Charged pyridinium oximes with thiocarboxamide moiety are equally or less effective reactivators of organophosphate-inhibited cholinesterases compared to analogous carboxamides.

The organophosphorus antidotes, so-called oximes, are able to restore the enzymatic function of acetylcholinesterase (AChE) or butyrylcholinesterase (BChE) via cleavage of organophosphate from the active site of the phosphylated enzyme. In this work, the charged pyridinium oximes containing thiocarboxamide moiety were designed, prepared and tested. Their stability and pKa properties were found to be analogous to parent carboxamides (K027, K048 and K203). The inhibitory ability of thiocarboxamides was found in low µM levels for AChE and high µM levels for BChE. Their reactivation properties were screened on human recombinant AChE and BChE inhibited by nerve agent surrogates and paraoxon. One thiocarboxamide was able to effectively restore function of NEMP- and NEDPA-AChE, whereas two thiocarboxamides were able to reactivate BChE inhibited by all tested organophosphates. These results were confirmed by reactivation kinetics, where thiocarboxamides were proved to be effective, but less potent reactivators if compared to carboxamides.

Mononucleoside phosphorodithiolates as mononucleotide prodrugs.

The synthesis and in vitro anti-HIV activity of a novel series of pronucleotides are reported. These prodrugs were characterized by a phosphorodithiolate structure, incorporating two O-pivaloyl-2-oxyethyl substituents as biolabile phosphate protections. The compounds were obtained following an original one-pot three-step procedure, involving the formation of a phosphorodithioite intermediate which is in situ oxidized. In vitro, comparative anti-HIV evaluations demonstrate that such original prodrugs are able to allow the efficient intracellular release of the corresponding 5'-mononucleotide. The pronucleotide of 2',3'-dideoxyadenosine (ddA) 3 exhibited a very potent antiretroviral effect with 50% effective concentration (EC50) values in nanomolar concentration range in various cell lines. In primary monocytes/macrophages, this derivative was 500 times more potent in inhibiting HIV replication (EC50 0.23 pM) than ddA and the selectivity index of the prodrug is fifty times higher than the one of the parent nucleoside.

Synthesis and Biological Evaluation of Dithiobisacetamides as Novel Urease Inhibitors.

Thirty-eight disulfides containing N-arylacetamide were designed and synthesized in an effort to develop novel urease inhibitors. Biological evaluation revealed that some of the synthetic compounds exhibited strong inhibitory potency against both cell-free urease and urease in intact cell with low cytotoxicity to mammalian cells even at concentration up to 250 µM. Of note, 2,2'-dithiobis(N-(2-fluorophenyl)acetamide) (d7), 2,2'-dithiobis(N-(3,5-difluorophenyl)acetamide) (d24), and 2,2'-dithiobis(N-(3-fluorophenyl)acetamide) (d8) were here identified as the most active inhibitors with IC50 of 0.074, 0.44, and 0.81 µM, showing 32- to 355-fold higher potency than the positive control acetohydroxamic acid. These disulfides were confirmed to bind urease without covalent modification of the cysteine residue and to inhibit urease reversibly with a mixed inhibition mechanism. They also showed very good anti-Helicobacter pylori activities with d8 showing a comparable potency to the clinical used drug amoxicillin. The impressive in vitro biological profile indicated their immense potential as therapeutic agents to tackle H. pylori caused infections.

Diversity-oriented routes to thiopeptide antibiotics: total synthesis and biological evaluation of micrococcin P2.

We report the first total synthesis of micrococcin P2 (MP2, 1) by a diversity-oriented route that incorporates a number of refinements relative to earlier syntheses. Biological data regarding the activity of 1 against a range of human pathogens are also provided. Furthermore, we disclose a chemical property of MP2 that greatly facilitates medicinal chemistry work in the micrococcin area and describe a method to obtain MP2 by fermentation in B. subtilis.

Synthesis and Antiproliferative Activity of New Thiosemicarboxamide Derivatives.

To discover new anticancer agents, two series of thiosemicarboxamide derivatives were synthesized and evaluated for their antiproliferative activity against human cancer cells in vitro. Most target compounds (especially 3f, 3g, and 3h) exhibit potent antiproliferative activity against HeLa cells. Importantly, compound 3h, bearing a 4-methylphenyl substituent at N position of thiourea moiety, has significant and broad-spectrum inhibitory activities against cancer cells (HepG2, HeLa, MDA-MB231, A875, and H460 cells) with low IC50 values (<5.0 µM) and shows low toxicity to normal LO2 and MRC-5 cells. Further studies show that compound 3h exerts high inhibitory activity in cancer cells by inducing the G2/M-phase arrest of cancer cells. Collectively, this study presents compound 3h as a new entity for the development of cell cycle arrest inducers for the treatment of cancer.

