its side chain α-nitrogen can only form one nitrogen bond. Additionally, proline is the only amino acid that does not form a red-purple colour when developed by spraying with ninhydrin for uses in chromatography. Proline, instead, produces an orange-yellow colour. Synthesis Racemic proline can be synthesized from diethyl malonate and acrylonitrile: See also Hyperprolinemia Inborn error of metabolism Prolidase deficiency Prolinol References Further reading . External links Proline MS Spectrum Proline biosynthesis Proline biosynthesis AMPA receptor agonists Kainate receptor agonists NMDA receptor agonists Proteinogenic amino acids Glucogenic amino acids Glycine receptor agonists Cyclic amino acids Pyrrolidines Secondary amino acids Excitatory amino acids