Exploration of larger central ring linkers in furamidine analogues: Synthesis and evaluation of their DNA binding, antiparasitic and fluorescence properties

The effects of replacing the central furan ring of furamidine with indole and benzimidazole on their DNA binding affinity, antiparasitic activity and fluorescence are reported. The bis-cyanophenylindoles required to make the corresponding amidines were prepared by sequential Stille and/or Suzuki coupling reactions. The bis-cyanophenylbenzimidazoles were obtained by coupling 4-cyanobenzaldehydes with the appropriate cyano substituted phenylenediamine. The bis-nitriles were converted to the diamidines by reaction with LiN[Si(CH3)3]2 or by Pinner methodology. Specifically, we have prepared new series of 2,6- and 2,5-diaryl indoles (6a,b, 12 and 17a–d) and the related benzimidazoles (24, 30 and 35). The new compounds bind in the DNA minor groove in DNA AT base pair sequences and eight of the ten new analogues exhibit ΔTm values comparable to or higher than that of furamidine. Six of ten of the new compounds exhibit lower IC50 values against Trypanosoma brucei rhodesiense (T. b. r.) and eight of ten exhibit lower IC50 values against Plasmodium falciparum (P. f.) than furamidine. Four of the ten show greater efficacy than furamidine in the rigorous T. b. r. STIB900 mouse model for African trypanosomiasis. Generally, the fluorescence properties of the new analogues are similar to that of DAPI.

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