Síntese e avaliação da atividade fitotóxica de novos oxabiciclos análogos ao ácido helmintospórico

• Autor(a) principal: Nogueira, Leonardo Brandão
• 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/123456789/2064
• topic: Cicloadição [4+3]; Planta daninha; Herbicida; Cátion oxialílico; [4+3] cycloaddition; Weeds; Herbicides; Oxallyl carbocation; CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA::QUIMICA ORGANICA

Microorganisms are capable of producing a variety of structurally diverse secondary metabolites. These metabolites have been considered as potential compounds to be used as herbicides or novel lead structures towards the development of weed controllers. The helminthosporic acid was isolated from the cultured broth of the plant pathogenic fungus Cochliobolus sativus (Ito & Kurib.) Drechsler ex Dastur (anamorph: Bipolaris sorokiniana (Sacc.) Shoem.) and exihibited plant growth regulatory activity. The present investigation describes the synthesis and biological evaluation of a series of compounds analogues to the helmintosphoric acid with potential phytotoxicity. The [4+3] cycloaddition reaction between oxallyl carbocation, generated in situ from 2,4- dibromopentan-3-one, and different furans afforded four oxabicycles in variable yields. Subsequently, the products of the cycloaddition reactions were submitted to straightforward functional group manipulations which not only afforded new derivatives but also allowed the evaluation of the significance of different functionalities for the biological activity. Thus, the compound 7-hydroxymethyl-1,2α,4α-trimethyl-8-oxabicicle [3.2.1]oct-6-en-one was converted to the corresponding aldehyde via pyridinium chlorochromate oxidation. The oxidation of the aldehyde with silver oxide afforded the carboxylic acid in moderate yield. The reduction of the carbonyl group of some cycloadducts was carried out with sodium borohydride. In order to test the significance of the double bond on the inhibitory activity, some oxabicycles derivatives were prepared by hydrogenation. The phytotoxic properties of the various oxabicycles were evaluated as the ability to interfere with the growth of Sorghum bicolor and Cucumis sativus seedlings at 5 x 10-4 mol L-1. Considering the species Cucumis sativus, 7- methoxycarbonil)-1,2α,4α-trimethyl-8-oxabicyclo[3.2.1]oct- 6-en-3-one was the most active compound causing 37.6% inhibition. For Sorghum bicolor, the most active substance corresponded to 7-(formyl)-1,2α,4α-trimethyl-8-oxabicyclo[3.2.1]oct-6-en-3-one causing 52% inhibition. In both species, the most active compounds were oxabycicles possessing a carbonyl group conjugated with a double bond.