Synthesis, complete NMR assignments, and NOE versus GIAO data assisted ab initio modelling the overall conformations of amide 3,4′-diquinolinyl sulfides in solution. Another approach to analysis of flexible systems

Abstract

Two isomeric amide sulfides 3 and 4 were prepared by the treatment of 6-substituted thioquinanthrene ( 2 ) with sodium methoxide and methyl iodide. Product structures were determined by 1H and 13C NMR spectroscopy in solution, including 2D experiments HSQC and HMBC at 11.75 T. The time-averaged conformations were elucidated, based on best fitting the measured data δ C and δ H to those computed by the ab initio GIAO NMR method at the HF/6-31G * level. All used input molecular models had been pre-selected before in the light of NOE experimental data. Excellent two-nuclear linear correlations δ C,H exp vs. δ C,H calc were achieved ( R>0.999). Spatial orientations of the ring substituents [SMe and, especially, of C(O)NMe 2] in both isomers were considered to rationalise the NMR spectra of these and other related amide systems. A protocol for the three-step conformational analysis is described in detail.