Cycloalkane-Fused 5H-Pyrido[3,2-b]indol-4-amines: Synthesis, Characterization, Molecular Docking, and In Vitro Cell-Viability Evaluation

A four-step synthetic route to functionalized cycloalkane-fused 5H-pyrido[3,2-b]indol-4-amines was developed from substituted 2-aminobenzonitriles. Initial N-alkylation with bromoacetonitrile was performed in a choline chloride/urea deep eutectic solvent, followed by K2CO3-promoted cyclization to give 3-aminoindole-2-carbonitriles in yields of up to 80%. Subsequent ZnI2-mediated condensation with cyclic ketones under sealed-tube conditions (130 °C, 20 min), followed by treatment with NaOH, afforded the corresponding cycloalkane-fused 5H-pyrido[3,2-b]indol-4-amines. The compounds were evaluated for their effects on cellular metabolic activity/viability using the MTT assay against four tumor-derived cell lines (SK-MEL-28, KB, BT-549, and SK-OV-3) and two established non-tumorigenic kidney-derived epithelial cell lines (LLC-PK1 and Vero). 3-Methyl-7,8,9,10,11,13-hexahydro-6H-cycloocta[5,6]pyrido[3,2-b]indol-12-amine showed the greatest apparent activity within the tested concentration range, with IC50 values reported as <12.5 µM against SK-MEL-28, KB and BT-549 cells. Exploratory molecular docking studies were also performed against selected cancer-related protein targets to examine possible binding modes. The results support further biological evaluation of this series.