X-ray crystal structures have been determined of five compounds closely related to N-benzyl-2-azaspiro[4.4]-nonane-l,3-dione (1), which is inactive as an anticonvulsant, and N-(benzyloxy)-2-azaspiro[4.4]nonane-1,3-dione (2), which is active. Conformational analyses have been carried out with (1), (2) and the new compounds N-(2′,4′-dichlorobenzyloxy)-2-azaspiro[4.4]nonane-l,3-dione (3), N-(2′-bromobenzyloxy)-2-azaspiro[4.4]nonane-l,3-dione (4), N-(4′-(trifluoromethyl)benzyloxy)-2-azaspiro[4.4]nonane-l,3-dione (5), which are all active anticonvulsants, and N-(4′-chlorobenzyloxy)-2-azaspiro[4.4]nonane-l,3-dione (6) and N-(4′-bromobenzyloxy)-2-azaspiro[4.4]nonane-1,3-dione (7), which are inactive. Regardless of the substitution pattern, the conformations of compounds (2)–(7) in the crystals are very similar. Among the low-energy conformations, which are well distributed in the conformational space, that present in its solid state is dominant. Ortho-substitution considerably cuts down the number of conformations accessible within the set energy limit. The results of these studies alone do not explain the differences in activity.
Combined quantum-mechanics/molecular-mechanics dynamics simulation of A-DNA double strands irradiated by ultra-low-energy carbon ions
