Av 500 ft nmr spectrometer

All chemicals were obtained from Merck or Sigma-Aldrich. The chemical reaction was monitored using thin-layer chromatography (TLC) using silica gel 60 F254-pre-coated glass plates with a thickness of 0.25 mm and a UV lamp to visualize the plate. Column chromatography was performed using silica gel (230–400 mesh). Optical rotations of the final compounds were measured with a Jasco P-2000 digital polarimeter. The infrared (IR) spectra were obtained with a Jasco FT/IR-4000 FTIR spectrometer. The NMR spectra were recorded on commercial instruments (Bruker AV 500 FT-NMR spectrometer). Low-resolution and high-resolution mass spectra were performed using Fourier-transfer mass spectrometry (FT-MS). Mass spectra were recorded in both positive modes with Bruker APEX II (National Sun Yat-sen University). Acid natural products were isolated from Prof. Tian-Shung Wu’s lab (Tainan, NCKU, Taiwan) [25 (link),27 (link),32 (link),33 (link)].

Mass spectra were obtained using a Bruker micro-TOFQ mass spectrometer (Bruker Daltonics, Bremen, Germany). Nuclear magnetic resonance spectra were acquired with a Bruker AV-500 FT-NMR spectrometer operating at 500.1 MHz for ¹H and at 125.8 MHz for ¹³C at 25 °C; chemical shifts are expressed in δ referring to the residual solvent signals δ_H 2.50 and δ_C 39.5 for DMSO-d₆, coupling constants, J., are in hertz. All chemical shifts are given in ppm. Column chromatography was performed over a RP-18 reversed-phase silica gel (S-50 μm; YMC, Kyoto, Japan). Analytical HPLC (Agilent technologies, Santa Clara, CA, USA) was performed on an Agilent 1260 system equipped with a G1311C quaternary pump, a G1329B autosampler, a G1316A thermostated column compartment, and a G1314F variable wavelength detector coupled with an analytical workstation. Semipreparative HPLC was performed on an Agilent ProStar SD-1 pump connected with an Agilent ProStar 320 UV–Vis detector (at 360 nm), utilizing a Shim-Pack PREP-ODS column (250 mm × 21.2 mm, i.d., 10 μm, Shimadzu, Kyoto, Japan). HPLC-grade water was purified using a Milli-Q system (Millipore, Boston, MA, USA). All solvents used for the chromatographic separations were distilled before use.

A Bruker AV-500 FT-NMR spectrometer was used, operating at 500.1 MHz for ¹H and at 125.8 MHz for ¹³C, chemical shifts are expressed in δ referring to the residual solvent signals δ_H 2.50 and δ_C 39.5 for DMSO-d₆, coupling constants, J, are in hertz. ESI-MS was acquired with a Bruck micro-TOFQ mass spectrometer (Bruck, Bremen, Germany). Column chromatography was performed over a RP-18 reversed-phase silica gel (S-50 μm; YMC, Kyoto, Japan). Thin-layer chromatography (TLC) analysis was carried out on a pre-coated TLC plate with silica gel RP-18 60 F254 (0.25 mm, Merck, Darmstadt, Germany). Detection was achieved by spraying the sample with 10% H₂SO₄ in MeOH followed by heating. Preparative HPLC was performed using a Shimadzu LC-6AD pump connected to a Shimadzu SPD-20A UV-VIS detector (at 254 nm) with a Shim Pak ODS column (250 mm × 21.2 mm, i.d., 10 μm, Shimadzu, Kyoto, Japan) and a Megress ODS column (250 mm × 20 mm, i.d., 10 μm, Jiangsu hanbon Science and Technology Co., Ltd., Huai′an, China). Analytical HPLC was performed with two LC-20AT solvent delivery pumps, an online mixer, a SIL-20A autosampler, a CTO-20A column temperature controller, and a SPD-M20A photodiode-array detector (Shimadzu). HPLC-grade water was purified using a Milli-Q system (Millipore, Boston, MA, USA). All solvents used for the chromatographic separations were distilled before use.