<i>In silico</i> STUDY OF CONJUGATED NITROGEN HETEROCYCLES AFFINITY IN THEIR BIOLOGICAL COMPLEXES

Abstract

For the estimation of the biological affinity of nitrogen-containing π-conjugated heterocyclic systems toward amino acid residues in proteins, the fragment-to-fragment approach was proposed. Two mechanisms of complexation between the heterocycle molecule with different donor/acceptor properties and the amino acid residue in the active part of the protein biomolecule were considered. One of these mechanisms is the π-stacking interaction and the other is formation of hydrogen bonds with model amino acid residues. It was found that heterocycles with a π-conjugated electron-acceptor moiety form a more stable heterocycle–biomolecule complex with protein fragments. Nitrogen-containing conjugated heterocycles with several nitrogen atoms form poly-hydrogen-bonded complexes. The stabilization energy of complexes with two pyrimidine–biomolecule hydrogen bonds increases by 4–6 kcal/mol compared to similar complexes with one hydrogen bond. Hydrophobic interactions are much more sensitive to the donor-acceptor properties of heterocycles in the formation of hydrogen-bonded complexes than in the formation of π-stacked complexes. The hydrophobic effect in the fragment-to-fragment approach allows us to see the values of the stabilization energies of the heterocycle–biomolecule complexes as close as possible to the experimentally studied biological systems.