Different chemical structures have been found to possess different anti-inflammatory activities. Inflammation is a normal and essential response to any noxious stimulus which threatens the host and may vary from a localized response to a more generalized one.
In view of the complexity and multitude of biochemical factors involved in inflammatory events, few general correlations of chemical structures and physicochemical properties with biological activities would be expected.
Nevertheless some general features seem to be commonly associated with a large number of active drugs. However, these main features are not sufficient, but they could reflect certain physicochemical requirements for in vivo efficacy. QSAR is a useful means for maximizing the potency of a new lead compound. In the lead optimization phase of the synthetic project various QSAR procedures with the aid of computer-technology have been proposed. Among them, the classical Hansch approach has been widely used leading to quite a few successful examples.
In the QSAR approaches, the prescription to optimise the lead structure is inferred from mathematical equations correlating variations in the potency of a certain biological activity with physicochemical and structural descriptors among congeneric molecules.
The QSAR procedures are based on physical organic concepts and involve calculational operations. In the last years, quantum-chemical descriptors have been used in QSAR studies, because of the large physical information content encoded in many of the descriptors. Several anti-inflammatory receptor site models have been proposed. Since inflammation is a complex phenomenon involving interrelationships between humoral and cellular reactions through a number of inflammatory mediators, there is not much evidence on QSAR studies.
Several QSAR studies have been reported obtaining only partial results. It was found that substituents which contribute to the high lipophilicity, were favourable to the activity. Substituents of short length H, CH3 have also a favourable effect. Satisfactory relationships between the in vivo activities and deprotonation energies, the HOMO energies and lipophilicities were found.