Synthesis of sugar-derived isoselenocyanates, selenoureas, and selenazoles

Organoselenium Compounds: Chemistry and Applications in Organic Synthesis

Selenium, originally described as a toxin, turns out to be a crucial trace element for life that appears as selenocysteine and its dimer, selenocystine. From the point of view of drug developments, selenium-containing drugs are isosteres of sulfur and oxygen with the advantage that the presence of the selenium atom confers antioxidant properties and high lipophilicity, which would increase cell membrane permeation leading to better oral bioavailability. In this article, we have focused on the relevant features of the selenium atom, above all, the corresponding synthetic approaches to access a variety of organoselenium molecules along with the proposed reaction mechanisms. The preparation and biological properties of selenosugars, including selenoglycosides, selenonucleosides, selenopeptides, and other selenium-containing compounds will be treated. We have attempted to condense the most important aspects and interesting examples of the chemistry of selenium into a single article.

First Exclusive Stereo- and Regioselective Preparation of 5-Arylimino-1,3,4-Selenadiazole Derivatives: Synthesis, NMR analysis, and Computational Studies

Isoselenocyanates are valuable coupling partners required for preparing key chemical intermediates and biologically active molecules in an accelerated and effective way. Likewise, (Z)-2-oxo-N-phenylpropanehydrazonoyl chlorides have been employed in numerous one-step heteroannulation reactions to assemble the structural core of several various kinds of heterocyclic compounds. Here, we describe the inverse electron demand 1,3-dipolar cycloaddition reaction of isoselenocyanates with a variety of substituted (Z)-2-oxo-N-phenylpropanehydrazonoyl chlorides to generate, regioselectively and stereoselectively, a series of 5-arylimino-1,3,4-selenadiazole derivatives comprising a multitude of functional groups on both aryl rings. The synthetic method features gentle room-temperature conditions, wide substrate scope, and good to high reaction yields. The selenadiazoles were separated by gravity filtration in all instances and chemical structures were validated by multinuclear NMR spectroscopy and high accuracy mass spectral measurements. First conclusive molecular structure elucidation of the observed 5-arylimino-selenadiazole regioisomer was verified by single-crystal X-ray diffraction analysis. Crystal-structure measurement was successfully carried out on (Z)-1-(4-(4-iodophenyl)-5-(p-tolylimino)-4,5-dihydro-1,3,4-selenadiazol-2-yl)ethan-1-one and (Z)-1-(5-((4-methoxyphenyl)imino)-4-(4-(methylthio)phenyl)-4,5-dihydro-1,3,4-selenadiazol-2-yl)ethan-1-one. Likewise, the (Z)-geometry of the hydrazonoyl chloride reactant was proven by X-ray diffraction studies. As representative examples, crystal-structure determination was carried out on (Z)-2-oxo-N-phenylpropanehydrazonoyl chloride and (Z)-N-(3,5-bis(trifluoromethyl)phenyl)-2-oxopropanehydrazonoyl chloride. Density functional theory calculations at the B3LYP-D4/def2-TZVP level were conducted to support the noted experimental findings and suggested mechanism.

