Angelita M. Barcellos

Synthesis of diaryl selenides using electrophilic selenium species and nucleophilic boron reagents in ionic liquids

We described herein the use of imidazolium ionic liquids [bmim]PF6 and [bmim]BF4 in the selective, metal and catalyst-free synthesis of unsymmetrical diaryl selenides by electrophilic substitution in arylboron reagents with arylselenium halides (Cl and Br) at room temperature. This is a general substitution reaction and it was performed with arylboronic acids or potassium aryltrifluoroborates bearing electron-withdrawing or electron-donating groups, affording the corresponding diaryl selenides in good to excellent yields. The ionic liquid [bmim][PF6] was easily recovered and utilized for further substitution reactions.

Antidepressant-like activity of dehydrozingerone: Involvement of the serotonergic and noradrenergic systems

Dehydrozingerone (DHZ) is a phenolic compound isolated from ginger rhizomes (Zingiber officinale). It is known for its diverse spectrum of biological activities as an antioxidant, anti-inflammatory and antitumor compound. The present study was designed to assess the antidepressant effect of DHZ and the involvement of the monoaminergic system and to evaluate its in vitro antioxidant activity in the hippocampus, cortex and cerebellum of mice. For this study, the tail suspension test (TST), forced swim test (FST) and yohimbine lethality test were performed. DHZ administered orally 30min prior to testing reduced the immobility time in the TST (1-40mg/kg) and the FST (10-40mg/kg), with no change in locomotor activity in the open field test. The antidepressant-like effect of DHZ (1mg/kg) was prevented by ketanserin (1mg/kg, i.p.; a 5-HT2A/2C receptor antagonist), ondansetron (1mg/kg, i.p.; a 5-HT3 receptor antagonist), prazosin (1mg/kg, i.p., an α1-adrenoceptor antagonist) and yohimbine (1mg/kg, i.p., an α2-adrenoceptor antagonist) pretreatments. Furthermore, DHZ administered at doses of 10 and 20mg/kg increased the lethality of yohimbine (35mg/kg, i.p.). DHZ had antioxidant activity on in vitro lipid peroxidation induced by sodium nitroprusside in all brain regions tested. The results revealed that DHZ has a potent antidepressant effect, which seems to involve the serotonergic and noradrenergic systems.

Polyethylene glycol-400/H3PO2: an eco-friendly reductive system for the synthesis of selanylesters

An alternative green method was described for the synthesis of selanylesters by reactions of acyl chlorides with arylselenols, generated in situ by reaction of diaryl diselenides with hypophosphorous acid (H3PO2) using polyethylene glycol-400 (PEG-400) as the solvent. These reactions proceeded efficiently at room temperature under N2 using a range of acyl chlorides and diaryl diselenides, both containing electron-withdrawing and electron-donating groups, affording the corresponding selanylesters in moderate to excellent yields. Additionally, PEG-400 can be recovered and directly reused for further reactions.

Green Hydroselenation of Aryl Alkynes: Divinyl Selenides as a Precursor of Resveratrol

A simple and efficient protocol to prepare divinyl selenides has been developed by the regio- and stereoselective addition of sodium selenide species to aryl alkynes. The nucleophilic species was generates in situ, from the reaction of elemental selenium with NaBH4, utilizing PEG-400 as the solvent. Several divinyl selenides were obtained in moderate to excellent yields with selectivity for the (Z,Z)-isomer by a one-step procedure that was carried out at 60 °C in short reaction times. The methodology was extended to tellurium, giving the desired divinyl tellurides in good yields. Furthermore, the Fe-catalyzed cross-coupling reaction of bis(3,5-dimethoxystyryl) selenide 3f with (4-methoxyphenyl)magnesium bromide 5 afforded resveratrol trimethyl ether 6 in 57% yield.

Tellurium-promoted stereoselective hydrodebromination of 1,1-dibromoalkenes: synthesis of (E)-bromoalkenes

We describe herein an efficient and simple method for the stereoselective hydrodebromination of 1,1-dibromoalkenes by using a catalytic amount of the nucleophilic species of tellurium, generated in situ by the reaction of elemental tellurium with NaBH4. By this methodology, (E)-bromoalkenes were obtained in moderate to excellent yields under mild reaction conditions, without the use of transition metals or base. Furthermore, a high stereoselectivity for the (E)-isomer was observed when 1,1-dibromoarylalkenes were used, thus indicating a promising alternative for future applications in organic synthesis.

Glicerol como Solvente em Síntese Orgânica

O glicerol e o principal co-produto na producao do biodiesel. Em 2015 foram produzidos 4 milhoes de m 3 de biodiesel a partir da biomassa brasileira, o que g erou mais de 300.000 m 3 de glicerol. O glicerol e aplicado ha decadas em diferentes segmentos industriais, tais como farmaceutico e alimenticio, bem como na industria de cosmeticos e higiene pessoal. Uma aplicacao nova para o glicerol, que vem crescendo nos ultimos anos, e seu uso como um solvente verde em reacoes orgânicas. Neste artigo de revisao sao apresentados e discutidos os trabalhos recentes desenvolvidos no Brasil e no exterior ao uso do glicerol como solvente em sintese orgânica.