Ricardo F. Schumacher

Convulsant effect of diphenyl diselenide in rats and mice and its relationship to plasma levels

Diphenyl diselenide [(PhSe)2], an organoselenium compound, presents pharmacological and toxicological properties in rodents. The aim of this study was to carry out the determination and quantification of (PhSe)2 in plasma after oral administration (p.o.) of this compound (500 mg/kg), dissolved in canola oil, in rats and mice. The second objective was to verify the involvement of different routes of administration ((p.o.), intraperitoneal (i.p.) and subcutaneous (s.c.)) and vehicle solutions (canola oil and dimethyl sulfoxide (DMSO)) in the appearance of seizure episodes and in the plasmatic levels of (PhSe)2 in rats and mice. Analysis of (PhSe)2 in blood samples was performed by gas chromatography/flame ionized detector system (GC/FID). Rat and mouse peak plasma (PhSe)2 levels were 13.13 and 10.11 microg/ml (C(max)), respectively, and occurred at 0.5h (T(max)) post-dosing. The use of different administration routes (p.o., i.p. and s.c.) and vehicle solutions (canola oil or DMSO) in rats and mice indicated that the appearance of seizures and (PhSe)2 plasmatic levels are dependent of administration routes (i.p.>p.o.>s.c.), vehicle solutions (DMSO>canola oil) and animal species (mice>rat).

Synthesis of 2,3-dihydroselenophene and selenophene derivatives by electrophilic cyclization of homopropargyl selenides.

The synthesis of several highly functionalized 2,3-dihydroselenophenes from homopropargyl selenides via electrophilic cyclization is described. Electrophiles such as I(2), ICl, and PhSeBr were used in a simple process employing CH(2)Cl(2) as solvent at room temperature, which gave the cyclized products in high yields. 4-Iodo-2,3-dihydroselenophenes obtained by this methodology were submitted to a dehydrogenation reaction using 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) to give 3-iodoselenophenes. 4-Iodo-5-phenyl-2,3-dihydroselenophene was also submitted to the thiol copper-catalyzed and Heck-type reactions giving the desired products under mild reaction conditions.

Room-Temperature Organocatalytic Cycloaddition of Azides with β-Keto Sulfones: Toward Sulfonyl-1,2,3-triazoles.

Organocatalytic enamine-azide [3 + 2] cycloadditions between β-keto sulfones and aryl azides can be performed at room temperature in good to excellent yields of products in the presence of catalytic amounts of pyrrolidine (5 mol %). The proposed organocatalytic methodology was found to be applicable to β-keto arylsulfones containing a range of substituents. A wide variety of aryl azides also work. Basically, this constitutes a remarkably efficient protocol for the synthesis of novel 1,2,3-triazole compounds.

Regioselective formation of tetrahydroselenophenes via 5-exo-dig-cyclization of 1-butylseleno-4-alkynes.

Results on the synthesis of tetrahydroselenophene derivatives from 1-butylseleno-4-alkynes by electrophilic cyclization using iodine as the electrophilic source are presented. This methodology was carried out via a simple process under mild reaction conditions providing the cyclized products in high yields. Electrophilic sources, such as PhSeBr, CuCl(2), and CuBr(2), were also used in this study. The tetrahydroselenophenes obtained by this protocol were submitted to cyanation, Suzuki, and Ullmann cross-coupling reactions to afford good yields of a cross-coupled product.

The potential antioxidant activity of 2,3-dihydroselenophene, a prototype drug of 4-aryl-2,3-dihydroselenophenes.

Here we present our results in palladium cross-coupling reaction of aryl boronic acids with 4-iodo-2,3-dihydroselenophene derivatives. The cross-coupled products were obtained in satisfactory yields. A dehydrogenation of 4,5-diphenyl-2,3-dihydroselenophene was activated by DDQ and the 2,3-diarylselenophene was obtained in good yield. Regarding the antioxidant activity, the selenophene derivative 3a was effective in counteracting lipid and protein oxidation as well as scavenging ABTS radical. The findings of the present study indicate that 3a is a prototype for future drug development programs to treat disorders mediated by reactive oxygen species.

