Novel coumarin aminophosphonates as potential multitargeting antibacterial agents against Staphylococcus aureus.

Unique coumarin aminophosphonates as new antibacterial agents were designed and synthesized to combat severely bacterial resistance. Bioactivity assessment identified that 3-hydroxylphenyl aminophosphonate 6f with low hemolytic activity not only exhibited excellent inhibition potency against Staphylococcus aureus at low concentration (0.5 µg/mL) in vitro but also showed considerable antibacterial potency in vivo. Meanwhile, the active compound 6f was capable of eradicating the S. aureus biofilm, thus alleviating the development of S. aureus resistance. Furthermore, the drug combination of compound 6f with norfloxacin could enhance the antibacterial efficacy. Mechanistic explorations manifested that molecule 6f was able to destroy the integrity of cell membrane, which resulted in the leakage of protein and metabolism inhibition. The cellular redox homeostasis was interfered through inducing the generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS), leading to the reduction of glutathione (GSH) activity and lipid peroxidation. Furthermore, compound 6f could intercalate into DNA base pair to hinder normal biological function. The above results provided powerful information for the further development of coumarin aminophosphonates as antibacterial agents.

Coumarin thiazoles as unique structural skeleton of potential antimicrobial agents.

A novel type of coumarin thiazoles as unique multi-targeting antimicrobial agents were developed through four steps including cyclization, nucleophilic substitution and condensation starting from commercial resorcine. Most of the prepared coumarin thiazoles displayed favorable inhibitory potency against the tested strains. Noticeably, methyl oxime V-a exerted potent inhibitory efficacy against methicillin-resistant Staphylococcus aureus (MRSA) at low concentration (1 µg/mL) and showed broad antimicrobial spectrum. Medicinal bioevaluations revealed that the active molecule V-a exhibited low toxicity toward mammalian cells, rapidly killing effect, good capability of eradicating MRSA biofilms and unobvious probability to engender drug resistance. Chemical biological methods were employed to investigate preliminary mechanism, which indicated that compound V-a was able to damage the integrity of membrane to trigger leakage of protein, insert into MRSA DNA to block its replication and induce the generation of reactive oxygen species (ROS) to inhibit bacterial growth. Computational study manifested that low HOMO-LUMO energy gap of molecule V-a was favorable to exert high antimicrobial activity.

Discovery of unique thiazolidinone-conjugated coumarins as novel broad spectrum antibacterial agents.

Unique coumarin conjugates with thiazolidinone as novel structural antibacterial modulators were exploited to combat the lethal multidrug-resistant bacterial infections. Bioactivity evaluation identified that indole-incorporated coumarin thiazolidinone conjugate 14a with low cytotoxicity to mammalian cells showed a broad antibacterial spectrum and exerted potent inhibition efficiencies to the tested germs at low concentrations (0.25-2 µg/mL). Moreover, the favorable performance of 14a in eradicating bacterial biofilm was beneficial to avert developing drug resistance. Mechanistic explorations revealed that molecule 14a was able to destroy cell membrane, leading to the leakage of intracellular materials and metabolism inhibition. The accumulation of excess reactive oxygen species (ROS) mediated by compound 14a could impede glutathione (GSH) activity and induce lipid peroxidation to suppress bacteria growth. Furthermore, compound 14a could not only intercalate into DNA base pair but also take part in non-covalent interaction with DNA gyrase B to hinder their biological function. Quantum chemical study indicated that molecule 14a had low HOMO-LUMO energy gap, which resulted in more stabilizing interactions and was conducive to displaying better antibacterial activity. ADMET analysis manifested that 14a possessed promising pharmacokinetic properties.