CONFORMATIONAL-ANALYSIS OF MODEL COMPOUNDS OF VITAMIN-D BY THEORETICAL CALCULATIONS

A conformational analysis of two model compounds of vitamin D was carr ied out by means of theoretical computations, Ab initio calculations w ere carried out using the standard 6-31G basis set at the Hartree-Foc k (I-IF) level of theory. In addition, the Moller-Plesset (MP2) correl ation treatment, was applied on the simplest model. Semiempirical calc ulations were also performed using the AM1 Hamiltonian. The results pr edict stable A-ring twist forms with energies in the order of 4-6 kcal /mol relative to the global minimum, significantly higher than those r eported from molecular mechanics calculations. In addition, a folded c onformation was found by the HF optimizations; however, its stability is predicted to be very poor. Comparison of the theoretical results wi th experimental data is discussed. (C) 1997 by John Wiley & Sons, Inc.