Biotinylated selenocyanates: Potent and selective cytostatic agents

Most of the currently available cytotoxic agents for tackling cancer are devoid of selectivity, thus causing severe side-effects. This situation stimulated us to develop new antiproliferative agents with enhanced affinity towards tumour cells. We focused our attention on novel chalcogen-containing compounds (thiosemicarbazones, disulfides, selenoureas, thio- and selenocyanates), and particularly on selenium derivatives, as it has been documented that this kind of compounds might act as prodrugs releasing selenium-based reactive species on tumour cells. Particularly interesting in terms of potency and selectivity was a pharmacophore comprised by a selenocyanato-alkyl fragment connected to a p-phenylenediamine residue, where the nature of the second amino moiety (free, Boc-protected, enamine-protected) provided a wide variety of antiproliferative activities, ranging from the low micromolar to the nanomolar values. The optimized structure was in turn conjugated through a peptide linkage with biotin (vitamin B₇), a cellular growth promoter, whose receptor is overexpressed in numerous cancer cells; the purpose was to develop a selective vector towards malignant cells. Such biotinylated derivative behaved as a very strong antiproliferative agent, achieving GI₅₀ values in the low nM range for most of the tested cancer cells; moreover, it was featured with an outstanding selectivity, with GI₅₀ > 100 µM against human fibroblasts. Mechanistic studies on the mode of inhibition of the biotinylated selenocyanate revealed (Annexin-V assay) a remarkable increase in the number of apoptotic cells compared to the control experiment; moreover, depolarization of the mitochondrial membrane was detected by flow cytometry analysis, and with fluorescent microscopy, what supports the apoptotic cell death. Prior to the apoptotic events, cytostatic effects were observed against SW1573 cells using label-free cell-living imaging; therefore, tumour cell division was prevented. Multidrug resistant cell lines exhibited a reduced sensitivity towards the biotinylated selenocyanate, probably due to its P-gp-mediated efflux. Remarkably, antiproliferative levels could be restored by co-administration with tariquidar, a P-gp inhibitor; this approach can, therefore, overcome multidrug resistance mediated by the P-gp efflux system.

Highly bioactive novel aryl-, benzyl-, and piperazine-selenoureas: synthesis, structural characterization and in vitro biological evaluation

Selenoureas are widespread as useful elements for constructing important species and biologically active molecules. Finding an efficient and straightforward method to prepare this motif and biologically screen derivatives thereof is crucial. Herein, we demonstrate the effectiveness of using ethanol as a solvent in the preparation of various substituted aryl-, benzyl-, and piperazine-selenoureas from isoselenocyanates and amines. The synthetic method includes mild reaction conditions, large substrate scope, and good isolated yields. Biological evaluation of the prepared products on MDA-MB-231 and MCF-7 cancer cell lines revealed several remarkably active compounds (IC₅₀ < 10 μΜ) with the best one exhibiting IC₅₀ values of 1.8 μΜ and 1.2 μΜ observed against the challenging former triple-negative breast cancer cell line and the latter one, respectively. The chemical structures of all new compounds were fully characterized by multinuclear nuclear magnetic resonance (NMR) spectroscopy and high accuracy mass measurements.

Thio- and selenosemicarbazones as antiprotozoal agents against Trypanosoma cruzi and Trichomonas vaginalis

Herein, we report the preparation of a panel of Schiff bases analogues as antiprotozoal agents by modification of the stereoelectronic effects of the substituents on N-1 and N-4 and the nature of the chalcogen atom (S, Se). These compounds were evaluated towards Trypanosoma cruzi and Trichomonas vaginalis. Thiosemicarbazide 31 showed the best trypanocidal profile (epimastigotes), similar to benznidazole (BZ): IC₅₀ (31)=28.72 μM (CL-B5 strain) and 33.65 μM (Y strain), IC₅₀ (BZ)=25.31 μM (CL-B5) and 22.73 μM (Y); it lacked toxicity over mammalian cells (CC₅₀ > 256 µM). Thiosemicarbazones 49, 51 and 63 showed remarkable trichomonacidal effects (IC₅₀ =16.39, 14.84 and 14.89 µM) and no unspecific cytotoxicity towards Vero cells (CC₅₀ ≥ 275 µM). Selenoisosters 74 and 75 presented a slightly enhanced activity (IC₅₀=11.10 and 11.02 µM, respectively). Hydrogenosome membrane potential and structural changes were analysed to get more insight into the trichomonacidal mechanism.

