氧氟沙星的核磁共振波谱性质研究

结合1H, 13C NMR, DEPT, COSY, HSQC, HMBC谱和碳氟偶合裂分行为, 对酸性及碱性溶液中氧氟沙星(Ofloxacin, OFL)的1H和13C谱分别进行归属, 研究了哌嗪环亚甲基构成的AA'BB'复杂自旋体系中各H的化学位移. 发现噁嗪环上的甲基处于直立键; 5H在酸性溶液中化学位移移向低场, 这可能与形成C—H…O弱氢键有关; 在碱性溶液中, OFL的羧基变为羧酸根, 造成羧基和羰基周围碳原子上π电子重新分布, 导致相应C的化学位移和碳氟偶合常数发生明显变化.

Studies on NMR Behavior of Ofloxacin in Different pH Environment

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.