Synthesis and Structural Characterization of 1-Mesityl-1,3-dihydro-imidazole-2-selone and Bis(1-mesitylimidazol-2-yl)diselenide: Experimental Evidence That the Selone Is More Stable Than the Selenol Tautomer

Selenization of Small Molecule Drugs: A New Player on the Board

There is an urgent need to develop safer and more effective modalities for the treatment of a wide range of pathologies due to the increasing rates of drug resistance, undesired side effects, poor clinical outcomes, etc. Throughout the years, selenium (Se) has attracted a great deal of attention due to its important role in human health. Besides, a growing body of work has unveiled that the inclusion of Se motifs into a great number of molecules is a promising strategy for obtaining novel therapeutic agents. In the current Perspective, we have gathered the most recent literature related to the incorporation of different Se moieties into the scaffolds of a wide range of known drugs and their feasible pharmaceutical applications. In addition, we highlight different representative examples as well as provide our perspective on Se drugs and the possible future directions, promises, opportunities, and challenges of this ground-breaking area of research.

Bis(1-methylimidazol-2-yl) diselenide and its evaluation as a chemical radio-protector: role of kinetic rate constants for ROS scavenging and glutathione peroxidase like activity

Bis(1-methylimidazol-2-yl) diselenide (MeImSe), a derivative of selenoneine, has been examined for bimolecular rate constants for scavenging of various radiolytically and non-radiolytically generated reactive oxygen species (ROS). Further, its potential to show glutathione peroxidase (GPx)-like activity and to protect in vitro models of DNA and lipid against radiation induced strand breakage and lipid peroxidation, respectively were studied. The results confirmed that MeImSe scavenged all major short-lived (hydroxyl radical) and long-lived (peroxyl radical, carbonate radical, nitrogen dioxide radical, hypochlorite and hydrogen peroxide) oxidants involved in the radiation toxicity either directly or through GPx-like catalytic mechanism. The rate constants of MeImSe for these oxidants were found to be comparable to analogous sulfur and selenium-based compounds. The enzyme kinetics study established that MeImSe took part in the GPx cycle through the reductive pathway. Further, MeImSe inhibited the radiation induced DNA strand cleavage and lipid peroxidation with half maximal inhibitory concentration (IC50) of ∼ 60 μM and ∼100 μM, respectively. Interestingly, MeImSe treatment in the above concentration range (>100 μM) did not show any significant toxicity in normal human lung fibroblast (WI26) cells. The balance between efficacy and toxicity of MeImSe as a chemical radioprotector was attributed to the formation of less reactive intermediates during its oxidation/reduction reactions as evidenced from NMR studies.HighlightsMeImSe, a derivative of selenoneine protects DNA and lipid from radiation damageMeImSe scavenges all major short- and long-lived oxidants involved in radiation toxicityRate constants of MeImSe for ROS scavenging determined by pulse radiolysis techniqueFirst organoselenium compound reported to scavenge nitrogen dioxide radicalMeImSe exhibits GPx-like activity through reductive pathway.

Oxidation of anti-thyroid drugs and their selenium analogs by ABTS radical cation

Lactoperoxidase was previously used as a model enzyme to test the inhibitory activity of selenium analogs of anti-thyroid drugs with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a substrate. Peroxidases oxidize ABTS to a metastable radical ABTS•+, which is readily reduced by many antioxidants, including thiol-containing compounds, and it has been used for decades to measure antioxidant activity in biological samples. We showed that anti-thyroid drugs 6-n-propyl-2-thiouracil, methimazole, and selenium analogs of methimazole also reduced it rapidly. This reaction may explain the anti-thyroid action of many other compounds, particularly natural antioxidants, which may reduce the oxidized form of iodine and/or tyrosyl radicals generated by thyroid peroxidase thus decreasing the production of thyroid hormones. However, influence of selenium analogs of methimazole on the rate of hydrogen peroxide consumption during oxidation of ABTS by lactoperoxidase was moderate. Direct hydrogen peroxide reduction, proposed before as their mechanism of action, cannot therefore account for the observed inhibitory effects. 1-Methylimidazole-2-selone and its diselenide were oxidized by ABTS•+ to relatively stable seleninic acid, which decomposed slowly to selenite and 1-methylimidazole. In contrast, oxidation of 1,3-dimethylimidazole-2-selone gave selenite and 1,3-dimethylimidazolium cation. Accumulation of the corresponding seleninic acid was not observed.

