DFT, solution, and crystal conformation of eremophilanolides

The minimum energy conformation of five eremophilanolides (1–5) from the tubercles of Psacalium paucicapitatum was calculated using density functional theory (DFT) at the B3LYP/6-31G∗ level. Comparison of the experimental 1H–1H coupling constant values of 1–5 with those generated employing a generalized Karplus-type relationship using dihedral angles extracted from the DFT calculation and from the crystal structures for 1 and 3–5 shows good agreement. The A ring of 1–5 adopts an almost perfect chair conformation with the Me-14 group in an axial position and the Me-15 in an equatorial position.