4,5-Diazafluorene derivatives and their silver(I) complexes: Synthesis and biological evaluation as antiproliferative agents

This work is focused on the synthesis and biological evaluation of 4,5-diazafluorene bipyridines and their silver(I) complexes. These 4,5-diazafluorene derivatives have two aromatic R groups at the C9 position (R = 4-C₆H₄X, X = H, 3; Me, 4; NH₂, 5; OH, 6; OMe, 7; Br, 8; F, 11; Cl, 12; I, 13; R = 3-Me-4-NH₂-C₆H₃, 9; 3,5-Me₂-4-NH₂-C₆H₂, 10). Their synthesis was carried out from a direct S_EAr from 4,5-diazafluoren-9-one and the corresponding aryl compound or via the diazonium salt strategy. These compounds were used as ligands to synthesize [Ag(N-N)₂]NO₃ complexes (3Ag-13Ag). The stability of these complexes in DMSO solution was studied showing that no dissociation was observed over 48 h. All compounds were characterized by NMR (¹H and ¹³C) and MS. The crystal structures of three complexes were determined by single-crystal X-ray diffraction revealing different coordination geometries in solid state. The cytotoxicity study of the compounds was analyzed in lung carcinoma (A-549), cervical carcinoma (HeLa), melanoma (HBT70) cancerous cell lines and in non-malignant lung fibroblasts (MRC-5) and normal human dermal fibroblasts (HDFn) cell lines. Only ligands 3, 7, 11, and 13 exhibited antiproliferative activity. On the other hand, most of the complexes were active suggesting a positive impact when silver is incorporated into the molecule. The selectivity index towards cancerous cells was calculated. Values from 3 to more than 16 were obtained suggesting that these silver complexes are promising molecules for future anticancer treatments. Drug-likeness and ADME properties were in silico calculated for the ligands. The P-gp interaction and P_app were experimentally evaluated. Regarding their action, ROS production does not appear to be the main mechanism by which these complexes exert their cytotoxicity, nor do they appear to be DNA intercalators or DNA covalent binders.