Thiomers of Chitosan and Cellulose: Effective Biosorbents for Detection, Removal and Recovery of Metal Ions from Aqueous Medium.

Removal of toxic metal ions using adsorbents is a well-known strategy for water treatment. While chitosan and cellulose can adsorb weakly some types of metals, incorporating thiols as metal chelating agents can improve their sorption behaviors significantly. Presented in this review are the various chemical modification strategies applicable for thiolation of chitosan and cellulose in the forms of mercaptans, xanthates and dithiocarbamates. Moreover, much attention has been paid to the specific strategies for controlling the thiolation degree and characterization approaches for establishing the structure-property relationship. Also, the kinetics and isotherm models that elucidate the adsorption processes and mechanisms induced by the thiomers have been explained. These thiomers have found great potentials in the applications associated with metal removal, metal recovery and metal detection.

Hexavalent thiofucosides to probe the role of the Aspergillus fumigatus lectin FleA in fungal pathogenicity.

Aspergillus fumigatus is a pathogenic fungus infecting the respiratory system and responsible for a variety of life-threatening lung diseases. A fucose-binding lectin named FleA which has a controversial role in A. fumigatus pathogenesis was recently identified. New chemical probes with high affinity and enzymatic stability are needed to explore the role of FleA in the infection process. In this study, we developed potent FleA antagonists based on optimized and non-hydrolysable thiofucoside ligands. We first synthesized a set of monovalent sugars showing micromolar affinity for FleA by isothermal titration calorimetry. The most potent derivative was co-crystallized with FleA to gain insights into the binding mode in operation. Its chemical multimerization on a cyclodextrin scaffold led to an hexavalent compound with a significantly enhanced binding affinity (Kd = 223 ± 21 nM) thanks to a chelate binding mode. The compound could probe the role of bronchial epithelial cells in a FleA-mediated response to tissue invasion.

Novel 1-(prop-2-yn-1-ylamino)-2,3-dihydro-1H-indene-4-thiol derivatives as potent selective human monoamine oxidase B inhibitors: Design, SAR development, and biological evaluation.

Successes have been achieved in developing human monoamine oxidase B (hMAO-B) inhibitors as anti-Parkinson's disease (PD) drugs. However, low efficiency and unwanted side effects of the marketed hMAO-B inhibitors hamper their medical applications, therefore, novel potent selective hMAO-B inhibitors are still of great interest. Herein we report 1-(prop-2-yn-1-ylamino)-2,3-dihydro-1H-indene-4-thiol derivatives as hMAO-B inhibitors, which were designed by employing a fragment-based drug design strategy to link rasagiline to hydrophobic fragments. Among the synthesized 31 compounds, K8 and K24 demonstrated very encouraging hMAO-B inhibitory activities and selectivity over hMAO-A, better than rasagiline and safinamide. In vitro studies indicated that K8 and K24 are nontoxic to nervous tissue cells and they have considerable effects against ROS formation and potential neuroprotective activity. Further mice behavioral tests demonstrated these two compounds have good therapeutic effects on MPTP-induced PD model mice. All these experiment results suggest that compounds K8 and K24 can be promising candidates for further research for treatment of PD.

Structure-based bioisosterism design of thio-benzoxazepinones as novel necroptosis inhibitors.

Necroptosis is reported to play a critical role in contributing to a variety of human pathologies. The benzoxazepinone GSK'772 is a potent necroptosis inhibitor optimized using a hit from a DNA-encoded library, which is currently in phase II clinical trials for psoriasis, rheumatoid arthritis, and ulcerative colitis. In the present study, the bioisosterism strategy was applied to replace the amide and benzene ring of GSK'772 based on the co-crystal structure of GSK'772 with its binding target RIPK1. As a result, the novel thio-benzoxazepinones exhibited higher anti-necroptosis activity in a human HT-29 cell necroptosis model. The effect on anti-necroptosis activity by the chirality was significantly reduced in the thio-benzoxazepinones, which was explained by the ligand conformation calculation. Among these analogues, compound 11 (S) and 12 (R) specifically inhibited necroptosis rather than apoptosis with EC50 values of 2.8 and 22.6 nM. They blocked necrosome formation by inhibiting the phosphorylation of RIPK1, RIPK3 and MLKL in necroptotic cells. Collectively, the highly potent thio-benzoxazepinones represent promising lead structures for further development of necroptosis-related diseases.

