Isoterism

Isosterism refers to the concept that molecules or ions have the same number of atoms and a similar arrangement of electrons, leading to comparable physical and chemical properties. Isosteres may not necessarily have the same elements, but their overall structure, electron configuration, and molecular shape are similar.

Types of isosterism:

1. Classical Isosteres: Atoms, ions, or molecules with the same number of valence electrons and similar size, like N₂ and CO.
2. Non-classical Isosteres (Bioisosteres): Substituents or groups within a molecule that do not follow the classical definition but mimic the chemical or biological activity. For example, in drug design, replacing a carboxyl group (-COOH) with a sulfonamide group (-SO₂NH₂) to achieve similar biological effects is an example of bioisosterism.

Isosterism is crucial in pharmaceutical chemistry for drug design and development, as it helps modify drugs to improve their efficacy, reduce side effects, or avoid metabolic degradation while maintaining or enhancing the desired biological activity.