Synthesis, electrochemistry, and molluscicidal activity of nitroaromatic compounds: Effects of substituents and the role of redox potential

Molluscicidal bioassays and electrochemical studies (measurement of first w ave reduction potential, Epcl) were performed on several synthetic nitroaro matics, in relation to possible correlation between biological activity, re dox potential and structural effects. Five of them presented a significant molluscicidal activity on Biomphalaria glabrata (LD50 < 20 ppm). The Epc1 v alues ranged from -0.532 to -0.857 V versus Ag/AgCl (0.1 M) (-0.260 to -0.5 85 V versus NHE), all of them, in the favorable range for reduction in vivo . Data comparison between Epcl and molluscicidal activity indicates that th e presence of the electroactive nitro group is important for the biological activity. Correlation with redox potential, however, was not evident. Stru ctural effects seem to be the most important parameter. Higher activity is noticeable for phenols, including the para-nitro azo or hydrazo-containing compounds. No activity was observed for compounds having the benzylic subst ituent in meta position to the nitro group. These results suggest that acti vity undoubtedly involves more than reduction characteristics and that the possible formation of electrophilic species, after nitro reduction, can pla y an important role in molluscicidal activity against B. glabrata. (C) 2001 Elsevier Science Ltd. All rights reserved.