Compound can be prepared in two different ways: 1) The reaction of N-trifluoroacetyl-L-glutamic acid 1-ethyl ester-5-acid chloride (I) with diazomethane in ether gives 6-diazo-5-oxonorleucine ethyl ester (II), which can be hydrolyzed by treatment with ammonia or NaOH in ethanol water. 2) The hydrogenation of gamma-benzyl ester of N-carboxy-L-glutamate anhydride (III) with H2 over Pd/C in ethyl acetate gives N-carboxy-L-glutamate anhydride (IV), which by reaction with refluxing SOCl2 yields L-4-[2-(chlorocarbonyl)ethyl]oxazolidine-2,5-dione (V). The reaction of (V) with diazomethane in ether affords L-4-(4-diazo-3-oxobutyl)oxazolidine-2,5-dione (VI), which is finally hydrolyzed with NaOH in water at room temperature.