Prodrugs of N-dicarboximide derivatives of the rat selective toxicant norbormide

Norbormide [5-(α-hydroxy-α-2-pyridylbenzyl)-7-(α-2-pyridylbenzylidene)-5-norbornene-2,3-dicarboximide] (NRB), an existing but infrequently used rodenticide, is known to be uniquely toxic to rats but relatively harmless to other rodents and mammals. However, one major drawback of NRB as a viable rodenticide relates to an evolutionary aversion developed by the rat leading to sub-lethal dosing due to either its unpleasant 'taste' or rapid onset of effects. A series of NRB-derived prodrugs were prepared in an effort to 'mask' this acute response. Their synthesis and biological evaluation (in vitro vasoconstrictory activity, in vitro hydrolytic and enzymatic stability and lethality/palatability in vivo) is described. Prodrug 2 displayed the most promising profile with respect to a delay in the onset of symptoms and was subsequently demonstrated to be significantly more palatable to rats. Moreover, prodrug 25 was found to be largely accepted by rats in a choice trial, resulting in high mortality.