Biphenyls privileged structures

Among the most popular privileged structures, historical representatives are arylethylamines (including indolylethylamines), diphenylmethane derivatives, tricyclic psychotropics and sulfonamides. Dihydropyridines [5], benzodiazepines, [2, 5], N-arylpiperazines, biphenyls and pyridazines [6] are more recent contributions. 

When used for relative similarity and diversity, only potential pharmacophores that contain the defined special centre-type are used. The frame of reference for similarity/diversity studies is thus changed to one that is focused on the feature of interest distances are now measured relative to this special centre. For example, the special centre could be the centroid of a substructure [10] such as biphenyl tetrazole or diphenylmethane, enabling the calculation and comparison of all 3D pharmacophoric shapes that contain this substructure the substructure is said to be privileged . For structure-based design, the potential pharmacophores in a site can be restricted to those that contain a specific site point (e.g. in a pocket, or at the entrance to a pocket). In the context of combinatorial library design, the relative measure can be those pharmacophoric shapes that contain a special site-point that represents where the attachment point for a reagent would be. In figure 1, the special point would be centre-type number 3, which can be reserved for this purpose. 

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