线性标度方法计算几个藜芦生物碱的13C NMR化学位移

13C NMR calculation on several alkaloids in veratrum nigrum:scaling method

本文采用几种密度泛函方法计算了环杷明(cyclopamine)的13C NMR化学位移。与实验值比较发现采用B97-2/pcSseg-1的气相优化结构结合SMD溶剂化模型计算获得的13C NMR化学位移最合适。在此基础上,对藜芦中的五种典型生物碱结构(环杷明、介芬胺、藜芦胺、计明胺和棋盘花胺)进行了相应的13C NMR化学位移计算。通过与实验值进行拟合,得到线性标度公式σ=(184.4-σcal)/1.0261。其相关系数R2=0.9976。此外,理论计算也可以解决化合物中的相似碳的13C NMR化学位移归属困难的问题。线性标度方法获得化学位移对建立天然产物的NMR数据库、匹配结构和解析实验测试数据提供了一种快捷可靠的解决方案。

Several density function theory(DFT)methods are tested for the calculation of 13C NMR of cyclopamine.It is found that the combination of B97-2/pcSseg-1 level and SMD solvent model is suitable to reproduce the experimental results by the use of the scaling method.In this way,five typical alkaloids,cyclopamine,jervine,veratramine,germine,and zygadenine,isolated from the veratrum nigrum plant,are take into account in this work.The predicted 13C NMR chemical shifts are very close to the experimental observation.The suggesting scaling formula isσ=(184.4-σcal)/1.0261.Additionally,this scaling formula could also be used to correct the wrong assignments in the experiment due to the similar environment of some C atoms.Therefore,it provides a convenient and reliable approach to build NMR database of natural products,match with a structure,and analyze NMR experimental data with the scaling method.