Isostere

Isosteres are molecules or ions with the same number of atoms and the same number of valence electrons. As a result, they can exhibit similar pharmacokinetic and pharmacodynamic properties.

Some examples of isoteres are:
*fluorine and hydrogen
*carbon dioxide (CO₂) and nitrous oxide (N₂O)

The isostere concept was formulated by Irving Langmuir in 1919, [Irving Langmuir. Isomorphism, isosterism and covalence. "J. Am. Chem. Soc." 1919, "41", 1543-1559. doi|10.1021/ja02231a009] and later modified by Grimm. Erlenmeyer extended the concept to biological systems in 1932. [Mukesh Doble, Anil Kumar Kruthiventi, Vilas Gajanan. "Biotransformations and Bioprocesses". CRC Press, 2004, p. 60. ISBN 0824747755] 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 biological compound containing an isostere is called a bioisostere. This is frequently used in drug manufacturing: the bioisostere will still be recognized and accepted by the body, but its functions there will be altered as compared to the parent molecule.

Bioisosteres are compoundswhich fit the broadest definition of isoteres and have the same type of biological activity. They are of two types: classical and nonclassical.

Non-Classical Isosteres are atoms or groups or atoms that do not have the same valency, but have similar physiochemical properties.

References