Application studies on vibrational circular dichroism as the chiroptical tool

碳水化合物的结构研究要求开发分析工具。VCD光谱具有潜在的用途，但与蛋白质和核酸相比，其在碳水化合物上的应用受到限制，部分原因是光谱的解释困难。通过系统的碳水化合物测量，我们发现轴向糖苷糖（即糖苷带）在1145 cm^<-1>附近出现了一个强烈的VCD峰。同位素取代表明，这一波段的振动中有明显的头元参与。为了用密度泛函理论（DFT）计算方法预测其振动模式，制备了设计合理的模型化合物，并将其计算谱与观测谱进行了比较。本研究首次对碳水化合物的VCD谱进行了可靠的预测。此外，发现糖苷带的符号不仅反映了头型构型，而且反映了吡喃糖的构型。各向同性和理论研究表明其振动模式为C1-H1变形与C1-O1拉伸耦合，表明其适用于更复杂的糖缀合物。最后，VCD技术首次应用于糖肽，并证明了同时分析碳水化合物和多糖部分。首次对识别相关的独特碳水化合物n -乙酰神经氨酸（Neu5Ac）进行了系统的VCD研究。合成了Neu5Ac衍生物的一个季C2不对称碳的两对异构体。酯羰基区周围的VCD光谱模式，以及其他中红外区域，将是区分C2立体化学的实用标记。VCD技术的其他应用还应用于生物活性化合物，如手性十字花科植物抗毒素和抗蛇毒的解毒剂化合物（(+)-alternamin），通过DFT理论计算，成功地在溶液站中分配了它们的立体化学。少

Structural studies of carbohydrates have required development of analytical tools. VCD spectroscopy has been of potential use, but its application to carbohydrates has been limited compared to proteins and nucleic acids partly due to the difficulties in the interpretation of the spectra. Through the systematical carbohydrate measurements, we have found an intense VCD peak appeared around 1145 cm^<-1> characteristic for axial glycosidic sugars i.e. the glycoside band. Isotope substitution indicated the profound participation of the anomeric moiety in the vibration of this band. To predict its vibrational mode by means of density functional theory (DFT) calculation, properly designed model compounds were prepared and their calculated spectra were compared with the observed ones. In this study, for the first time, carbohydrate VCD spectra were reliably predicted. Furthermore, the sign of the glycoside band was found to reflect not only the anomeric configuration but also the pyranose conf … More ormation. The isotropic and theoretical studies characterized its vibrational mode as the C1-H1 deformation coupled with C1-O1 stretching, which indicated the applicability to more complicated glycoconjugates. Finally, VCD technique was first applied to glycopeptides, and demonstrated the simultaneous analysis on both the carbohydrate and aglycan parts.Systematic VCD studies of N-acetylneuraminic acid (Neu5Ac), a recognition related unique carbohydrate, were performed for the first time. Two pairs of anomeric isomers regarding a quaternary C2 asymmetric carbon of Neu5Ac derivatives were synthesized. VCD spectral patterns around the ester carbonyl region, as well as other Mid-IR regions would be practical markers to distinguish the C2 stereochemistry.Other applications of the VCD technique were also applied to biologically active compounds such as chiral cruciferous phytoalexins and the antidote like compound against snake venom ((+)-alternamin), leading to successful assignments of their stereochemistries in solution station with the aids of their DFT theoretical calculations. Less