Risley J M, Van Etten R L
Biochemistry. 1982 Dec 7;21(25):6360-5. doi: 10.1021/bi00268a007.
The 18O isotope induced shift in 13C nuclear magnetic resonance (NMR) spectroscopy affords a new and convenient method for the study of oxygen exchange at the anomeric carbon atom of simple sugars. The efficacy of the technique was confirmed by a study of the oxygen exchange reaction of D-[1-13C] glucose. At pH 7.0 and 61 degrees C, the incorporation of 18O from solvent H2(18)O onto the C-1 carbon atom of the diastereomeric alpha- and beta-pyranose sugars was followed by 13C NMR spectroscopy in a continuous assay mode. The pseudo-first-order rate constant for exchange of both the alpha and the beta anomers was 9.5 X 10(-5) s-1, which is in agreement with a rate constant obtained in a previous study by a chemical conversion-mass spectrometry technique. The new technique was applied to a study of the oxygen exchange at the anomeric carbon atom of D-[1-13C]erythrose, a furanose sugar for which no experimental data were available. In unbuffered, aqueous solutions the incorporation of the 18O label from the medium (H2(18)O) onto the C-1 carbon atom of the alpha- and beta-D-[1-13C]erythrose and the D-[1-13C]erythrose hydrate forms was followed by 13C NMR at 10, 23, and 36 degrees C. From analysis of the data for the alpha and beta diastereomers, the pseudo-first-order rate constants for exchange were 1.4 X 10(-4) s-1 at 10 degrees C, 4.8 X 10(-4) s-1 at 23 degrees C, and 8 X 10(-4) s-1 at 36 degrees C, and the apparent energy of activation for the exchange reaction was 12.1 kcal/mol. Particularly in conjunction with the use of specifically 13C-enriched sugars, the new technique for studying oxygen exchange reactions of carbohydrates has many distinct advantages over earlier approaches, including the ability to follow simultaneously the exchange reactions of all of the sugar species for which a 13C NMR signal can be detected, the continuity of the assay, the avoidance of possible artifacts due to incomplete or selective derivatization reactions, and the simplicity of the data analysis.
18O同位素诱导的13C核磁共振（NMR）光谱位移为研究单糖异头碳原子上的氧交换提供了一种新的便捷方法。通过对D-[1-13C]葡萄糖的氧交换反应研究，证实了该技术的有效性。在pH 7.0和61℃条件下，采用连续测定模式，通过13C NMR光谱跟踪溶剂H2(18)O中的18O掺入非对映体α-和β-吡喃糖的C-1碳原子的过程。α-和β-异头物交换的准一级速率常数均为9.5×10(-5) s-1，这与先前通过化学转化-质谱技术获得的速率常数一致。这项新技术被应用于研究D-[1-13C]赤藓糖（一种呋喃糖）异头碳原子上的氧交换，此前尚无关于它的实验数据。在未缓冲的水溶液中，于10、23和36℃下，通过13C NMR跟踪介质（H2(18)O）中的18O标记掺入α-和β-D-[1-13C]赤藓糖以及D-[1-13C]赤藓糖水合物形式的C-1碳原子的过程。通过对α-和β-非对映体数据的分析，交换的准一级速率常数在10℃时为1.4×10(-4) s-1，23℃时为4.8×10(-4) s-1，36℃时为8×10(-4) s-1，交换反应的表观活化能为12.1 kcal/mol。特别是与使用特定13C富集的糖类相结合时，研究碳水化合物氧交换反应的新技术相对于早期方法具有许多明显优势，包括能够同时跟踪所有可检测到13C NMR信号的糖种类的交换反应、测定的连续性、避免因不完全或选择性衍生化反应导致的可能假象以及数据分析的简便性。
