Replacement Of Sulfur Research Articles

Zur Chemie CO‐ und CS‐funktioneller Pentaazaspiro[4.5]decane: Ringöffnungs‐ und Ringverengungsreaktionen

On the Chemistry of CO and CS Functional Pentaazaspiro[4.5]decanes: Ring Opening and Ring Contraction Reactions[4.5]‐Spiropentaazacycles 1–5 containing CO or CS functions react with methylenetriphenylphosphorane, depending upon the ring position of the CO and CS groups, either within the scheme of a Wittig reaction (6, 7) or under opening of the six‐membered ring to give cyclic orthoamides (8, 9). With trimethyloxonium tetrafluoroborate, in addition to the replacement of sulfur against oxygen, the contraction of the ring system to give a [4.4]‐spirotetraazacycle 10 is observed.

Biosynthesis of 5-methylaminomethyl-2-selenouridine, a naturally occurring nucleoside in Escherichia coli tRNA

A selenium-containing nucleoside, 5-methylaminomethyl-2-selenouridine (mnm 5se 2U), is present in lysine- and glutamate-isoaccepting tRNA species of Escherichia coli. The synthesis of mnm 5se 2U is optimum ( 4 mol 100 mol tRNA) when selenium is present at about 1 μ m concentration and is neither decreased by a high (8 m m) level of sulfur in the medium nor increased by excessive (10 or 100 μ m) levels of selenium. Lysine- and glutamate-isoaccepting tRNA species that contain 5-methylaminomethyl-2-thiouridine (mnm 5s 2U) coexist with the seleno-tRNAs in E. coli cells and a reciprocal relationship between the mnm 5se 2U- and the mnm 5s 2U-containing species is maintained under a variety of growth conditions. The complete 5-methylaminomethyl side chain is not a prerequisite for introduction of selenium at the 2-position. In E. coli mutants deficient in the ability to synthesize the 5-methylaminomethyl substituent, both the 2-thiouridine and the corresponding 2-selenouridine derivatives of intermediate forms are accumulated. Broken cell preparations of E. coli synthesize mnm 5se 2U in tRNAs by an ATP-dependent process that appears to involve the replacement of sulfur in mnm 5s 2U with selenium.

Oxidation of copper chevrel compound Cu xMo 6S 8 (x∼2)

Oxidation of Chevrel-type Cu xMo 6S 8 (x ∼2) has been studied below 650 °C in air. Data of differential thermal analysis and thermogravimetry revealed that the oxidation progressed stepwise. The first reaction starts at 200 °C, forming CuO and Cu ∼1Mo 6S 8. The heterogeneous oxidation of Cu ∼1Mo 6S 8 particles proceeds very rapidly between 300° and 350 °C, where the oxidized phase was supposed to be amorphous. Further heating above 350 °C produces CuMoO 4, MoO 3, and SO 2 gas as oxidation products. The replacement of sulfur with oxygen in Cu-Chevrel compound was not found in the present experiments.

Composition and temperature-induced instabilities in the Chevrel phases InMo 6S 8−xSe x

We report the effect of selenium for sulfur replacement and of temperature on both the structural and physical properties of the Chevrel phases InMo 6S 8−xSe x. X-ray studies show phase transitions that are the first known rhomboderal to rhomboderal phase transitions reported for Chevrel phases. They are characterized by a large discontinuous change in the rhomboderal angle α r of about 2°. The temperatures at which the instabilities occur correlate with the observed anomalies in both magnetic and transport properties as well as with the presence of endothermic peaks in calorimetry measurements.

Regio- and stereoselective reductive replacement of allylic oxygen, sulfur, and selenium functional groups by hydride via catalytic activation by palladium(0) complexes

Regio- and stereoselective reductive replacement of allylic oxygen, sulfur, and selenium functional groups by hydride via catalytic activation by palladium(0) complexes

Penetration of cephalosporins and corresponding 1-oxacephalosporins through the outer layer of Gram-negative bacteria and its contribution to antibacterial activity.

1-Oxacephalosporins had a higher ability to penetrate through the outer layer of the envelope of gram-negative bacteria than the corresponding cephalosporins. In spite of the liability of 1-oxa congeners to beta-lactamases, they attained higher periplasm concentrations at a given concentration outside the cells. The replacement of sulfur in the cephem nucleus by oxygen was accompanied by an increment of the hydrophilic character of the molecule, which suggests that this character was favorable for outer layer penetration. 1-Oxacephalosporins showed enhanced antibacterial activity in short-term measurement and exerted their antibacterial action at lower periplasm concentrations. Thus, the enhanced antibacterial activity of 1-oxacephalosporins seems to be due to their higher penetrability and their intrinsic inhibitory activity against the peptidoglycan biosynthesis system.

