Biosynthesis of 2'-deoxycoformycin: evidence for ring expansion of the adenine moiety of adenosine to a tetrahydroimidazo[4,5-d][1,3]diazepine system

2'-Deoxycoformycin (2'-dCF), a nucleoside antitumor agent produced in trace quantities by Streptomyces antibioticus, has been shown in earlier work to originate from the intact carbon-nitrogen framework of adenosine. Additional experiments using 13C and two-dimensional Fourier transform NMR techniques, together with radiolabeling studies, identify the C-1 of D-ribose, and not the tetrahydrofolate C-1 pool, as the source of the C-7 carbon in the aglycon of 2'-dCF. These results show that the adenine portion of adenosine (or a nucleotide thereof) undergoes a unique ring expansion, by insertion of a -CH2-unit between the N-1 and C-6 of the adenine ring, to furnish the 1,3-diazepine portion of 2'-dCF