The identification of alkaloids from the stems of Picrasma quassioides via computer-assisted structure elucidation and quantum chemical calculations

Chemical constituents from the twigs and leaves of Picrasma quassioides

Two new compounds, including a norsesquiterpenoid, annuionone H (1), and a quassinoid, picraqualide G (2), along with eleven known compounds (3-13), were isolated from the twigs and leaves of Picrasma quassioides. Comprehensive spectroscopic analyses and NMR calculation with DP4+ analysis were used to identify their structures. Moreover, of all these compounds, compound 4 showed a week inhibition rate in the anti-inflammatory screening results against mouse macrophage J774A.1 cell.

Bioassay-guided isolation of α-Glucosidase inhibitory constituents from Hypericum sampsonii

This study employed the α-glucosidase inhibitory activity model as an anti-diabetic assay and implemented a bioactivity-guided isolation strategy to identify novel natural compounds with potential therapeutic properties. Hypericum sampsoniiwas investigated, leading to the isolation of two highly modified seco-polycyclic polyprenylated acylphloroglucinols (PPAPs) (1 and 2), eight phenolic derivatives (3-10), and four terpene derivatives (11-14). The structures of compounds 1 and 2, featuring an unprecedented octahydro-2H-chromen-2-one ring system, were fully characterized using extensive spectroscopic data and quantum chemistry calculations. Six compounds (1, 5-7, 9, and 14) exhibited potential inhibitory effects against α-glucosidase, with IC₅₀ values ranging from 0.050 ± 0.0016 to 366.70 ± 11.08 μg·mL^-1. Notably, compound 5 (0.050 ± 0.0016 μg·mL^-1) was identified as the most potential α-glucosidase inhibitor, with an inhibitory effect about 6900 times stronger than the positive control, acarbose (IC₅₀ = 346.63 ± 15.65 μg·mL^-1). A docking study was conducted to predict molecular interactions between two compounds (1 and 5) and α-glucosidase, and the hypothetical biosynthetic pathways of the two unprecedented seco-PPAPs were proposed.

β-Carboline alkaloids from Picrasma quassioides and their 3D-QSAR study on anti-inflammation in LPS-induced RAW 264.7 cells

Two new β-carboline alkaloids (1-2), 1-pyrrolidone propionyl-β-carboline (1) and 1-(3-hydroxy-2-oxopiperidine-1-ethyl)-4,8-dimethoxyl-β-carboline (2), named kumujantine W and J respectively, together with ten known compounds (3-12) were isolated from the stems of Picrasma quassioides (D. Don) Benn. Their structures were elucidated from spectral data including 1D and 2D NMR, UV, IR, HR-ESI-MS spectroscopic analysis and ECD calculations as well as by comparison to the reference databases or literature. The anti-inflammatory effects of these alkaloids (1-12) and six other β-carboline alkaloids (13-18) in LPS-induced RAW 264.7 cells were evaluated by measuring nitric oxide (NO) concentrations. Among them, compounds 1, 3, 6, 15, and 17 could inhibit the secretion of NO, displaying significant anti-inflammatory activity without affecting cell viability in vitro, and 3D-QSAR analysis further revealed the influence of groups on the activity in β-carboline alkaloids.

Chemical constituents from Solanum nigrum and their neuroprotective activities

Ten compounds (1-10) including four new compounds (1-4) and six known compounds (5-10) were isolated from Solanum nigrum. Their structures were elucidated on the basis of spectroscopic data, gauge-including atomic orbital (GIAO) calculation of NMR data, DP4+ probability analysis and comparison of their experimental and calculated electronic circular dichroism (ECD) spectral data. All the isolated compounds were tested for their neuroprotective activities against H₂O₂-induced damage in SH-SY5Y cells. Among them, compounds 1, 5 and 7 displayed moderate neuroprotective effects.