Rhenium(I)-tricarbonyl complexes with methimazole and its selenium analogue: Syntheses, characterization and cell toxicity

This study explores the effect of a thione/selone ligand on the cell toxicity (in vitro) and light activity of diimine Re(CO)₃⁺ complexes. Six rhenium(I) complexes with general formula fac-[Re(CO)₃(N,N')X]⁺ were prepared, where X = 2-mercapto-1-methylimidazole (methimazole; MMI), and 1-methylimidazole-2-selone (MSeI); N,N' = 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen) and 2,9-dimethyl-1,10-phenanthroline (dmphen). Their triflate salts were characterized using single-crystal X-ray diffraction, ¹H, ¹³C and 2D NMR, UV-vis and vibrational spectroscopy. Their cytotoxic properties were tested, showing significant cytotoxicity (IC₅₀ = 8.0-55 μM) towards the human breast cancer cell line MDA-MB-231. The half-inhibitory concentration (IC₅₀) for fac-[Re(CO)₃(dmphen)(MMI)]⁺, the most toxic complex in this series (8.0 ± 0.2 μM), was comparable to that of the corresponding aqua complex fac-[Re(CO)₃(dmphen)(H₂O)]⁺ with IC₅₀ = 6.0 ± 0.1 μM. The fac-[Re(CO)₃(bpy)(MMI/MSeI)]⁺ complexes were somewhat less toxic towards the human embryonic kidney cell line HEK-293 T after 48 h of exposure. The stability of the complexes upon irradiation was monitored using UV-vis spectroscopy, with no CO released when exposed to UV-A light (λ = 365 nm).

2-Selenouridine, a Modified Nucleoside of Bacterial tRNAs, Its Reactivity in the Presence of Oxidizing and Reducing Reagents

The 5-substituted 2-selenouridines are natural components of the bacterial tRNA epitranscriptome. Because selenium-containing biomolecules are redox-active entities, the oxidation susceptibility of 2-selenouridine (Se2U) was studied in the presence of hydrogen peroxide under various conditions and compared with previously reported data for 2-thiouridine (S2U). It was found that Se2U is more susceptible to oxidation and converted in the first step to the corresponding diselenide (Se2U)₂, an unstable intermediate that decomposes to uridine and selenium. The reversibility of the oxidized state of Se2U was demonstrated by the efficient reduction of (Se2U)₂ to Se2U in the presence of common reducing agents. Thus, the 2-selenouridine component of tRNA may have antioxidant potential in cells because of its ability to react with both cellular ROS components and reducing agents. Interestingly, in the course of the reactions studied, we found that (Se2U)₂ reacts with Se2U to form new ‘oligomeric nucleosides′ as linear and cyclic byproducts.

Reactions of N-heterocyclic carbene-based chalcogenoureas with halogens: a diverse range of outcomes

We have investigated the reactions of chalcogenoureas derived from N-heterocyclic carbenes, referred to here as [E(NHC)], with halogens. Depending on the structure of the chalcogenourea and the identity of the halogen, a diverse range of reactivity was observed and a corresponding range of structures was obtained. Cyclic voltammetry was carried out to characterise the oxidation and reduction potentials of these [E(NHC)] species; selenoureas were found to be easier to oxidise than the corresponding thioureas. In some cases, a correlation was found between the oxidation potential of these compounds and the electronic properties of the corresponding NHC. The reactivity of these chalcogenoureas with different halogenating reagents (Br₂, SO₂Cl₂, I₂) was then investigated, and products were characterised using NMR spectroscopy and single-crystal X-ray diffraction. X-ray analyses elucidated the solid-state coordination types of the obtained products, showing that a variety of possible adducts can be obtained. In some cases, we were able to extrapolate a structure/activity correlation to explain the observed trends in reactivity and oxidation potentials.

