*4.1.2 Ligand-based drug repurposing*

In the absence of structural information about the microbial target protein from source, structural databases, or homology modeling, the structure-based repositioning and discovery efforts are hampered. Nevertheless, there are other virtual screening methods such as ligand-based screening methods, which can be employed for drug repurposing. The process involves the generation of a ligand-based mathematical "QSAR (quantitative structure–activity relationship) model" and ligand-based 3-dimensional (3D) "pharmacophore fingerprint" using in-house or approved microbial target site inhibitors as the active set I. The drugs sought to be repurposed are arranged in set II and screened using the derivatized models for their optimum physicochemical descriptors and/or conformational search for active pharmacophore. The potential molecules through ligand-based screening approach will be shortlisted for phenotype-based HTS studies [14].
