- Intramolecular Electrostatic and General Acid Catalysis in the Hydrolysis of O,S-Thioacetals
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The pH-independent release of thiophenolate ion from phthalaldehydic acid O-methyl S-phenyl thioacetal in H2O at 50 deg C and at pH values where the carboxyl group is ionized is 22 times faster than the corresponding reaction in hydrolysis of the terephthalaldehydic acid derivative.This rate difference arises becouse of electrostatic stabilization of the developing carbanium ion by the neighboring carboxylate ion.In the view of the large amount of C-S bond breaking in the transition state the rate enhancement due to electrostatic effects must be near maximal in water for reactions in which a methoxybenzyl carbonium ion is produced.The plot of log kobsd vs. pH for release of thiosalicylic acid from phthalaldehydic acid O-methyl S-(o-carboxyphenyl) thioacetal at 50 deg C in 50percent dioxane-H2O shows hydronium ion catalysis at low pH, and from pH 3 to 7 the profile is bell shaped.The value of the rate constant k2 for hydronium ion catalyzed reaction of the dianionic species is 6*106 greater than the second-order rate constant kH for hydronium ion catalyzed hydrolysis of the dimethyl ester and is 360-fold greater than the corresponding rate constant of terephthalaldehydic acid O-methyl S-(o-carboxyphenyl) thioacetal.The hydronium ion catalyzed neutral species reaction of phthaladehydic acid O-methyl S-(o-carboxyphenyl) thioacetal is retarded in 50percent dioxane-H2O as compared with H2O, but k2 is accelerated 50-fold.Both carboxyl groups are participating in hydrolysis of the monoanionic species, i.e., intramolecular general acid catalysis is occurring in conjunction with electrostatic stabilization effects.It is likely that intramolecular general acid catalysis also occurs in hydrolysis of benzaldehyde O-methyl S-(o-carboxyphenyl) thioacetal and terephthalaldehydic acid O-methyl S-(o-carboxyphenyl) thioacetal, but rate enhancements are small in comparison with corresponding O,O-acetals.The significant electrostatic stabilization effects in the general-acid-catalyzed reaction of phthalaldehydic acid O-methyl S-(o-carboxyphenyl) thioacetal in contrast with the absence of such effects in the intramolecular general-acid-catalyzed reaction of phthalaldehydic acid O-methyl O-salicyl acetal shows that much more bond breaking is required in the transition state in reaction of the thioacetal.The factors influencing concerted bifunctional catalysis are discussed.
- Fife, Thomas H.,Przystas, Theodore J.
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- First electrospun immobilized molybdenum complex on bio iron oxide nanofiber for green oxidation of alcohols
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Bio iron oxide was synthesized from natural Sesbania sesban plant and modified by a molybdenum complex (Fe2O3/MoSB). Fe2O3/MoSB was deposited on polyvinyl alcohol (PVA) using a conventional single nozzle electrospinning technique (PVA/Fe2O3/MoSB). TEM, SEM, AFM, FT-IR, TGA, EDAX, and elemental analysis were used to determine fiber compositional information. The catalytic efficiency of electrospun PVA/Fe2O3/MoSB nanofiber in the oxidation of alcohols was exploited. The green reactions were conducted at solvent free conditions as a green media in the presence of H2O2 to have the desired aldehydes and tert-butyl hydrogen peroxide to obtain acid products in high yields and excellent selectivity. The survival of this nanocomposite was investigated and it could be reused and recycled in consecutive runs.
- Noghi, Sedighe Abbaspour,Naeimi, Atena,Hamidian, Hooshang
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Read Online
- Scaffold Diversity Inspired by the Natural Product Evodiamine: Discovery of Highly Potent and Multitargeting Antitumor Agents
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A critical question in natural product-based drug discovery is how to translate the product into drug-like molecules with optimal pharmacological properties. The generation of natural product-inspired scaffold diversity is an effective but challenging strategy to investigate the broader chemical space and identify promising drug leads. Extending our efforts to the natural product evodiamine, a diverse library containing 11 evodiamine-inspired novel scaffolds and their derivatives were designed and synthesized. Most of them showed good to excellent antitumor activity against various human cancer cell lines. In particular, 3-chloro-10-hydroxyl thio-evodiamine (66c) showed excellent in vitro and in vivo antitumor efficacy with good tolerability and low toxicity. Antitumor mechanism and target profiling studies indicate that compound 66c is the first-in-class triple topoisomerase I/topoisomerase II/tubulin inhibitor. Overall, this study provided an effective strategy for natural product-based drug discovery. (Figure Presented).
