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Abstract:The title compound (2) was prepared in high yield by catalytic transfer hydrogenation of the 6-nitro precursor (1), using hydrazine hydrate as the hydrogen source. Under the conditions employed, the ester groups remain unaffected. The new compound was fully characterised by elemental analysis, . Such compounds are known to act as topoisomerase II poisons and as another common structural feature they possess a heteroaromatic ring fused to the carbazole 2,3-bond. Typically, this is a pyridine unit (like in olivacine and its isomer, ellipticine [3]), but there are also examples for various diazine-fused 1-methyl-and 1,4-dimethylcarbazoles, exhibiting antitumor activity [4]. Among them, pyridazino [4,5-b]carbazoles (representing a 3-aza-olivacine scaffold) have been reported by us [5][6][7][8] and others [9]. As a key intermediate for the synthesis of these tetracycles, 1-methylcarbazole-2,3-dicarboxylic esters have been used and the latter were found to provide a convenient access also to some cytotoxic 4-methylpyrrolo [3,4-b]carbazole-1,3(2H,5H)-diones [10], which again feature the 1-methylcarbazole motif. In the course of extensive structural variation of the A-ring substitution pattern of such b-fused 1-methylcarbazoles, we recently reported the synthesis and cyclisation reactions of some halo-and nitro-substituted 1-methylcarbazole-2,3-dicarboxylic acid dimethyl esters [11]. As a further extension of our building-block library, we here describe the convenient preparation of dimethyl 6-amino-1-OPEN ACCESS