Siudem Paweł, Bukowicki Jarosław, Wawer Iwona, Paradowska Katarzyna
Department of Physical Chemistry, Faculty of Pharmacy, Medical University of Warsaw Banacha 1 PL-02097 Warsaw Poland
The State Higher Vocational School Rynek 1 PL-38400 Krosno Poland.
RSC Adv. 2020 May 11;10(31):18082-18092. doi: 10.1039/d0ra01320j. eCollection 2020 May 10.
Capsaicinoids are alkaloid type capsaicin analogs with prospective pharmacological activity. However their solid state conformations have not been studied yet. As part of the study, cross polarization (CP) magic angle spinning (MAS) solid state C and N NMR spectra of dihydrocapsaicin (DHCAP) and nonivamide (NVA) were recorded. Solid state chemical shifts differ from their solution counterparts; remarkable differences occur for carbons C2', C6' and C7' linked to C1' in DHCAP and with methylene carbons C4-C8 in NVA. The doubling of some resonances in the spectra of solid NVA indicates that there are two molecules in the crystallographic asymmetric unit. DFT GIAO calculations of shielding constants were performed for several geometric isomers, including molecules with different orientations of aliphatic chain with respect to aromatic ring. Low-energy conformers were found by genetic algorithm methodology. Comparison of experimental C chemical shifts with theoretical (GIAO DFT) shielding parameters was helpful in predicting the most reliable geometry in the solid state. Cross polarization time constants and relaxation times in the rotating frame were obtained from variable-contact cross-polarization experiments. are longer in the order: NVA < CAP < DHCAP.
辣椒素类化合物是具有潜在药理活性的生物碱类辣椒素类似物。然而，它们的固态构象尚未得到研究。作为该研究的一部分，记录了二氢辣椒素（DHCAP）和壬酰香草胺（NVA）的交叉极化（CP）魔角旋转（MAS）固态碳和氮核磁共振谱。固态化学位移与其溶液中的对应物不同；在DHCAP中与C1'相连的碳C2'、C6'和C7'以及在NVA中与亚甲基碳C4 - C8处出现了显著差异。固态NVA谱中一些共振峰的加倍表明在晶体学不对称单元中有两个分子。对几种几何异构体进行了屏蔽常数的密度泛函理论（DFT）GIAO计算，包括脂肪链相对于芳香环具有不同取向的分子。通过遗传算法方法找到了低能量构象。将实验测得的碳化学位移与理论（GIAO DFT）屏蔽参数进行比较，有助于预测固态中最可靠的几何结构。通过可变接触交叉极化实验获得了交叉极化时间常数和旋转坐标系中的弛豫时间。其顺序为：NVA < CAP < DHCAP，其中 更长。