Cyclization of Homopropargyl Chalcogenides by Copper(II) Salts: Selective Synthesis of 2,3‐Dihydroselenophenes, 3‐Arylselenophenes, and 3‐Haloselenophenes/thiophenes

Copper(II) halide mediated cyclization of homopropargyl chalcogenides gave three types of chalcogenophene derivatives. Selective product formation was achieved by controlling solvent, temperature, and atmosphere. By using CuBr2 and 1,2-dichloroethane at room temperature under ambient atmosphere, 4-bromo dihydroselenophene derivatives were obtained, whereas CuBr2 and 1,2-dichloroethane at reflux gave selectively 2-substituted selenophenes. When 1,2-dichloroethane was replaced by dimethylacetamide, 3-halo-selenophenes were obtained exclusively. The versatility of chalcogenophenes was also studied by reaction of 3-haloselenophenes with terminal alkynes under Sonogashira conditions affording the cross-coupled products. In addition, the reaction of 3-haloselenophenes with boronic acids gave the corresponding Suzuki-type products in good yields.

Ultrasound-promoted organocatalytic enamine–azide [3 + 2] cycloaddition reactions for the synthesis of ((arylselanyl)phenyl-1H-1,2,3-triazol-4-yl)ketones

The use of sonochemistry is described in the organocatalytic enamine–azide [3 + 2] cycloaddition between 1,3-diketones and aryl azidophenyl selenides. These sonochemically promoted reactions were found to be amenable to a range of 1,3-diketones or aryl azidophenyl selenides, providing an efficient access to new ((arylselanyl)phenyl-1H-1,2,3-triazol-4-yl)ketones in good to excellent yields and short reaction times. In addition, this protocol was extended to β-keto esters, β-keto amides and α-cyano ketones. Selanyltriazoyl carboxylates, carboxamides and carbonitriles were synthesized in high yields at short times of reaction under very mild reaction conditions.

Organoselenium compounds from purines: Synthesis of 6-arylselanylpurines with antioxidant and anticholinesterase activities and memory improvement effect

We describe here a simple method for the synthesis of 6-arylselanylpurines with antioxidant and anticholinesterase activities, and memory improvement effect. This class of compounds was synthesized in good yields by a reaction of 6-chloropurine with diaryl diselenides using NaBH4 as reducing agent and PEG-400 as solvent. Furthermore, the synthesized compounds were evaluated for their in vitro antioxidant and acetylcholinesterase (AChE) inhibitor activities. The best AChE inhibitor was assessed on the in vivo memory improvement. Our results demonstrated that the 6-((4-chlorophenyl)selanyl)-9H-purine and 6-(p-tolylselanyl)-9H-purine presented in vitro antioxidant effect. In addition, 6-((4-fluorophenyl)selanyl)-9H-purine inhibited the AChE activity and improved memory, being a promising therapeutic agent for the treatment of Alzheimers disease.

Synthesis of 3-(1H-1,2,3-Triazol-1-yl)-2-(arylselanyl)pyridines by Copper-Catalyzed 1,3-Dipolar Cycloaddition of 2-(Arylselanyl)-3-azido-pyridines with Terminal Alkynes

We present here our results in the synthesis of eleven new 3-(1H-1,2,3-triazol-1-yl)-2-(arylselanyl)pyridines by copper-catalyzed azide-alkyne cycloaddition reactions. The reactions were performed in the presence of catalytic amount of copper(II) acetate and sodium ascorbate using a mixture of tetrahydrofuran/water (1:1) as solvent at room temperature in air. The reaction is tolerant to different functional groups such as substituted-benzene rings, alcohol and ester and none electronic or steric influence was observed. All the products were obtained in good to excellent yields. Alternatively to the conventional oil bath heating, the use of microwave irradiation or ultrasound methods is also presented as alternative energy sources.

Synthesis of 2-acyl-benzo[1,3-d]selenazoles via domino oxidative cyclization of methyl ketones with bis(2-aminophenyl) diselenide

A general, practical and simple one-pot synthesis of 2-acyl-benzo[1,3-d]selenazoles was developed by reacting a wide range of 2-arylethane-1,2-diones, generated in situ from commercially available aryl methyl ketones, with bis(2-aminophenyl) diselenide, promoted by Na2S2O5 in DMSO at 100 °C. Comparatively, the reactions were conducted under conventional heating and microwave irradiation. The use of focused microwave irradiation drastically decreased the reaction time from 48 to 2 h with a gain in the reaction yield for most cases. Still, 2-phenylacyl-benzo[1,3-d]selenazole was elected to react with sodium borohydride and butylmagnesium bromide, giving the respective secondary and tertiary alcohols under mild reaction conditions.