C5-Substituted 2-Selenouridines Ensure Efficient Base Pairing with Guanosine; Consequences for Reading the NNG-3' Synonymous mRNA Codons

5-Substituted 2-selenouridines (R5Se2U) are post-transcriptional modifications present in the first anticodon position of transfer RNA. Their functional role in the regulation of gene expression is elusive. Here, we present efficient syntheses of 5-methylaminomethyl-2-selenouridine (1, mnm5Se2U), 5-carboxymethylaminomethyl-2-selenouridine (2, cmnm5Se2U), and Se2U (3) alongside the crystal structure of the latter nucleoside. By using pH-dependent potentiometric titration, pKa values for the N3H groups of 1–3 were assessed to be significantly lower compared to their 2-thio- and 2-oxo-congeners. At physiological conditions (pH 7.4), Se2-uridines 1 and 2 preferentially adopted the zwitterionic form (ZI, ca. 90%), with the positive charge located at the amino alkyl side chain and the negative charge at the Se2-N3-O4 edge. As shown by density functional theory (DFT) calculations, this ZI form efficiently bound to guanine, forming the so-called “new wobble base pair”, which was accepted by the ribosome architecture. These data suggest that the tRNA anticodons with wobble R5Se2Us may preferentially read the 5′-NNG-3′ synonymous codons, unlike their 2-thio- and 2-oxo-precursors, which preferentially read the 5′-NNA-3′ codons. Thus, the interplay between the levels of U-, S2U- and Se2U-tRNA may have a dominant role in the epitranscriptomic regulation of gene expression via reading of the synonymous 3′-A- and 3′-G-ending codons.

Coordination of 1-methyl-1,3-dihydro-2H-benzimidazole-2-selone to zinc and cadmium: Monotonic and non-monotonic bond length variations for [H(sebenzimMe)]2MCl2 complexes (M = Zn, Cd, Hg)

The reactions of 1-methyl-1,3-dihydro-2H-benzimidazole-2-selone, H(sebenzimMe), towards the zinc and cadmium halides, MX2 (M = Zn, Cd; X = Cl, Br, I), afford the adducts, [H(sebenzimMe)]2MX2, which have been structurally characterized by X-ray diffraction. The halide ligands of each of these complexes participate in hydrogen bonding interactions with the imidazole N-H moieties, although the nature of the interactions depends on the halide. Specifically, the chloride and bromide derivatives, [H(sebenzimMe)]2ZnX2 and [H(sebenzimMe)]2CdX2 (X = Cl, Br), exhibit two intramolecular N-H•••X interactions, whereas the iodide derivatives, [H(sebenzimMe)]2ZnI2 and [H(sebenzimMe)]2CdI2, exhibit only one intramolecular N-H•••I interaction. Comparison of the M-Se and M-Cl bond lengths of the chloride series, [H(sebenzimMe)]2MCl2 (M = Zn, Cd, Hg), indicates that while the average M-Cl bond lengths progressively increase as the metal becomes heavier, the variation in M-Se bond length exhibits a non-monotonic trend, with the Cd-Se bond being the longest. These different trends provide an interesting subtlety concerned with use of covalent radii in predicting bond length differences. In addition to tetrahedral [H(sebenzimMe)]2CdCl2, [H(sebenzimMe)]3,CdCl2•[H(sebenzim)Me]4CdCl2, which features both five-coordinate and six-coordinate coordinate centers, has also been structurally characterized. Finally, the reaction between CdI2 and H(sebenzimMe) at elevated temperatures affords the 1-methylbenzimidazole complex, [H(sebenzimMe)]-[H(benzimMe)]CdI2, a transformation that is associated with cleavage of the C-Se bond.

