Ionic liquid-assisted synthesis of dihydropyrimidin(thi)one Biginelli adducts and investigation of their mechanism of urease inhibition

Abstract

Twenty-six Biginelli adducts were synthesized through an ionic liquid-assisted synthesis with up to 92% yield. Sixteen of these Biginelli adducts were then assayed to determine their antiureolytic activity against purified urease from jack beans. The substances BA7-S, BA9-S and BA11-S were shown to be as efficient inhibitors as hydroxyurea, a positive control used in in vitro screening assay against urease. Fluorescence studies revealed that BA7-S, BA9-S, BA11-S and BA5-S possessed high binding constant values of 5.95, 6.72, 4.55, and 4.28 M⁻¹, respectively, while BAS12-S, without substituents, showed a low value of log K_b = 2.16 M⁻¹. In addition, in the most thermodynamically favorable BA5-S and BA7-S urease complexes, the corresponding Biginelli adducts were capable of interacting with the active site of urease through non-ionic interactions, such as hydrophobic interactions, or hydrogen and van der Waals interactions, respectively. In silico studies also supported that the BAs interact with the active site, confirming the fluorescence and kinetic assay studies, which clearly indicate that BA5-S and BA7-S are competitive inhibitors (K_i = 0.96 and 0.57 mM, respectively). In silico studies also showed that the substituents in the aromatic ring interact with Ni atoms to form a stable complex.