- Wang, Shengzheng,Fang, Kun,Dong, Guoqiang,Chen, Shuqiang,Liu, Na,Miao, Zhenyuan,Yao, Jianzhong,Li, Jian,Zhang, Wannian,Sheng, Chunquan
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p. 6678 - 6696
(2015/09/07)
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- Efficient Cu-catalyzed base-free C-S coupling under conventional and microwave heating. A simple access to S-heterocycles and sulfides
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S-aryl thioacetates can be prepared by reaction of inexpensive potassium thioacetate with both electron-rich and electron-poor aryl iodides under a base-free copper/ligand catalytic system. CuI as copper source affords S-aryl thioacetates in good to excellent yields, by using 1,10-phenanthroline as a ligand in toluene at 100°C after 24 h. Under microwave irradiation the time was drastically reduced to 2 h. Both procedures are simple and involve a low-cost catalytic system. This methodology was also applied to the "one-pot" synthesis of target heterocycles, such as 3H-benzo[c][1,2]dithiol-3-one and 2-methylbenzothiazole, alkyl aryl sulfides, diaryl disulfides and asymmetric diaryl sulfides in good yields.
- Soria-Castro, Silvia M.,Penenory, Alicia B.
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p. 467 - 475
(2013/05/08)
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- CuI-nanoparticles-catalyzed selective synthesis of phenols, anilines, and thiophenols from aryl halides in aqueous solution
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CuI-nanoparticles-catalyzed selective synthesis of phenols, anilines, and thiophenols from aryl halides was developed in the absence of both ligands and organic solvents. Anilines were formed selectively with ammonia competing with hydroxylation and thiophenols were generated selectively with sulfur powder after subsequent reduction competing with hydroxylation and amination.
- Xu, Hua-Jian,Liang, Yu-Feng,Cai, Zhen-Ya,Qi, Hong-Xia,Yang, Chun-Yan,Feng, Yi-Si
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p. 2296 - 2300
(2011/06/17)
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- A general and efficient approach to aryl thiols: Cul-catalyzed coupling of aryl iodides with sulfur and subsequent reduction
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A Cul-catalyzed coupling reaction of aryl iodides and sulfur powder takes place in the presence of K2CO3 at 90 °C. The coupling mixture is directly treated with NaBH4 or triphenylphosphine to afford aryl thiols in good to
- Jiang, Yongwen,Qin, Yuxia,Xie, Siwei,Zhang, Xiaojing,Dong, Jinhua,Ma, Dawei
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supporting information; scheme or table
p. 5250 - 5253
(2009/12/28)
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- Identification of 2-amino-5-(thioaryl)thiazoles as inhibitors of nerve growth factor receptor TrkA
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2-Amino-5-(thioaryl)thiazoles are potent inhibitors of TrkA (e.g., 20h, TrkA IC50 = 0.6 nM) that show anti-proliferative effect in cellular assays. A proposed inhibitor binding mode to TrkA active site is consistent with key SAR observations.
- Kim, Soong-Hoon,Tokarski, John S.,Leavitt, Kenneth J.,Fink, Brian E.,Salvati, Mark E.,Moquin, Robert,Obermeier, Mary T.,Trainor, George L.,Vite, Gregory G.,Stadnick, Linda K.,Lippy, Jonathan S.,You, Dan,Lorenzi, Matthew V.,Chen, Ping
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p. 634 - 639
(2008/09/18)
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- METHOD FOR PRODUCING THIOSALICYLIC ACID
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The present invention relates to a method for causing sodium sulfide or a mixture of sodium sulfide and sulfur to react with diazonium salt formed by diazotizing anthranilic acid, wherein the Na/S atomic ratio as calculated on the basis of the employed sodium sulfide and sulfur is adjusted to within the range of 1.33 to 2.0 during the reaction. Thus is made practicable the manufacture of thiosalicylic acid in a high yield without going through the individual route of isolating and reducing dithiosalicylic acid.
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- A general and highly regio and stereoselective method for the synthesis of (E)-2-(2-arylvinyl)-3,1-benzoxathiin-4-ones through palladium-copper catalysis
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A palladium-copper-catalysed procedure for the synthesis of (E)-2-(2-arylvinyl)-3,1-benzoxathiin-4-ones 5a-5h is developed. 3-[2-(Methoxycarbonyl)phenylthio]propyne 2 reacts with aryl iodides 3a-3h in the presence of bis(triphenylphosphine)palladium(II) dichloride, copper(I) iodide and triethylamine in acetonitrile to furnish the disubstituted alkynes 4a-4h in good yields (70-84%). These on alkaline hydrolysis and subsequent cyclisation of the carboxylic acids formed with copper(I) iodide (20 mol%) and triethylamine in tetrahydrofuran under reflux afford (E)-2-(2-arylvinyl)-3,1-benzoxathiin-4-ones 5a-5h in 61-70% yield rather than the expected benzoxathiepinones 6. The reactions of (E)-2-(2-arylvinyl)-3,1-benzoxathiin-4-ones 5a and 5g with nucleophites and the hydrogenation of compounds 5a, 5b and 5d are also studied.
