2-Keto-3-methylbutyric acid 2-Ketovaline 2-Oxo-3-methylbutanoate 2-Oxoisopentanoate 2-Oxoisovalerate 3-Methyl-2-oxobutanoate 3-Methyl-2-oxobutanoic acid 3-Methyl-2-oxobutyric acid C00141 alpha-Ketovaline