Dual lc 20ad solvent delivery system

All of the solvents, reagents, and chemicals used in this study were purchased from Aldrich Chemical (Saint Louis, MO, USA) and Merck AG (Saint Louis, MO, USA). Thin-layer chromatography (TLC) was conducted on pre-coated silica gel 60 GF₂₅₄ plates (Merck, Darmstadt, Germany) with an absorbent thickness of 0.25 mm sprayed with Ce(SO₄)₂ solution for spot visualization. Preparative TLC was performed on square glass plates with a side length of 0.2 m coated with 0.5 mm Kieselgel F₂₅₄ (Merck), which were air-dried and used without prior activation. Column chromatography (CC) was performed on silica gel (Kieselgel 60, 70–230 mesh ASTM; Merck). HPLC was performed using a Shimadzu dual LC-20AD solvent delivery system with a Shimadzu SPD-M20A UV/vis photodiode array detector. Nuclear magnetic resonance (¹H NMR and ¹³C NMR) spectra were recorded in acetone-d₆ or CDCl₃ with tetramethylsilane as an internal standard on a Bruker Avance III 700 MHz spectrometer equipped with a 5 mm ¹³C cryogenic probe or a Bruker 500 MHz spectrometer. High-resolution ESI mass spectrometry was performed in positive ion mode on a 6230 TOF mass spectrometer (Agilent Technologies, Santa Clara, CA).