Síntese de chalconas substituídas e seus híbridos na busca de novos herbicidas

Abstract

For several years, the commonly marketed synthetic herbicides have been the main method of weed management. However, the emergence of herbicide resistance and its negative effects on both health and the environment induced an increased social concern about its use and stimulated the interest in discovering ecological herbicidal compounds without compromising the production of agricultural culture. Considering this need, the present study synthesized a collection of chalcone derivatives and evaluated their ability to inhibit photosynthesis by blocking electron transport. In the first part of this study, Claisen Schmidt condensation was used to synthesize chalcones with different substituents, grouped in either electron donor or receptor donor (55a-m), and the yields ranging between 27-98%. The herbicidal activity of chalcones was determined by three tests. In a preliminary test, measurements of a chlorophylls fluorescence in spinach discs were made after exposing the compounds 55a-m to 100μM, in order to make a pre-selection of more active compounds. The substances 55a, 55d, 55g, 55i, 55j, 55k and 55l were the most active compounds in the semi in vivo test and therefore were forwarded to the in vivo test performed on the species Ipomoea grandifolia. Chalcones 55a, 55d, 55g and 55k l have been shown to inhibit electron flow in FSII and FSI causing a decrease in the biomass production of the weed I. grandfolia. Among those, the compounds 55a and 55g are selective for maize cultivation while compounds 55a and 55l are selective for bean cultivation. The elucidation of the mechanism of action of these compounds may be considered a relevant contribution in this area, since there are no reports in the literature about the use of these chalcones as photosynthesis inhibitors. In the second part of this study, chalcones 55e and 55j were reduced for their subsequent use in the multicomponent reaction to form chalcone hydrotriazine 57, which was obtained with 90% yield. A reaction methodology was developed using the nucleophilic aromatic substitution reaction with chalcone 55k and indole 62 producing the hybrid chalcone indole 63 with 58% yield, a compound not yet reported in the literature. In order to conclude the present study, the next step will focus on elucidating the herbicidal activity of the formed molecular hybrid compounds.