Sulfur bridging group

In the synthesis of commercial sulfur-heterocycles two interesting reactions are used (i) diphenylamines may be connected by a sulfur bridge in the orfho-positions (ii) the amino grouping of sulfonamides undergoes condensation reactions with neighboring imino- and amide groups. 

In nickel and palladium dithiobenzoato complexes, four-membered chelate rings are formed (366), whereas, in the corresponding phenyl-dithio acetates [M2(S2CCH2Ph)4], the dithio ligands act as bridging groups between the two metal atoms, with the formation of binuclear units (367). The molecular structure of the latter compounds shows that each metal atom is coordinated to four sulfur atoms and to the other metal atoms in a square-pyramidal geometry. Other evidence for... 

Example Peptides often contain sulfur from cysteine. Provided there are at least two cysteines in the peptide molecule, the sulfur can be incorporated as thiol group (SH, reduced) or sulfur bridge (S-S, oxidized). Often, both forms are contained in the same sample. At ultrahigh-resolution, the contributions of these compositions to the same nominal m/z can be distinguished. The ultrahigh-resolution matrix-assisted laser desorption/ionization (MALDI) FT-ICR mass spectrum of native and reduced [D-Pen jenkephalin gives an example of such a separation (Fig. 3.25). [39] The left expanded view shows fully resolved peaks due to and C2 isotopomers of the native and the all- C peak of the reduced compound at m/z 648. The right expansion reveals the peak of the native plus the... 

The diversity of structural types within this group of compounds is well recognized. Sammes arbitrarily divided DKPs into five main structural types or groups (1) simple dioxypiperazines, (2) the echinulins and related derivatives, (3) hydroxypyrazine derivatives, (4) sulfur-bridged derivatives, and (5) bicyclomycin and dibromophakellin. 

Finally, replacement of the methylene bridge by a sulfur bridge leads to compoxmds such as 117 and 123 which are major tranquilizers. Thus, Ullmann condensation of thiosalicylic acid 112 with ortho-chloronitrobenzene affords thioether 113 the nitro group is then reduced to the aniline (114). Cycliza-tion as above leads to the lactam 115, which is then converted to the iminochloride derivative (116). Condensation with N-methylpiperazine affords clothiapine... 

The utility of intermediary sulfur bridging has been evidenced by the Eschenmoser group [445]. An example of their method was applied in studies [446] directed towards the synthesis of vitamin B,2. 

A few mechanisms were postulated for this reaction (6). No matter what mechanism is considered, the oxidation of elemental sulfur or thiosulfate is accompanied by reductive cleavage of the sulfur-sulfur bridges. In the case of sulfur, the intermediate involved is a cyclic form of sulfur, probably Ss, although there is little difference observed for different allotrophic forms of sulfur such as rhombic, precipitated, and amphorous. These cyclic sulfides form the basis of polysulfanes and polythionates which could be metabolized readily by Thiobacilli (as shown in Figure 3). Actually, sulfur oxidation begins with its reduction, in which the gluathione-sulfhydryl groups located near the cell surface take part ... 

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