Síntese e avaliação da fitotoxicidade de γ-lactonas

• Autor(a) principal: Resende, Gabriela da Costa
• Data de Publicação: 2011
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/2128
• topic: Herbicida; Lactonas; Fotoquímica; Agroquímicos; Herbicide; Lactones; Photochemistry; Agrochemicals; CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA::QUIMICA ORGANICA

The γ-lactones constitute a structural moiety found in several compounds that show, among other biological activities, potential herbicidal activity. The aim of this work was to synthesize a series of γ-lactones with simplified structure and evaluate the phytotoxic activity evaluation of these compounds. The 5-hydroxyfuran-2(5H)-one (2), whose hydroxyl group was later functionalized to obtain three α,β-unsaturated lactones, was synthesized from the photooxidation of furfural (1) in the presence of rose bengal and oxygen in 80% yield. A solution of lactone (2) in isopropyl alcohol refluxed with p-toluenesulfonic acid led to the ether 5-isopropiloxyfuran-2(5H)-one (3) with 61% yield. The acetylation of (2) with acetic anhydride catalyzed by DMAP resulted in the formation of 5-acetiloxyfuran-2(5H)-one (4) (95% yield). The 5-butanosulfonylfuran-2(5H)-one (5) was synthesized from the reaction of the lactone (2) with butanosulfonyl chloride (96% yield). The unsaturated lactones were submitted to addition reactions, followed by other chemical modifications, to afford 13 saturated lactones. The photochemical addition of isopropyl alcohol to the lactones (3) and (4) employing low pressure mercury lamps (4 x 15 Watts) resulted in lactones 4-(1'-hydroxy-1'-methylethyl)-5-isopropiloxytetrahydrofuran-2-one (6) and 4-(1'-hydroxy-1'-methylethyl)-5-acetiloxytetrahydrofuran-2-one (7) in 91 and 99% yield respectively. The photochemical addition of methanol to lactone (3) did not result in the expected photoadduct but in the acyclic ester methyl 3-methoxy-4-oxobutanoate (8) (58% yield). Under acid conditions, the lactone (5) is rearranged to form the 4-formyl-5,5-dimethyltetrahydrofuran-2-one (9) with yields varying from 15 to 28% depending on the solvent used in the reaction. During this reaction, the formation of acetals 4-(dimethoxymethyl)-5,5-dimethyltetrahydrofuran-2-one (10) and 4-(diethoxymethyl)-5,5-dimethyltetrahydrofuran-2-one (11) was also observed with yields of 48 and 54% respectively. Treatment of aldehyde (9) with the phosphonate carbanion prepared in situ from the reaction between potassium tert-butoxide and trimethyl fosfonoacetate led to the alkenes (Z)-methyl 3-(2,2-dimethyl-5-oxotetrahydrofuran-3-yl) acrylate (12) and (E)-methyl 3-(2,2-dimethyl-5-oxotetrahydrofuran-3-yl)acrylate (13) in 42% yield. A mixture of alkenes was submitted to catalytic hydrogenation with Pd/C resulting in the formation of the ester methyl 3-(2,2-dimethyl-5-oxotetrahydrofuran-3-yl)propanoate (14) with 98% yield. By varying the storage conditions, the formation of 3-(2,2-dimethyl-5-oxotetrahydrofuran-3-yl)propanoic acid (15) was also observed. Finally, the lactones 5-isopropoxy-4-(pyrrolidin-1-yl)tetrahydrofuran-2-one (16) (65% yield) and 5-acetiloxy-4-(pyrrolidin-1-yl)tetrahydrofuran-2-one (17) (6% yield) were obtained by 1,4-addition of the pyrrolidine to lactones (3) and (4), respectively. The synthesized compounds were fully characterized by infrared spectroscopy, hydrogen and carbon nuclear magnetic resonance (1H NMR e 13C NMR) spectroscopy, mass spectrometry and melting point. Among all of them, the lactones (5), (6),(7), (10), (11), (12), (13), (16) and (17) were unpublished. The phytotoxic activity of the lactones (2), (3), (4), (6), (7), (10), (11), (12), (13), (14), (15), (16) and (17) was evaluated in vitro on the growth of wheat coleoptiles. Among the compounds tested, the most active at the concentration of 1000 μmol/L were α,β-unsaturated lactones (2), (3) and (4) together with lactone (16), containing a pyrrolidine ring . Although most of the compounds have shown some activity, the percentages of inhibition were small and not statistically different from the control after the third dilution (100 μmol/L). It was concluded that regardless of saturation, the presence of γ-lactone moiety is essential for the biologic activity, but their presence has no implications with this activity.