Estudo químico, atividade antimicrobiana e antioxidante das folhas de Talauma ovata A.St.Hil. (Magnoliaceae)
Resumo
Resumo: A presente dissertação descreve o estudo fitoquímico e as atividades antimicrobiana e antioxidante das folhas de Talauma ovata St. Hil. (Magnoliaceae), conhecida popularmente como "pinha-do brejo" ou "baguaçu". As folhas foram coletadas em janeiro/2003 no Bosque da Biologia (USP-SP). A fração hidroalcoolica do extrato em hexano das folhas foi reunida com o extrato em diclorometano após análise prévia por CCDC e comparação de dados espectrais, mostrando que ambos possuíam compostos semelhantes. O fracionamento cromatográfico desta mistura levou ao isolamento de três novas neolignanas e dez substâncias conhecidas pertencentes à classe dos lignóides (neolignanas e bis-norneolignanas) e sesquiterpenóides. Estas substâncias foram identificadas através de análise dos seus dados espectrométricos (UV, IV, RMN) e comparação com dados da literatura. Os compostos conhecidos foram identificados como: as neolignanas (+)-licarina-A (To-1), (+)-acuminatina (To-2), (+)-aldeído da licarina-A (To-3), (+)-kadsurenina-M (To-4), (+)-oleiferina-C (To-5) e (+)-oleiferina-A (To-6) e os terpenóides (-)-partenolido (To-10), (-)-michelenolido (To-11), (-)-11,13-deidrocompressanolido (To-12) e (-)-espatulenol (To-13). Destes licarina-A, oleiferina-C e partenolido já haviam sido encontrados em estudos anteriores com a planta. As novas neolignanas foram identificadas como: (+)-talaumina-A (To-7) (7S*, 8R*,8’R* - 3,4: 3’,4’-bis-(metilenodioxi)-lignana-7-ol), (+)-talaumina-B (To-8) (7S*, 8R*,8’R* - 3’,4’- dimetoxi- 3,4-metilenodioxi-lignana-7-ol), talaumina-C (To-9) (7S, 8R ,8’R – 3, 4 : 3’,4’- tetrametoxi-lignana-7-ol). As substâncias novas e a conhecida oleiferina-A foram acetiladas com anidrido acético e piridina, rendendo os correspondentes acetatos, que são inéditos. As novas neolignanas também foram submetidas à reação de ciclização, rendendo os correspondentes derivados ariltetralínicos, sendo que os derivados da talaumina-A e talaumina-B são inéditos. A atividade antimicrobiana do extrato em diclorometano e das substâncias isoladas foi avaliada contra várias cepas de bactérias e fungos. O extrato mostrou fraca atividade contra algumas cepas de Staphylococcus sp e Candida sp. Dentre as substâncias puras apenas licarina-A, talaumina-A e partenolido foram ativas. As duas primeira apresentaram moderada atividade antifúngica contra cepas de Cândida sp e partenolido mostrou-se moderadamente ativo contra algumas cepas de Staphylococcus sp. As neolignanas majoritárias licarina-A, acuminatina e talaumina-A foram testadas para atividade antioxidante. Apenas a primeira apresentou atividade moderada. Abstract: This work describes the phytochemical study and antimicrobial and antioxidant activities of leaves of Talauma ovata St. Hil., a Brazilian plant known as "baguaçú" or "pinhado-brejo. Leaves were collected in São Paulo, SP, Brazil, in January 2003. Dried and powdered material was extracted, at room temperature, with hexane and dichloromethane, successively. The hexane extract was submitted to partition between hexane and MeOH-H2O (9:1) and the hydro-alcoholic layer was combined with dichloromethane extract. Chromatographic fractionation of this mixture yielded three new neolignans with along ten known compounds. Their structures were elucidated by extensive spectroscopic methods including 1D (1H and 13C) and 2D NMR (HSQC and HMBC) experiments as well as comparison with literature. The known compounds were identified to be the neolignans: (+)- licarin-A (To-1) and their bis-norneolignan aldehyde (To-3), (+)-acuminatin (To-2), (+)-kadsurenin M (To-4), (+)-oleiferin-C (To-5) and (+)-oleiferin-A (To-6); and the terpenes: (-)-parthenolide (To-10), (-)-michelenolide (To-11), (-)-11,13-dehydrocompressanolide (To-12) and (-)- spathulenol (To-13). The compounds licarin-A, oleiferin-C and parthenolide have ever been previously reported in T. ovata. The new neolignans were identified as (+)-talaumin-A (To-7) (7S*, 8R*,8’R* - 3,4: 3’,4’-bis-(methylenedioxy)-lignan-7-ol), (+)-talaumin-B (To-8) (7S*, 8R*,8’R* - 3’,4’- dimethoxy- 3,4-methylenedioxy-lignan-7-ol) and (+)-talaumin-C (To-9) (7S, 8R ,8’R – 3, 4 : 3’,4’- tetramethoxy-lignan-7-ol). The new compounds and the known oleiferin-A were submitted to acetylation with acetic anhydride in pyridine, followed by usual work-up, yielding the respective acetates, which are new. The new neolignans also were submitted to cyclization acid catalyzed to give the respective aryltetraline derivatives. The compounds obtained from talaumin-A and talaumin-B are new, while talaumin-C yielded the known isogalbulin (To-9a). The antimicrobial activity of dichloromethane extract and isolated compounds were evaluated against several bacteria and fungi. The extract showed weak activity against some strains of Staphylococcus sp and Candida sp. Among pure compounds evaluated licarin-A and talaumin-A exhibited moderate activity against strains of Candida sp, while parthenolide was active against Staphylococcus sp. The major neolignans licarin-A, acuminatin and talaumin-A were also evaluated for antioxidant activity. Only the first one showed moderate activity.
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