The synthesis of aranoza (IV) was accomplished by the condensation of N-methylurea (II) with L-arabinose (I), which yields 3-a-L-arabinopyranosyl-1-methylurea (III), followed by nitrosation of the latter. In slightly alkaline conditions or upon heating, aranoza undergoes intramolecular carbamoylation to produce N1O3-carbonyl-a-L-arabinopyranosylamine (V), gaseous N2 and methanol. It is important that diazomethane (CH2N2) is not formed under these conditions as demonstrated by gas chromatography and mass spectrometry.