Universidade de Vigo, Facultad de Química, Department of Organic Chemistry, As Lagoas-Marcosende, 36315 Vigo, Spain.
Magn Reson Chem. 2010 Jul;48(7):543-9. doi: 10.1002/mrc.2618.
Solution NMR methods were used for the structural characterization of the acetoxyendiyne E/Z configuration of the marine natural products peyssonenynes A and B and their synthetic analogs derived from palmitic acid. The scarcity of protons in the proximity of the olefin precluded the determination of the double bond geometry using (1)H NMR methods that rely on proton-proton scalar couplings or experiments such as NOESY or ROESY. Long range (1)H-(13)C heteronuclear scalar couplings, (n)J(CH), measured with the 2D excitation sculptured indirect detection experiment (EXSIDE) proved useful and highly reliable for the analysis of the enol acetate geometry. In addition, it was found that the chemical shift of some carbon atoms in the proximity of the olefin was also sensitive to the double bond configuration of these molecules providing an even simpler way to determine their geometry. This protocol showed its robustness by similar analysis of simpler silyl-protected acetoxyenynes derived from fatty acids. These NMR experimental results and stereochemical predictions were rationalized by DFT calculations.
采用溶液 NMR 方法对海洋天然产物 peyssonenynes A 和 B 及其衍生自棕榈酸的合成类似物的乙缩醛端炔 E/Z 构型进行结构表征。由于烯烃附近质子的稀缺性，无法使用依赖质子-质子标量偶合或 NOESY 或 ROESY 等实验的（1）H NMR 方法来确定双键的几何形状。通过二维激发雕刻间接检测实验（EXSIDE）测量的长程（1）H-（13）C 异核标量耦合（n）J（CH）对于分析烯醇乙酸酯的几何形状非常有用且高度可靠。此外，还发现烯烃附近一些碳原子的化学位移也对这些分子的双键构型敏感，提供了一种更简单的确定其构型的方法。该方案通过对简单的脂肪酸保护的硅基乙酰氧基炔的类似分析证明了其稳健性。这些 NMR 实验结果和立体化学预测通过 DFT 计算得到了合理化。
