Abstract
Three compounds were isolated from Maytenus acanthophylla Reissek (Celastraceae): the pentacyclic triterpenes lup-20(29)-en-3β-ol (lupeol, 1) and 3β-lup-20(29)-en-3-yl acetate (2) and the carbohydrate 1,2,3,4,5,6-hexa-O-acetyldulcitol (3);lupeol was also isolated from Xylosma flexuosa. The compounds’ structures were elucidated by spectroscopic and spectrometric analysis. Compound 1 acts as an energy transfer inhibitor, interacting with isolated CF1 bound to thylakoid membrane, and dulcitol hexaacetate 3 behaves as a Hill reaction inhibitor and as an uncoupler, as determined by polarography. Chlorophyll a (Chl a) fluorescence induction kinetics from the minimum yield F0 to the maximum yield FM provides information of the filling up from electrons coming from water to plastoquinone pool with reducing equivalents. In this paper we have examined the effects of compounds 1 and 3 on spinach leaf discs. Compound 1 induces the appearance of a K-band, which indicates that it inhibits the water splitting enzyme. In vivo assays measuring the fluorescence of chl a in P. ixocarpa leaves sprayed with compound 1, showed the appearance of the K-band and the PSII reaction centers was transformed to “heat sinks” or silent reaction centers unable to reduce QA. However, 3 also induced the appearance of a K band and a new band I appears in P. ixocarpa plants, therefore it inhibits at the water splitting enzyme complex and at the PQH2 site on b6f complex. Compounds 1 and 3 did not affect chlorophyll a fluorescence of L. perenne plants.
Highlights
Maytenus acanthophylla Reissek (Celastraceae) is a medicinal plant found in Bahia state, Brazil [1]where it is vulnerable to extinction and the sp. is already considered extinct in Minas Gerais [2]
These results suggested that the 3β-ol moiety on lupeol is important for its activity, since when it was acetylated this suppressed drastically its inhibitory activity
When the spinach leaf discs were treated with 3 (150 and 300 μM), the following phenomenological energy fluxes per excited cross section ABS/CS0, TR0/CS, and ET0/CS were reduced by 50% with both concentrations; these results indicate that photosystem II (PSII) electron transport chain and pigment protein were damaged with compound 3, function was increased by 10 and 30%, respectively, with both concentrations, indicating that the PSII electron flow function worked with major efficiency
Summary
Maytenus acanthophylla Reissek (Celastraceae) is a medicinal plant found in Bahia state, Brazil [1]where it is vulnerable to extinction and the sp. is already considered extinct in Minas Gerais [2]. Where it is vulnerable to extinction and the sp. Its chemical constituents isolated from roots include gutta-percha, flavonoids, alditol, lupanes, oleanane, ursane, and quinonamethides [3]. Xylosma flexuosa (Flacourtiaceae) is a tree or sometimes a shrub distributed in Mexico, Guatemala, Honduras, El Salvador, Nicaragua, Costa Rica, Panamá, Venezuela and Curaçao [4]. In Mexico it is vulnerable to extinction. The chemical constituents of the methanol extract of Xylosma flexuosa are (rel)-2-([2,6-dibenzoyl]- -glucopyranosyloxy)-5-hydroxybenzoyl1R,2R,6R-trihydroxy-3-oxocyclohex-4-enoate (xilosmin) and three glycosides: Salirespolide, poliotrisoside and 2′-benzoylpoliotrisoside [5]. As part of our study of bioactive metabolites from species of the Flacourtiaceae and Celastraceae plant families, the present investigation describes the isolation, identification, and photosynthetic inhibitory activities of two triterpenes: lupeol, 3β-lup-20(29)-en-3-ol (1), 3β-lup-20(29)-en-3-yl acetate (2) and the carbohydrate 1,2,3,4,5,6-hexa-O-acetyldulcitol (3) (Figure 1) obtained from
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