Classical Isosteres are

molecules A molecule is a group of two or more atoms that are held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemistry ...

ions An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

with similar shape and often electronic properties. Many definitions are available. 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 In medicinal chemistry, bioisosteres are chemical substituents or groups with similar physical or chemical properties which produce broadly similar biological properties in the same chemical compound. In drug design, the purpose of exchanging one b ...

. This is frequently used in

drug design Drug design, often referred to as rational drug design or simply rational design, is the invention, inventive process of finding new medications based on the knowledge of a biological target. The drug is most commonly an organic compound, organi ...

: the bioisostere will still be recognized and accepted by the body, but its functions there will be altered as compared to the parent molecule.

History and additional definitions

Non-classical isosteres do not obey the above classifications, but they still produce similar biological effects

in vivo Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, an ...

. Non-classical isosteres may be made up of similar atoms, but their structures do not follow an easily definable set of rules. The isostere concept was formulated by

Irving Langmuir Irving Langmuir (; January 31, 1881 – August 16, 1957) was an American chemist, physicist, and metallurgical engineer. He was awarded the Nobel Prize in Chemistry in 1932 for his work in surface chemistry. Langmuir's most famous publicatio ...

in 1919, and later modified by Grimm. Hans Erlenmeyer extended the concept to biological systems in 1932.Mukesh Doble, Anil Kumar Kruthiventi, Vilas Gajanan. ''Biotransformations and Bioprocesses''. CRC Press, 2004, p. 60. H. Erlenmeyer, Ernst Willi: ''Zusammenhänge zwischen Konstitution und Wirkung bei Pyrazolonderivaten.'' In: ''Helvetica Chimica Acta.'' 18, 1935, S. 740, .Hans Erlenmeyer, Martin Leo: ''Über Pseudoatome.'' In: ''Helvetica Chimica Acta.'' 15, 1932, S. 1171, . Classical isosteres are defined as being atoms, ions and molecules that had identical outer shells of electrons, This definition has now been broadened to include groups that produce compounds that can sometimes have similar biological activities. Some evidence for the validity of this notion was the observation that some pairs, such as

benzene Benzene is an Organic compound, organic chemical compound with the Chemical formula#Molecular formula, molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal Ring (chemistry), ring with one hyd ...

thiophene Thiophene is a heterocyclic compound with the formula C4H4S. Consisting of a planar five-membered ring, it is aromatic as indicated by its extensive substitution reactions. It is a colorless liquid with a benzene-like odor. In most of its reacti ...

furan Furan is a Heterocyclic compound, heterocyclic organic compound, consisting of a five-membered aromatic Ring (chemistry), ring with four carbon Atom, atoms and one oxygen atom. Chemical compounds containing such rings are also referred to as f ...

, and even

pyridine Pyridine is a basic (chemistry), basic heterocyclic compound, heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom . It is a highly flammable, weak ...

, exhibited similarities in many physical and chemical properties.

References

{{reflist Theoretical chemistry Drug discovery