Bioisostere

[1] In drug design,[2] the purpose of exchanging one bioisostere for another is to enhance the desired biological or physical properties of a compound without making significant changes in chemical structure.

Classical bioisosterism was originally formulated by James Moir and refined by Irving Langmuir[3] as a response to the observation that different atoms with the same valence electron structure had similar biological properties.

However, with a blocked pathway for metabolism, the drug candidate may have a longer half-life.

Whereas classical bioisosteres commonly conserve much of the same structural properties, nonclassical bioisosteres are much more dependent on the specific binding needs of the ligand in question and may substitute a linear functional group for a cyclic moiety, an alkyl group for a complex heteroatom moiety, or other changes that go far beyond a simple atom-for-atom switch.

It has been proposed that key force field features, that is the pharmacophore, be patented instead.