Citotoxicity assay by the neutral red incorporation method. Eukaryotic cells (BSC-40) were grown as adherent culture in a 96-well microplate. The compounds were added at concentrations showed in the graphics (16 to 0.25 μg/mL) for 24 h. No drug was added in the first well (control test). The relation between sample absorbance and control absorbance calculated the relative absorbance. Compounds: a) I; b) II; c) III; d) IV. The measurements are expressed as average of replicates.