In a series of recent publications [1][2][3][4] we have developed a method of frontal polyhedra (FP) for establishing the quantitative structure-activity relationships (QSAR). The method is based on modeling a proposed receptor by a set of structural fragments (multiplets) containing the activity centers. The fitting of some ligand molecule to the receptor is assessed by taking a kind of"prints" from approximately planar peripheral faces of the molecule and searching for the optimum superimpositions of the prints of this molecule onto the above multiplets. The ability of local description of molecules on the level of three-dimensional (3D) structure provides applicability of the PM method to a series of compounds with structurally different ligands [1][2][3]. Recently we have developed a modified version of the PM method, which solves to a considerable degree the task of describing conformationally labile molecules. This was demonstrated by establishing 3D-QSAR in a series of of Baker triazines-dihydrofolate reductase inhibitors [4], the molecules of which exhibit internal mobility.In this work the modified PM method is applied to a series of urea derivatives-liver cytochrome P-450 inductors [5 -7]. These ligands have markedly differing dimensions and shapes and possess internal rotational degrees of freedom. This last circumstance hinders the use of other approaches to solving the 3D-QSAR task for these compounds [8,9].Despite achievements in the biochemistry of cytochrome P-450 [10, I 1], no attempts at QSAR analysis for inductors of the phenobarbital type have been practically undertaken. This group of inductors was only characterized by a few generalizations made on a qualitative level [6,7].I Polzunov Altai State Technical University, Barnanl, Russia. 2 Tomsk Polytechnical University, Tomsk, Russia. 3 Siberian State Medical University, Tomsk, Russia.
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DESCRIPTION OF METHOD
General characteristic. The modified PM method [4]is based on representing ligands by combinations of fragments. Each terminal atom X connecting the given fragment to other parts of the molecule is ascribed a set of descriptors ax, characterizing this atom and the related radical R x. The quantities ax~ describe projections of the terminal atom on the prints and are taken into account in searching for the optimum superimpositions. Because the prints are taken only from rigid fragments, the structural information contained in these prints is independent of the internal rotation of molecules. It was suggested that the descriptors ax, can be represented by the effective charge on atom X, the refractivity, and the lipophilicity of radical R x [4]. If atomXis not terminal, it is described only by the effective charge.The results of searching for the optimum superimpositions with the aid ofa combinatory algorithm [2] based on the A optimum criterion F [1, 2] led to the N x K assignment matrix V where N is the number of compounds in the series studied and K is the total number of active centers in the multiplets [4]. In this work we have also ...