- Nandi, Bidisha,Kundu, Nitya G.
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p. 1649 - 1655
(2007/10/03)
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- Novel inhibitors of the prenylated protein methyltransferase reveal distinctive structural requirements
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Inhibitors of a prenylated protein methyltransferase were synthesized and evaluated. S-farnesyl-5-fluorothiosalicylic acid and the 5-chloro analog (but not the 4-fluoro, 4-chloro or 3-chloro analogs) were potent inhibitors, as was the parent compound S-farnesyl thiosalicylic acid (FTS), whose methyl ester was far less active. S-geranyl and S-geranylgeranyl thiosalicylic acids were more than ten times less potent than FTS.
- Marciano, Daniele,Aharonson, Ziporet,Varsano, Tal,Haklai, Roni,Kloog, Yoel
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p. 1709 - 1714
(2007/10/03)
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- Elimination reactions of β-Cyano Thioethers: Evidence for a Carbanion Intermediate and a Change in Rate-Limiting Step
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The addition reactions of thiol anions to form adducts with acrylonitrile (1), 1-chloroacrylonitrile (2), and fumaronitrile (3) and the corresponding elimination reactions were examined in aqueous solution, generally containing 8.3percent Me2SO at 25 deg C.Deuterium exchange into the methanethiol and thiosalicylate adducts of 1 is faster than elimination.Deuterium exchange causes biphasic kinetics for elimination reactions in D2O of the p-nitrothiophenol, but not of the pentafluorothiophenol, adducts 1 and 2.The kinetic solvent deuterium isotope effects of knHOH/knDOD = 2.0 for addition of thiosalicylate to form 3 and 1.1-1.2 for addition of β-mercaptoethanol and thioacetic acid anions to form 1 are smaller than the product discrimination isotope effects of kH/kD = 3.2, 2.8 and 3.2 for these reactions.These differences show that the reactions proceed through a carbanion intermediate that is protonated faster than it expels basic thiol anions.These results exclude a concerted mechanism for addition-elimination with a concurrent, separate exchange reaction.The solvent kinetic deuterium isotope effect is 3.9 for the addition of thionitrobenzoate dianion to form 3.Buffer catalysis of elimination becomes more significant with more acidic leaving groups and is larger for 3 than for 1 with a given leaving group.The results show that the rate-limiting step changes from addition-elimination of the thiol anion to proton transfer with decreasing pKa of the thiol; the same change is favored by addition of CN to the α-position for a given thiol.The effect of the α-CN group is attributed to conjugation with the developing double bond in the transition state for elimination.The Broensted slope is β = 0.90 for rate-limiting deprotonation of the pentafluorothiophenol adduct 3 and Broensted-type plots against the pKa of the leaving group have slopes of β1g = -0.25 and -0.54 for predominantly rate-limiting deprotonation and leaving group expulsion, respectively.
- Fishbein, James C.,Jencks, William P.
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p. 5075 - 5086
(2007/10/02)
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- Syntheses of Mercaptobenzoic Acids and Mercaptopyridines Using Elemental Sulfur in the Presence of NaOH-KOH
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Mercaptobenzoic acids and mercaptopyridines were synthesized by using mercaptylation of halogeno compounds with elemental sulfur in the presence of molten salts (NaOH-KOH).This procedure was also applied to the preparation of selenoaryl compounds by using elemental selenium.Based on the behavior of the molten salts and sulfur, Na2S and K2S were considered to be the active species for the mercaptylation.KEYWORDS-mercaptylation; molten salt; o-mercaptobenzoic acid; o-selenobenzoic acid; 2-mercaptopyridine
- Kamiyama, Tsutomu,Enomoto, Saburo,Inoue, Masami
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p. 5184 - 5189
(2007/10/02)
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- Some Reactions of 3,1-Benzoxathian-4-ones
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3,1-Benzoxathian-4-ones (II) have been thiated with Lawesson reagent (I) and also with P4S10 to give a mixture of IV, V and VI.These thianones (II) react too with Grignard reagents to give 4-alkyl/aryl-2-phenyl-3,1-benzoxathian-4-ols (VIII), and with alkoxides and mercaptides to give bis(2-substituted phenyl) disulphides (IX). 2-Phenyl-1, 3-benzodithiane-4-thione (Vc) reacts with primary amines and hydrazines to give the imino and hydrazono derivatives (X).The reactions of Vc with diphenyl diazomethane, diazofluorene and copper-bronze have also been studied.