Synthesis of sulfonopeptides.

Sulfonopeptides as the sulfur analogues of natural peptides have been widely used as enzyme inhibitors due to their tetrahedral sulfonamide moiety, which can mimic the transition-state analogues of hydrolysis of the ester and amide bonds. Synthetic methods of sulfonopeptides are reviewed. The synthetic methods of sulfonopeptides include the condensation of N-protected amino acid/peptide acids and 2-aminoalkanesulfonic acids, coupling of N-protected 2-aminoalkanesulfonyl chlorides and amino acid esters/peptide esters, sulfinylation of amino acid esters/peptide esters with N-protected 2-aminoalkanesulfinyl chlorides and subsequent oxidation, the alkylation of taurine-containing peptides, and the displacement of N-aminoacyl/peptidyl 2-aminoalkyl halides/methanesulfonates with sulfites. Hybrid sulfonophosphinopeptides are prepared through the Mannich-type reaction of N-protected 2-aminoalkanesulfonamides/peptidylsulfonamides, aldehydes, and aryldichlorophosphines/phosphorus trichloride followed by the aminolysis with amino acid/peptide esters or hydrolysis. The developed synthetic methods provide diverse synthetic routes for biologically important sulfonopeptides as the candidates of medicinal agents.

Development of phenyltriazole thiol-based derivatives as highly potent inhibitors of DCN1-UBC12 interaction.

Defective in cullin neddylation 1(DCN1) is a co-E3 ligase that is important for cullin neddylation. Dysregulation of DCN1 highly correlates with the development of various cancers. Herein, from the initial high-throughput screening, a novel hit compound 5a containing a phenyltriazole thiol core (IC50 value of 0.95 µM for DCN1-UBC12 interaction) was discovered. Further structure-based optimization leads to the development of SK-464 (IC50 value of 26 nM). We found that SK-464 not only directly bound to DCN1 in vitro, but also engaged cellular DCN1, suppressed the neddylation of cullin3, and hindered the migration and invasion of two DCN1-overexpressed squamous carcinoma cell lines (KYSE70 and H2170). These findings indicate that SK-464 may be a novel lead compound targeting DCN1-UBC12 interaction.

New multitarget directed benzimidazole-2-thiol-based heterocycles as prospective anti-radical and anti-Alzheimer's agents.

A series of new heterocycles (4-18) was synthesized by the structural modification of benzimidazole-2-thiol (BT, 2-MBI). The structures of the synthesized compounds were confirmed with the help of high-resolution mass spectrometry (HRMS) and 1 HNMR spectroscopy. High inhibitions of the oxidants such as ABTS and DPPH were observed for compounds 9 [IC50 (s) = 167.4 µM (ABTS), 139.5 µM (DPPH)], 10 [IC50 (s) = 186.5 µM (ABTS), 155.4 µM (DPPH)], 11 [IC50 (s) = 286.1 µM (ABTS), 189.1 µM (DPPH)], 12 [IC50 (s) = 310.8 µM (ABTS), 162.2 µM (DPPH)], 14 [IC50 (s) = 281.3 µM (ABTS), 205.7 µM (DPPH)], 15 [IC50 (s) = 284.1 µM (ABTS), 177.3 µM (DPPH)], and 16 [IC50 (s) = 344.7 µM (ABTS), 270.2 µM (DPPH)] as compared with Ascorbic acid [IC50 (s) = 340.9 µM (ABTS), 164.3 µM (DPPH)]. The anti-Alzheimer's activity was performed in vitro against cholinesterase enzymes (AChE, BChE). Compound 11 was able to show significant inhibitions [IC50 (s) = 121.2 µM (AChE), 38.3 µM (BChE)] as against that of galantamine [IC50 (s) = 139.4 µM (AChE), 40.3 µM (BChE)]. Compound 14 was found as a very good inhibitor of butyrylcholinesterase (IC50 = 35.4 µM) as compared with standard galantamine. Molecular docking was further performed to investigate the mechanism of anticholinesterase activity.

Decarboxylative thiolation of redox-active esters to free thiols and further diversification.

