Silica gel gf254

All conventional reagents and solvents are purchased directly from commercial companies and no further purification is required. Organic solvents were purchased from Sinopharm chemical reagent Co., Ltd. and purified by distillation and moisture was excluded from the glass apparatus using CaCl₂ drying tubes. Throughout this study, silica gel H (200–300 mesh; Qingdao Marine Chemical Factory, Qingdao, China) was used for the column chromatography. For thin layer chromatographic (TLC) plates, Silica gel (GF254) (Qingdao Marine Chemical Factory, Qingdao, China) were used for thin layer chromatographic (TLC) analysis, and all of the spots and bands were detected by UV irradiation (254, 365 nm). The intermediates and products were characterized by electrospray ionization mass spectrometry (TripleTOF5600þ; AB SCIEX Pte. Ltd., Boston, MA, USA), ¹H NMR and ¹³C NMR (Bruker AM500 spectrometer; Bruker Corporation, Berne, Switzerland). The derivatives were dissolved in 100% dimethyl sulfoxide (DMSO; Beyotime Biotechnology, Haimen, China), stored at 4 °C prior to antiviral evaluation, and used within 6 months. For solubility, the stock solutions, at a concentration of 50 mg/mL, were sonicated for approximately 10 min to ensure that the derivatives were fully dissolved and mixed.

The nuclear magnetic resonance (NMR) spectra were measured on a Bruker Biospin AV400 instrument at 400 MHz for ¹H NMR spectra and 100 MHz for ¹³C NMR spectra, with deuterated dimethylsulfoxide (DMSO-d6) as the solvent. The high-resolution mass spectra were acquired with a Q-TOF mass spectrometer (Impact II, Bruker). Thin-layer chromatography (TLC) was performed on silica gel plates (silica gel GF254, Qingdao Marine Chemical Plant, China) visualized at 254 nm. The derivatives were purified by flash column chromatography in silica gel (particle size 200–300 mesh) to get the pure compounds. 3D-QSAR procedures were carried out using SYBYL-X 2.0 (Tripos, Inc.). A multimode reader (Infinite M200, Tecan) was used to detect the cytotoxicity.

The nuclear magnetic resonance (NMR) spectra were recorded on Bruker 400 MHz NMR spectrometer. HRESIMS analyses were carried out on an LTQ-Orbitrap XL (Thermo Scientific, Waltham, MA, USA). HPLC was performed on an Agilent 1200. Semi-preparative HPLC was performed on a Waters 1525 Binary HPLC Pump (Agilent Eclipse XDB-C₁₈, 5 µm, 9.4 × 250 mm) with a Waters 996 Photodiode Array Detector (Milford, MA, USA). Sephadex LH-20 was obtained from GE Amersham Biosciences (Piscataway, NJ, USA). Column chromatography (CC) was performed over reversed-phase (RP) C₁₈ silica gel (Merck, Darmstadt, Germany). Silica gel GF₂₅₄ for thin-layer chromatography (TLC) was purchased from Qingdao Marine Chemical Ltd. (Qingdao, China). Optical rotations were measured on an Auton Paar MCP200 Automatic Polarimeter. IR spectra (KBr) were obtained on a Thermo Fisher Scientific Nicolet 6700 FT-IR spectrometer (Waltham, MA, USA). Compounds were visualized under UV light and by iodine vapor.