RESUMO
The relationship between the herbicidal activity of a number of novel 1,2,5-oxadiazole N-oxides and some physicochemical properties potentially related with this bioactivity, such as polarity, molecular volume, proton acceptor ability, lipophilicity, and reduction potential were studied. The semiempirical molecular orbital method AM1 was used to calculate theoretical descriptors such as dipolar moment, molecular volume, Mulliken's charge and the octanol/water partition coefficients (log P(o/w)). The values of the reduction potentials (E(r)) were obtained by cyclic voltammetry. In addition, the retention 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-oxide derivatives. The log (k'w) values show good correlation with the calculated values of log P(o/w), showing that the chromatographic parameter can be used as lipophilicity descriptor for these compounds. The multiple regression analysis between the descriptors for the N-oxide derivatives and the herbicide activity indicate that the variance in the biological activity can be explained by changes in the lipophilicity and in the reduction potential.
Assuntos
Óxidos N-Cíclicos/química , Óxidos N-Cíclicos/farmacologia , Herbicidas/química , Herbicidas/farmacologia , Oxidiazóis/química , Oxidiazóis/farmacologia , Cromatografia Líquida de Alta Pressão , Espectroscopia de Ressonância de Spin Eletrônica , Plantas/efeitos dos fármacos , Teoria Quântica , Análise de Regressão , Silanos/químicaRESUMO
The liquid chromatographic retention factors extrapolated to pure water, k'(w), for several 6,7-diaryl-pteridine derivatives in both an octadecylsilane (ODS) and an immobilized artificial membrane column (IAM.PC.DD2), using acetonitrile-aqueous buffer pH = 7.45 as mobile phase, were obtained. The logarithms of the k'(w) values in the IAM.PC.DD2 column, log k'(w) (IAM), show good correlation with the calculated values of the octanol-water partition coefficients, log P(o/w), showing that the chromatographic parameter can be used as lipophilicity descriptor for the studied pteridines. However, interactions other than the lipophilic ones seem to be involved in the ODS column. Previous studies have shown that pteridines have antihelmintic properties. In spite of the complexity of the studied biological system as compared with the chromatographic one, good correlation between the descriptors obtained in the IAM column and biological activity (expressed as the log of the inhibitory concentration required to obtain up to 50% in the reduction of population growth of nematodes, log IC(50)) was observed.