Phenylpyruvic acid is a keto-acid that is an intermediate or catabolic byproduct of phenylalanine metabolism. It has a slight honey-like odor. Levels of phenylpyruvate are normally very low in blood or urine. High levels of phenylpyruvic acid can be found in the urine of individuals with phenylketonuria (PKU) an inborn error of metabolism.

Emeheterone is a natural product from the fresh fruiting bodies of the basidiomycetes Albatrellus confluens.

Methyl 2-hydroxy-4-methylvalerate is one of dominant volatile compounds in Zhenjiang aromatic vinegar.