in combating antibiotic resistance. (R)-Hydroxy-1,5-naphthyridinone left-hand side (LHS) oxabicyclooctane linked pyridoxazinone right-hand side (RHS) containing NBTIs showed a potent Gram-positive antibacterial profile. SAR around the RHS moiety, including substitutions around pyridooxazinone, pyridodioxane, and phenyl propenoids has been described. A fluoro substituted pyridoxazinone showed an MIC against Staphylococcus aureus of 0.5 µg/mL with reduced functional hERG activity (IC50 333 µM) and good in vivo efficacy [ED90 12 mg/kg, intravenous (iv) and 15 mg/kg, oral (p.o.)]. A pyridodioxane-containing NBTI showed a S. aureus MIC of 0.5 µg/mL, significantly improved hERG IC50 764 µM and strong efficacy of 11 mg/kg (iv) and 5 mg/kg (p.o.). A phenyl propenoid series of compounds showed potent antibacterial activity, but also showed potent hERG binding activity. Many of the compounds in the hydroxy-tricyclic series showed strong activity against Acinetobacter baumannii, but reduced activity against Escherichia coli and Pseudomonas aeruginosa. Bicyclic heterocycles appeared to be the best RHS moiety for the hydroxy-tricyclic oxabicyclooctane linked NBTIs.

Development of a DNA-binding TEMPO derivative for evaluation of nuclear oxidative stress and its application in living cells.

Oxidative stress in nuclei is known to induce either oxidative modification of DNA bases or single/double-strand breaks, which may lead to carcinogenesis. To evaluate the redox status in nuclei in living cells, we designed a novel nucleus-localizing redox spin probe, F-DisT, which contains a fluorescein fluorophore linked to a DNA minor-groove-binding moiety. Nuclear distribution of the probe was easily confirmed by colocalization with a nuclear stain, Hoechst 33342, in confocal microscopy. Measurement of oxidative stress with F-DisT in a murine macrophage cell line exposed to endotoxin (lipopolysaccharide) showed a remarkable increase in the ESR signal decay rate. This increase was significantly inhibited by N(ω)-nitro-l-arginine (nitric oxide synthase inhibitor) and diphenyleneiodonium chloride (NADPH oxidase inhibitor). These results indicate that nitric oxide and superoxide contribute to oxidative stress in nuclei. Similar studies in membrane or mitochondria using respective organelle-specific spin probes indicated that the redox microenvironments in these organelles are markedly different from that in nuclei. Thus, subcellular redox microenvironments show marked variability in endotoxin-stimulated living cells.

Novel mitochondria-localizing TEMPO derivative for measurement of cellular oxidative stress in mitochondria.

Neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases, and apoptosis, are thought to be associated with oxidative stress affecting mitochondria. In this study, we designed and synthesized a fluorescein-tagged TEMPO derivative, compound 1, with triphenylphosphino moiety. Synthesized 1 localized in mitochondria and detected oxidative stress in an endotoxic model of a mouse macrophage-like cell line. Compound 1 is therefore a potentially useful probe for evaluating oxidative stress in mitochondria.

Novel membrane-localizing TEMPO derivatives for measurement of cellular oxidative stress at the cell membrane.

Oxidative stress affecting lipid membranes is considered to be closely related to cardiovascular disease and brain ischemia. In this study, we designed and synthesized membrane-localizing TEMPO derivatives and demonstrated that one of these synthesized probes, compound 1, localized and detected oxidative stress in the cell membrane in an endotoxic model of a mouse macrophage-like cell line. Compound 1 is therefore a potentially useful probe for evaluating oxidative stress at the cell membrane.