Eduardo E. Alberto

Catalytic application of selenium and tellurium compounds as glutathione peroxidase enzyme mimetics

This review covers the past decade of intensive research on the design, synthesis and screening of organoselenides and tellurides as catalyst able to mimic the activity of the selenoenzyme glutathione peroxidase (GPx). This important enzyme forms part of the detoxification system in humans which deals with harmful peroxides and their byproducts formed during oxygen metabolism. Several strategies to enhance the GPx-like activity of compounds such as diselenides, selenides and tellurides have been proposed in recent years. Different mechanisms of action of these compounds are also presented in this review highlighting new advances in this exciting research field.

GPx-Like Activity of Selenides and Selenoxides: Experimental Evidence for the Involvement of Hydroxy Perhydroxy Selenane as the Active Species

The reaction mechanism of the GPx-like oxidation of PhSH with H(2)O(2) catalyzed by selenoxides proceeds via formation of the hydroxy perhydroxy selenane, which is a stronger oxidizing agent than selenoxide. A hydroxy perhydroxy selenane intermediate was observed by electrospray ionization mass spectrometry and (77)Se NMR spectroscopy in reactions of selenoxide 8 with H(2)O(2).The initial velocity of oxidation of PhSH by H(2)O(2) with selenoxide 8 is 4 orders of magnitude higher than that of 8 without peroxide. Selenoxide 8 is not reduced to selenide 6 by PhSH in the presence of H(2)O(2). While electronic substituent effects have minimal impact on the catalytic performance of selenoxides, chelating groups increase the rate of catalysis.

Eco-friendly cross-coupling of diaryl diselenides with aryl and alkyl bromides catalyzed by CuO nanopowder in ionic liquid

An eco-friendly cross-coupling reaction of aryl and alkyl bromides with diselenides using a catalytic amount of CuO nanopowder as a catalyst and an ionic liquid as a recyclable solvent is reported. The system shows high efficiency to catalyze this transformation, and in a green fashion due to the recyclable approach and the non-residual design protocol. This procedure has been utilized for the synthesis of a variety of diaryl selenides in good to excellent yields from the readily available aryl and alkyl bromides and diselenides.

C–S cross-coupling of thiols with aryl iodides under ligand-free conditions using nano copper oxide as a recyclable catalyst in ionic liquid

A recyclable copper nanopowder catalyst in ionic liquid is effective for promotion of the cross-coupling reaction of various thiols with aryl iodides under ligand-free conditions. Compared to the usual organic solvents, [bmmim]BF4 exhibited higher performance with the advantage of being able to be reused for up to four successive runs.

Synthesis of Diorganyl Selenides Mediated by Zinc in Ionic Liquid

A new approach for the synthesis of diorganyl selenides is described. By using economically attractive zinc dust in BMIM-BF(4), a series of diorganyl selenides were efficiently achieved in excellent yields, under neutral reaction conditions. Compared to the usual organic solvents, BMIM-BF(4) exhibited higher performance with the advantage to be reused up to five successive runs.

Chalcogen-containing oxazolines in the palladium-catalyzed asymmetric allylic alkylation

A comparative study about the ability of chiral chalcogen-containing oxazolines to act as chiral ligands in the palladium-catalyzed allylic alkylation of rac-1,3-diphenyl-2-propenyl acetate with dimethyl malonate is reported. Differences in the catalytic performance are observed with sulfur, selenium and tellurium analogues.

Evaluation of the biological effects of (S)-dimethyl 2-(3-(phenyltellanyl) propanamido) succinate, a new telluroamino acid derivative of aspartic acid

Abstract(S)-dimethyl 2-(3-(phenyltellanyl) propanamido) succinate, a new telluroamino acid derivative, showed remarkable glutathione peroxidase (GPx)-like activity, attesting to its antioxidant potential. However, the stability and toxicity of this compound has not yet been investigated. The present study was designed to investigate the pharmacological/toxicological properties of this compound in vitro and in vivo. In vitro, this telluroamino acid derivative significantly blocked spontaneous and Fe(II)-induced TBARS formation in rat brain homogenates, demonstrating high antioxidant activity. In addition, it exhibited GPx-like and thiol oxidase activities. However, when subcutaneously administered to mice, (S)-dimethyl 2-(3-(phenyltellanyl) propanamido) succinate indicated genotoxic and mutagenic effect in adult male mice. Considering the differential effects of (S)-dimethyl 2-(3-(phenyltellanyl) propanamido) succinate in vitro and in vivo, additional experiments are needed to elucidate the mechanism(s) by which this compound displays its antioxidant/toxicological effects.

Activation of Peroxides by Organoselenium Catalysts: A Synthetic and Biological Perspective

The activation of peroxides by organoselenium catalysts in a synthetic and biological perspective is presented herein. The relevance of this process is evident in oxidation reactions, which impact a number of synthetic and biochemical transformations. Particular emphasis will be given to discuss the use of hydrogen peroxide. Reactions such as Baeyer-Villiger, epoxidations, oxidation of bromide salts to positive bromine species (Haloperoxidase like activity), oxidation of thiols to disulfides (Glutathione Peroxidase like activity), among others catalyzed by organoselenium compounds will be disclosed in details. Additionally, the influence of substituents effects on organoselenium compounds in relation to their performance as catalysts towards the above mentioned reactions will be discussed, as well as the mechanistic aspects.