6-Diazo-5-oxo-L-nor-Leucine (L-6-Diazo-5-oxonorleucine; DON) is a glutamine antagonist that irreversibly inhibits the catabolic effect of glutamine. 6-Diazo-5-oxo-L-nor-Leucine shows good anticancer activity (especially in pancreatic cancer) and reduces the self-renewal potential and metastatic capacity of tumour cells. 6-Diazo-5-oxo-L-nor-Leucine also possesses antibacterial and antiviral activity.