Evaluation of benzthiazolidine-based formamidinium salts for the synthesis of penem-type β-lactams by uncatalysed carbonylation of acyclic diaminocarbenes

The reaction of [iPr2N=CHCl]Cl with 2-phenylbenzthiazolidine (Ph-BtzH) and subsequent anion metathesis afforded the formamidinium salt [(Ph-Btz)CH(NiPr2)][PF6] ([1aH][PF6]). The reaction of [1aH][PF6] with (Me3Si)2NNa in the presence of grey selenium furnished the selenourea derivative 1aSe as trapping product of the acyclic diaminocarbene 1a. In the absence of selenium, a 2H-1,4-benzothiazine derivative (2) was obtained, which is an isomer of 1a, whose formation is plausibly initiated by deprotonation of [1aH]+ not at the cationic N2CH unit, but at the neighbouring PhCH position. CO was ineffective as trapping reagent for 1a. [1aH][PF6], 1aSe and 2 have been structurally characterised by X-ray diffraction.

Stable and Persistent Acyclic Diaminocarbenes with Cycloalkyl Substituents and Their Transformation to β-Lactams by Uncatalysed Carbonylation with CO

Four new acyclic diaminocarbenes (ADACs), viz. [(cyclo-C_n H_2n-1 )₂ N]₂ C (n=5-7) and iPr₂ N-C-N(cyclo-C₆ H₁₁ )₂ , were synthesised by reacting the corresponding formamidinium hexafluorophosphates with NaN(SiMe₃ )₂ . Their nucleophilicities and electrophilicities were respectively judged from the ¹ J_CH values determined for the N₂ CH unit of the corresponding formamidinium cations and from the ⁷⁷ Se NMR chemical shifts of the selenourea derivatives obtained from the reaction of elemental selenium with the corresponding ADACs. An ambiphilic profile essentially identical to that of the "Alder carbene" (iPr₂ N)₂ C was found in each case. Similar to the latter carbene, the new ADACs undergo a well-defined thermal decomposition by β-fragmentation, affording an alkene and a formamidine. The stabilities of [(cyclo-C_n H_2n-1 )₂ N]₂ C depend strongly on the value of n, following the order 6>5>7, with the latter congener being too unstable for isolation. [(cyclo-C₆ H₁₁ )₂ N]₂ C shows no thermal decomposition at room temperature in solution and is thus significantly more stable than (iPr₂ N)₂ C. The stability of iPr₂ N-C-N(cyclo-C₆ H₁₁ )₂ is intermediate between that of (iPr₂ N)₂ C and [(cyclo-C₆ H₁₁ )₂ N]₂ C, its β-fragmentation selectively affording propene and iPrN=CH-N(cyclo-C₆ H₁₁ )₂ . [(cyclo-C_n H_2n-1 )₂ N]₂ C (n=5-7) react readily with CO under mild conditions, selectively affording trisubstituted spirocyclic β-lactam derivatives with an antimicrobial activity spectrum similar to that of penicillin G.

A Library of Selenourea Precursors to PbSe Nanocrystals with Size Distributions near the Homogeneous Limit

We report a tunable library of N,N,N'-trisubstituted selenourea precursors and their reaction with lead oleate at 60-150 °C to form carboxylate-terminated PbSe nanocrystals in quantitative yields. Single exponential conversion kinetics can be tailored over 4 orders of magnitude by adjusting the selenourea structure. The wide range of conversion reactivity allows the extent of nucleation ([nanocrystal] = 4.6-56.7 μM) and the size following complete precursor conversion (d = 1.7-6.6 nm) to be controlled. Narrow size distributions (σ = 0.5-2%) are obtained whose spectral line widths are dominated (73-83%) by the intrinsic single particle spectral broadening, as observed using spectral hole burning measurements. The intrinsic broadening decreases with increasing size (fwhm = 320-65 meV, d = 1.6-4.4 nm) that derives from exciton fine structure and exciton-phonon coupling rather than broadening caused by the size distribution.

Synthesis, characterization, DFT calculations, and electrochemical comparison of novel iron(ii) complexes with thione and selone ligands

Characterization of Fe(ii)–thone and –selone complexes revealed that these ligands oxidize before Fe(ii), suggesting an iron-binding mechanism for similar antioxidants.

