a-oxobutyrate
2-oxobutanoate
2-Ketobutyric acid
2-oxobutyric acid
2-oxobutyrate
2-oxobutanoic acid

C4H6O3

It's an a-keto acid (molecule formed after the deamination of an amino acid - in this case threonine).

Synthesis of glycine, serine and cysteine (3D)
Catabolism of methionine, threonine, valine and isoleucine (3D)
Synthesis of alanine, valine, isoleucine and leucine (3D)
Propanoate metabolism (Kyoto University)
C5-Branched dibasic acid metabolism (Kyoto University)