Exocyclic Sulfur Research Articles

S- and N-alkylation of 2,2′-(alkane-α,ω-diyldisulfanediyl)-bis(1,3-benzothiazoles) with 1-iodopropan-2-one in the presence of iodine

The alkylation of 2,2′-(methylenedisulfanediyl)- and 2,2′-(ethane-1,2-diyldisulfanediyl)bis-(1,3-benzothiazoles) with 1-iodopropan-2-one involves exclusively the exocyclic sulfur atoms. The presence of an electron-withdrawing carbonyl group between the bridging methylene units in 1,3-bis(1,3-benzothiazol-2-ylsulfanyl)propane-2-one forces the alkylation to occur at the endocyclic nitrogen atoms.

Preparation and biological properties of 2-thio-containing pyrimidines and their condensed analogs.

The known methods for synthesis of thioxopyrimidines and their condensed analogs with exocyclic sulfur atom are summarized and discussed. The most popular approaches are based on [3+3], [4+2], [5+1] cyclization processes or domino reactions. The literature data analysis shows that the title compounds possess diverse biological activities, such as antioxidant, radioprotective, analgesic, antiinflammatory, antihypertensive, anxiolytic, anamnestic, anticonvulsant, antimicrobial, fungicidal, herbicidal, antiviral, and anticancer.

Study of the mechanism of formation of heterocyclic disulfonium dications from 1,3-benzothiazole-2-thiol and 1-iodopropan-2-one

The potential energy surface for the formation of heterocyclic disulfonium dications from 1,3-benzothiazole-2-thiol and 1-iodopropan-2-one has been analyzed at the DFT B3LYP level of theory. The reaction involves oxidation of 1,3-benzothiazole-2-thiol to the corresponding disulfide, followed by alkylation of the exocyclic sulfur atoms. Stabilization of the salt with iodide anion is initiated by thermodynamically controlled reaction with molecular iodine, leading to the formation of stable structure with triiodide anion.

Novel gold(I) complexes with 5-phenyl-1,3,4-oxadiazole-2-thione and phosphine as potential anticancer and antileishmanial agents

The current anticancer and antileishmanial drug arsenal presents several limitations concerning their specificity, efficacy, costs and the emergence of drug-resistant cells lines, which encourages the urgent need to search for new alternatives. Inspired by the fact that gold(I)-based compounds are promising antitumoral and antileishmanial drug candidates, we synthesized novel gold(I) complexes containing phosphine and 5-phenyl-1,3,4-oxadiazole-2-thione and evaluated their anticancer and antileishmanial activities. Synthesis was performed by reacting 5-phenyl-1,3,4-oxadiazole-2-thione derivatives with chloro(triphenylphosphine)gold(I) and chloro(triethylphosphine)gold(I). The novel compounds were characterized by infrared, Raman, 1H, 13C nuclear magnetic resonance, high-resolution mass spectra, and x-ray crystallography. The coordination of the ligands to gold(I) occurred through the exocyclic sulfur atom. All gold(I) complexes were active at low micromolar or nanomolar range with IC50 values ranging from <0.10 to 1.66 μM against cancer cell lines and from 0.9 to 4.2 μM for Leishmania infantum intracellular amastigotes. Compound (6-A) was very selective against murine melanoma B16F10, colon cancer CT26.WT cell lines and L. infantum intracellular amastigotes. Compound (7-B) presented the highest anticancer activity against both cancer cell lines while the promising antileishmanial lead was compound (6-A). Tiethylphosphine gold(I) complexes were more active than the conterparts triphenylphosphine derivatives for both anticancer and antileishmanial activities. Triethylphosphine gold(I) derivatives presented antimony cross-resistance in L. guyanensis demonstrating their potential to be used as chemical tools to better understand mechanisms of drug resistance and action. These findings revealed the anticancer and antileishmanial potential of gold(I) oxadiazole phosphine derivatives.

