ABSTRACT
The concept of pharmacophore modeling is one of the oldest yet most widely used concepts in today's drug discovery research. The essential substructural moieties of a molecule necessary for its pharmacological activity are called pharmacophores. This terminology was first introduced by Ehrlich ( 1 ), following the term chromophore, which was used to represent the functional groups responsible for the color of a compound. The interest in the idea of pharmacophores has grown enormously in recent years owing to the availability of various automated computerized software for identifying pharmacophores as well as their geometry (2-7). The pharmacophoric information as well as their three-dimensional structure can often be used to identify novel pharmacologically active lead compounds by searching various databases of known chemicals, like the Available Chemical Directory (ACD) (8). Compounds having similar pharmacophoric groups often have similar biological activity. Understandably, the existence of similar or the same pharmacophoric groups does not guarantee that biological activity will be similar. The differentiating structural moieties may cause enough repulsive inter-
action with the target protein/receptor to diminish or abolish its binding affinity, or its chemical or physicochemical properties may be altered enough to prevent it from reaching the binding site.
