D-Alanine-3,3,3-d3 is a labelled form of D-Alanine (A480995) which is an amino acid that is commonly found in bacteria, such as Streptococcus faecalis. It is essential for the biosynthesis of peptidoglycan crosslinking sub-units that are used for bacterial cell walls. D-Alanine is also known to cause cytotoxic oxidative stress in brain tumour cells.