Classical Isosteres are molecules or ions with similar shape and often electronic properties. Many definitions are available.Richard Silverman, The Organic Chemistry of Drug Design and Drug Action, Second Edition, 2004 but the term is usually employed in the context of bioactivity and drug development. Such biologically-active compounds containing an isostere is called a bioisostere. This is frequently used in drug design:Nathan Brown. Bioisosteres in Medicinal Chemistry. Wiley-VCH, 2012, p. 237. the bioisostere will still be recognized and accepted by the body, but its functions there will be altered as compared to the parent molecule.
