... European Journal of Medicinal Chemistry. ... The 1 H NMR spectra of 6 displayed two doublets appearing at about δ 3.85 (J HA–HB = 18–21 Hz) and δ 3.70 ppm (J HA–HB = 18–21 Hz) (about δ 3.73 and 3.55 ppm for 6a–c) due to geminal coupling of H B with H A at position-4 ...