posted on 2016-01-27, 00:00authored byTakashi Kamachi, Kazunari Yoshizawa
A conformational search program for
finding low-energy conformations
of large noncovalent complexes has been developed. A quantitatively
reliable semiempirical quantum mechanical PM6-DH+ method, which is
able to accurately describe noncovalent interactions at a low computational
cost, was employed in contrast to conventional conformational search
programs in which molecular mechanical methods are usually adopted.
Our approach is based on the low-mode method whereby an initial structure
is perturbed along one of its low-mode eigenvectors to generate new
conformations. This method was applied to determine the most stable
conformation of transition state for enantioselective alkylation by
the Maruoka and cinchona alkaloid catalysts and Hantzsch ester hydrogenation
of imines by chiral phosphoric acid. Besides successfully reproducing
the previously reported most stable DFT conformations, the conformational
search with the semiempirical quantum mechanical calculations newly
discovered a more stable conformation at a low computational cost.