Chemoselective Preparation of New Families of Phenolic-Organoselenium Hybrids-A Biological Assessment

Being aware of the enormous biological potential of organoselenium and polyphenolic compounds, we have accomplished the preparation of novel hybrids, combining both pharmacophores in order to obtain new antioxidant and antiproliferative agents. Three different families have been accessed in a straightforward and chemoselective fashion: carbohydrate-containing N-acylisoselenoureas, N-arylisoselenocarbamates and N-arylselenocarbamates. The nature of the organoselenium framework, number and position of phenolic hydroxyl groups and substituents on the aromatic scaffolds afforded valuable structure–activity relationships for the biological assays accomplished: antioxidant properties (antiradical activity, DNA-protective effects, Glutathione peroxidase (GPx) mimicry) and antiproliferative activity. Regarding the antioxidant activity, selenocarbamates 24–27 behaved as excellent mimetics of GPx in the substoichiometric elimination of H₂O₂ as a Reactive Oxygen Species (ROS) model. Isoselenocarbamates and particularly their selenocarbamate isomers exhibited potent antiproliferative activity against non-small lung cell lines (A549, SW1573) in the low micromolar range, with similar potency to that shown by the chemotherapeutic agent cisplatin (cis-diaminodichloroplatin, CDDP) and occasionally with more potency than etoposide (VP-16).

Acylselenoureas, selenosemicarbazones and selenocarbamate esters: Versatile ligands in coordination chemistry

Acylselenoureas, selenosemicarbazones and selenocarbamate esters from complexes with various transition- and main-group-metals, adopting several coordination modes.

Room-Temperature Metal-Free Multicomponent Polymerizations of Elemental Selenium toward Stable Alicyclic Poly(oxaselenolane)s with High Refractive Index

Selenium-containing polymers are a group of fascinating functional polymers with unique structures, properties, and applications, which have been developed recently but only with limited examples. The challenges of developing selenium-containing polymers with structural and functional diversity include the lack of economic and safe monomers, lack of efficient and convenient synthetic approaches, and poor stability of selenium-involving covalent bonds. In this work, room-temperature metal-free multicomponent polymerizations (MCPs) of elemental selenium, diisocyanides, and dipropargyl alcohols were developed, and polymers with a selenium-containing aliphatic heterocycle, 1,3-oxaselenolane, were synthesized through these MCPs directly from elemental selenium. The alicyclic poly(oxaselenolane)s enjoyed high yields (up to 93%), high molecular weights (up to 15 600 g/mol), high thermal and chemical stability, good solubility and processability. With the structural design of the poly(oxaselenolane)s and their high selenium contents of up to 33.7 wt %, the refractive indices of their spin-coated thin films could reach 1.8026 at 633 nm and maintain 1.7770 at 1700 nm. It is anticipated that these efficient, convenient, mild, and economic multicomponent polymerizations of elemental selenium can promote the selenium-related polymer chemistry and accelerate the exploration of diversified selenium-containing functional polymer materials.

Isoselenocyanates: Synthesis and Their Use for Preparing Selenium-Based Heterocycles

Isoselenocyanates (ISCs) are a class of organoselenium compounds that have been recognized as potential chemotherapeutic and chemopreventative agents against cancer(s) and infectious diseases. ISC compounds are chemically analogous to their isosteric relatives, isothiocyanates (ITCs); however, they possess increased biological activity, such as enhanced cytotoxicity against cancer cells. ISCs not only serve as significant products, but also as precursors and essential intermediates for a variety of organoselenium compounds, such as selenium-containing heterocycles, which are biologically active. While syntheses of ISCs have become less difficult to accomplish, the syntheses of selenium-containing heterocycles are often difficult due to the use of highly toxic selenium reagents. Because of this, ISCs can serve as versatile reagents for the preparation of these heterocycles. In this review, the classical and recent syntheses of ISCs will be discussed, along with notable and recent synthetic work employing ISCs to access novel selenium-containing heterocycles.

