2-oxo-4-hydroxyvalerate 4-HYDROXY-2-KETOVALERATE 4-hydroxy-2-keto-pentanoic acid 4-hydroxy-2-ketovaleric acid 4-hydroxy-2-oxo-pentanoic acid 4-hydroxy-2-oxo-valerate 4-hydroxy-2-oxo-valeric acid 4-hydroxy-2-oxopentanoate 4-hydroxy-2-oxovaleric acid HKP