An ab Initio Investigation of the Interactions Involving the Aromatic Group of the Set of Fluorinated N-(4-Sulfamylbenzoyl)benzylamine Inhibitors and Human Carbonic Anhydrase II

Abstract

In this work we investigate the interactions that occur between the aromatic portion of the set of fluorinated N-(4-sulfamylbenzoyl)benzylamine (SBB) inhibitors and two residues of Human Carbonic Anhydrase II (HCAII), namely Phe-131 and Pro-202. Calculations were carried out at the MP2/aug-cc-pVDZ level of theory and the counterpoise scheme of Boys and Bernardi was employed to account for the basis set superposition error. The most striking result obtained here is that the SBB phenyl ring interacts at least as strongly with the proline pyrrolidine ring as with the phenylalanine phenyl ring, which is surprising because aromatic-aromatic interactions have long been thought to be particularly favorable in protein and protein-ligand structure. Comparison of the MP2 binding energies to those obtained with the Hartree-Fock method indicates that the attraction between the proline pyrrolidine ring and the SBB phenyl ring is largely attributable to dispersion forces. These favorable interactions between pyrrolidine and phenyl rings may have important implications in protein structure because there is potential for proline residues to interact with phenylalanine residues in a fashion analogous to that seen here. A preliminary protein data bank search indicates that the proline-phenylalanine contacts are about 40% as common as those between two phenylalanines. It is also found here that the number and pattern of fluorine substituents on the SBB phenyl ring is much less important in determining the SBB-HCAII binding energy than the relative geometric configuration of the interacting pairs.