Chemical Journal of Chinese Universities

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Studies on NMR Behavior of Ofloxacin in Different pH Environment

QI Jian1, GAO Xiu-Xiang1, ZHAO Mei-Xian2, XIANG Jun-Feng3, LIN Chong-Xi1*, XU Yi-Zhuang1*, WU Jin-Guang1   

    1. College of Chemical and Molecular Engineering, Peking University, Beijing 100871, China;
    2. Applied Chemistry Department, School of Science, Beijing University of Chemical Technology, Beijing 100029, China;
    3. Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, China
  • Received:2006-07-24 Revised:1900-01-01 Online:2007-05-10 Published:2007-05-10
  • Contact: LIN Chong-Xi

Abstract: Systematic NMR spectroscopic investigation on ofloxacin in both acidic and alkaline solutions was carried out via 1H, 13C NMR, DEPT, COSY, HSQC spectra together with HMBC techniques. Complete assignment on 1H and 13C NMR of ofloxacin was obtained in different pH environments where the coupling constant between 13C and 19F was found to be very helpful for the assignment of aromatic 13C NMR signals. Additionally, the chemical shifts of 1H from the complex spin systems such as AA'BB' were obtained using HSQC technique. Comparisons were made among the NMR spectra in acidic solution and those in alkaline solution, which demonstrate that: (1) deprivation of H+ from COOH in alkaline solution destroys the hydrogen bond between COOH and carbonyl group in ofloxacin. This brings about the redistribution of π elelctrons around the carboxyl and carbonyl groups so that significant variations of 13C NMR chemical shift and coupling constant JFC are observed. (2) In the alkaline solution, the removal of proton from N4 in piperazine ring induces considerable variation of chemical shift of methylene groups and causes remarkable changes of dynamic behavior of the piperazine ring.

Key words: Quinolone, Ofloxacin, NMR, Piperazine ring

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