Exploration of DAPI analogues: Synthesis, antitrypanosomal activity, DNA binding and fluorescence properties

The DAPI structure has been modified by replacing the phenyl group with substituted phenyl or heteroaryl rings. Twelve amidines were synthesized and their DNA binding, fluorescence properties, in vitro and in vivo activities were evaluated. These compounds are shown to bind in the DNA minor groove with high affinity, and exhibit superior in vitro antitrypanosomal activity to that of DAPI. Six new diamidines (5b, 5c, 5d, 5e, 5f and 5j) exhibit superior in vivo activity to that of DAPI and four of these compounds provide 100% animal cure at a low dose of 4 × 5 mg/kg i.p. in T. b. rhodesiense infected mice. Generally, the fluorescence properties of the new analogues are inferior to that of DAPI with the exception of compound 5i which shows a moderate increase in efficacy while compound 5k is comparable to DAPI.