Simmler Charlotte, Lankin David C, Nikolić Dejan, van Breemen Richard B, Pauli Guido F
UIC/NIH Center for Botanical Dietary Supplements Research, Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, College of Pharmacy, 833 S. Wood Street, Chicago, IL 60612, USA.
UIC/NIH Center for Botanical Dietary Supplements Research, Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, College of Pharmacy, 833 S. Wood Street, Chicago, IL 60612, USA.
Fitoterapia. 2017 Sep;121:6-15. doi: 10.1016/j.fitote.2017.06.017. Epub 2017 Jun 21.
In an effort to explore the residual complexity of naturally occurring chalcones from the roots of Glycyrrhiza inflata (Fabaceae), two new licochalcone A (LicA) derivatives were isolated as trace metabolites from enriched fractions. Both constituents contain a dihydrofuran moiety linked to carbons C-4 and C-5 of the retrochalcone core. Compound 1 (LicAF1) represents a new chemical entity, whereas compound 2 (LicAF2) has previously been reported as a Lewis acid catalyzed rearrangement of LicA. Evaluation of chirality revealed that both dihydrofuran derivatives existed as a mixture of R and S enantiomers. Interestingly, when solutions were exposed to sunlight, both dihydrofuran retrochalcones, initially isolated as trans isomers, were found to rapidly isomerize yielding trans and cis isomers. Analysis of the 1D H NMR spectra of the photolysis products revealed the presence of two sets of proton resonances ascribed to each of the geometric isomers. An up-field shift of all proton resonances arising from the cis isomer was observed, suggesting that anisotropic shielding effects were introduced through an overall perturbation of the 3-dimensional structure upon photoisomerization. Similar up-field shifts were observed in the C spectrum of the cis isomer, except for the CO, C-α, and C-6 carbons, which experienced downfield shifts. Analogous NMR results were observed for LicA. Hence, the results presented herein encompass the isolation and full characterization of LicAF analogs 1 and 2, and observations of their trans-to-cis photoisomerization through the systematic analysis of their NMR spectra.
为了探索胀果甘草（豆科）根中天然存在的查耳酮的残余复杂性，从富集级分中分离出两种新的甘草查耳酮A（LicA）衍生物作为痕量代谢物。两种成分都含有一个与反式查耳酮核心的C-4和C-5碳相连的二氢呋喃部分。化合物1（LicAF1）代表一种新的化学实体，而化合物2（LicAF2）先前已报道为LicA的路易斯酸催化重排产物。手性评估表明，两种二氢呋喃衍生物均以R和S对映体的混合物形式存在。有趣的是，当溶液暴露在阳光下时，最初以反式异构体形式分离的两种二氢呋喃反式查耳酮都被发现迅速异构化，生成反式和顺式异构体。光解产物的一维氢核磁共振谱分析显示存在两组分别归属于每种几何异构体的质子共振。观察到顺式异构体产生的所有质子共振都有一个高场位移，这表明在光异构化过程中，三维结构的整体扰动引入了各向异性屏蔽效应。在顺式异构体的碳谱中也观察到类似的高场位移，但羰基碳、α-碳和C-6碳除外，它们经历了低场位移。LicA也观察到类似的核磁共振结果。因此，本文给出的结果包括LicAF类似物1和2的分离和全面表征，以及通过对其核磁共振谱的系统分析对它们从反式到顺式光异构化的观察。
