Sulfonium derivatives

With certain 6-substituents on the penam nucleus, it has been possible to isolate sulfonium derivatives (Scheme 16) (79JCS(P1)3175). As expected, these are highly reactive compounds. 

The sulfur analogue of the Hauser ortho-substitution rearrangement provides access to an arylacet-ic NSAID. Reaction of the aminobenzophenone 176 with ethyl methylthioacetate and tert-butyl hypochlorite gives the intermediate 178. The reaction probably proceeds by way of formation of the S-chlorinated sulfonium derivative 177 displacement on sulfur will lead to the salt 178. Treatment with triethylamine leads initially to the betaine 179. Electrocyelic rearrangement of that transient intermediate leads, after rearomatization, to the homoanthranilic acid 180. Internal ester-amine interchange leads then to indolone 181 [45]. The thiomethyl group is then removed with Raney niekel. Saponifieation of intermediate 182 affords bromfenac (183) [46J. 

A sulfonium derivative, abbreviated AdoMet or SAM, that is primarily generated by the action of methionine adenosyltransferase (ATP + L-methionine + H2O SAM + Pi + pyrophosphate). SAM is a major methylat-... 

Cysteine peptides may be converted to sulfonium derivatives by reaction with alkyl halides. The resulting sulfonium salts undergo /3-elimina-... 

The method described above gives direct analysis of methionine sulfoxide content in proteins. Another method makes use of carboxy-methylation of methionine at acid pH to give the carboxymethyl-sulfonium derivative ( 3.5). Methionine sulfoxide, which is not affected by the carboxymethylation reaction, is then oxidized to the sulfone which is stable to acid hydrolysis and can easily be quantitated. This is possible because methionine carboxymethyl-sulfonium salts are not affected by performic acid oxidation, although they are degraded by acid hydrolysis. Therefore, the methionine sulfone content is equal to the methionine sulfoxide content plus any sulfone that may have been initially present (shown by analysis before oxidation). 

Helquist has focused efforts on developing synthetically useful cyclopropanation reagents based upon the use of stable organoiron compounds which may be regarded, at least formally, as direct precursors of reactive carbene complexes. Sulfonium derivatives 1 and alkenyl complexesi have proven to be... 

Dimethyl-S-ethylthioethyl phosphorothiolate Sulfonium derivative, sulfoxide, and sulfone H20... 

The experimental studies on the chemistry of sulfur compounds have led Oae to develop the concept of ligand coupling,in which two stereochemical elements are implied the intramolecular coupling of two groups is concerted with extrusion of the reduced heteroatom, and the stereochemistry of the reagents is maintained throughout the whole process to eventually afford products with retention of configuration. The importance of these facts was deduced from the mechanistic studies performed on sulfonium derivatives which dealt mostly with the stereochemical evolution of the intermediate. The retention of stereochemistry was more extensively studied in the case of the reactions of sulfoxide derivatives. 

The 5-arylation of sulfides is greatly improved by copper catalysis. The uncatalysed reaction requires heating under reflux to afford modest to moderate yields of the 5-aryl sulfonium derivatives. By contrast, upon copper catalysis, the reaction proceeds at room temperature to afford good to high yields of the 5-aryl sulfonium derivatives. 2-146,151 Moreover, the reaction was extended to the double arylation of the more readily available aiylthiols.l Similarly, the reaction of areneselenolates with diaryliodonium salts led to diarylselenides and triarylselenonium salts were easily obtained by copper catalysed arylation of diarylselenides. 2... 

Oxidation of alcohols under extremely mild conditions can be effected using a procedure that is mechanistically related to the DMSO method. Dimethyl sulfide is converted to a sulfonium derivative by reaction with N-chlorosuccinimide. This sulfur species reacts readily with alcohols, generating the same kind of alkoxysul-fonium salts that are involved in the DMSO procedures. In the presence of mild base, elimination of dimethyl sulfide completes the oxidation. ... 

This side reaction is relatively innocuous because the by-product is irreversibly bound to the polymer and only the yield is affected not the purity of the synthetic peptide. More disturbing is the succinimide ring formation at aspartyl residues exposed to HF. Alkylation of the indole ring in tryptophan, the phenolic side chain in tyrosine and the sulfur atom in methionine must be suppressed by the addition of scavengers. The often appUed anisole is less than unequivocal in this role it can be the source of methyl groups which convert the methionine thioether to a tertiary sulfonium derivative. The acid stable thioanisole seems to be a better scavenger. 

