6-(N-benzoylamino)purine as a novel and potent inhibitor of xanthine oxidase: inhibition mechanism and molecular modeling studies

Abstract

The inhibition of xanthine oxidase (XO) activity by the purine analogue 6-(N-benzoylamino)purine was evaluated and compared with the standard inhibitor, allopurinol and the parent compound adenine. 6-(N-benzoylamino)purine is a highly potent inhibitor of XO (IC₅₀ = 0.45 μM) and comparable to allopurinol (IC₅₀ = 0.80 μM). Furthermore, 6-(N-benzoylamino)purine neither produced any enzymatic superoxide nor reduced XO by an electron transfer reaction unlike allopurinol. 6-(N-benzoylamino)purine (K_i = 0.0475 μM) is about 10000-fold more potent as a XO inhibitor compared to the only known purine analogue 8-bromoxanthine (K_i = 400 μM). 6-(N-Benzoylamino)purine is a competitive inhibitor of XO and the inhibition was not completely reversed even at 100 μM xanthine concentration. The calculated interaction energy [E_complex- (E_ligand + E_protein)] of -30.5, -22.6, and -17.2 kcal/mol, respectively, of 6-(N-benzoylamino)purine, 8-bromoxanthine and the parent compound adenine provided the rationale for the better enzyme inhibitory activity of 6-(N-benzoylamino)purine. To understand the role of the benzamido group in the inhibition process, molecular docking studies were carried out and it was revealed that the hydrogen bonding interactions involving N-7 of the purine ring and the N−H of Arg880, N−H of the purine ring and OH of Thr1010, as well as non-bonded interactions of the benzamido group of 6-(N-benzoylamino)purine with amino acid residues Gly799, Glu802, Phe914, Ala1078, Ala1079 and Glu1261 in the active site of XO play an important role in the stabilization of the E-I complex.