Vxr 400 spectrometer

All the reagents were obtained commercially and used without further purification. Thiazolidine-2,4-dione 1 and (4-oxo-2-thioxo-3-thiazolidinyl)acetic acid 3 were purchased from Sigma-Aldrich. Purity of the compounds was checked by thin layer chromatography using silica-gel 60 F254-coated Al plates (Merck) and spots were observed under UV light. ¹H NMR and ¹³C NMR spectra were recorded on a Bruker Avance spectrometer (600 and 150 MHz, respectively) and Varian VXR-400 spectrometer at 400 MHz and 101 MHz, respectively, at 298 K in CDCl₃ or DMSO-d₆ at a concentration of samples of 5–15 mmol, with TMS as internal reference for ¹H and ¹³C NMR spectra. The signal assignments of compound 11, 12, 15, and 17 were performed using 2D spectra (DQF-COSY, ¹³C–¹H HSQC, and ¹³C–¹H HMBC); the chemical shifts are expressed in ppm (δ scale) using DMSO and CDCl₃ as an internal standard, and the coupling constants are expressed in Hz. The mass-spectral measurements were carried out by ESI method on micrOTOF-QII (Brucker Daltonics GmbH). Analytical HPLC was performed on a Shimadzu LC-20AD system using Kromasil-100-5-C18 (Akzo-Nobel) column, 4.6 × 250 mm, temperature 20 °C, UV detection, mobile phase A—0.2% HCOONH₄), mobile phase B-MeCN, (pH 7.4), and fl-1ml/min.