Celecoxib is a non-steroidal anti-inflammatory drug (NSAID). It suppresses the hormones, which cause pain and inflammation. It is a COX-2 (Cyclooxygenase) inhibitor, thus, preventing the activity of the COX-2 enzyme. Inhibitory activity increases in the absence of methyl group or when it is replaced by a chlorine substituent.
However, in the clinical practice, neither methyl group nor chlorine substituent was removed from the structure. This is because these groups are essential for initiating the drug binding and its interaction with the substrate.
The methyl group offers stability to the molecule and binding with its substrates. The methyl group donates electron to its substrate thus, maintaining the drug bonding. On the contrary, addition of a chlorine functional group will lead to a change in molecular dynamics. The chlorine group withdraws electrons through resonance or induction.