Polyfunctionalized organoselenides: New synthetic approach from selenium-containing cyanohydrins and anti-melanoma activity.

A series of seleno-containing polyfunctionalized compounds was synthesized exploring cyanohydrin chemistry, including α-hydroxy esters, α-hydroxy acids, 1,2-diols, and 1,2-diacetates, with yields ranging from 26 up to 99 %. The cytotoxicity of all synthesized compounds was then evaluated using a non-tumor cell line (BALB/3T3 murine fibroblasts), and those deemed non-cytotoxic had their anti-melanoma activity evaluated using B16-F10 murine melanoma cells. These assays identified two compounds with selective cytotoxic activity against the tested melanoma cell line, showing a potential anti-melanoma application.

Exploring the mechanism of the reductive amination of acetophenones via the Borch approach: the role of the acid catalyst.

The energetic viability of several mechanistic variations of the reductive amination of acetophenones via the Borch approach was re-examined through density functional theory calculations. The crucial involvement of the acid catalyst is evident not only in the elimination of water, but also in the initial nucleophilic step. This role increases with the electron-donating capability of the substituent positioned at the para-position of acetophenone.

Synthesis, Mechanism Elucidation and Biological Insights of Tellurium(IV)-Containing Heterocycles.

Inspired by the synthetic and biological potential of organotellurium substances, a series of five- and six-membered ring organotelluranes containing a Te-O bond were synthesized and characterized. Theoretical calculations elucidated the mechanism for the oxidation-cyclization processes involved in the formation of the heterocycles, consistent with chlorine transfer to hydroxy telluride, followed by a cyclization step with simultaneous formation of the new Te-O bond and deprotonation of the OH group. Moreover, theoretical calculations also indicated anti-diastereoisomers to be major products for two chirality center-containing compounds. Antileishmanial assays against Leishmania amazonensis promastigotes disclosed 1,2λ4 -oxatellurane LQ50 (IC50 =4.1±1.0; SI=12), 1,2λ4 -oxatellurolane LQ04 (IC50 =7.0±1.3; SI=7) and 1,2λ4 -benzoxatellurole LQ56 (IC50 =5.7±0.3; SI=6) as more powerful and more selective compounds than the reference, being up to four times more active. A stability study supported by 125 Te NMR analyses showed that these heterocycles do not suffer structural modifications in aqueous-organic media or at temperatures up to 65 °C.

Synthesis, Antioxidant Activity and Cytotoxicity of N-Functionalized Organotellurides.

The use of antioxidants is the most effective means to protect the organism against cellular damage caused by oxidative stress. In this context, organotellurides have been described as promising antioxidant agents for decades. Herein, a series of N-functionalized organotellurium compounds has been tested as antioxidant and presented remarkable activities by three different in vitro chemical assays. They were able to reduce DPPH radical with IC50 values ranging from 5.08 to 19.20 µg mL-1, and some of them also reduced ABTS+ radical and TPTZ-Fe3+ complex in ABTS+ and FRAP assays, respectively. Initial structure-activity relationship discloses that the nature of N-substituent strongly influenced both activity and cytotoxicity of the studied compounds. Furthermore, radical scavenging activities of N-functionalized organotellurides have been compared with those of their selenilated congeners, demonstrating that the presence of tellurium atom has an essential role in antioxidant activity.

Investigation of Chemical Stability of Dihalogenated Organotelluranes in Organic-Aqueous Media: The Protagonism of Water.