1 Introduction

1.1 Selenium and Health

2 Isoselenocyanates

2.1 Preparation of Isoselenocyanates

3 Selenium-Containing Heterocycles

3.1 Notable Synthetic Work

3.2 Recent Synthetic Work

3.2.1 Synthesis of N-(3-Methyl-4-phenyl-3H-selenazol-2-ylidene)benzamide­ Derivatives

3.2.2 Synthesis and X-ray Studies of Diverse Selenourea Derivatives

3.2.3 Synthesis of Heteroarene-Fused [1,2,4]Thiadiazoles/Selenadiazoles via Iodine-Promoted [3+2] Oxidative Cyclization

3.2.4 2-Amino-1,3-selenazole Derivatives via Base-Promoted Multicomponent Reactions

4 Conclusion

Novel Selenoureas Based on Cinchona Alkaloid Skeleton: Synthesis and Catalytic Investigations

An efficient approach to the synthesis of chiral selenoureas consisting of Cinchona alkaloid scaffolds was described. The new selenoureas were assessed as bifunctional organocatalysts in the asymmetric Michael addition reactions under mild conditions. The best results were obtained for selenoureas bearing the 4-fluorophenyl group. These catalysts promoted the reactions with enantioselectivities of up to 96% ee. Additionally, the catalytic performance of the thiourea and selenourea counterpart was compared.

Synthesis and antiproliferative evaluation of novel steroid-benzisoselenazolone hybrids

The two different types of steroidal benzisoselenazolone hybrids were synthesized by incorporating benzisoselenazolone scaffold into dehydroepiandrosterone and B-norcholesterol. The antiproliferative activity of the synthesized compounds against some carcinoma cell lines were investigated. The results showed that some of these compounds have better inhibitory activity than abiraterone on the proliferation of tumor cells associated with human growth hormone, and have less cytotoxicity on normal human cells. In particular, the IC₅₀ values of the compound 8a and 8f are 5.4 and 6.5 µmol/L against human ovarian carcinoma (SKOV3) cell line, and possess SI values of 13.9 and 10.5, respectively. The information obtained from the studies may be useful for the design of novel chemotherapeutic drugs.

Reactions of Nitroxides, Part 17. Synthesis, Fungistatic and Bacteriostatic Activity of Novel Five- and Six-Membered Nitroxyl Selenoureas and Selenocarbamates

The reactions of 3-isoselenocyanato-2,2,5,5-tetramethylpyrrolidine-1-oxyl, 3-isoselenocyanatomethyl-2,2,5,5-tetramethyl-3-pyrrolidine-1-oxyl, and 4-isoselenocyanato-2,2,6,6-tetramethylpiperidine-1-oxyl with selected amines and alcohols give the corresponding novel nitroxyl selenoureas and selenocarbamates, all bearing a nitroxyl moiety. Synthesized selenoureas and selenocarbamates show significant activity against pathogenic fungi and bacteria. In contrast to piperidine nitroxides, pyrrolidine, five-membered nitroxyl selenoureas and selenocarbamates show excellent antifungal and antibacterial activity against pathogenic fungi and bacteria, respectively.

Selenocoumarins as new multitarget antiproliferative agents: Synthesis, biological evaluation and in silico calculations

Herein we report a straightforward preparation of new antiproliferative agents based on the hybridization of a coumarin skeleton and an organoselenium motif. Three families were obtained: isoselenocyanate, selenocarbamates and selenoureas. The main purpose of these hybrid structures is the development of new antiproliferative agents with a multitarget mode of action. A strong correlation between the nature of the organosenium scaffold and the antiproliferative activity was observed. Thus, whereas selenocarbamates proved to be inactive, or moderate antiproliferative agents, isoselenocyanate and most of the selenoureas behaved as strong antiproliferative agents, with GI₅₀ values within the low micromolar range. Interestingly, a good selectivity toward tumor cell lines was found for some of the compounds. Moreover, an increase in the ROS level was observed for tumor cells, and accordingly, these pro-oxidant species might be involved in their mode of action. Overall, title compounds were found not to be substrates for P-glycoprotein, which is overexpressed in many cancer cells as a way of detoxification, and thus, to develop drug resistance. In silico calculations revealed that the selenoderivatives prepared herein might undergo a strong interaction with the active site of HDAC8, and therefore, be potential inhibitors of histone deacetylase 8. In vitro assessment against HDAC8 revealed a strong inhibition of such enzyme exerted by selenoureas, particularly by symmetrical coumarin-containing selenourea. Two compounds showed good antiproliferative data and appear as plausible leads for further testings. The symmetrical coumarin 6 displays the best in vitro inhibition of HDAC8, but is affected by P-gp. In contrast, the N-butyl selenourea coumarin derivative 5a escapes P-gp resistance but has lower HDAC8 inhibition activity.

