Classical Isosteres are
molecules or
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 conven ...
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 to another chemical compound. In drug design, the purpose of exchanging one bi ...
. This is frequently used in
drug design
Drug design, often referred to as rational drug design or simply rational design, is the inventive process of finding new medications based on the knowledge of a biological target. The drug is most commonly an organic small molecule that acti ...
: 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, and ...
. 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 in 1919, and later modified by Grimm.
Hans Erlenmeyer
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* Hans (name), a masculine given name
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** Navraj Hans, Indian singer, actor, entrepreneur, cricket player and performer, son of Hans Raj Hans
** Yuvraj Hans, Punjabi ...
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 chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...
,
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 react ...
,
furan, and even
pyridine
Pyridine is a basic 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, weakly alkaline, water-miscible liquid with a ...
, exhibited similarities in many physical and chemical propertiesiea
References
Theoretical chemistry
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