Apex 4 instrument

All used reagents were purchased from commercial suppliers without further purification. The reactions were carried out in oven-dried or flamed graduated vessels. Solvents were dried and purified by conventional methods before use. All reactions were monitored using Merck aluminum plated pre-coated with silica gel PF254 and detected by visualization of the plate under UV lamp (λ = 254 or 365). Column chromatography was performed using silica gel 60, 0.040–0.063 mm (230–400 mesh). ¹H and ¹³C NMR spectra were recorded on a Bruker Avance DPX-300 MHz and DPX-500 MHz instruments. Splitting patterns are designated as s, singlet; d, doublet; dd, doublet of doublet; t, triplet; q, quartet; m, multiplet; br, broad. Chemical shifts (δ) are given in ppm with reference to TMS as an internal standard. High-resolution mass spectra (HRMS) were measured by Electrospray Ionization (ESI) on a Bruker APEX-IV instrument. The samples were dissolved in acetonitrile and infused using a syringe pump with a flow rate of 120 μL/min. External calibration was conducted using Arginine cluster in a mass range m/z 175–871. For all HRMS data, mass error: 0.00–0.50 mDa.

Melting points of the EβF analogues were determined on a Cole-Parmer apparatus equipped with an uncorrected thermometer (Shanghai precision instrument and Meter Co., Ltd., Shanghai, China). IR spectra were recorded on neat samples on an IR-435 spectrophotometer (Shimadzu, Kyoto, Japan) using KBr pellets. ¹H-NMR spectra (300 MHz) and ¹³C-NMR spectra (75 MHz) were recorded on an Avance DPX300 spectrometer (Bruker, Karlsruhe, Germany). ¹H-NMR chemical shifts are reported in δ (ppm) relative to the signal of tetramethylsilane (TMS) as internal standard, using CDCl₃ as solvent. The ¹³C-NMR chemical shifts (δ) were reported in parts per million using the solvent peak as reference. High resolution mass spectra were determined under electron impact (150 eV) conditions using a Bruker APEX IV instrument. Silica gel (Merck 60, 230–300 mesh, Qingdao Haiyang Chemical Co., Ltd., Qingdao, China) was used for column chromatography with petroleum ether and ethyl acetate as eluents. All starting materials, reagents and solvents were analytical grade reagents and were commercially available, and all solvents were purified and dried before used.