Synthesis and Leishmanicidal Activity of Novel Urea, Thiourea, and Selenourea Derivatives of Diselenides

A novel series of thirty-one N-substituted urea, thiourea, and selenourea derivatives containing diphenyldiselenide entities were synthesized, fully characterized by spectroscopic and analytical methods, and screened for their in vitro leishmanicidal activities. The cytotoxic activity of these derivatives was tested against Leishmania infantum axenic amastigotes, and selectivity was assessed in human THP-1 cells. Thirteen of the synthesized compounds showed a significant antileishmanial activity, with 50% effective concentration (EC₅₀) values lower than that for the reference drug miltefosine (EC₅₀, 2.84 μM). In addition, the derivatives 9, 11, 42, and 47, with EC₅₀ between 1.1 and 1.95 μM, also displayed excellent selectivity (selectivity index ranged from 12.4 to 22.7) and were tested against infected macrophages. Compound 11, a derivative with a cyclohexyl chain, exhibited the highest activity against intracellular amastigotes, with EC₅₀ values similar to those observed for the standard drug edelfosine. Structure-activity relationship analyses revealed that N-aliphatic substitution in urea and selenourea is recommended for the leishmanicidal activity of these analogs. Preliminary studies of the mechanism of action for the hit compounds was carried out by measuring their ability to inhibit trypanothione reductase. Even though the obtained results suggest that this enzyme is not the target for most of these derivatives, their activity comparable to that of the standards and lack of toxicity in THP-1 cells highlight the potential of these compounds to be optimized for leishmaniasis treatment.

Selenium analogs of phenoxypropionic and phenoxyacetic herbicides

Selenium analogs of phenoxyacetic herbicides, namely 2-(2,4-dichlorophenoxy)propionic acid (2,4-DP), 2-(2,4-dichlorophenoxy)acetic acid (2,4-D), 2-(4-chloro-2-methylphenoxy)propionic acid (MCPP), 2-(4-chloro-2-methylphenoxy)acetic acid (MCPA), 2-(2,4,5-trichlorophenoxy)propionic acid (2,4,5-TP), and 2-(2,4,5-trichlorophenoxy)acetic acid (2,4,5-T), were synthesized in two steps. Iodo aryl derivatives were dimerized with elemental selenium in the presence of CuO as catalyst to the corresponding diselenides. Diselenides were reduced with NaBH4 to a selenide anion and condensed with either propionic or chloroacetic acid to achieve the selenium analogs of phenoxyacetic herbicides. These selenium analogs show moderate herbicidal and fungistatic activity.

Isoselenocyanates versus Isothiocyanates and Isocyanates

Alkyl and aryl isoselenocyanates are well known intermediates in the synthesis of various organoselenium compounds, but the knowledge of the physicochemical properties of simple unsaturated derivatives is still fragmentary. Vinyl-, 2-propenyl-, and cyclopropyl isoselenocyanates have been prepared by reaction of selenium in powder with the corresponding isocyanides. The isoselenocyanates of this series, with a variable distance between the N═C═Se group and the unsaturated or pseudounsaturated group, have been studied by UV-photoelectron spectroscopy and quantum-chemical calculations. For each of these three isoselenocyanates, the exploration of conformers and geometrical optimization always converge toward only one local minimum. The vinyl and cyclopropyl derivatives are characterized by similar order of magnitude of interactions between the NCSe group and the substituent, while for allylic compound two noninteracting moieties should be considered. The same conclusions were obtained for vinylic and cyclopropylic sulfur and oxygen derivatives. Thus the type and extent of interactions between the N═C═X (X = O, S, Se) group and an unsaturated (vinyl, allyl, or cyclopropyl) moiety are now clarified.