The biological activity of tellurium compounds is closely related to the tellurium oxidation state or some of their structural features. Hypervalent dihalogenated organotelluranes 1-[butyl(dichloro)-λ4-tellanyl]-2-(methoxymethyl)benzene (1a) and 1-[butyl(dibromide)-λ4-tellanyl]-2-(methoxymethyl)benzene (1b) have been described as inhibitors of proteases (cysteine and threonine) and tyrosine phosphatases. However, poor attention has been given to their physicochemical properties. Here, a detailed investigation of the stability in water of these organotelluranes is reported using 125Te NMR analysis. Dihalogenated organotelluranes 1a and 1b were both stable in DMSO- d6 (from 25 to 75 °C), demonstrating their thermal stability. However, the addition of a phosphate buffer solution (pH 2-8) to 1a or 1b resulted in an immediate conversion to a new Te species, assumed to be the corresponding telluroxide. Similar behavior was observed in pure water, demonstrating the low chemical stability of these dihalogenated species in the presence of water. These results allow concluding that previous biological activity reported for dihalogenated organotelluranes 1a and 1b could be attributed to the corresponding derivatives from the reaction with water. In the same way as for AS-101, we demonstrated that organotelluranes 1a and 1b are not stable in aqueous solution. It suggests a proactive role of these organotelluranes in previously reported biological activity.

Optimization of biodiesel synthesis by esterification using a fermented solid produced by Rhizopus microsporus on sugarcane bagasse.

A fermented solid containing lipases was produced by solid-state fermentation of Rhizopus microsporus on sugarcane bagasse enriched with urea, soybean oil, and a mineral solution. The dry fermented solid produced using R. microsporus (RMFS) was used to catalyze the synthesis of alkyl-esters by esterification in a solvent-free system containing ethanol and oleic acid (as a model system) or a mixture of fatty acids obtained from the physical hydrolysis of soybean soapstock acid oil (FA-SSAO) in subcritical water. The conversions were 93.5 and 84.1%, for oleic acid and FA-SSAO, respectively, at 48 h and 40 °C, at a molar ratio (MR) of ethanol to fatty acid of 5:1. A further increase in the MR to 10:1 improved the production of ethylic-esters, giving conversions at 48 h of 98 and 86% for oleic acid and FA-SSAO, respectively. The results obtained in this work foster further studies on scaling-up of an environmentally friendly process to produce biofuels.

Ovicidal activity of diaryl dichalcogenides and ivermectin on Fasciola hepatica: A novel candidate for a blending-based therapeutic strategy.

Fasciolosis is a food and waterborne disease caused by Fasciola spp., representing a global health burden to various hosts, including humans and other animals. This study investigates the in vitro activity of tellurium- and selenium-containing diaryl dichalcogenides: diacetal ditelluride (LQ07), diacetal diselenide (LQ62), and diacetyl diselenide (LQ68) alone and in combination with ivermectin (IVM) against eggs of Fasciola hepatica. The eggs were exposed for 12 h with each organochalcogen (OC) (0.1 - 2 mmol l-1) and IVM (0.01 - 2 mmol l-1) following an incubation of 15 days, allowing embryonation. The inhibitory concentration of 50 % (IC50) of each OC or IVM was tested with the IC10, IC30, and IC50 of IVM or each OC, respectively. LQ07, LQ62, and LQ68, as well as IVM, demonstrated a concentration-dependent ovicidal activity. The peak ovicidal activity of 99.74 % was achieved when IVM was tested at 2.0 mmol l-1. LQ62 and LQ68 demonstrated greater ovicidal activity, having an IC50 < 0.32 mmol l-1 being 6.25-fold more toxic than IVM alone. The percentage of dead eggs was significantly higher in the IVM group (early mortality), as Se-containing OCs led to the (miracidia) embryonation of the eggs with no hatching (late mortality). Blending Se-containing OCs and IVM showed an additive effect of up to 27 % against F. hepatica eggs. The present data contribute to the potential use of blending-based therapeutic strategies to combat F. hepatica infections in eradication programs worldwide. The combinations may also act against multidrug-resistant strains, reinstating drug-based parasite control.

Hypervalent organochalcogenanes as inhibitors of protein tyrosine phosphatases.

A series of organochalcogenanes was synthesized and evaluated as protein tyrosine phosphatases (PTPs) inhibitors. The results indicate that organochalcogenanes inactivate the PTPs in a time- and concentration-dependent fashion, most likely through covalent modification of the active site sulfur-moiety by the chalcogen atom. Consequently, organochalcogenanes represent a new class of mechanism-based probes to modulate the PTP-mediated cellular processes.

