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 and comparable to allopurinol . Furthermore, 6-(N-benzoylamino)purine neither produced any enzymatic superoxide nor reduced XO by an electron transfer reaction unlike allopurinol. 6-(N-benzoylamino)purine is about 10000-fold more potent as a XO inhibitor compared to the only known purine analogue 8-bromoxanthine . 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 [Ecomplex − (Eligand+Eprotein)] 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.