Methylmalonic is an organic compound with the molecular formula C3H5NO2. It is also known as 3-methylsuccinic acid or methylsuccinic acid. Methylmalonic acid is a dicarboxylic acid that occurs naturally in some plants and animals, serving as an intermediate in the breakdown of certain amino acids. In biochemistry, it plays a role in the citric acid cycle (also known as the Krebs cycle or TCA cycle), where it is produced by the oxidation of succinic acid. Methylmalonic acid can also be synthesized from methanol and malonic acid through a process called reductive carboxylation, which involves the reduction of carbon dioxide to an organic molecule using a reducing agent such as sodium borohydride or hydrogen.