A new series of ketoprofen analogs were synthesized to evaluate their biological activities as selective cyclooxygenase-2 (COX-2) inhibitors. In vitro COX-1 and COX-2 inhibition studies showed that all compounds were potent and selective inhibitors of the COX-2 isozyme with IC(50) values in the highly potent 0.057-0.085 microM range, and COX-2 selectivity indexes in the 115 to >1298.7 range. Compounds possessing azido pharmacophore group (8a and 8b) exhibited highly COX-2 inhibitory selectivity and potency even more than reference drug celecoxib. Molecular modeling studies indicated that the azido substituent can be inserted deeply into the secondary pocket of COX-2 active site for interactions with Arg(513).