Discovery of Isograndidentatin D, a Novel Phenolic Glycoside, and Anti-Helicobacter pylori Phenolics from Salix koreensis Twigs

Salix koreensis Anderss (Salicaceae), commonly referred to as Korean willow, is native to East Asia, particularly Korea and China, and it has been used in traditional Korean folk medicine for its potent anti-inflammatory, analgesic, and antioxidant properties. In our ongoing research efforts to discover biologically new natural products, phytochemical analysis on an ethanolic extract of S. koreensis twigs yielded the isolation and identification of ten phenolic compounds (1–10), including a newly discovered phenolic glycoside (1) named isograndidentatin D, isolated via HPLC purification. The structure of compound 1 was determined through extensive 1D and 2D NMR spectral data analysis and high-resolution electrospray ionization mass spectrometry (HR-ESIMS). Its absolute configuration was established using DP4+ probability analysis combined with gauge-including atomic orbital NMR chemical shift calculations and chemical reaction methods. The other known compounds were identified as isograndidentatin B (2), trichocarposide (3), glanduloidin C (4), tremuloidin (5), 3-O-acetylsalicin (6), 2-O-acetylsalicin (7), salicin (8), salireposide (9), and coumaric acid (10), confirmed by comparing their NMR spectra with previously reported data and further verified through liquid chromatography/mass spectrometry (LC/MS) analysis. The isolated compounds 1–10 were tested for their anti-Helicobacter pylori activities. Among these, compounds 4 and 5 demonstrated moderate anti-H. pylori activity at a concentration of 100 μM. Specifically, compound 5 showed an inhibitory activity of 35.9 ± 5.4%, making it slightly more potent than compound 4, with 34.0 ± 1.0% inhibition. These results were comparable to that of quercetin, a known anti-H. pylori agent used as a positive control in this study, which showed 38.4 ± 2.3% inhibition. The remaining compounds exhibited very weak inhibitory effects. This study highlights the potential of S. koreensis twigs as a valuable natural source of bioactive compounds for therapeutic applications against H. pylori.