Human Serum Albumin Interactions with Bioactive 3H-Imidazo[4,5-A]Acridin-11(6H)-Ones Studied by Fluorescence Spectroscopy

Abstract

The key intermediates 3H-imidazo[4′,5′:3,4]benzo[c]isoxazoles were synthesized by the reaction of N-alkyl-5-nitrobenzimidazoles with aryl acetonitriles under basic conditions. These compounds were converted to 3H-imidazo[4,5-a]acridin-11(6H)-ones by the Tanasescu reaction in excellent yields. The structures of all newly synthesized compounds were confirmed by IR, ¹H NMR, and mass spectroscopic data. The interactions of 3H-imidazo[4,5-a]acridin-11-ones with human serum albumin (HSA) have been studied by fluorescence spectroscopy. The binding of 3H-imidazo[4,5-a]acridin-11(6H)-ones quenches the HSA fluorescence, revealing a 1 : 1 interaction with a binding constant of about 4.50 × 10⁴ – 1.25 × 10⁵ M^-1. A decrease in the fluorescence intensity at 339.41 nm, when excited at 280 nm, is attributed to changes in the environment of protein fluorophores caused by the presence of the ligands. Differences in the interactions of 3H-imidazo[4,5-a]acridin-11(6H)-one derivatives with HSA were observed using the spectrofluorimetry technique. Thermodynamic characteristics and the parameters of HSA binding with these compounds are in accordance with the antibacterial activity of various derivatives of 3H-imidazo[4,5-a]acridin-11(6H)-one.