Isostere
Encyclopedia
Isosteres are molecules or ions with the same number of atom
s and the same number of valence electrons.
Some examples of isoteres include:
The isostere concept was formulated by Irving Langmuir
in 1919, and later modified by Grimm. Friedrich Erlenmeyer
extended the concept to biological systems in 1932. 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
and thiophene
, thiophene and furan
, and even benzene and pyridine
, exhibited similarities in many physical and chemical properties.
A biologically-active compound containing an isostere is called a bioisostere
. This is frequently used in drug design
: the bioisostere will still be recognized and accepted by the body, but its functions there will be altered as compared to the parent molecule.
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
s and the same number of valence electrons.
Some examples of isoteres include:
- SodiumSodiumSodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
and hydrogenHydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly... - Carbon dioxideCarbon dioxideCarbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
(CO2) and nitrous oxideNitrous oxideNitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...
(N2O) - SiliconSiliconSilicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
and carbonCarbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
The isostere concept was formulated by Irving Langmuir
Irving Langmuir
Irving Langmuir was an American chemist and physicist. His most noted publication was the famous 1919 article "The Arrangement of Electrons in Atoms and Molecules" in which, building on Gilbert N. Lewis's cubical atom theory and Walther Kossel's chemical bonding theory, he outlined his...
in 1919, and later modified by Grimm. Friedrich Erlenmeyer
Friedrich Gustav Carl Emil Erlenmeyer
Friedrich Gustav Carl Emil Erlenmeyer was a German chemist and the discoverer of the Erlenmeyer-Plöchl azlactone and amino acid synthesis. He was the son of Richard August Carl Emil Erlenmeyer....
extended the concept to biological systems in 1932. 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
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....
and thiophene
Thiophene
Thiophene is a heterocyclic compound with the formula C4H4S. Consisting of a flat five-membered ring, it is aromatic as indicated by its extensive substitution reactions. Related to thiophene are benzothiophene and dibenzothiophene, containing the thiophene ring fused with one and two benzene...
, thiophene and furan
Furan
Furan is a heterocyclic organic compound, consisting of a five-membered aromatic ring with four carbon atoms and one oxygen. The class of compounds containing such rings are also referred to as furans....
, and even benzene and pyridine
Pyridine
Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one C-H group replaced by a nitrogen atom...
, exhibited similarities in many physical and chemical properties.
A biologically-active compound containing an isostere is called a bioisostere
Bioisostere
In medicinal chemistry, bioisosteres are substituents or groups with similar physical or chemical properties which produce broadly similar biological properties to a chemical compound. In drug design, the purpose of exchanging one bioisostere for another is to enhance the desired biological or...
. This is frequently used in drug design
Drug design
Drug design, also sometimes referred to as rational drug design or structure-based drug design, is the inventive process of finding new medications based on the knowledge of the biological target...
: the bioisostere will still be recognized and accepted by the body, but its functions there will be altered as compared to the parent molecule.