NMR Spectroscopy
The 1D and 2D NMR spectra, including 1H,13C DEPTQ (Distortionless Enhancement by Polarization Transfer with retention of Quaternaries), selective TOCSY (TOtal Correlation SpectroscopY), selective ROESY (Rotation frame nuclear Overhauser Effect SpectroscopY),1H-1H DQF-COSY (Double-Quantum Filtered COrrelation SpectroscopY),1H-13C HSQC (Heteronuclear Single Quantum Coherence) and 1H-13C HMBC (Heteronuclear Multiple Bond Coherence) were recorded using an Avance III HD Ascend 500 MHz spectrometer (Bruker BioSpin, Rheinstetten, Germany) in deuterated methanol (MeOH-d4 ) at 30° C. NMR spectra were calibrated to the signal of residual solvent: δ 3.31 for 1H and 49.0 for 13C.