Quantum pharmacologic studies applicable to the design of anticonvulsants: theoretical conformational analysis and structure-activity studies of barbiturates.

We report the first large-scale systematic quantitative structure-activity relationship (QSAR) study of barbiturates, correlating molecular structures with anticonvulsant activity. To achieve this QSAR study, we devised a four-step strategy. In step 1, an optimal quantum mechanical technique for determining the geometry and shape (conformation) of barbiturates was ascertained; this is the AM1 semiempirical molecular orbital method. In step 2, the AM1 method was used to optimize the structures and molecular properties of 48 barbiturates with varying anticonvulsant activity. In step 3, discriminant analysis and regression analysis statistical calculations were used to correlate the molecular properties of the 48 analogues against maximal electroshock (MES) and subcutaneous metrazol (s.c.Met)-induced seizures. In step 4, the contribution of molecular electrostatic properties to barbiturate anticonvulsant activity was further refined by quantum mechanical derived molecular electrostatic potential (MEP) maps. Using this four-step strategy, we defined the pharmacophore, the portion of a molecule responsible for bioactivity, for anti-MES and anti-s.c.Met activity. For anti-s.c.Met activity, barbiturate lipophilicity and geometry are important considerations; for anti-MES activity, barbiturate topologic and electronic properties have increased relevance.