Lepimer

Lepimer is a term used in stereochemistry to describe a stereoisomer that differs from another stereoisomer at exactly one stereogenic center. In this sense, lepimers are a subset of diastereomers and are distinct from enantiomers, which differ at all stereogenic centers and are non-superimposable mirror images.

In carbohydrate and amino acid chemistry, the term epimer is the standard descriptor for such a relationship. Lepimer appears in some older or nonstandard literature and is not consistently defined across sources. Because terminology can vary between authors, lepimer is often considered synonymous with epimer in practice, though this usage is not universal and may be inconsistent.

When a molecule contains multiple stereogenic centers, switching the configuration at a single center while leaving the others unchanged yields a stereoisomer related to the reference by a single-center difference; this is what is sometimes called a lepimer (or, more often, an epimer) depending on the source. In contrast, changing more than one center produces other diastereomers, and changing all centers yields an enantiomer when the molecule has only one chiral framework.

Today, the term lepimer is rarely emphasized in formal coursework and most modern literature prefers the precise and widely accepted term epimer. Lepimer may still appear in historical discussions or when tracing the evolution of stereochemical nomenclature.

See also: Epimer, Stereochemistry.