J-based analysis and DFT-NMR assignments of natural complex molecules:: Application to 3β,7-dihydroxy-5,6-epoxycholestanes

In order to reproduce the stereochemical dispositions of the epoxy and hydroxy functionalities, four 3 beta,7-hydroxy-5,6-epoxycholestanes were easily prepared from cholesterol, and their NMR spectroscopic data were experimentally obtained from 1D and 2D NMR experiments. An exhaustive QM-J-based analysis was then performed to replicate the experimental H-H and C-H coupling constants as well as the C-13 NMR chemical shifts. The B3LYP GIAO methodology with the 6-311-G(d,p) basis set was chosen and showed that the data obtained from rings A and B were sufficient to calculate the correct stereochemistry of the 5,6-epoxy and 7-hydroxy groups. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).