New selenosteroids as antiproliferative agents

Starting from natural steroids (diosgenin, hecogenin, smilagenin, estrone), we have prepared a wide panel of selenoderivatives, including benzoselenazolones, selenosemicarbazones, isoselenocyanates, selenoureas, selenocyanates and diselenides, with the aim of developing new families of potential chemotherapeutic agents. The modification of the organoselenium moieties, and their position on the steroid provided valuable information concerning the antiproliferative activities. Among all the families accessed herein, the best profile was achieved for selenoureas on the A ring of estrone, which exhibited GI₅₀ values in the range 2.0-4.1 μM for all the tested tumor cell lines, with increased potency compared with commonly used chemotherapeutic agents, like 5-fluorouracil and cisplatin. Cell cycle analysis revealed that selenoureas induced accumulation of cells in the G₁ phase of the cell cycle in the breast cancer cell lines HBL-100 and T-47D; therefore, a different mechanism than cisplatin, that induces cell cycle accumulation in the S phase as a result of DNA damage, must be involved. In the rest of the tumor cells, a slight increase of the S compartment was observed. Moreover, selenosteoids turned out to be excellent glutathione peroxidase (GPx) mimics for the catalytic removal of deleterious H₂O₂ (t_1/2 8.0-22.5 min) and alkyl peroxides (t_1/2 23.0-38.9 min) when used in substoichiometric amounts (1% molar ratio), thus providing a valuable tool for reducing the intrinsic oxidative stress in tumor progression.

Chalcogen-containing phenolics as antiproliferative agents

Aim: The increasing number of cancer cases has stimulated researchers to seek for novel approaches. We have combined two bioactive moieties: a polyphenolic scaffold and an organoselenium motif. Four different families (isothiocyanates/thioureas, and their selenium isosters) derived from dopamine, (±)-norepinephrine and R-epinephrine were accessed. Results: Heterocumulenes derived from dopamine and β-O-methylnoradrenaline were strong antiproliferative agents (GI50<10 μM). Selenoureas derived from β-O-methylnoradrenaline bearing electron-withdrawing groups (halogen, -NO2, -Ph) on the phenyl ring, were also strong antiproliferative agents, besides exhibiting good antiradical and glutathione peroxidase-like activities. Up to a 14-fold increased activity was achieved compared with classical chemotherapeutic agents, exhibiting also different mechanisms of action (cell cycle assays). Redox analysis on HeLa cells suggested an increase of ROS levels after the incubation period. Conclusion: the combination of organoselenium and phenolic moieties might provide valuable lead compounds with relevant antiproliferative properties.

New tacrine dimers with antioxidant linkers as dual drugs: Anti-Alzheimer's and antiproliferative agents

We have designed a series of tacrine-based homo- and heterodimers that incorporate an antioxidant tether (selenoureido, chalcogenide) as new dual compounds: for the treatment of Alzheimer's disease and as antiproliferative agents. Symmetrical homodimers bearing a dichalcogenide or selenide-based tether, the best compounds in the series, were found to be strong and highly selective electric eel AChE inhibitors, with inhibition constants within the low nanomolar range. This high inhibitory activity was confirmed on recombinant human AChE for the most interesting derivatives. The three most promising homodimers also showed a good inhibitory activity towards amyloid-β self aggregation. The symmetric disulfide derivative bis[5-(1',2',3',4'-tetrahydroacridin-9'-ylamino)pentyl]disulfide (19) showed the best multipotent profile and was not neurotoxic on immortalized mouse cortical neurons even at 50 μM concentration. These results represent an improvement in activity and selectivity compared to parent tacrine, the first marketed drug against Alzheimer's disease. Title compounds also exhibited excellent in vitro antiproliferative activities against a panel of 6 human tumor cell lines, with GI₅₀ values within the submicromolar range for the most potent derivatives (0.12-0.95 μM); such values represent a spectacular increase compared to currently-used chemotherapeutic agents, such as 5-FU (up to 306-fold) and cisplatin (up to 162-fold). Cell cycle experiments indicated the accumulation of cells in the G₁ phase of the cycle, a different mechanism than the reported for cisplatin. The breast cancer cell lines turned out to be the most sensitive one of the panel tested.

