3oxobutanoate

3-oxobutanoate, commonly known as acetoacetate, is the deprotonated form of 3-oxobutanoic acid (acetoacetic acid). Its structure is CH3-CO-CH2-COO−, a beta-keto carboxylate that contains an active methylene group between two carbonyls, giving rise to enolizable acidity and versatile reactivity in organic synthesis and metabolism.

In solution, 3-oxobutanoate is the conjugate base of acetoacetic acid. The molecule has an acidic methylene hydrogen and carboxylate functionality; the alpha-hydrogens (between the two carbonyls) are relatively acidic, enabling enolate formation under basic conditions. The carboxylate group remains deprotonated at physiological pH in many contexts.

Biologically, acetoacetate is one of the ketone bodies produced by the liver during fasting or carbohydrate restriction, along with beta-hydroxybutyrate and acetone. It serves as an energy substrate for extrahepatic tissues, including the brain and heart. In tissues, acetoacetate is activated to acetoacetyl-CoA by the enzyme succinyl-CoA:3-ketoacid CoA transferase (SCOT) using succinyl-CoA, and is subsequently split into two acetyl-CoA molecules that feed into the citric acid cycle. Ketone body levels, including acetoacetate, rise during prolonged fasting, prolonged exercise, or diabetic ketoacidosis.

In chemistry, acetoacetate is a versatile building block for enolate chemistry and condensation reactions, used in various carbon–carbon bond-forming methods. Sodium and other metal salts of acetoacetate are common reagents in organic synthesis and bioconversion studies. Detection of acetoacetate in clinical samples can be performed by nitroprusside-based assays, such as in urine ketone tests.