Purines. LXIII. Syntheses of Azepinomycin, an Antitumor Antibiotic from Streptomyces Species, and Its 3-β-D-Ribofuranodise and Their 8-Imino Analogues

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Three variants of a syntheric route to the antitumor antibiotic azepinomycin (3) from 1-substituted N'-alkoxy-5-formamidoimidazole-4-carboxamidine (type 10) are described. The synthesis started with the monocycles 10a-c and proceeded through the intermediates 11a-c, 12a-c, 13a-c, 14a-c, and 4a, b and 3-β-D-ribofuranosylazepinomycin (4c). The benzyl version (series a), including the permutation 14a→15→3, was found to produce the antibiotic (3) most efficiently. The starting materials 10a-c were readily prepared from the 9-substituted adenines 7a-c via the N-oxides 8a-c and the 1-alkoxy derivatives 9a-c. The 8-imino analogues (17 and 18) of 3 and 4c were also synthesized from 12a and 12c, respectively.