New Stable and Persistent Acyclic Diaminocarbenes

The portfolio of acyclic diaminocarbenes (ADACs) has been substantially expanded, owing to the synthesis of eleven new formamidinium salts, mostly of the type [(iPr2N)CH(NRR')][PF6], for use as immediate carbene precursors. The corresponding ADACs (iPr2N)C(NRR') were sufficiently stable for isolation in the case of NRR' = 2-methylpiperidino (13), 3-methylpiperidino (14), 4-methylpiperidino (15), morpholino (17) and NiPrPh (20), but had to be trapped in situ in the case of NRR' = 2,2,6,6-tetramethylpiperidino (12) and NiPrMe (19). The tetraaryl-substituted ADACs (Ph2N)2C (22) and (Ph2N)C[N(C6F5)2] (24) also could only be generated and trapped in situ. Trapping with elemental selenium was particularly efficient, affording the corresponding selenourea derivative in all cases, whereas trapping with [{Rh(μ-Cl)(cod)}2] did not work for 12 and 24. The (77)Se NMR chemical shifts, δ((77)Se), of the selenourea compounds derived from the new ADACs lie in the range 450-760 ppm, which indicates a much higher electrophilicity and π-accepting capability of ADACs in comparison with NHCs, which typically exhibit δ((77)Se)<200 ppm. The extreme low-field shift of 758 ppm observed for 12Se can be rationalised by the results of DFT calculations, which revealed that ADAC 12 has a minimum energy conformation with the 2,2,6,6-tetramethylpiperidino unit perpendicular to the N2C plane, which suppresses the π donation of this amino group and causes an unusually low LUMO energy and high electrophilicity.

Protolytic cleavage of Hg-C bonds induced by 1-methyl-1,3-dihydro-2H-benzimidazole-2-selone: synthesis and structural characterization of mercury complexes

Multinuclear ((1)H, (77)Se, and (199)Hg) NMR spectroscopy demonstrates that 1-methyl-1,3-dihydro-2H-benzimidazole-2-selone, H(sebenzim(Me)), a structural analogue of the selenoamino acid, selenoneine, binds rapidly and reversibly to the mercury centers of HgX2 (X = Cl, Br, I), while X-ray diffraction studies provide evidence for the existence of adducts of composition [H(sebenzim(Me))]xHgX2 (X = Cl, x = 2, 3, 4; X = I, x = 2) in the solid state. H(sebenzim(Me)) also reacts with methylmercury halides, but the reaction is accompanied by elimination of methane resulting from protolytic cleavage of the Hg-C bond, an observation that is of relevance to the report that selenoneine demethylates CysHgMe, thereby providing a mechanism for mercury detoxification. Interestingly, the structures of [H(sebenzim(Me))]xHgX2 exhibit a variety of different hydrogen bonding patterns resulting from the ability of the N-H groups to form hydrogen bonds with chlorine, iodine, and selenium.

Chalcogen analogues of nicotine lactam studied by NMR, FTIR, DFT and X-ray methods

The selenoanalogue of nicotine has been synthesized and characterized by spectroscopic and X-ray diffraction methods. The crystals of selenonicotine are isomorphic with the thionicotine homologue and consist of molecules engaged in columnar π⋯π stacking interactions between antiparallely arranged pyridine moieties. These interactions, absent in other crystals containing nicotine fragments, seem to be induced by the presence of a lactam group. The molecular structures in the vacuum of the oxo-, thio- and selenonicotine homologues have been calculated by the DFT method and compared with the available X-ray data. The delocalized structure of thionicotine is stabilized by intramolecular C-H⋯S hydrogen bond, which becomes weaker in the partial zwitterionic resonance structure of selenonicotine in favor of multiple C-H⋯Se intermolecular hydrogen-bonds. The calculated data allow a complete assignment of vibration modes in the solid state FTIR spectra. The (1)H and (13)C NMR chemical shifts were calculated by the GIAO method with B3LYP/6-311G(3df) level. A comparison between experimental and calculated theoretical results indicates that the density functional B3LYP method provided satisfactory results for predicting FTIR, (1)H, (13)C NMR spectra properties.