Thiols are important precursors for the synthesis of a variety of pharmaceutically important sulfur-containing compounds. In view of the versatile reactivity of free thiols, here we report the development of a visible light-mediated direct decarboxylative thiolation reaction of alkyl redox-active esters to free thiols based on the abundant carboxylic acid feedstock. This transformation is applicable to various carboxylic acids, including primary, secondary, and tertiary acids as well as natural products and drugs, forging a general and facile access to free thiols with diverse structures. Moreover, the direct access to free thiols affords an advantage of rapid in situ diversification with high efficiency to other important thiol derivatives such as sulfide, disulfide, thiocyanide, thioselenide, etc.

Allosteric kidney-type glutaminase (GLS) inhibitors with a mercaptoethyl linker.

A series of allosteric kidney-type glutaminase (GLS) inhibitors possessing a mercaptoethyl (SCH2CH2) linker were synthesized in an effort to further expand the structural diversity of chemotypes derived from bis-2-(5-phenylacetamido-1,3,4-thiadiazol-2-yl)ethyl sulfide (BPTES), a prototype allosteric inhibitor of GLS. BPTES analog 3a with a mercaptoethyl linker between the two thiadiazole rings was found to potently inhibit GLS with an IC50 value of 50 nM. Interestingly, the corresponding derivative with an n-propyl (CH2CH2CH2) linker showed substantially lower inhibitory potency (IC50 = 2.3 µM) while the derivative with a dimethylsulfide (CH2SCH2) linker showed no inhibitory activity at concentrations up to 100 µM, underscoring the critical role played by the mercaptoethyl linker in the high affinity binding to the allosteric site of GLS. Additional mercaptoethyl-linked compounds were synthesized and tested as GLS inhibitors to further explore SAR within this scaffold including derivatives possessing a pyridazine as a replacement for one of the two thiadiazole moiety.

Ruthenium(II) Phosphine/Mercapto Complexes: Their in Vitro Cytotoxicity Evaluation and Actions as Inhibitors of Topoisomerase and Proteasome Acting as Possible Triggers of Cell Death Induction.

In this paper, a series of new ruthenium complexes of the general formula [Ru(NS)(dpphpy)(dppb)]PF6 (Ru1-Ru3), where dpphpy = diphenyl-2-pyridylphosphine, NS ligands = 2-thiazoline-2-thiol (tzdt, Ru1), 2-mercaptopyrimidine (pySm, Ru2), and 4,6-diamino-2-mercaptopyrimidine (damp, Ru3), and dppb = 1,4-bis(diphenylphosphino)butane, were synthesized and characterized by elemental analysis, spectroscopic techniques (IR, UV/visible, and 1D and 2D NMR), and X-ray diffraction. In the characterization, the correlation between the phosphorus atoms and their respective aromatic hydrogen atoms of the compounds in the assignment stands outs, by 1H-31P HMBC experiments. The compounds show anticancer activities against A549 (lung) and MDA-MB-231 (breast) cancer cell lines, higher than the clinical drug cisplatin. All of the complexes are more cytotoxic against the cancer cell lines than against the MRC-5 (lung) and MCF-10A (breast) nontumorigenic human cell lines. For A549 tumor cells, cell cycle analysis upon treatment with Ru2 showed that it inhibits the mitotic phase because arrest was observed in the Sub-G1 phase. Additionally, the compound induces cell death by an apoptotic pathway in a dose-dependent manner, according to annexin V-PE assay. The multitargeted character of the compounds was investigated, and the biomolecules were DNA, topoisomerase IB, and proteasome, as well as the fundamental biomolecule in the pharmacokinetics of drugs, human serum albumin. The experimental results indicate that the complexes do not target DNA in the cells. At low concentrations, the compounds showed the ability to partially inhibit the catalytic activity of topoisomerase IB in the process of relaxation of the DNA plasmid. Among the complexes assayed in cultured cells, complex Ru3 was able to diminish the proteasomal chymotrypsin-like activity to a greater extent.

Using sulfuramidimidoyl fluorides that undergo sulfur(VI) fluoride exchange for inverse drug discovery.

Drug candidates that form covalent linkages with their target proteins have been underexplored compared with the conventional counterparts that modulate biological function by reversibly binding to proteins, in part due to concerns about off-target reactivity. However, toxicity linked to off-target reactivity can be minimized by using latent electrophiles that only become activated towards covalent bond formation on binding a specific protein. Here we study sulfuramidimidoyl fluorides, a class of weak electrophiles that undergo sulfur(VI) fluoride exchange chemistry. We show that equilibrium binding of a sulfuramidimidoyl fluoride to a protein can allow nucleophilic attack by a specific amino acid side chain, which leads to conjugate formation. We incubated small molecules, each bearing a sulfuramidimidoyl fluoride electrophile, with human cell lysate, and the protein conjugates formed were identified by affinity chromatography-mass spectrometry. This inverse drug discovery approach identified a compound that covalently binds to and irreversibly inhibits the activity of poly(ADP-ribose) polymerase 1, an important anticancer target in living cells.

