Thiol-groups

Thiol Groups. Thiol groups generated on the surface of a polymeric support material12 allow the chemically reversible immobilization of enzymes, through a redox process involving the formation of disulfide bonds with cysteine residues  

With this scheme, the subsequent addition of a disulfide reducing agent, such as mercaptoethanol or dithiothreitol, allows the recovery of the immobilized enzyme. 

HS-3 participation was found to be more effective than HO-3 participation by a comparison of the results of solvolysis of cis- and trans-2-chlorocyclohexanols and 2-chlorohexanethiols. As with the oxygen compounds, both cis- and fran5-2-chlorocyclohexanethiol were found to react with enhanced rates, presumably by hydrogen participation [Eq. (43)], and 

Thietanes can be prepared by reactions involving neighboring sulfur groups. For example, the D-mannitol derivative (112) is converted into the interesting tricyclic D-iditol derivative (113) with methanolic sodium methoxide.  

S-5 participation also occurs readily. Thus a sulfur bridge results on treatment of 6-0-toluene-p-sulfonyl-2,3,4-tri-0-acetyl-j -D-glucopyranosyl ethyl xanthate or thioacetate (114) with sodium methoxide in methanol, although 0 -5 participation is also possible.  

Johnson and Kingsbury have used S-5 participation in their recently devised syntheses for some rigid tricyclic sulfur compounds. The p-bromo-benzenesulfonates (115) were converted to (116) by the sequence shown. Esters of (116) should make intriguing models for solvolytic studies. 

One interesting example of S -6 participation occurs on treatment of 6-chloropenicillanic acid (117) with sodium methoxide. The pathway through esters (118) and (119) was proposed as a route to the formation of (120). Spectrophotometric evidence was gained to support the intermediacy of (119). 

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Glycosidic thiol groups can be introduced into glycosyl bromides by successive reactions with thiourea and aqueous sodium disulfite (D. Horton, 1963 M. Cemy, 1961, 1963). Such thiols are excellent nucleophiles in weakly basic media and add to electrophilic double bonds, e.g., of maleic esters, to give Michael adducts in high yields. Several chiral amphiphiles have thus been prepared without any need for chromatography (J.-H. Fuhrhop, 1986 A). 

The piefeiied route depends upon the avajlabihty of a hydrogen atom in the beta-position to the thiol group. In other words, a-toluenethiol (in toluene) decomposes to give 1,2-diphenylethane and hydrogen sulfide, via the homolytic route, whereas 2-methyl-2-propanethiol decomposes to give 2-methyl-1-propene and hydrogen sulfide. 

Thiol groups in the 2-, 3- and 6-positions have been desulfurized with Raney nickel under the usual conditions to give the corresponding unsubstituted compounds. 

The base-catalyzed reaction of thiothreitol with methyl dithiobenzoate selectively protects a thiol group as an 5-thiobenzoyl derivative in the presence of a hydroxyl group.-... 

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