1D TOCSY技术用于水溶液中氨基葡萄糖结构指认

1D TOCSY Technique for Sequential Structure Assignment of Glucosamines in Aqueous Solution

氨基糖类化合物在水溶液中容易发生变旋,由单一构型化合物变为α,β两种构型的混合物,加之糖环质子化学位移差异不大,导致信号相互重叠交叉严重,极大增加了核磁谱图解析的难度。利用1D TOCSY技术,其中整形脉冲选择Gaussian脉冲,激发中心为异头质子峰（样品383分别为δH5.39,4.89;样品170分别为δH5.13,4.64）,信号激发宽度为16 Hz,通过改变整形脉冲的混合时间（10~200 ms）,获得系列1D TOCSY谱,由近到远顺序提取同一异构体不同位置质子信息,实现对D-氨基葡萄糖盐酸盐（样品383）和N-乙酰-D-氨基葡萄糖（样品170）在水溶液中的复杂常规氢谱的有效分解和两种构型异构体信号的快速分组,从而完成不同构型化合物的质子信号的归属,并确认两种异构体构型及其比例。辅以13C NMR、DEPT135、HSQC和HMBC数据信息完成对其构型混合物结构的全解析,以建立一种利用核磁共振解析氨基葡萄糖类化合物在水溶液中复杂结构的方法。

Peak overlap is one of the major factors complicating the analysis of NMR spectra. For glucosamine compounds,such as N-acetyl-D-glucosamine and D-glu-cosamine hydrochloride,anomerization occurs readily and leads to a mixture of α and β anomers in aqueous solution. As a result,peaks overlap seriously in1 H NMR spectra. A selective excitation NMR technique,one dimensional total correlation spectroscopy（ 1D TOCSY） offers a robust approach to resolving seriously overlapped spectra. In 1D TOCSY experiment,one of anomeric protons in glucosamines（ for compound 383： δH5. 39,4. 89; for compound 170： δH5. 13,4. 64） was selectively excited,and the corresponding signal was transferred to protons within the same spin system in a stepwise process with an increased mixing time（ 10-200 ms） of the shaped pulse（ Gaussian pulse）. Through a series of these ＂ proton-relay ＂ spectra,the peaks and conformations of each anomer were assigned. As a set of suitable spectra including13 C NMR,DEPT135,HSQC and HMBC were obtained,the structural elucidation of these anomeric components were achieved. A rapid NMR method for the structure assignment of α and β anomers mixture of glucosamines was established.