Application studies on vibrational circular dichroism as the chiroptical tool

碳水化合物的结构研究需要开发分析工具。VCD光谱学具有潜在的用途，但与蛋白质和核酸相比，它在碳水化合物中的应用一直受到限制，部分原因是很难解释光谱。通过系统的碳水化合物测定，我们发现在1145 cm~(-1)~(-1)附近出现了一个强烈的VCD峰，这是轴向糖苷糖的特征，即糖苷带。同位素替代表明，异常分子参与了这一带的振动。为了通过密度泛函理论(DFT)计算来预测其振动模式，制备了适当设计的模型化合物，并将其计算光谱与观测光谱进行了比较。在这项研究中，首次可靠地预测了碳水化合物的VCD光谱。此外，糖苷带的符号不仅反映了异构体构型，而且反映了吡喃糖conf…更多的整形。各向同性理论研究表明，其振动模式为C_1-H_1形变和C_1-O_1伸缩，这表明它适用于更复杂的糖共轭化合物。最后，首次将VCD技术应用于糖肽，实现了糖类和糖聚糖部分的同时分析，并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。合成了两对关于Neu5Ac衍生物的季碳C2不对称的异构体。VCD技术的其他应用还应用于手性十字花科植物抗毒素和抗蛇毒解毒剂类化合物((+)-Alternamin)等生物活性化合物，并借助其密度泛函理论计算，成功地归属了它们在溶液中的立体化学性质。较少

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