Quantum Mechanical-NMR-Aided Configuration and Conformation of Two Unreported Macrocycles Isolated from the Soft Coral Lobophytum sp.: Energy Calculations versus Coupling Constants.

Two new macrocyclic cembranoids were isolated from the South China Sea soft coral Lobophytum sp. Quantum mechanical-nuclear magnetic resonance (QM-NMR) methods were decisive in their structural elucidation. Better performance in arriving at definitive structures was obtained by QM-NMR methods upon incorporation of 3JHH values. The validity of this approach also supported an alternative conformational proposal versus that obtained by X-ray crystallography.