Antithyroid drugs and their analogues: synthesis, structure, and mechanism of action

Thyroid hormones are essential for the development and differentiation of all cells of the human body. They regulate protein, fat, and carbohydrate metabolism. In this Account, we discuss the synthesis, structure, and mechanism of action of thyroid hormones and their analogues. The prohormone thyroxine (T4) is synthesized on thyroglobulin by thyroid peroxidase (TPO), a heme enzyme that uses iodide and hydrogen peroxide to perform iodination and phenolic coupling reactions. The monodeiodination of T4 to 3,3',5-triiodothyronine (T3) by selenium-containing deiodinases (ID-1, ID-2) is a key step in the activation of thyroid hormones. The type 3 deiodinase (ID-3) catalyzes the deactivation of thyroid hormone in a process that removes iodine selectively from the tyrosyl ring of T4 to produce 3,3',5'-triiodothyronine (rT3). Several physiological and pathological stimuli influence thyroid hormone synthesis. The overproduction of thyroid hormones leads to hyperthyroidism, which is treated by antithyroid drugs that either inhibit the thyroid hormone biosynthesis and/or decrease the conversion of T4 to T3. Antithyroid drugs are thiourea-based compounds, which include propylthiouracil (PTU), methimazole (MMI), and carbimazole (CBZ). The thyroid gland actively concentrates these heterocyclic compounds against a concentration gradient. Recently, the selenium analogues of PTU, MMI, and CBZ attracted significant attention because the selenium moiety in these compounds has a higher nucleophilicity than that of the sulfur moiety. Researchers have developed new methods for the synthesis of the selenium compounds. Several experimental and theoretical investigations revealed that the selone (C═Se) in the selenium analogues is more polarized than the thione (C═S) in the sulfur compounds, and the selones exist predominantly in their zwitterionic forms. Although the thionamide-based antithyroid drugs have been used for almost 70 years, the mechanism of their action is not completely understood. Most investigations have revealed that MMI and PTU irreversibly inhibit TPO. PTU, MTU, and their selenium analogues also inhibit ID-1, most likely by reacting with the selenenyl iodide intermediate. The good ID-1 inhibitory activity of PTU and its analogues can be ascribed to the presence of the -N(H)-C(═O)- functionality that can form hydrogen bonds with nearby amino acid residues in the selenenyl sulfide state. In addition to the TPO and ID-1 inhibition, the selenium analogues are very good antioxidants. In the presence of cellular reducing agents such as GSH, these compounds catalytically reduce hydrogen peroxide. They can also efficiently scavenge peroxynitrite, a potent biological oxidant and nitrating agent.

2-Seleno-1-alkylbenzimidazoles and their Diselenides: Synthesis and Structural Characterization of a 2-Seleno-1-methylbenzimidazole Complex of Mercury

2-Seleno-1-methylbenzimidazole, H(sebenzimMe), can be synthesized from 1-methylbenzimidazole by sequential treatment with (i) BunLi, (ii) elemental selenium and (iii) HCl(aq). This method is also applicable to the synthesis of 2-seleno-1-t-butylbenzimidazole, H(sebenzimBut ). Single crystal X-ray diffraction and NMR spectroscopic data demonstrate that H(sebenzimMe) and H(sebenzimBut ) exist as the selone rather than the selenol tautomers, which is in accord with the results of density functional theory (B3LYP) calculations. The data also indicate that the selone is best represented as a C+-Se- zwitterion rather than as a C=Se doubly bonded species. Aerobic oxidation of H(sebenzimMe) and H(sebenzimBut ) in the presence of Et3N yields the diselenides, (sebenzimMe)2 and (sebenzimBut )2. In addition, H(sebenzimMe) reacts with HgCl2 to give [H(sebenzimMe)]2HgCl2, the first structurally characterized example of a 2-seleno-1-alkylimidazole mercury complex.

