Ltqft ultra instrument

The intermediate 2-mercapto-5-aryl-1,3,4-oxadiazoles a–k (scheme 1) were synthesized as previously reported [24 (link)]. Other reagents were of analytically grade and purchased from commercial resources. Fraxinellone (1) was isolated from Dictamnus dasycarpus and its purity was more than 99% as measured with reverse phase high-performance liquid chromatography (RP-HPLC). Analytical thin-layer chromatography (TLC) and preparative thin-layer chromatography (PTLC) were prepared by silica gel plates using silica gel GF₂₅₄ (Qingdao Haiyang Chemical Co., Ltd, Qingdao, China). Melting points were determined on a digital melting-point apparatus and were uncorrected (Beijing Tech Instrument Co., Ltd). Optical rotation was measured using an Autopol III automatic polarimeter (Rudolph Research Analytical, NJ, USA). Infrared spectra (IR) were recorded on a PE-1710 FT-IR spectrometer (Perkin-Elmer, Waltham, MA, USA). NMR spectra were obtained in CDCl₃ on a Bruker Avance (400 MHz) spectrometer using tetramethylsilane (TMS) as the internal standard (Bruker, Bremerhaven, Germany). High-resolution mass spectra (HR-MS) were carried out with LTQ FT Ultra instrument (Thermo Fisher Scientific Inc., Waltham, MA, USA).
Scheme 1.

Synthetic route for the preparation of fraxiellone-based thioethers containing 1,3,4-oxadiazole moiety (4a–k and 5a–k).