2D-HOHAHA和ROESY方法归属复杂天然有机化合物的NMR谱线

Structural Elucidation and ~1H Spectral Assignments of Complex Natural Organic Compounds by 2D-HOHAHA and ROESY Methods

用同核化学位移相关谱及旋转坐标系中的同核化学位移相关谱和旋转坐标系中的同核NOE实验等新的二维核磁共振方法对首次从西洋参叶中分离出的Ocotillol型皂甙(OTS)的~1H化学位移进行了完全归属,为OTS分子溶液中的三维空间结构研究提供了可靠的结构参数.

Because of the serious spectral overlap in several regions of the 1H spectrum, the 1H chemical shifts of an ocotillol-type saponin, which was first isolated from the leaves of panax Quinquetolium L. , are completely assigned by recently developed two dimensional homonuclear Hartmann-Hahn spectroscopy (2D-HOHAHa) and rotating frame nuclear Overhauser effect spectroscopy (ROESY). The 2D-HOHAHA experiment is able to obtain the phase sensitive two dimensional spectrum with all peaks in the near absorption mode, and the cross peaks multiplets are nearly in-phase. So the high detection resolution and sensitivity of 2D-HOHAHA experiment make it possible to observe the cross peaks overlapped such as H13-H17 and H23a-H23e, and that covered by diagonal peaks with high strength in COSY spectrum, such as H2a-H2e. On the other hand, during the spin locking period of 2D-HOHAHA experiment, relayed magnetization transfer will occurs. For shorter mixing period (shorter than 20 ms) little RELAY signals can be observed, but for longer mixing times single-RELAY and multiple-RELAY effects become significant. Through the RELAY cross peaks appeared in 2D-HOHAHA spectrum of OTS, the accurate 'H chemical shifts of some proton signals in severe spectral overlap regions are assigned, such as, the 1H chemical shifts of H22a, H22e, Hla, H1e and H9 proton are 1. 592, 1. 857, 1. 026, 1. 640 and 1. 586 ppm respectively. The spin-locking NOE experiment is used to provide through-space connectivity between the various coupling networks of protons. The linking position of glucosyl with aglycone in OTS and the chemical shift assignments of methyl protons which are easily distinguished but difficultly assigned are determined by ROESY spectrum.