1-Methyl-2,3-dihydro-1H-benzimidazole-2-selone

The title compound C₈H₈N₂Se, is the product of the reaction of 2-chloro-1-methyl­benzimidazole with sodium hydro­selenide. The mol­ecule is almost planar (r.m.s. deviation = 0.041 Å) owing to the presence of the long chain of conjugated bonds (Se=C—NMe—C=C—C=C—C=C—NH). The C=Se bond length [1.838 (2) Å] corresponds well to those found in the close analogs and indicates its pronounced double-bond character. In the crystal, mol­ecules form helicoidal chains along the b axis by means of N—H⋯Se hydrogen bonds.

1,3-Benzothia-zole-2(3H)-selone

The title compound, C(7)H(5)NSSe, is the product of the reaction of 2-chloro-benzothia-zole with sodium hydro-selenide. The mol-ecule is almost planar (r.m.s. deviation = 0.018 Å) owing to the presence of the long chain of conjugated bonds (Se=C-N-C=C-C=C-C=C). The geometrical parameters correspond well to those of the analog N-methyl-benzothia-zole-2(3H)-selone, demonstrating that the S atom does not take a significant role in the electron delocalization within the mol-ecule. In the crystal, mol-ecules form centrosymmetric dimers by means of inter-molecular N-H⋯Se hydrogen bonds. The dimers have a nonplanar ladder-like structure. Furthermore, the dimers are linked into ribbons propagating in [010] by weak attractive Se⋯S [3.7593 (4) Å] inter-actions.

Synthesis, characterization, and DFT studies of thione and selone Cu(I) complexes with variable coordination geometries

Coordination of Cu(I) halides with N,N'-dimethylimidazole selone (dmise) and thione (dmit) ligands was examined by treating CuX (X = Cl, Br, I) with one or two equivalents of dmise or dmit. The reaction of CuI and CuBr with one molar equivalent of dmise results in unusual selenium-bridged tetrameric Cu(4)(μ-dmise)(4)(μ-X)(2)X(2) copper complexes with average Cu-Se bond lengths of 2.42 Å and a Cu(2)(μ-X)(2) core (X = I (1) or Br (6)) that's in a rhomboidal structure. The reaction of CuX (X = Cl, Br, and I) with two equivalents of dmit or dmise results in trigonal planar Cu(I) complexes of two different conformations with the formula Cu(dmit)(2)X (3a, 3b, 4, and 7) or Cu(dmise)(2)X (2, 5, and 8) with average Cu-S and Cu-Se bond lengths of 2.23 Å and 2.34 Å, respectively. The coordination geometry around the copper center in complexes 1 to 8 is determined by the type of halide and chalcogenone ligand used, intramolecular π-π interactions, and short contact interactions between X-H (X = I, Br, Cl, Se or S). The theoretical DFT calculations are in good agreement with experimental X-ray structural data and indicate that dmise ligands are required for formation of the tetrameric complexes 1 and 6. Electrochemical studies show that the trigonal copper selone complexes have more negative potentials relative to analogous copper thione complexes by an average of 108 mV.

Antithyroid drug carbimazole and its analogues: synthesis and inhibition of peroxidase-catalyzed iodination of L-tyrosine

Synthesis and biological activity of the antithyroid drug carbimazole (CBZ) and its analogues are described. The introduction of an ethoxycarbonyl group in methimazole and its selenium analogue not only prevents the oxidation to the corresponding disulfide and diselenide but also reduces the zwitterionic character. A structure-activity correlation in a series of CBZ analogues suggests that the presence of a methyl substituent in CBZ and related compounds is important for their antithyroid activity.

