NMR Analysis of Synthetic Oligosaccharide Fragments of the OSP of E. coli O-148

已经采用的NMR技术包括一维（1D）1H、1D 13 C、二维（2D）1H-1H相关光谱（COSY）、2D 1H-1H总相关光谱（TOCSY）、2D 13 C-1H杂原子单量子相关光谱（HSQC）、2D 13 C-1H杂原子多键相关（HMBC）、2D 1H-偶联13 C-1H HSQC、和1D ~ 1H-偶联~（13）C NMR。COSY技术给出了关于1H光谱归属的信息，TOCSY程序提供了单个糖残基的单独1H子光谱，HSQC方法通过关联1H和13 C化学位移提供13 C光谱归属，HMBC脉冲序列通过关联它们的1H或13 C化学位移与糖环中的核的化学位移来描绘取代基的位置。1H-偶联1D 13 C和1H-偶联2D HSQC技术用于测量寡糖的13 C-1H偶联常数。后一种2D方法是特别有用的，当1H-耦合，1D 13 C NMR光谱是不充分分散的一个简单的分析。测量1 JC-1、H-1值，通常给出寡糖中所有异头键的构型（α或β）信息。通常可从1H NMR谱测量的3 JH-1、H-2值获得表征信息，但吡喃甘露糖和吡喃鼠李糖除外，其α和β端基异构体的值相似。 8-mer和12-mer在D_2O溶液中的~ 1H谱存在宽化现象，影响了谱图的分析和归属。考虑到这种宽度可能是由于8-mer和12-mer溶液的粘度，我们在50 ℃和60 ℃的高温下获得了12-mer的1H和13 C光谱，但这没有帮助。我们正在研究的可能性，意想不到的光谱的宽度是由于顺磁性金属离子污染物的8聚体和12聚体。碳水化合物通常是优良的金属络合剂，并且在清除的顺磁性金属离子存在下观察到的偶尔光谱增宽是众所周知的现象。因此，我们用Chelex 100阳离子交换树脂（钠型）处理8聚体，以去除任何多价顺磁性离子。在这种处理之后，8聚体显示出改善的1H光谱分辨率。

The NMR techniques that have been employed include one-dimensional (1D) 1H, 1D 13C, two-dimensional (2D) 1H-1H correlation spectroscopy (COSY), 2D 1H-1H total correlation spectroscopy (TOCSY), 2D 13C-1H heteronuclear single quantum correlation spectroscopy (HSQC), 2D 13C-1H heteronuclear multiple bond correlation (HMBC), 2D 1H-coupled 13C-1H HSQC, and 1D 1H-coupled 13C NMR. The COSY technique gives information about 1H spectral assignments, the TOCSY procedure provides separate 1H sub-spectra for individual sugar residues, the HSQC method provides 13C spectral assignments by correlating the 1H and 13C chemical shifts, and the HMBC pulse sequence delineates the positions of substituents by correlating their 1H or 13C chemical shifts with those of nuclei in the sugar rings. The 1H-coupled 1D 13C and 1H-coupled 2D HSQC techniques are used to measure 13C-1H coupling constants of the oligosaccharides. The latter 2D method is particularly useful when the 1H-coupled, 1D 13C NMR spectra are insufficiently dispersed for a facile analysis. 1JC-1,H-1 values were measured, typically giving information on the configuration (alpha or beta) of all the anomeric linkages in the oligosaccharide. Confirmatory information is often available from the 3JH-1,H-2 values measured from the 1H NMR spectra, with the exception of mannopyranose and rhamnopyranose, for which the values of the alpha and beta anomers are similar. A problem has been encountered with broadness of the 1H spectra of the 8-mer and 12-mer in D2O solutions, which could inhibit the analysis and assignment of the spectra. Thinking that this broadness might be due to viscosity of the solutions of the 8-mer and 12-mer, we acquired 1H and 13C spectra of the 12-mer at elevated temperatures, 50 C and 60 C, but this did not help. We are investigating the possibility that the unexpected broadness of the spectra is due to paramagnetic metal ion contaminants in the 8-mer and 12-mer. Carbohydrates are often excellent metal-complexing agents, and the occasional spectral broadening observed in the presence of scavenged paramagnetic metal ions is a well-known phenomenon. We have therefore treated the 8-mer with Chelex 100 cation exchange resin (sodium form) in an effort to remove any polyvalent, paramagnetic ions. Following this treatment, the 8-mer has shown improved 1H spectral resolution.