Pyrrole-2-carboxylic acid was first identified as a degradation product of sialic acids then as a derivative of the oxidation of the D-hydroxyproline isomers by mammalian D-amino acid oxidase.

2,6-Dibromophenol is extracted from the skin and muscle of flatfish.

D-(-)-Lactic acid is a normal intermediate in sugar fermentation (oxidation, metabolism).