Pantoic acid is the alpha hydroxy acid with the formula HOCH<sub>2</sub>C(CH<sub>3</sub>)<sub>2</sub>CH(OH)CO<sub>2</sub>H. The compound is almost always encountered in a biological context, as an aqueous solution of its conjugate base pantoate HOCH<sub>2</sub>C(CH<sub>3</sub>)<sub>2</sub>CH(OH)CO<sub>2</sub><big>-</big>. The amide of pantoic acid with ò-alanine is pantothenic acid (vitamin B<sub>5</sub>), a component of coenzyme A.
Its biosynthesis proceeds from ketoisovalerate by hydroxymethylation:
This conversion is catalyzed by ketopantoate hydroxymethyltransferase, which gives ketopantoic acid. This compound is reduced by ketopantoate reductase to (R)-pantoic acid, using NADPH as the hydride source.
The amide derived from pantoic acid and GABA is the pharmaceutical drug hopantenic acid.