A comprehensive conformational analysis of bullacin B, a potent inhibitor of complex I. Molecular dynamics simulations and ab initio calculations. 
Using a conformational systematic search combined with semiempirical and ab initio (RHF/3-21G and RHF/6-31G(d)) calculations, the conformational space of bullacin B was examined for the first time.  In addition, molecular dynamics simulations were carried out to better evaluate the conformational behavior of this acetogenin.  Our results indicate that bullacin B possesses a significant molecular flexibility.  Although many different conformations were identified, at ab initio level, the L forms were energetically mostly preferred.  Our results support the use of molecular dynamics simulations for this compound suggesting that a combined decane/water system is a good solvent system to simulate the biological environment of this molecule acting as inhibitor of complex I.