Conformational study of 3β,16β-dihydroxyfriedelane by NMR and ab initio calculations

Abstract

The complete chemical shift assignments of 3b,16b-dihydroxyfriedelane, a natural compound isolated from the hexane extract of Maytenus acanthophylla leaves was achieved through 1D/2D NMR spectral data. Combining ab initio Hartree-Fock [HF/6-31G(d)] and Density Functional Theory [DFT/B3LYP/6-31G(d,p)] calculations with NMR spectral data, it was possible to establish the predominance of the chair-chair-chair-boat-boat conformation for the five six-membered ring systems in this pentacyclic triterpene.

Computational Prediction of1H and13C Chemical Shifts: A Useful Tool for Natural Product, Mechanistic, and Synthetic Organic Chemistry

“…Other examples include the use of computed chemical shifts to examine unusual multicenter bonding arrays, to help characterize host–guest systems , and to study numerous tautomerization ,− and conformational processes. − …”

Combined experimental powder X-ray diffraction and DFT data to obtain the lowest energy molecular conformation of friedelin

“…Based on 1D/2D NMR spectral data, the five-ring conformation of PCTT dissolved in deuterated solvent has been established. For pachisandiol, the chair-chair-chair-boat-boat (c-c-c-b-b) conformation was attributed to rings A, B, C, D and E, respectively 1 and c-c-c-c-c-c 2 for 16a-hydroxy-friedelin, both dissolved in CDCl 3 . However, it is important to consider the interference of deuterated solvent and the temperature of the analysis in determining the molecular conformation of the compound.…”