Syntheses and antibacterial activity of soluble 9-bromo substituted indolizinoquinoline-5,12-dione derivatives.

In our previous research, 9-bromo indolizinoquinoline-5,12-dione 1 has been found to be a good anti-MRSA agent. However, it had very low bioavailability in vivo possibly due to its low solubility in water. In order to obtain the derivatives with higher anti-MRSA activity and good water solubility, twenty eight bromo-substituted indolizinoquinoline-5,12-dione derivatives were synthesized in the present study. The antibacterial activity of the synthesized compounds was evaluated against one gram-negative and some gram-positive bacterial strains including 100 clinical MRSA strains. The UV assays were carried out to determine the solubility of six active compounds 16, 21, 23 and 27–29. The most potent compound 28 exhibited strong activity against clinical MRSA strains with both MIC50 and MIC90 values lower than 7.8 ng/mL. Compound 27 had good water solubility of 1.98 mg/mL and strong activity against clinical MRSA strains with MIC50 value of 63 ng/mL and MIC90 value of 125 ng/mL, 16-fold higher than that of Vancomycin.