MOLECULAR MECHANICS-BASED CONFORMATIONAL-ANALYSIS OF PREVITAMIN D ANDITS A-RING ANALOGS

The ground-state conformational analysis of previtamin D and analogues with different substituents at C-3, C-1, and C-10 have been performed by force-held calculations. Differences in the photochemistry of thes e analogues are discussed in view of the concept of ground-state confo rmational control in photochemical reactions. The effect of complexes of previtamin D with silanol derivatives, formed via hydrogen bonds, o n their conformational equilibrium has been calculated. An increase in the population of cZc conformers with increasing size of the silanol molecules (as a model for a heterogeneous silica surface) was observed .