Synthesis of 4- and 5-arylthiazolinethiones as inhibitors of indoleamine 2,3-dioxygenase

Docking studies of 4-phenylthiazolinethione on human IDO1 suggest complexation of the heme iron by the exocyclic sulfur atom further reinforced by hydrophobic interactions of the phenyl ring within pocket A of the enzyme. On this basis, chemical modifications were proposed to increase inhibition activity. Synthetic routes had to be adapted and optimized to yield the desired substituted 4- and 5-arylthiazolinethiones. Their biological evaluation shows that 5-aryl regioisomers are systematically less potent than the corresponding 4-aryl analogs. Substitution on the phenyl ring does not significantly increase inhibition potency, except for 4-Br and 4-Cl derivatives.

Effects of coordination mode of 2-mercaptothiazoline on reactivity of Au(I) compounds with thiols and sulfur-containing proteins

Gold(I) based drugs are interesting for their potential medical use. The relatively facile ligand substitution in linear gold(I) compounds makes the identification of active species complicated. Ligands such as PR3 and CN− are likely to be carrier ligands due to their strong trans-directing properties and will dictate the nature of substitution reactions. The 2-mercaptothiazoline (mtz) ligand is an N,S-heterocyclic compound which presents an exocyclic thiol sulfur as well as a heterocyclic nitrogen. The coordination of mtz to transition metals can be modulated by the trans ligand and complexes with metal bound through the nitrogen and/or the exocyclic sulfur are known. Therefore, the complexes [NCAu(N-mtz)] (N-coordinated) and [(Ph3P)Au(S-mtz)] (S-coordinated) were investigated to compare the influence of CN− and PR3 as well as the coordination mode of the mtz ligand on reactivity with thiols and sulfur-containing proteins. As a further comparison the compound [(Ph3P)AuCN] was also studied. Human serum albumin, egg white lysozyme and, principally, the C-terminal zinc finger (ZF2) of the nucleocapsid NCp7protein of HIV-1 were studied. Results from zinc finger studies show that the coordination structure can determine the reactivity toward biomolecules. Due to ligand scrambling, the complex [NCAu(N-mtz)] forms very reactive species in solution generating [NCyAux-biomolecule] adducts, where x,y≤3. The observation by mass spectrometry of [(CN)Au]-ZF confirms the ability of Au(I) compounds to form [(Ligand)Au] adducts on zinc fingers, in contrast to Au(III), where all ligands are lost upon reaction with the zinc finger. On the other hand, [(Ph3P)Au(S-mtz)] also generates the [(Ph3P)2Au]+ species due to ligand scrambling, that showed lower reactivity, probably due to steric hindrance. For this complex [(Ph3P)Au-biomolecule] and [Au-biomolecule] adducts are dominant. The results corroborate the hypothesis of modulation through coordination as the reactivity clearly depends on not only the ligand, but also the coordination mode.

A DFT study on tautomerism of selenorhodanine and its substituted derivatives

Rhodanine (2-thioxo-4-thiazolidinone) is a compound with a strong biological activity. It is also a ligand widely used in coordination chemistry. Replacing its exocyclic sulfur atom with selenium generates so called selenorhodanine. Selenorhodanine can exist in several tautomeric forms. Thus, the main aim of our research is to study the tautomeric equilibria in un substitued and substituted selenorhodanines. Substitution of nitrogen as well as the carbon atoms of the selenorhodanine ring with several substituents is considered. In order to achieve this goal we performed DFT calculations at the B3LYP/6-311++G∗∗ level for five theoretically possible tautomers of selenorhodanine. The results of performed calculations show that the most stable structure of selenorhodanine is similar to the equilibrium structures of rhodanine and thiazolidine-2,4-dione. We also calculated tautomeric equilibria for substituted selenorhodanines at the same level of theory and analyzed how the formation of intramolecular hydrogen bonds between some substituents and selenorhodanine ring can influence tautomeric equilibria in the compounds of interest.

Novel antitumor adamantane-azole gold(I) complexes as potential inhibitors of thioredoxin reductase.

