ABSTRACT
The concept of chirality and its importance as a determinant of the pharmacological properties of drugs have been a part of scientific knowledge since the middle to late 1800s [1]. The property of enantiomerism is conferred on a molecule when it is present in two isomers that form nonsuperimposable mirror images of one another (Fig. 1). Most often these molecules possess a center of asymmetry focused on one specific atom in the molecule. With respect to these centers of asymmetry, chiral drugs may take several forms. In most cases, the chiral center is a tetrahedral carbon atom to which are attached four distinct substituents. Alternatively, chiral drugs may possess sulfur or phosphorous atoms at their centers of asymmetry (Fig. 2). Less commonly, chirality may be conferred on some drugs on the basis of the presence of a plane of asymmetry in the molecule (Fig. 2). Such compounds are known as geometric isomers.
