Modeling of previtamin D conformational equilibrium: effect of intramolecular electrostatic interactions

The effect of intramolecular electrostatic interactions on previtamin D conformational equilibrium has been studied by MMX force-field calculations using charge-charge and dipole-dipole approximations in parallel with the analysis of simple model compounds. The very fine balance between steric and electrostatic factors determining the conformational preference has been demonstrated and is discussed in terms of a classical charge-charge interactions. The results of this search are discussed with respect to available experimental data and give clues to the noticeable incidence of atomic point charges in previtamin D ground-state equilibrium. Comparison of the results with those of semi-empirical AM1 calculations reveals that conformational search results on previtamin D are highly dependent on the computational model used and indicate that care is required both in the selection of the computational method and in the interpretation of the results. (C) 1998 Elsevier Science B.V.