Gold complexes that could act as antitumor agents have attracted great attention. Heterocyclic compounds and their metal complexes display a broad spectrum of pharmacological properties. The present study reports the preparation and characterization of four novel gold(I) complexes containing tertiary phosphine and new ligands 5-adamantyl-1,3-thiazolidine-2-thione, 3-methyladamantane-1,3,4-oxadiazole-2-thione. Spectroscopic data suggest that gold is coordinated to the exocyclic sulfur atom in all cases, as confirmed by X-ray crystallographic data obtained for complex (1) and supported by quantum-mechanical calculations. The cytotoxicity of the compounds has been evaluated in comparison to cisplatin and auranofin in three different tumor cell lines, colon cancer (CT26WT), metastatic skin melanoma (B16F10), mammary adenocarcinoma (4T1) and kidney normal cell (BHK-21). The gold complexes were more active than their respective free ligands and able to inhibit the thioredoxin reductase (TrxR) enzyme, even in the presence of albumin. Molecular modeling studies were carried out to understand the interaction between the compounds and the TrxR enzyme, considered as a potential target for new compounds in cancer treatment. The docking results show that the adamantane ring is essential to stabilize the ligand-enzyme complex prior the formation of covalent bond with gold center. The structure of the new gold compounds was established on the basis of spectroscopic data, DFT calculations and X-ray diffraction. TrxR inhibition was evaluated and the results correlated with the assays in tumor cells, suggesting the TrxR as possible target for these compounds.

A sulfur-rich π-electron acceptor derived from 5,5′-bithiazolidinylidene: charge-transfer complex vs. charge-transfer salt

Novel π-electron acceptors are still highly desirable for the formation of conducting salts or as n-dopable semiconductors. We describe here two synthetic approaches to substitute a dicyanovinylidene group, CC(CN)2 to a thioketone (CS) in the recently described DEBTTT acceptor where DEBTTT stands for (E)-3,3′-diethyl-5,5′-bithiazolidinylidene-2,4,2′,4′-tetrathione. These electron withdrawing groups enhance the electron accepting ability as demonstrated through electrochemical investigations, without hindering the formation of short intra- and intermolecular S⋯S contacts in the solid state. Association of this acceptor 1 with tetramethyltetrathiafulvalene (TMTTF) and decamethylferrocene (Fe(Cp*)2) afforded 1 : 1 adducts which were analyzed by single crystal X-ray diffraction. Combined with vibrational and magnetic properties, it appears that [TMTTF][1] behaves as a neutral charge-transfer complex while [Fe(Cp*)2][1] is an ionic salt. The concentration of the spin density on the exocyclic sulfur atoms in 1−˙ favors the setting of direct antiferromagnetic interactions in [Fe(Cp*)2][1].

Neutral mononuclear luminescent Pd(II) complexes with heterocyclic thiolate ligands and chelating phosphines. Structural and photophysical assignments

Two heterocyclic thiolate ligands, namely pymt and py2S (pymt=pyrimidine2-thiolate and py2S=pyridine-2-thiolate) and the diphosphines bis(diphenylphosphino)methane (dppm), 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), were used in the synthesis of three neutral Pd(II) complexes (cis-[Pd(dppm)(pymt)2] (1), cis-[Pd(dppe)(pymt)2] (2) and cis-[Pd(dppp)(pyrt)2] (3)). Crystallographic analysis of the isolated complexes reveals their square planar arrangement and the coordination of the thiolate moieties through their exocyclic sulfur atom. The complexes absorb in the visible part of the spectrum through charge transfer transitions while after photoexcitation at 385nm they appear to emit with a broad band located at 465nm.