The wear comfort of a fiber is determined by its softness, thermal isolation properties, water uptake, and permeability properties. The more or less hydrophobic synthetic fibers are consequently hydrophilized to improve wear comfort. The hydrophilization should increase dampness uptake, improve softness, decrease the tendency to soil, and reduce electrostatic charging. In high-grade finishing, the fibers or weaves are treated for this purpose with ethoxylated fatty alcohols, fatty acids, fatty amides, or with quaternary ammonium or sulfonium derivatives. Alternatively, the fibers can be hydrophilized by grafting with, for example, acrylamide or methacrylic acid. 

The mechanism proposed to explain these observations shows that the oxygen of DMSO must attack the acyl carbon of oxalyl chloride in an acyl substitution reaction (Chapter 19, Section 19.2) to form an acyl-sulfonium derivative, 39. This intermediate decomposes with loss of carbon dioxide (COg) and carbon monoxide (CO) to give a chlorosulfonium salt, 40. Sulfonium salt 40 has an electrophilic sulfur that is attacked by the nucleophilic oxygen of an alcohol such as... 

It is well known that sulfonium salts derived from methionine may decompose in many ways. Electron-withdrawing groups on the sulfur atom promote the breakdown of the sulfonium salt by bimolecular or intramolecular nucleophilic displacement. In the case of acetyl-methionine sulfonium derivatives (21) the displacement reaction takes place with the participation of the C-carbonyl group via a 1,5-interactipn, resulting in elimination of the dialkyl sulfide and formation of homoserine iminolactone (22) which on hydrolysis gives homoserine lactone (23) (reaction 17) . Best results are obtained when the reac-... 

Other sulfur-containing compounds were investigated, particularly sulfonium derivatives. Sulfonium compounds can be highly efficient inhibitors for both H2SO4 and but they generally have poor thermal stability therefore, they are... 

Horner et al. have studied the mechanisms by which onium compounds inhibit steel corrosion. Kichigin et al. studied tetra-n-butylammonium cation (TBA ) and other quaternary nitrogen compounds in the presence of iodide, and Aramaki et al. studied TBA+ in the presence of halides, SOj", SCN , SH , NOJ, and N3. In all these cases, halides were shown to be necessary for good inhibitor performance and the observed behavior was consistent with competitive co-adsorption of ion pairs (side by side). Sulfonium derivatives also require the presence of halide ions and, likewise, apparently co-adsorb to form ion pairs on the surface. As discussed below, unsaturated oxygen compounds, such as aldehydes and acetylenic alcohols, also require a halide ion for good performance. 

Adenosylmethionine is a sulfonium derivative of methionine and has a higher energy content than the parent methionine. The compound has been synthesized (75) and the synthetic product shown to participate in enzymic reactions to the extent expected (76). 

In summary, data presented in Table 14.3 demonstrate that the B-sulfonium derivatives of 10-and 12-vertex monocarbaborates H and J have lower activation energies to epimerization at the sulfur center and smaller energy difference between the axial and equatorial epimers than for the C(l) isomers. The latter is related to the significant difference in the cage-S bond length. The concentration of the axial epimer is calculated at 25-30% for the B-isomers, and an order of magnitude smaller for the C(l) isomers. 

The sulfonium derivatives 5 and 73 form less stable nematic phases than the pyridinium analogs." The butoxy derivative 73 has lower NI than the pyridinium 70 by 59 K and the pentyl derivative 5 crystallizes at about 60°C, 54 K below NI for pyridinium 71, without showing a mesophase. Two other derivatives 84a and 84b" permitted the assessment of the substituent effect on melting temperature. Thus, extending the alkoxy chain from methoxy (84a) to butoxy (84b) lowers the mp by 17 K, and appending a pentyl chain in 73 lowers the melting point by additional 38 K. 

The action of cysteine desulfhydrase is inhibited by hydrogen cyanide. Binkley and du Vigneaud (15) have observed that the production of hydrogen sulfide, which appears in the comrse of the reaction due either to homocysteine desulfhydrase or to cysteine desulfhydrase, is arrested in the presence of hydrogen cyanide, without however diminishing appreciably the yield of cysteine. This observation shows that the mechanism in question does not come into play in the experiments of Binkley and du Vigneaud, but the re.sults do not show that this mechanism plays no role in the animal. The theory of Toennies (121) assumes the existence of a direct transsulfuration between methionine and serine. This theory is based on the ability of methionine sulfur to form sulfonium derivatives... 

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