Structure-activity relationships of hypervalent organochalcogenanes as inhibitors of cysteine cathepsins V and S.

A new series of organotelluranes were synthesized and investigated, and the structure-activity relationships in cysteine proteases inhibition were determined. It was possible to identify the relevance of structural components linked to the reactivity of these compounds as inhibitors. For example, dibromo-organotelluranes showed to be more reactive than dichloro-organotelluranes towards cysteine cathepsins V and S. Besides, no remarkable enantio-selectivity was verified. In general the achiral organotelluranes were more reactive than the chiral congeners against cysteine cathepsins V and S. A reactivity order for organochalcogenanes and cysteine cathepsins was proposed after the comparison of the inhibitory potencies of organotelluranes with the related organoselenanes.

Enzymatic kinetic resolution of tert-butyl 2-(1-hydroxyethyl)phenylcarbamate, a key intermediate to chiral organoselenanes and organotelluranes.

The enzymatic kinetic resolution of tert-butyl 2-(1-hydroxyethyl) phenylcarbamate via lipase-catalyzed transesterification reaction was studied. We investigated several reaction conditions and the carbamate was resolved by Candida antarctica lipase B (CAL-B), leading to the optically pure (R)- and (S)-enantiomers. The enzymatic process showed excellent enantioselectivity (E > 200). (R)- and (S)-tert-butyl 2-(1-hydroxyethyl)phenylcarbamate were easily transformed into the corresponding (R)- and (S)-1-(2-aminophenyl)ethanols.

Immobilization of Pseudomonas cepacia lipase on layered double hydroxide of Zn/Al-Cl for kinetic resolution of rac-1-phenylethanol.

Layered double hydroxides (LDHs) are cheap materials suitable for immobilization of enzymes. In this study, we prepared Zn/Al-Cl LDHs with different Zn:Al molar ratios for immobilization of the lipase from Pseudomonas cepacia. The best values for activity retention (188%), immobilization efficiency (96%) and hydrolytic activity in organic medium (279 U g-1) were obtained with a molar ratio of Zn:Al of 4:1, a protein loading of 162 mg g-1 and Tris-HCl buffer (10 mmol L-1, pH 7.5) as the solvent for preparing the lipase solution. The immobilized lipase keeps its activity when stored at 4 °C during 30 days. The immobilized lipase gave a conversion of 50% in 1 h for the kinetic resolution of the alcohol rac-1-phenylethanol, with both ees and eep higher than 99% and E higher than 200. In the reutilization study, 30 successive 1-h kinetic resolutions were done with the same batch of immobilized enzyme. For all 30 resolutions, 50% conversion was maintained, with ees and eep higher than 99% and E higher than 200. These are promising results that lay the basis for further studies of immobilization of lipases onto LDHs for applications in organic media.

Diacetal Ditellurides as Highly Active and Selective Antiparasitic Agents toward Leishmania amazonensis.

Leishmaniasis is a neglected tropical disease and a public health concern in at least 98 countries, affecting mainly the poorest populations. Pharmaceuticals and chemotherapies available for leishmaniasis treatment have several limitations, which clearly justify the efforts to find new potential antileishmanial drugs. In this context, antiprotozoal activities toward different Leishmania species have been reported for hypervalent tellurium compounds, which motivated us to investigate, for the first time, the leishmanicidal properties of some nonhypervalent diaryl ditellurides. Thus, this work describes in vitro activity against Leishmania amazonensis and the cytotoxicities of diaryl ditellurides. Ditelluride LQ7 revealed a strong leishmanicidal activity on promastigotes and amastigotes at submicromolar levels (IC50 = 0.9 ± 0.1 and 0.5 ± 0.1 µmol L-1, respectively) and presented selectivity indexes greater than those of reference drug miltefosine. This preliminary study suggests that diaryl ditellurides may be promising scaffolds for the development of new agents for leishmaniasis treatment.

