Grepafloxacin, a 5-methyl-7-piperazinyl-3"-methyl analogue of ciprofloxacin, was used to obtain stepwise-selected mutants of Streptococcus pneumoniae 7785. Analysis of the quinolone resistance-determining regions of the gyrA, gyrB, parC, and parE genes in these mutants revealed that gyrA mutations preceded those in parC. Given that ciprofloxacin (5-H,7-piperazinyl) and AM-1121 (5-H,7-piperazinyl-3"-methyl) both act through topoisomerase IV, we conclude that the 5-methyl group of grepafloxacin favors gyrase in S. pneumoniae.
Julia E Morris, Xiao-Su Pan, L Mark Fisher. Grepafloxacin, a dimethyl derivative of ciprofloxacin, acts preferentially through gyrase in Streptococcus pneumoniae: role of the C-5 group in target specificity. Antimicrobial agents and chemotherapy. 2002 Feb;46(2):582-5
PMID: 11796384
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