Síntese de derivados de 3-Indolil-glicina via reação multicomponente de Aza-Friedel-Crafts e avaliação da atividade fitotóxica

Abstract

It is notable that with technological advances and scientific research, organic synthesis has provided the synthesis of several compounds that are essential to meet the needs of mankind. 3-Indolyl-glycine derivatives have been the subject of several studies, since they are precursors of non-proteinogenic amino acids that act as synthetic intermediates of compounds with important biological activity. However, the synthetic routes described in the literature for these compounds present disadvantages, since they use organic solvents, extreme temperatures, non-recoverable catalysts and long reaction periods. Thus, the search for the development of alternative methodologies has attracted great attention in Organic Synthesis in order to reduce environmental impact, reduce process costs and minimize waste formation. In view of this scenario, the proposal of a new methodology for the synthesis of 3-indolyl glycine derivatives, via a multi-component reaction (Aza-Friedel-Crafts) between indoles, ethylglyoxalate and anilines, which follow the principles established by Green Chemistry, are somewhat of great interest to be studied. After a systematic study of the reaction conditions, two synthetic methodologies were established. In the first methodology a catalyst and surfactant was used in the reaction, under ambient temperature, however this condition led to the formation of by-product from the rearrangement of the desired product. In addition, the catalytic system of this synthetic methodology presented potential to be recycled, but its (re) use showed a decrease in yields, and it is not feasible to use this methodology. Thus, another synthetic methodology was proposed, in which only surfactant was used without the use of the catalyst, with heating of 50 ºC. The second methodology was more feasible, since the yields of the products obtained with the variation of the indole substrate were excellent. The synthesized compounds were evaluated for their biological activity. Bioassays of phytotoxic activity on lettuce seeds (Lactuca sativa) were carried out, in which it was verified that these compounds interfere in seed germination and root growth. Compounds 4b, 4j and 4n showed remarkable germination inhibitory activity at the concentration of 25 ppm. In inhibition of growth, compounds 4a, 4l and 4n showed inhibitory activity already at concentrations of 10 ppm. Such compounds were as active as the glyphosate and atrazine herbicides tested. It is emphasized that compound 4n had inhibitory activity both for germination and for growth of the species studied. Thus, the compounds presented in this paper provide an experimental basis for future studies on pesticides based on 3-Indolyl-glycine derivatives, since it has potential applications for herbicidal activity.