Synthesis, bio-physical and anti-leishmanial studies of some novel indolo[3,2-a]phenanthridine derivatives

Eight indolo[3,2-a]phenanthridine derivatives have been synthesized in a regioselective manner involving intramolecular Heck-type arylation as a key step. The compounds display interesting photophysical proprties and hence evaluated for their ability to interact with ct-DNA. Preliminary biophysical studies via UV and Fluorescence spectrophotometric titration with ct-DNA, and dye displacement studies with well known intercalator ethidium bromide and the groove binder Hoechst 33,258 reveal that the binding mode is probably minor groove binding. The prepared indolophenanthridine derivatives have also been evaluated as anti-leishmanial agents for the first time. MTT-assays for cell cytotoxicity against Leishmania promastigotes and Leishmania amastigotes were studied with the compounds 10b-f, 12-14 for the determination of their IC₅₀ values. Cytotoxicity was determined using a murine RAW 264.7 cell line and human embryonic kidney cell line HEK 293. In L. donovani amastigote assay, compounds 10e, 10f and 12 showed good activity with relatively low cytotoxicity against RAW 264.7, resulting in acceptable selectivity indices. Selectivity index determination indicated compounds to be potent anti-leishmanial agents while 10b, 10c and 14 showed moderate selectivity index. Moreover, cell-cycle analysis of four different compounds 10b, 12, 13 and 14, representative of each group, was performed by FACS as an attempt to understand the mechanism of actions of these different sub-classes of the compounds on Leishmania.