Surface interactions of gold nanorods and polysaccharides: From clusters to individual nanoparticles.

Gold nanorods (AuNRs) are suitable for constructing self-assembled structures for the development of biosensing devices and are usually obtained in the presence of cetyltrimethylammonium bromide (CTAB). Here, a sulfated chitosan (ChiS) and gum arabic (GA) were employed to encapsulate CTAB/AuNRs with the purpose of studying the interactions of the polysaccharides with CTAB, which is cytotoxic and is responsible for the instability of nanoparticles in buffer solutions. The presence of a variety of functional groups such as the sulfate groups in ChiS and the carboxylic groups in GA, led to efficient interactions with CTAB/AuNRs as evidenced through UV-vis and FTIR spectroscopies. Electron microscopies (HR-SEM and TEM) revealed that nanoparticle clusters were formed in the GA-AuNRs sample, whereas individual AuNRs, surrounded by a dense layer of polysaccharides, were observed in the ChiS-AuNRs sample. Therefore, the presented work contributes to the understanding of the driving forces that control the surface interactions of the studied materials, providing useful information in the building-up of gold self-assembled nanostructures.

Immobilization and characterization of a new regioselective and enantioselective lipase obtained from a metagenomic library.

In previous work, a new lipase and its cognate foldase were identified and isolated from a metagenomic library constructed from soil samples contaminated with fat. This new lipase, called LipG9, is a true lipase that shows specific activities that are comparable to those of well-known industrially-used lipases with high activity against long-chain triglycerides. In the present work, LipG9 was co-expressed and co-immobilized with its foldase, on an inert hydrophobic support (Accurel MP1000). We studied the performance of this immobilized LipG9 (Im-LipG9) in organic media, in order to evaluate its potential for use in biocatalysis. Im-LipG9 showed good stability, maintaining a residual activity of more than 70% at 50 °C after incubation in n-heptane (log P 4.0) for 8 h. It was also stable in polar organic solvents such as ethanol (log P -0.23) and acetone (log P -0.31), maintaining more than 80% of its original activity after 8 h incubation at 30 °C. The synthesis of ethyl esters was tested with fatty acids of different chain lengths in n-heptane at 30 °C. The best conversions (90% in 3 h) were obtained for medium and long chain saturated fatty acids (C8, C14 and C16), with the maximum specific activity, 29 U per gram of immobilized preparation, being obtained with palmitic acid (C16). Im-LipG9 was sn-1,3-specific. In the transesterification of the alcohol (R,S)-1-phenylethanol with vinyl acetate and the hydrolysis of the analogous ester, (R,S)-1-phenylethyl acetate, Im-LipG9 showed excellent enantioselectivity for the R-isomer of both substrates (E> 200), giving an enantiomeric excess (ee) of higher than 95% for the products at 49% conversion. The results obtained in this work provide the basis for the development of applications of LipG9 in biocatalysis.

20S proteasome as novel biological target for organochalcogenanes.

A series of hypervalent selenium- and tellurium-containing compounds (organoselenuranes and organotelluranes) was evaluated aiming novel inhibitors of a threonine protease, namely the 20S proteasome (20S PT). In vitro assays demonstrated high inhibitory potency and specificity of these compounds toward the ß2 catalytic site of the 20S PT. Organotelluranes were identified as more potent inhibitors than organoselenuranes since their IC50 ranged from 3.5 to 16 µM while for organoselenuranes the IC50 ranged from 16 to 35 µM indicating great potential to be explored in 20S proteasome inhibition. Cellular assays with those compounds were employed to verify the cytotoxicity and ability to inhibit 20S proteasome in cell. These assays demonstrated that organoselenuranes are capable of maintaining their selectivity in cell while the organotelluranes became inactive under cellular conditions. Stability studies of the organochalcogenanes were performed by (77)Se and (125)Te NMR analysis. It was observed that organotelluranes are stable under enzymatic assay conditions and, organoselenuranes, the structures responsible for inhibitory activity are cyclized organoselenuranes.