Synthesis and anticancer evaluation of certain indolo[2,3-b]quinoline derivatives

The present report describes the synthesis and anticancer evaluation of certain 11-substituted 6H-indolo[2,3-b]quinolines and their methylated derivatives. These 6H-indolo[2,3-b]quinoline derivatives 11-13 were prepared from the commercially available 1,4-dihydroxyquinoline through alkylation, chlorination, nucleophilic reaction, and ring cyclization. Depending on the ratio of 11, (MeO)2SO2, and K2CO3, alkylation occurred primarily on N-5 (1:0.8:0.8) or N-6 (1:1.5:1.5) leading to the isolation of 14a or 14b as a major product. Accordingly, major product 15a (2/(MeO)2SO2/K2CO3=1:2:2) or 15b (1:1:1), respectively, was obtained by alkylation of 12 while 16a (13/(MeO)2SO2/K2CO3=1:2:2) or 16b (1:1:1), respectively, was obtained by alkylation of 13. The in vitro anticancer assay indicated 5-methylated derivatives 14a, 15a, 16a are more cytotoxic than their respective 6-methylated counterparts 14b, 15b, 16b and 6H-indolo[2,3-b]quinoline precursors 11, 12, 13. Among them, 11-(4-methoxyanilino)-6-methyl-6H-indolo[2,3-b]quinoline (16a) was the most cytotoxic with a mean GI50 value of 0.78 microM and also exhibited selective cytotoxicities for HL-60 (TB), K-562, MOLT-4, RPMI-8226, and SR with GI50 values of 0.11, 0.42, 0.09, 0.14, and 0.19 microM, respectively.