Markush

Markush refers to a notation used in chemistry and patent law to describe a family of related compounds within a single structural framework. The Markush concept allows a core molecular skeleton to be paired with variable substituents, defined by placeholders such as R, R1, R2, or by enumerated lists of possible groups. The term is derived from early 20th century patent practice in which a single claim could cover many individual compounds by specifying generic substituents rather than each compound separately.

In a Markush structure, a central core is shown with one or more positions for substituents. These positions are defined by Markush groups that may consist of a set of alternative radicals (for example, R ∈ {methyl, ethyl, n-propyl}) or more complex branches capable of including heteroatoms, rings, or functional groups. Markush notation can also include optional substituents or multiple, independent substituent sets. The practical effect is to describe a large class of chemical entities with a compact representation, enabling broad patent claims while maintaining a single structural framework.

Use and implications: Markush claims are common in pharmaceutical and chemical patents because they enable protection of many possible compounds under one claim. However, they require clear and enabling disclosure so that the broader class is well defined and reproducible. Patent offices assess whether the scope is definite enough to be enforceable and to guide search and examination processes.

In summary, the Markush approach is a foundational tool in chemical patent drafting for describing families of related compounds through a single, flexible structural representation.