- El-Barbary, A. A.,Hammouda, H. A.,El-Borai, M.
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p. 770 - 773
(2007/10/02)
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- The Influence of Intramolecular Hydrogen Bonding on Proton-Transfer Reactions. A Temperature-Jump Study of Acid-Base Reactions Involving Substituted Salicylic Acids
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The temperature-jump relaxation technique has been used to study the kinetics of proton transfer between salicylic acid derivatives (3,5-dinitrosalicylic acid, DNSA, and thiosalicylic acid, TSA) and a second donor/acceptor system (ammonia or cacodylic acid).Depending on the system, the investigations have been carried out between pH 6.0 and 9.0.The concentration dependencies of the observed relaxation time demonstrate that not only the direct proton-transfer process but also the hydrolytic or protolytic pathway, respectively, contribute to the overall reaction under the given conditions.The rate constants for proton transfer from the monoprotonated salicylate anions to the acceptors NH3, cacodylate-, and OH- are far below the diffusion-controlled values, even if these reactions are thermodinamically favored.This decrease in reactivity indicates that the proton to be transferred is engaged in an internal H bond in the mononegative salicylate anions.The strength of the internal H bond is much lower in TSA than in DNSA.
- Diebler, H.,Secco, F.,Venturini, M.
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p. 4229 - 4232
(2007/10/02)
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- Conformational Behaviour of Medium-sized Rings. Part 10. Dithiosalicylides and Trithiosalicylides
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The trithiosalicylide derivatives (8)-(11) have been synthesised and shown by temperature-dependent 1H n.m.r. spectroscopy to exist in solution as ring inverting (35a)(35b) enantiomeric helical conformations with trans-thioester linkages.The free energies of activation for these conformational changes are ca. 10 kcal mol-1 higher than those for the similar process in the corresponding trisalicylides.In contrast with the trisalicylides, the trithiosalicylides can only ring invert between enantiomeric helical conformations via intermediates containing a cis-thioester linkage.The dithiosalicylide derivatives (3)-(7) have been synthesised; the temperature dependence of the 1H n.m.r. spectrum of di-o-thiothymotide (7) has been interpreted in terms of ring inversion (40a)(40b) between enantiomeric boat conformations.Comparison of the ΔG value of 24.6 kcal mol-1 for this conformational change with that of 17.7 kcal mol-1 previously obtained for di-o-thymotide (41) suggests that cis-thioester linkages are subject to more resonance stabilisation than are cis-ester linkages.
- Guise, G. Bruce,Ollis, W. David,Peacock, Judith A.,Stephanatou, Julia Stephanidou,Stoddart, J. Fraser
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p. 1637 - 1648
(2007/10/02)
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- Aspects of Tautomerism: Part X - Neighbouring Group Effects on the Structure and Reactivity Patterns of Acid Chlorides
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The influence of neighbouring groups on the structure and reactivity patterns of over one hundred acid chlorides derived from γ- and δ-keto acids, 1,2- and 1,3-dicarboxylic acid half-esters and diacid chlorides have been examined.Contrary to reports in the literature, text books and monographs, evidence has been obtained for the non-existence of tautomerism between the isomeric pairs of either acid chlorides or half-ester acid chlorides.ce.
- Bhatt, M. Vivekananda,El Ashry, Shaker H.,Somayaji, Vishwanatha
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p. 473 - 486
(2007/10/02)
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- Pesticidal compositions containing phosphoric esters and divalent sulphur compounds
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Pesticidal composition comprising: a pesticidal, phosphoric ester the molecule of which has at least one alkyl group of 1 to 3 carbon atoms, 0.05 to 10% of an agent stabilizing the said ester against decomposition by protonisation, together with adjuvants characterized in that the stabilizing agent comprises at least one sulphur compound containing per molecule at least one divalent sulphur atom of which one valence is bonded to an atom chosen from sulphur, carbon, nitrogen, hydrogen, and metals capable of giving a salt, the other valence being bonded to an atom chosen from hydrogen, the carbon atom already noted, a second carbon atom, the nitrogen atom already noted, a second nitrogen atom, the metal atom already noted in the case of a metal of valence greater than one, a second atom of metal and oxygen when the first valence is not attached to an atom of hydrogen, the proportion of sulphur calculated with reference to the weight of the sulphur compound being between 5 and 99%. Process for stabilizing a phosphoric ester of which the molecule possesses at least one alkyl group containing 1 to 3 carbon atoms characterized in that there is added to the phosphoric ester or to a mixture which contains it, 0.05 to 10% calculated on the weight of the phosphoric acid ester of an agent capable of stabilizing the said phosphoric ester against protonisation and comprising at least one sulphur compound such as that defined thereupon.
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