5-Heteroatom substituted pyrazoles as canine COX-2 inhibitors. Part III: molecular modeling studies on binding contribution of 1-(5-methylsulfonyl)pyrid-2-yl and 4-nitrile.

The structure-activity relationship toward canine COX-1 and COX-2 in vitro whole blood activity of 4-hydrogen versus 4-cyano substituted 5-aryl or 5-heteroatom substituted N-phenyl versus N-2-pyridyl sulfone pyrazoles is discussed. The differences between the pairs of compounds with the 4-nitrile pyrazole derivatives having substantially improved in vitro activity are highlighted for both COX-2 and COX-1. This difference in activity may be due to the contribution of the hydrogen bond of the 4-cyano group with Ser 530 as shown by our molecular modeling studies. In addition, our model suggests a potential contribution from hydrogen bonding of the pyridyl nitrogen to Tyr 355 for the increased activity over the phenyl sulfone analogs.