Design of chalcogen-containing norepinephrines: efficient GPx mimics and strong cytotoxic agents against HeLa cells

AIM

Numerous chronic diseases exhibit multifactorial etiologies, so focusing on a single therapeutic target is usually an inadequate treatment; instead, multi-target drugs are preferred. Herein, a panel of phenolic thioureas and selenoureas were designed as new prototypes against multifactorial diseases concerning antioxidation and cytotoxicity, as a pro-oxidant environment is usually found in such diseases.

RESULTS

Selenoureas were excellent antiradical agents and biomimetic catalysts of glutathione peroxidase for the scavenging of H₂O₂. They were also potent and selective cytotoxic agents against cancer cells, in particular HeLa (IC₅₀ 2.77-6.13 μM), apoptosis being involved. Selenoureas also reduced oxidative stress in HeLa cells (IC₅₀= 3.76 μM).

CONCLUSION

Phenolic selenoureas are promising lead structures for the development of drugs targeting multifactorial diseases like cancer.

An Efficient One-Pot Synthesis of 2-Amino-1,3,4-Selenadiazoles

An efficient one-pot synthesis of 2-amino-1,3,4-selenadiazoles from isoselenocyanates, hydrazine hydrate and aromatic aldehydes has been developed. This approach provides a simple, mild and facile way to construct various derivatives in moderate to good yields (57–82%). A plausible mechanism is proposed for the formation of the target products.

Synthesis of Cyanamides from Isoselenocyanates Promoted by Recyclable Ionic Liquid-Supported (Diacetoxyiodo)Benzene

One-pot synthesis of cyanamides from isoselenocyanates through deselenisation promoted by ionic liquid-supported hypervalent iodine(III) reagent 1-(4-diacetoxyiodobenzyl)-3-methylimidazolium tetrafluoroborate ([dibmim]+[BF4]−) was developed. This approach provided a simple, mild and environmentally benign way to construct cyanamides in good yields. Moreover, powder Se and [dibmim]+[BF4]− could be easily recycled. It was the first example of [dibmim]+[BF4]− to be used as a deselenising agent.

Chirality sensing of tertiary alcohols by a novel strong hydrogen-bonding donor - selenourea

In this paper, a novel type of chiral bisselenourea sensor was first synthesized and used as a strong hydrogen-bonding donor for highly efficient chiral recognition of a diverse range of tertiary alcohols.

Chemical sensors are powerful for the fast recognition of chiral compounds. However, the established sensing systems are less effective for chiral tertiary alcohols. The chiral tertiary alcohol group is an important structural unit in natural products and drug molecules, and its enantioselective recognition represents a significant and challenging task. In this paper, a novel type of chiral bisselenourea sensor was first synthesized and used as a strong hydrogen-bonding donor for highly efficient chiral recognition of a diverse range of tertiary alcohols. The obtained sharply split NMR signals are well-distinguishable with a large (up to 0.415 ppm) chemical shift nonequivalence. The NMR signal of the hydroxyl hydrogen atom was first employed for enantiomeric excess determination of tertiary alcohols, giving accurate results with <2% absolute errors. The 2D NOESY spectra and computational studies suggest that the geometrical differentiation of the formed diastereomeric complexes between the sensor and tertiary alcohols enables the chiral discrimination of the hydroxyl hydrogen signals of the tertiary alcohol in the ¹H NMR spectrum.