Two Efficient Methods for Replacement of Sulfur by Oxygen in a Thionolactone

Abstract Selective methods for conversion of thionoesters or thiono-lactones to the corresponding ordinary esters or lactones through replacement of sulfur by oxygen are generally lacking, apart from the long known reaction using aqueous silver nitrate1 and related processes with lead1 or mercury2 carboxylates. Our recent preparation of bicyclic thionolactone 1 3 affords a convenient substrate for examination of possible reagents for this transformation. A particularly useful property of 1 is that tetrahedral intermediates 2 and 3, formed on nucleophilic addition of Nu− to 1, have a stereoelectronically favored3,4 pathway for cleavage of the lactone bridge. Such cleavage in 1 is effectively irreversible, since it will be quickly followed by inversion to the stable diequatorial conformer of cis-3-hydroxycyclohexaneacetic acid (4) or an appropriate derivative, depending on the specific nature of Nu−. This feature makes 1 a sensitive test of methods for replacement of sulfur by oxygen without competing ruptu...

1-Oxacephalosporins: enhancement of .beta.-lactam reactivity and antibacterial activity

The effect of replacement of sulfur in the cephem nucleus by oxygen upon the beta-lactamase stability, infrared carbonyl frequency of the beta-lactam ring, and antibacterial activity was investigated. The replacement reduced the stability of beta-lactam compounds to beta-lactamases, increased the IR frequencies, and enhanced the intrinsic antibacterial activity against bacterial strains without beta-lactamase. The instability of 1-oxacephalosporins to beta-lactamases, in other words, high reactivity to the enzymes, seemed to be due to the enhanced chemical reactivity of their beta-lactam rings which was indicated by their higher IR beta-lactam carbonyl frequencies. Based on a view that acylation of the enzyme by beta-lactam compounds occurred in both cases of beta-lactamase hydrolysis and target enzyme inhibition, the suggestion was made that one of the factors which conferred the higher intrinsic antibacterial activity on 1-oxacephalosporins was their high reactivity to the target enzyme(s), as was the case with beta-lactamases.

Transmutation of natural amino acid residues: replacement of sulfur by oxygen in derivatives of cysteine and other mercaptans

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTransmutation of natural amino acid residues: replacement of sulfur by oxygen in derivatives of cysteine and other mercaptansSue Kirkman and Richard WolfendenCite this: J. Am. Chem. Soc. 1978, 100, 18, 5943–5944Publication Date (Print):August 1, 1978Publication History Published online1 May 2002Published inissue 1 August 1978https://doi.org/10.1021/ja00486a056RIGHTS & PERMISSIONSArticle Views50Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (287 KB) Get e-Alerts Get e-Alerts

Cyanoguanidine-thiourea equivalence in the development of the histamine H2-receptor antagonist, cimetidine.

In the histamine H2-receptor antagonist metiamide (2a) isosteric replacement of thione sulfur (=S) by carbonyl oxygen (=O) or imino nitrogen (=NH) affords the urea 2c and guanidine 2d which are antagonists of decreased potency. The guanidine is very basic and at physiological pH is completely protonated. However, introduction of strongly electronegative substituents into the guanidine group reduces basicity and gives potent H2-receptor antagonists, viz. the cyanoguanidine 2b (cimetidine, "Tagamet") and nitroguanidine 2e. A correspondence between the activity of thioureas and cyanoguanidines is demonstrated for a series of structures 1-4. The close correspondence between cyanoguanidine and thiourea in many physicochemical properties and the pharmacological equivalence of these groups in H2-receptor antagonists leads to the description of cyanoguanidine and thiourea as bioisosteres. Acid hydrolysis of the cyanoguanidine 2b yields the carbamoylguanidine 2f at ambient temperatures and the guanidine 2d at elevated temperatures. Cimetidine is slightly more active than metiamide in vivo as an inhibitor of histamine-stimulated gastric acid secretion and has clinical use in the treatment of peptic ulcer and associated gastrointestinal disorders.

N‐(morpholinothio)imides as curing agents in semiefficient vulcanization systems

AbstractSemiefficient vulcanization systems (semi‐EV) are often used when a stock requires good aging properties as well as good fatigue resistance. A partial replacement of sulfur in a conventional cure system with 4,4′‐dithiobismorpholine or 2‐mercaptabenzothiazyl 4‐morpholino disulfide (BMD) is an example of semi‐EV system. However, with BMD the scorch time is not always long enough for multisteps involved in the manufacturing of tires. Such new cure retarders as N‐(cyclohexylthio)phalimide or N, N′‐bis(cyclohexylthio)oxanilide showed very little efficiency in BMD cure systems. This paper describes the usage of new curing agents, (N‐morpholinothio)imides, which can overcome the disadvantage of scorchness in BMD cure system and provide excellent aging properties. This is rationalized by the formation of BMD during vulcanization. The facile formation of BMD from N‐(4‐morpholinothio)phthalimide (MTP) and 2‐mercaptobenzothiazole (MBT) serves to illustrate the feasibility of in situ formation of BMD during cure and to explain long scorch time observed with N‐(4‐morpholinothio)imides.

