Síntese e avaliação da atividade fitotóxica de análogos ao alternariol

• Autor(a) principal: Geraldo, Guilherme Carvalho
• Data de Publicação: 2008
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/2071
• topic: Alternariol; Herbicidas; Fungos fitopatogênicos; Acoplamento de Suzuki; Alternariol; Herbicides; Plant pathogenic fungi; Suzuki coupling reaction; CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA::QUIMICA ORGANICA

Alternariol is an aromatic lactone produced by fungal phytopathogenic species of Nimbya and Alternaria. These species are known to cause leaf necrosis that generate the death of the plant, including species of weeds like Alternanthera philoxeroides. It´s believed that the phytotoxicity of these fungi is associated with the production of this compound and may also be present other secondary metabolites. This present work had as objective the synthesis and the phytotoxic activity evaluation of alternariol analogues. Two kinds of aromatic aldehydes were used to these synthesis (2-bromo-4,6-dimethoxybenzaldehyde, obtained by Vilsmeyer formylation, and 2-bromobenzaldehyde) that were coupled with various boronic acids by the Suzuki coupling reaction. The resulting biaryls were oxidized with sodium chlorite (NaClO2) to obtain the corresponding carboxylic acids that were treated with boron tribromide (BBr3) to remove the hydroxyl protection with consequent cyclization and formation of the lactonic ring of the alternariol analogues. Eight new compounds were obtained: 7,9- dihydroxy-2-methyl-6H-benzo[c]chromen-6-one (34.5%), 2- chloro-7,9-dihydroxy-6H-benzo[c]chromen-6-one (55.0%), 3- fluoro-7,9-dihydroxy-6H-benze[c]chromen-6-one (48.5%), 2- fluoro-7,9-dihydroxy-6Hbenzo[c]chromen-6-one (69.0%), 2- methyl-6H-benzo[c]chromen-6-one (79.0%), 2-chloro-6H- benzo[c]chromen-6-one (93.5%), 3-fluoro-6Hbenzo[c] chromen-6-one (97.2%) and 2-fluoro-6H-benzo[c]chromen-6- one (93.3%). The synthesized compounds were characterized using spectroscopy IV, mass spectrometry, 1H- and 13C-NMR spectroscopy, as well as bidimensional NMR techniques like HETCOR. The phytotoxic activities of only three substances were evaluated (7,9-dihydroxy-2-methyl-6H-benzo[c] chromen-6-one, 2-chloro-7,9-dihydroxy-6H-benzo[c] chromen-6-one and 2-methyl-6H-benzo[c]chromen-6-one), due the unavailability of fresh chloroplasts in Italy at the time when the other compounds were synthesized. The three substances were evaluated using the Hill reaction in vitro, which measures the ability of certain compounds in inhibit photosynthetic electron transport, having the potassium ferricyanate as the non-biological electron acceptor. For this, intact chloroplasts, isolated from leaves of spinach (Spinacia oleracea) were used. Among all the tested substances, two of them had very expressive inhibition results: 2-chloro-7,9- dihydroxy-6H-benzo[c]chromen-6-one and 7,9-dihydroxy-2- methyl-6Hbenzo[c]chromen-6-one showed IC50 values of 7.2 and 22.8 μM, respectively.