Applications of bis(1-R-imidazol-2-yl)disulfides and diselenides as ligands for main-group and transition metals: kappa2-(N,N) coordination, S-S bond cleavage, and S-S/E-E (E = S, Se) bond metathesis reactions

Bis(1-R-imidazol-2-yl)disulfides, (mim(R))2 (R = Ph, Bu(t)), and diselenides, (seim(Mes))2, serve as bidentate N,N-donor ligands for main-group and transition metals. For example, [kappa2-(mim(Bu)(t))2]MCl2 (M = Fe, Co, Ni, Zn), [kappa2-(mim(Ph))2]MCl2 (M = Co, Zn), [kappa2-(mim(Bu)(t))2]CuX (X = Cl, I), and [kappa2-(seim(Mes))2]MCl2 (M = Fe, Co, Ni) are obtained by treatment of (mim(Bu)(t))2 or (seim(Mes))2 with the respective metal halide and have been structurally characterized by X-ray diffraction. On the other hand, the zerovalent nickel complex Ni(PMe3)4 effects cleavage of the disulfide bond of (mim(Bu)(t))2 to give square-planar trans-Ni(PMe3)2(mim(Bu)(t))2 in which the (mim(Bu)(t)) ligands coordinate via nitrogen rather than sulfur, a most uncommon coordination mode for this class of ligands. Although [kappa2-(mim(R))2]MCl2 (M = Fe, Co, Ni, Zn) are not subject to homolytic cleavage of the S-S bond because the tetravalent state is not readily accessible, the observation that [kappa2-(mimPh)2]CoCl2 and [kappa2-(mim(Bu)(t))2]CoCl2 form an equilibrium mixture with the asymmetric disulfide [kappa2-(mim(Ph))(mim(Bu)(t))]CoCl2 indicates that S-S bond cleavage via another mechanism is possible. Likewise, metathesis between disulfide and diselenide ligands is observed in the formation of [kappa2-(mim(Bu)(t))(seim(Mes))]CoCl2 upon treatment of [kappa2-(mim(Bu)(t))2]CoCl2 with [kappa2-(seim(Mes))2]CoCl2.

Applications of Tripodal [S(3)] and [Se(3)] L(2)X Donor Ligands to Zinc, Cadmium and Mercury Chemistry: Organometallic and Bioinorganic Perspectives

The tripodal tris(2-mercapto-1-R-imidazolyl)hydroborato ligand system, [Tm(R)], and its selenium counterpart, [Tse(R)], provide useful platforms for investigating organometallic and bioinorganic aspects of the chemistry of zinc, cadmium and mercury in sulfur-rich and selenium-rich coordination environments. For example, the tridentate [Tm(R)] ligand provides an [S(3)] donor array that is of use for mimicking aspects of zinc enzymes and proteins that have sulfur-rich active sites, such as the Ada DNA repair protein. With respect to mercury, an interesting application of the [Tm(Bu(t) )] ligand is the synthesis of the mercury alkyl compounds [Tm(Bu(t) )]HgR (R = Me, Et) that react with PhSH to yield [Tm(Bu(t) )]HgSPh and RH, a reaction that emulates mercury detoxification by the organomercurial lyase, MerB. In addition to the tridentate [Tm(R)] and [Tse(R)] ligands, applications of the bidentate counterparts, [Bm(R)] and [Bse(R)] are also described.

Bis- and tris(2-seleno-1-methylimidazolyl)hydroborato complexes, {[BseMe]ZnX}2(X = Cl, I), [BseMe]2Zn and [TseMe]Re(CO)3: Structural evidence that the [BseMe] ligand is not merely a “heavier” version of the sulfur counterpart, [BmMe]

New bidentate and tridentate ligands that feature selenium donors, namely the bis- and tris(2-seleno-1-methylimidazolyl)hydroborato ligands [BseMe] and [TseMe], have been constructed via the reaction of MBH4(M=Na, K) with 1-methylimidazole-2-selone. Comparison of the structure of {[BseMe]ZnI}2 with its sulfur counterpart, [BmMe]ZnI, demonstrates that the seleno ligand exhibits a greater tendency than the mercapto ligand to bridge two metal centers, while comparison of [TseMe]Re(CO)3 and [TseMes]Re(CO)3 indicates that the [TseMe] ligand is more electron donating and less sterically demanding than the [TseMes] ligand.