Monomethyl fumarate

Monomethyl fumarate is a trans-2-butenedioic acid derivative with one carboxylic acid group esterified to methyl. Its conjugated diene system and single ester functionality distinguish it from dimethyl fumarate. This impurity arises via partial esterification during fumaric acid derivative synthesis or through methanolysis of parent APIs. Structurally, it retains the trans-double bond critical to fumaric acid's pharmacophore. Analytically, it serves as an HPLC reference standard for quantifying process-related impurities in fumarate-based APIs.