Alkylation of 1,3-benzothiazin-4-one 2-oxo-, 2-arylimino-, and 2-thioxo derivatives

Sodium salt of 3Н -benzo[e][1,3]thiazine-2,4-dione is easily alkylated at position 3. In the case of 2-(arylimino)-2,3-dihydrobenzo[e][1,3]-thiazin-4-ones, the alkylation reaction at this position occurs regioselectively. Alkylation of 2-thioxo-2,3-dihydrobenzo[e][1,3]thiazin-4-one under the same conditions produced regioisomers, but S-alkylation at the exocyclic sulfur atom occurred in the presence of triethylamine. The reaction of 1-(4-oxo-3,4-dihydrobenzo[e][1,3]thiazin-2-ylidene)guanidine with methyl anthranilate led to the formation of tetracyclic quinazolinо[2,1-b]quinazolinedione.

Formation and structure of two luminescent salts of [Au(SCSN3)2]- obtained through the [2 + 3] cyclization of carbon disulfide and azide ion.

The colorless, two-coordinate gold(i) complex, [(H2O)3Na][Au(SCSN3)2], has been synthesized through the [2 + 3] cyclic reaction of carbon disulfide and sodium azide in the presence of the labile complex (tht)AuCl. Metathesis of [(H2O)3Na][Au(SCSN3)2], with tetra(phenyl)arsonium chloride produced colorless needles of (Ph4As)[Au(SCSN3)2]. The structure of [(H2O)3Na][Au(SCSN3)2] involves linear gold coordination by two exocyclic sulfur atoms of the 1,2,3,4-thiatriazole-5-thiolate anions. These two-coordinate anions self-associate to form extended, zig-zag chains that are connected by aurophilic bonding with Au∙∙∙Au distances of 3.2653(3) Å and 3.3090(3) Å. Remarkably, the individual S-Au-S units that are connected though aurophilic interactions are eclipsed. The structure of (Ph4As)[Au(SCSN3)2] also contains linear, two-coordinate gold ions with bonding to the 1,2,3,4-thiatriazole-5-thiolate anionic ligands through the exocyclic sulfur atoms. However, in this salt, the anions self-associate through AuAu bonds (Au∙∙∙Au distance of 3.2007(3) Å) to form simple dimers, which also have an eclipsed arrangement of the ligands. Electronic structure calculations strongly suggest that the staggered geometry for the [(Au(SCSN3))2](+) dimer is energetically favored relative to the eclipsed geometry. However, attractive π-stacking interactions appear to promote the observed eclipsed arrangement of the ligands.

Synthesis and Characterization of 5-Substituted- (2-methylbenzimidazol-1-yl)-1,3,4-oxadiazole-2-thione and Its Metal Complexes of Fe(III), Hg(II), Zn(II) and Sn(II)

A ligand 5-Substituted-(2-methylbenzimidazol-1-yl)-1,3,4-oxadiazole-2-thione (L) and its Fe(III),Hg(II),Sn(II) and Zn(II) complexes were synthesized. The authenticity of the ligand and its transition metal complexes were established by elemental analyses, conductance and magnetic susceptibility measurements, as well as spectroscopic (IR, 1 H NMR, UV-Vis and Mass) and thermal studies. All complexes exhibit the composition ML2X2 where M =Fe(III),Hg(II), Zn(II) and Sn(II), L=Ligand, X=OAc and chloride ions. The IR spectral studies revealed the existence thiol-thione tautamerism in the ligand molecule. The ligand acts as a bidentate coordinating through the N-3 nitrogen and the exocyclic sulfur atoms of ox diazole rings. Antimicrobial screening of the ligand and its metal complexes were determined against the bacteria Escherichia coli and Salmonella paratyphi A.

N-Heterocyclic-based adsorbents for antibody purification-effect of ligand structure

A new set of ligands based on substituted pyridine and other N-heterocyclic structures, possessing an aliphatic primary amino group tether and an exocyclic sulphur atom, has been prepared and immobilized onto epoxy-activated matrices such as Sepharose 6 Fast Flow®. The derived adsorbents have been evaluated for their utility to capture and purify humanized monoclonal antibodies. Favourable binding properties were assessed from screening assays to determine optimal conditions for the capture and elution of the monoclonal antibodies. Static and dynamic binding experiments were employed to derive the equilibrium dissociation constants KD 's and binding capacities Qmax 's. Typically, the KD values were in the range of 2-5 μM and the Qmax values between 20 and 75 mg mAb/ml resin, depending on the stereo-electronic properties of the substituent in the N-heterocyclic ring structure. The effect of ligand structure on the selectivity of these adsorbents was also investigated, and criteria for their use in the purification of monoclonal antibodies from cell culture supernatants established.

