A pharmacophore is an abstract description of molecular features that are necessary for molecular recognition of a ligand by a biological macromolecule. IUPAC defines a pharmacophore to be "an ensemble of steric and electronic features that is necessary to ensure the optimal supramolecular interactions with a specific biological target and to trigger (or block) its biological response". A pharmacophore model explains how structurally diverse ligands can bind to a common receptor site. Furthermore, pharmacophore models can be used to identify through de novo design or virtual screening novel ligands that will bind to the same receptor.
Typical pharmacophore features include hydrophobic centroids, aromatic rings, hydrogen bond acceptors or donors, cations, and anions. These pharmacophoric points may be located on the ligand itself or may be projected points presumed to be located in the receptor.
The features need to match different chemical groups with similar properties, in order to identify novel ligands. Ligand-receptor interactions are typically “polar positive”, “polar negative” or “hydrophobic”. A well-defined pharmacophore model includes both hydrophobic volumes and hydrogen bond vectors.
The process for developing a pharmacophore model generally involves the following steps:
As the biological activities of new molecules become available, the pharmacophore model can be updated to further refine it.
In modern computational chemistry, pharmacophores are used to define the essential features of one or more molecules with the same biological activity. A database of diverse chemical compounds can then be searched for more molecules which share the same features arranged in the same relative orientation. Pharmacophores are also used as the starting point for developing 3D-QSAR models. Such tools and a related concept of "privileged structures", which are "defined as molecular frameworks which are able of providing useful ligands for more than one type of receptor or enzyme target by judicious structural modifications", aid in drug discovery.
Historically, pharmacophores were established by Lemont Kier, who first mentions the concept in 1967 and uses the term in a publication in 1971.
The development of the concept is often erroneously accredited to Paul Ehrlich. However neither the alleged source nor any of his other works mention the term "pharmacophore" or make use of the concept.
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