Lyciumsterols A-K (1-11), 11 new octahydroxylated C21 steroids, were isolated from the root bark of Lycium chinense, along with 15 known compounds. Characterization of these C21 steroids showed the presence of eight hydroxy groups on the C21 steroid skeleton with a (2E,4E)-5-phenyl-2,4-pentadienoate group at C-12 or C-20 and various 2,6-deoxy sugar residues at C-3. The structures of these compounds were elucidated using spectroscopic data interpretation. Compounds 2, 3, and 7 exhibited dose-dependent protective effects on pancreatic islet cells and may help to improve cell viability. In addition, it was found that compounds 7, 8, 9, and 11 exhibited autophagy activation.
In recent years, certain "new" naturally occurring compounds (1-28) with 3,5-dioxygenated aromatic rings have been reported. A comparison of the NMR data of these compounds with the data of four model compounds (A-D) indicated that the structures of these "new" compounds were erroneous. The reason for the incorrect elucidation of the structures of 1-28 was attributed to "deceptively simple" (1)H NMR spectra, which displayed two broad singlets with integrations of 1:2 for H-2 and H-5, H-6, respectively. To expose the misleading results from the spectra, serial (1)H NMR experiments on compounds A-D were performed using various deuterated solvents and temperatures. The results revealed separated proton signals for the ABX system in certain deuterated solvents. Additionally, the characteristic differences between 3,4- and 3,5-dioxygenated aromatic rings in their (13)C NMR spectra are summarized based on our experiment and data reported. This approach is useful for analyzing the patterns of dioxygenated aromatic rings in natural products, especially when "deceptively simple" (1)H NMR spectra are displayed.
Lycium chinense Mill. is a deciduous shrub in the Solanaceae family that is known for its fruits (Lycii fructus) and root bark (Lycii cortex). In our ongoing search for a-glucosidase inhibitors from the root bark of L.chinense, lyciumflavane A, one new flavane with an unusual benzofuran unit, one new amide possessing a naphthalene skeleton, one new sesquiterpene, three new lignan glucosides, and three new phenolic glucosides were isolated along with eight known compounds. Their structures were elucidated using NMR, HRESIMS, UV, ECD, and IR spectroscopic data. Their a-glucosidase inhibitory activity was screened using acarbose as a positive control (IC 50 ¼ 385 mM). Compound 1 showed strong inhibitory activity against a-glucosidase (IC 50 ¼ 20.89 mM).
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