Relationship Between Physicochemical Properties and Herbicidal Activity of 1,2,5-Oxadiazole N-Oxide Derivatives

Abstract

The relationship between the herbicidal activity of a number of novel 1,2,5-oxadiazole N-oxides and some physicochemical properties potentially related with thisbioactivity, such as polarity, molecular volume, proton acceptor ability, lipophilicity, andreduction potential were studied. The semiempirical molecular orbital method AM1 wasused to calculate theoretical descriptors such as dipolar moment, molecular volume,Mulliken ́s charge and the octanol/water partition coefficients (log Po/w). The values ofthe reduction potentials (Er) were obtained by cyclic voltammetry. In addition, theretention factors (log k’w) on a reversed-phase high-performance liquid chromatography(RP-HPLC) column in pure aqueous mobile phases were measured for several N-oxidederivatives. The log k’w values show good correlation with the calculated values of logPo/w, showing that the chromatographic parameter can be used as lipophilicity descriptorfor these compounds. The multiple regression analysis between the descriptors for the N-oxide derivatives and the herbicide activity indicate that the variance in the biologicalactivity can be explained by changes in the lipophilicity and in the reduction potential.

Keywords

• 1
• 2
• 5-Oxadiazole N-oxide derivatives
• herbicides
• lipophilicity