Synthesis and cytotoxic activity of gold(I) complexes containing phosphines and 3-benzyl-1,3-thiazolidine-2-thione or 5-phenyl-1,3,4-oxadiazole-2-thione as ligands

Heterocyclic compounds and their metal complexes display a broad spectrum of pharmacological properties. This work reports the preparation and characterization of four novel gold(I) complexes containing tertiary phosphine and 3-benzyl-1,3-thiazolidine-2-thione, 5-phenyl-1,3,4-oxadiazole-2-thione as ligands. The reaction of chloro(triphenylphosphine)gold(I) and chloro(triethylphosphine)gold(I) with thioamides, 3-benzyl-1,3-thiazolidine-2-thione and 5-phenyl-1,3,4-oxadiazole-2-thione in dichloromethane or dichloromethane/acetone resulted in the formation of the gold(I) complexes of general formula: [SAuPR3]Cl, S=3-benzyl-1,3-thiazolidine-2-thione, R=Ph or Et and [SAuPR3], S=5-phenyl-1,3,4-oxadiazole-2-thione, R=Ph or Et. Spectroscopic evidence suggested that gold is coordinated to the exocyclic sulfur atom in all cases and this was confirmed by X-ray crystallographic data obtained for complex (4). The cytotoxicity of the compounds has been evaluated in comparison to cisplatin in two different tumor cell lines, colon cancer (CT26WT) and metastatic skin melanoma (B16F10), and also in a kidney normal cell (BHK-21). The gold complexes showed a better activity than cisplatin and presented a high selectivity index.

ChemInform Abstract: Peculiar Electrophilic Heterocyclization of 5‐Allyl‐6‐thioxopyrazolo[3,4‐d]pyrimidin‐4‐one.

AbstractDepending on the substituent on the exocyclic sulfur, 5‐allyl‐6‐thioxopyrazolo[3,4‐d]pyrimidin‐4‐one (I) can be anellated on halogenation as either thiazoline or oxazoline ring.

Structural and Mechanistic Basis for Enhanced Translational Efficiency by 2-Thiouridine at the tRNA Anticodon Wobble Position

The 2-thiouridine (s2U) at the wobble position of certain bacterial and eukaryotic tRNAs enhances aminoacylation kinetics, assists proper codon–anticodon base pairing at the ribosome A-site, and prevents frameshifting during translation. By mass spectrometry of affinity-purified native Escherichia coli tRNA1GlnUUG, we show that the complete modification at the wobble position 34 is 5-carboxyaminomethyl-2-thiouridine (cmnm5s2U). The crystal structure of E. coli glutaminyl-tRNA synthetase (GlnRS) bound to native tRNA1Gln and ATP demonstrates that cmnm5s2U34 improves the order of a previously unobserved 11-amino-acid surface loop in the distal β-barrel domain of the enzyme and imparts other local rearrangements of nearby amino acids that create a binding pocket for the 2-thio moiety. Together with previously solved structures, these observations explain the degenerate recognition of C34 and modified U34 by GlnRS. Comparative pre-steady-state aminoacylation kinetics of native tRNA1Gln, synthetic tRNA1Gln containing s2U34 as sole modification, and unmodified wild-type and mutant tRNA1Gln and tRNA2Gln transcripts demonstrates that the exocyclic sulfur moiety improves tRNA binding affinity to GlnRS 10-fold compared with the unmodified transcript and that an additional fourfold improvement arises from the presence of the cmnm5 moiety. Measurements of Gln–tRNAGln interactions at the ribosome A-site show that the s2U modification enhances binding affinity to the glutamine codons CAA and CAG and increases the rate of GTP hydrolysis by E. coli EF-Tu by fivefold.