Hydro-osmotic activity of ‘carba’ analogues of oxytocin and [8-Arginine] vasopressin on frog ( Rana esculenta) bladder

The biological potency of neurohypophysial hormone analogues in stimulating water transport across the frog bladder ( Rana esculenta) was estimated from the pD 2 (negative logarithm of the peptide concentration eliciting 50% of its maximal hydroosmotic effect) and from the maximal response. Most analogues elicited maximal responses similar to those of the natural hormones. Both replacement of sulfur by a methylene group in the disulfide bridge and omission of the terminal amino group in oxytocin reduced hydroosmotic activity; carba substitution in oxytocin led to a greater drop in pD 2 than the same substitution in deamino-oxytocin. On the contrary, the effects of substituting phenylalanine for tyrosine and of omitting the amino group were almost additive. Elimination of the carboxyl-terminal tripeptide sequence considerably reduced hydroosmotic potency; pressinamide was inactive up to 3 μg/ml. The highly potent antidiuretic peptides, deamino-[D-Arg 8] vasopressin and deamino-6-carba-[D-Arg 8]vasopressin, were weakly active in the hydroosmotic assay.

Comparative studies of the antineoplastic activity of 5-hydroxy-2-formylpyridine thiosemicarbazone and its seleno- semicarbazone, guanylhydrazone and semicarbazone analogs

Several analogs of 5-hydroxy-2-formylpyridine thiosemicarbazone (5-HP) that contain isosteric replacement of sulfur by Se, NH or O have been synthesized. Measurement of the antineoplastic activity of these compounds in mice bearing Sarcoma 180 ascites cells indicated that 5-HP was the most active of these agents; the seleno analog was intermediate in potency, and the guanylhydrazone and semicarbazone were inactive against this tumor. 5-HP and its seleno analog both caused marked inhibition of DNA synthesis in vitro, as measured by the incorporation of thymidine-methyl- 3H, 5- 3H-cytidine or adenine-8- 14C into DNA. The syntheses of RNA and protein were relatively unaffected by these agents under the conditions employed. None of the compounds prevented the incorporation of 5- 3H-cytidine into acid-soluble pyrimidine ribonucleotides, but 5-HP and its selenosemicarbazone markedly depressed the subsequent progression of radioactivity into pyrimidine deoxyribonucleotide pools, suggesting that these two derivatives inhibited the enzyme ribonucleoside diphosphate reductase in situ. Both 5-HP and the seleno analog inhibited the isolated enzyme ribonucleoside diphosphate reductase from the Novikoff rat hepatoma; to achieve 50 per cent inhibition required 3.5 × 10 −6 and 6.8 × 10 −6 M respectively. Metal/ ligand ratios and the association constants for these ligands with cobalt and copper were determined. The cobalt/ligand ratio for 5-HP and its seleno analog was 1:2 and the copper/ ligand ratio for these agents was 1:1. Metal/ligand ratios for the guanylhydrazone and semicarbazone derivatives were 1:3 for cobalt and 1:2 for copper. Association constants for 5-HP and the seleno derivative with cobalt were 56 × 10 9 and 7.6 × 10 9 respectively. The findings demonstrated that 5-HP was the optimum member of this series with respect to antineoplastic potency and that tumor-inhibitory activity correlated with the degree of inhibition of the synthesis of DNA and the capacity for metal binding.

Selenium as an acid labile sulfur replacement in putidaredoxin

Selenium as an acid labile sulfur replacement in putidaredoxin

Emission Spectra of Impurity Activated ( Zn , Cd ) ( S , Se , Te ) Phosphors: II . Silver Activated Phosphors

Silver activated and phosphors are essentially single band emitters. The emission band shifts monotonically to lower quantum energies with increasing replacement of Zn by Cd. In contrast, gradual replacement of sulfur in or by selenium, or of selenium in by tellurium, causes little or no shift of the emission band but gradual replacement by a new band. Silver is a two‐band emitter in all intermediate , , and (to some extent) phosphors. The dependences are demonstrated in recombination term schemes assuming predominantly ionic crystal bonding and validity of the Schön‐Klasens model of luminescence.

5‐Ethoxy‐3‐(trichloromethyl)‐1,2,4‐oxadiazole

Abstract5‐Ethoxy‐3‐(trichloromethyl)‐1, 2, 4‐oxadiazole (V) was synthesized to elucidate the chemistry involved in the preparation of the hitherto unreported alkoxy‐1, 2, 4‐oxadiazoles and to determine the effect of the isosteric replacement of sulfur by oxygen on antifungal activity. Heating the “amino‐oxime” tautomer II of trichloroacetamidoxime with ethyl chloroformate furnished exclusively the O‐acylated product III. The trans configuration of III accounts for its resistance to cyclize under a variety of conditions, in contrast to the general behaviour of acylated amidoximes. Pyrolysis of III at 160° yielded IV which exists in the keto form. Refluxing IV with ethyl iodide in the presence of silver oxide gave an isomeric mixture which was separated by v.p.c. to give V and VI. Compound V retained 60% of the overall activity of the corresponding sulfur analog.