Enhancement of the antibacterial activity of ciprofloxacin against Staphylococcus aureus by 3-alkyl esters and 3-aryl esters of hexahydroquinoline derivatives

In this study, 3-alkyl and 3-aryl esters of hexahydroquinoline derivatives were screened for their ability to decrease bacterial resistance to ciprofloxacin (CAS 85721-33-1), which is extensively used to treat bacterial infections. A group of 3-alkyl and 3-aryl esters of hexahydroquinoline derivatives in which 2-aryl thiazole is substituted at 4-position were synthesized. The enhancement of the antibacterial activity of ciprofloxacin by these new synthetic compounds was evaluated against a resistant clinical strain of Staphylococcus aureus. The agar disk diffusion method was used to determine the antibacterial activity of different synthetic compounds in the absence and presence of ciprofloxacin. These results indicate that the antibacterial effect of ciprofloxacin is enhanced by two 3-alkyl esters of hexahydroquinoline derivatives (7b-3 and 7b-4).The enhancing effect of 7b-4 on the antibacterial activity of ciprofloxacin was greater than that of compound 7b-3. In comparison to the other synthetic compounds, 7b-4 showed a 5.61-fold increase of the inhibition zone on the ciprofloxacin supplemented plates. The result demonstrated that compounds 7b (3 and 4) could serve as valuable probes to study the structure-function relationships of agents that reverse the resistance to ciprofloxacin.