D-proline is an isomer of the naturally occurring amino acid L-Proline. D-amino acids have been found in relatively high abundance in human plasma and saliva. These amino acids may be of bacterial origin but there is also evidence that they are endogenously produced through amino acid racemase activity.

Argireline (Acetyl hexapeptide-3) is composed of chains of amino acids known as peptides. Argireline significantly inhibits Ca2+ dependent neurotransmitter release (acetylcholine) at the neuromuscular junction.

Naxitamab (Hu3F8) is a humanized monoclonal antibody targeting GD2 with antitumor activity, used to study neuroblastoma, osteosarcoma, and other GD2-positive cancers.