N-a-Acetyl-L-arginine also known as N-ac-L-arg-OH or N-alpha-acetylarginine belongs to the class of organic compounds known as n-acyl-l-alpha-amino acids.

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.

Beta-leucine?is a beta-amino acid that is?pentanoic acid?substituted at positions 3 and 4 by?amino?and?methyl?groups respectively. It has a role as a human metabolite.