Metoprolol Fumarate

Metoprolol Fumarate is the trans-2-butenedioate ester derivative of Metoprolol, featuring a methoxyphenylpropanolamine core conjugated to fumaric acid. The fumarate moiety introduces a conjugated diene system and carboxylate groups, forming a zwitterionic salt with the parent drug's amine. This impurity arises during API synthesis via acid-base interaction between Metoprolol and fumaric acid. Structurally distinct from the parent compound due to the trans-configuration of the double bond in the fumarate ester, it serves as an HPLC reference standard for quantifying fumarate-related impurities in Metoprolol formulations.