An L-glutamine diazo analogue amino acid antibiotic isolated from a species of the bacterial genus Streptomyces with potential antineoplastic activity. Diazooxonorleucine inhibits several glutamine-dependent biosynthetic pathways involved in the syntheses of D-glucosamine phosphate, purines and pyrimidines. This agent inhibits phosphate-activated glutaminase, a key enzyme for the synthesis of releasable glutamine, depleting cells of this essential amino acid and reducing their capacity to proliferate.