Taraxerol 4-Methoxybenzoate, an in vitro Inhibitor of Photosynthesis Isolated from Pavonia multiflora A. St-Hil. (Malvaceae)

Anacardic Acid Derivatives Affect the in Vitro Reactions of Photosynthesis

The dichloromethane extract of the cashew nuts from Anacardium occidentale was fractionated by rotation locular countercurrent chromatography aimed at discovering metabolites that could be useful as new models for photosynthesis inhibitors. The chemical fractionation afforded a complex mixture of anacardic acids, which upon catalytic hydrogenation yielded anacardic acid (1). Methylation of 1 via reaction with diazomethane afforded an ester 2. Both compounds were evaluated using polarographic approaches and fluorescence studies of chlorophyll a (ChL a). The in vitro assays informed the decision for the classification of 1 and 2 as Hill reaction inhibitors. Besides that, 1 inhibited the donor side of the PSII, while 2 acted as an energy transfer inhibitor. Therefore, this study is important for the development of herbicides.

The Biosynthesis and Medicinal Properties of Taraxerol

Taraxerol is a pentacyclic triterpenoid that is actively produced by some higher plants as part of a defense mechanism. The biosynthesis of taraxerol in plants occurs through the mevalonate pathway in the cytosol, in which dimethylallyl diphosphate (DMAPP) and isopentyl pyrophosphate (IPP) are first produced, followed by squalene. Squalene is the primary precursor for the synthesis of triterpenoids, including taraxerol, β-amyrin, and lupeol, which are catalyzed by taraxerol synthase. Taraxerol has been extensively investigated for its medicinal and pharmacological properties, and various biotechnological approaches have been established to produce this compound using in vitro techniques. This review provides an in-depth summary of the hypothesized taraxerol biosynthetic pathway, the medicinal properties of taraxerol, and recent developments on tissue culture for the in vitro production of taraxerol.

Effects of Acetogenins from Annona coriacea on the in Vitro Reactions of Photosynthesis

Our search for candidates for photosynthesis inhibitors is allowing us to report the effect of two acetogenins identified in Annona coriacea Mart. leaves, ACG-A and ACG-B, a non-adjacent bis-THF and a mono-THF types, respectively. This is an important class of natural products which presents biological properties such as anticancer, neurotoxic, larvicidal and insecticidal. However, this is only the second report associated to its herbicidal activity. Their mechanisms of action on the light reactions of the photosynthesis were elucidated by polarographic techniques. Compounds inhibited the noncyclic electron transport on basal, phosphorylating, and uncoupled conditions from H₂ O to methyl viologen (MV); therefore, they act as Hill reaction inhibitors. Studies on fluorescence of chlorophyll a (ChL a) indicated that they inhibited the acceptor side of PSII between P680 and PQ-pool, exactly as the commercial herbicide DCMU does.