Conformationally-Locked N-Glycosides with Selective β-Glucosidase Inhibitory Activity: Identification of a New Non-Iminosugar-Type Pharmacological Chaperone for Gaucher Disease

A series of conformationally locked N-glycosides having a cis-1,2-fused pyranose-1,3-oxazoline-2-thione structure and bearing different substituents at the exocyclic sulfur has been prepared. The polyhydroxylated bicyclic system was built in only three steps by treatment of the corresponding readily available 1,2-anhydrosugar with KSCN using TiO(TFA)(2) as catalyst, followed by S-alkylation and acetyl deprotection. In vitro screening against several glycosidase enzymes showed highly specific inhibition of mammalian β-glucosidase with a marked dependence of the potency upon the nature of the exocyclic substituent. The most potent representative, bearing an S-(ω-hydroxyhexadecyl) substituent, was further assayed as inhibitor of the human lysosomal β-glucocerebrosidase and as pharmacological chaperone in Gaucher disease fibroblasts. Activity enhancements in N370S/N370S mutants analogous to those achieved with the reference compound ambroxol were attained with a more favorable chaperone/inhibitor balance.

Synthesis, crystal structure, spectral characterization, and DFT studies on 4-((1-phenyl-1H-tetrazol-5-ylthio)methyl)benzoic acid

A new thiotetrazole compound, 4-((1-phenyl-1H-tetrazol-5-ylthio)methyl) benzoic acid (1), has been synthesized and characterized by elemental analysis, 1H and 13C NMR, ESI-MS, FT-IR, UV–vis, fluorescence spectra, and single-crystal X-ray diffraction analysis. The structural analysis reveals that compound 1 adopts a nonplanar geometric structure and exhibits an extensive but not uniform π delocalization with all members of the tetrazolyl ring and the exocyclic sulfur atom. A density functional theory (DFT) calculation at B3LYP/6-31G** level of theory was performed to elucidate the structure of this thiotetrazole system. And the time-dependent DFT (TD-DFT) calculations of absorption spectra reveal two electron-transition bands derived from the contribution of π → π* transitions, which are in agreement with experimental results. Moreover, compound 1 exhibits a blue-light emission (λem = 441 nm) in the solid state at room temperature. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 23:435–443, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.21034

Bismuth(III) Saccharinate and Thiosaccharinate Complexes and the Effect of Ligand Substitution on Their Activity against Helicobacter pylori

Five bismuth(III) saccharinate and thiosaccharinate complexes, [Ph2Bi(sac)]∞1, [Bi(sac)3]n2, [Ph2Bi(tsac)]∞4, [PhBi(tsac)2]n5, [Bi(tsac)3]n6 (sacH = saccharin, tsacH = thiosaccharin), have been synthesized and fully characterized. The tendency for ligand redistribution in [Ph2Bi(sac)]∞ has been investigated in solution by NMR spectroscopy. The structures of [Ph2Bi(sac)]∞1 and [Ph2Bi(tsac)]∞4 have been confirmed by X-ray crystallography. In Ph2Bi(sac) the sac ligand is bound to a four-coordinate bismuth center via its imino nitrogen atom with an accompanying long-range Bi–O interaction. However, in the structure of [Ph2Bi(tsac)]∞ the ligand is σ-bound through the exocyclic sulfur atom, giving a thiolate complex, confirming the more thiophilic nature of bismuth(III). Both complexes consist of polymeric chain structures with formally four-coordinated bismuth atoms. The complexes were assessed for their activity against H. pylori. The activity is both ligand dependent and sensitive to the degree of ligand substitution. The saccharinate complexes, 1 and 2, show activity comparable with standard tris-carboxylato bismuth(III) compounds, 6.25 μg/mL, while the activity of the thiolato complexes, 4–6, increases dramatically on increasing the number of thiolate groups from one to three (range 50–6.25 μg/mL). Saccharin, thiosaccharin, and BiPh3 were found to be inactive.