Photoactivatable Odorants for Chemosensory Research.

The chemosensory system of any animal relies on a vast array of detectors tuned to distinct chemical cues. Odorant receptors and the ion channels of the TRP family are all uniquely expressed in olfactory tissues in a species-specific manner. Great effort has been made to characterize the molecular and pharmacological properties of these proteins. Nevertheless, most of the natural ligands are highly hydrophobic molecules that are not amenable to controlled delivery. We sought to develop photoreleasable, biologically inactive odorants that could be delivered to the target receptor or ion channel and effectively activated by a short light pulse. Chemically distinct ligands eugenol, benzaldehyde, 2-phenethylamine, ethanethiol, butane-1-thiol, and 2,2-dimethylethane-1-thiol were modified by covalently attaching the photoremovable protecting group (8-cyano-7-hydroxyquinolin-2-yl)methyl (CyHQ). The CyHQ derivatives were shown to release the active odorant upon illumination with 365 and 405 nm light. We characterized their bioactivity by measuring activation of recombinant TRPV1 and TRPA1 ion channels expressed in HEK 293 cells and the electroolfactogram (EOG) response from intact mouse olfactory epithelium (OE). Illumination with 405 nm light was sufficient to robustly activate TRP channels within milliseconds of the light pulse. Photoactivation of channels was superior to activation by conventional bath application of the ligands. Photolysis of the CyHQ-protected odorants efficiently activated an EOG response in a dose-dependent manner with kinetics similar to that evoked by the vaporized odorant amyl acetate (AAc). We conclude that CyHQ-based, photoreleasable odorants can be successfully implemented in chemosensory research.

Design and synthesis of efficient heavy-atom-free photosensitizers for photodynamic therapy of cancer.

Novel thiocarbonyl derivatives (NIS and CRNS) with excellent ROS generation abilities are synthesized and studied as potential photosensitizers for one- and two-photon excited photodynamic therapy. In particular, NIS-Me and CRNS display outstanding phototoxicity toward HeLa cells under two-photon excitation (800 nm) with negligible dark toxicity.

Synthesis of Thiol Derivatives of Biological Active Compounds for Nanotechnology Application.

An efficient method of thiol group introduction to the structure of common natural products and synthetic active compounds with recognized biological efficacy such genistein (1), 5,11-dimethyl-5H-indolo[2,3-b]quinolin (2), capecitabine (3), diosgenin (4), tigogenin (5), flumethasone (6), fluticasone propionate (7), ursolic acid methyl ester (8), and ß-sitosterol (9) was developed. In most cases, the desired compounds were obtained easily via two-step processes involving esterification reaction employing S-trityl protected thioacetic acid and the corresponding hydoxy-derivative, followed by removal of the trityl-protecting group to obtain the final compounds. The results of our preliminary experiments forced us to change the strategy in the case of genistein (1), and the derivatization of diosgenin (4), tigogenin (5), and capecitabine (3) resulted in obtaining different compounds from those designed. Nevertheless, in all above cases we were able to obtain thiol-containing derivatives of selected biological active compounds. Moreover, a modelling study for the two-step thiolation of genistein and some of its derivatives was accomplished using the density functional theory (B3LP). A hypothesis on a possible reason for the unsuccessful deprotection of the thiolated genistein is also presented based on the semiempirical (PM7) calculations. The developed methodology gives access to new sulphur derivatives, which might find a potential therapeutic benefit.

Thiyl Radicals: Versatile Reactive Intermediates for Cyclization of Unsaturated Substrates.

Sulfur centered radicals are widely employed in chemical synthesis, in particular for alkene and alkyne hydrothiolation towards thioether bioconjugates. The steadfast radical chain process that enables efficient hydrothiolation has been explored in the context of cascade reactions to furnish complex molecular architectures. The use of thiyl radicals offers a much cheaper and less toxic alternative to the archetypal organotin-based radical methods. This review outlines the development of thiyl radicals as reactive intermediates for initiating carbocyclization cascades. Key developments in cascade cyclization methodology are presented and applications for natural product synthesis are discussed. The review provides a chronological account of the field, beginning in the early seventies up to very recent examples; a span of almost 50 years.