Phenolic thio- and selenosemicarbazones as multi-target drugs

A series of isosteric phenolic thio- and selenosemicarbazones have been obtained by condensation of naturally-occurring phenolic aldehydes and thio(seleno)semicarbazides. Title compounds were designed as potential multi-target drugs, and a series of structure-activity relationships could be established upon their in vitro assays: antioxidant activity, α-glucosidase inhibition and antiproliferative activity against six human tumor cell lines: A549 (non-small cell lung), HBL-100 (breast), HeLa (cervix), SW1573 (non-small cell lung), T-47D (breast) and WiDr (colon). For the antiradical activity, selenium atom and 2 or 3 phenolic hydroxyl groups proved to be essential motifs; remarkably, the compound with the most potent activity, with a trihydroxyphenyl scaffold (EC50 = 4.87 ± 1.57 μM) was found to be stronger than natural hydroxytyrosol, a potent antioxidant present in olive oil (EC50 = 13.80 ± 1.41 μM). Furthermore, one of the thiosemicarbazones was found to be a strong non-competitive inhibitor of α-glucosidase (Ki = 9.6 ± 1.6 μM), with an 8-fold increase in activity compared to acarbose (Ki = 77.9 ± 11.4 μM), marketed for the treatment of type-2 diabetes. Most of the synthesized compounds also exhibited relevant antiproliferative activities; in particular, seleno derivatives showed GI50 values lower than 6.0 μM for all the tested cell lines; N-naphthyl mono- and dihydroxylated derivatives behaved as more potent antiproliferative agents than 5-fluorouracil or cisplatin.

Regioselective one-pot three component synthesis of chiral 2-iminoselenazolines under sonication

A one-pot multi component reaction of selenoureas, which are in situ generated from l-amino esters and isoselenocyanates, with α-bromoketone under ultrasonication.

Synthesis and antioxidant activity of O-alkyl selenocarbamates, selenoureas and selenohydantoins

The preparation of three different families of lipophilic organoselenium compounds (aryl- and sugar-derived selenoureas, O-alkyl selenocarbamates and selenohydantoins) has been carried out in order to evaluate their in vitro antioxidant profile, analyzing the influence of the selenium-containing functional group, and the substituents on the activity. Title compounds have therefore been studied for the first time as free radical, hydrogen peroxide, alkyl peroxides and nitric oxide scavengers using colorimetric methods; furthermore, their glutathione peroxidase-like activity has also been analyzed by NMR spectroscopy. Free radical scavenging activity has been evaluated using the DPPH method; the strongest free radical scavengers were found to be both, aryl- and sugar-derived selenoureas, with EC₅₀ values ranging 19-46 μM. Concerning anti-H₂O₂ activity, measured by the horseradish peroxidase-mediated oxidation of phenol red, the best results were achieved for aryl selenohydantoins, showing a 61-76% inhibition at 0.5 mM concentration. Organoselenium compounds were also found to be capable of inhibiting the chain reaction involving lipid peroxidation (ferric thiocyanate method); thus, when tested at 0.74 mM, sugar selenocarbamates exhibited 49-71% inhibition of alkyl peroxides-mediated degradation of linoleic acid. Nitric oxide scavenging was studied by transforming sodium nitroprusside into nitrite ion, which in turn was transformed into an easily UV-detectable azocompound; aryl selenocarbamates exhibited 64-80% inhibition at 0.71 mM concentration. It has also been demonstrated that selenoxo compounds can behave as excellent glutathione peroxidase mimics; thus a 0.05 molar equiv. of the title compounds catalyzed efficiently the H₂O₂-mediated oxidation of dithiothreitol into the corresponding cyclic disulfide, mimicking removal of H₂O₂ exerted by glutathione peroxidase; t(1/2) values were found to be quite low for aryl- and sugar-derived selenoureas (2.0-12.7 min).

One-Pot Synthesis of 5-Arylamino-1,3,4-Selenadiazol-2(3H)-Ones from Arylisoselenocyanates

A one-pot reaction of arylisoselenocyanates, hydrazine and bis(trichloromethyl) carbonate, in the presence of a base provides an efficient route for the synthesis of 5-arylamino-1,3,4-selenadiazol-2(3H)-ones in good to excellent yields. A plausible mechanism is proposed for the reaction.