A-Thiolation

Thiol—Disulfide Interchange Reactions. The interchange between thiols and disulfides has been reviewed (50). This reaction is base-catalyzed. It involves the nucleophihc attack of a thiolate ion on a disulfide. This is shown in equations 35, 36, and 37. 

Treatment of thiiranes with lithium aluminum hydride gives a thiolate ion formed by attack of hydride ion on the least hindered carbon atoms (76RCR25), The mechanism is 5n2, inversion occurring at the site of attack. Polymerization initiated by the thiolate ion is a side reaction and may even be the predominant reaction, e.g. with 2-phenoxymethylthiirane. Use of THF instead of ether as solvent is said to favor polymerization. Tetrahydroborates do not reduce the thiirane ring under mild conditions and can be used to reduce other functional groups in the presence of the episulfide. Sodium in ammonia reduces norbornene episulfide to the exo thiol. 

Thiols, the sulfur analogs of alcohols, are usually prepared by Sjv 2 reaction of an alkyl halide with thiourea. Mild oxidation of a thiol yields a disulfide, and mild reduction of a disulfide gives back the thiol. Sulfides, the sulfur analogs of ethers, are prepared by an Sk2 reaction between a thiolate anion and a primary or secondary alkyl halide. Sulfides are much more nucleophilic than ethers and can be oxidized to sulfoxides and to sulfones. Sulfides can also be alkylated by reaction with a primary alkyl halide to yield sulfonium ions. 

The halides in mer-OsCl3(PR3)3 can be replaced by a thiolate ligand to give paramagnetic Os(SC6F5)3(PR3)2 an agostic Os—F—C interaction is believed to complete the coordination sphere of osmium [156]. 

The experiments with 2-(3-butenyloxy)benzenediazonium ions (10.55, Z = 0, n = 2, R=H) and benzenethiolate showed a significant shift of the product ratio in favor of the uncyclized product 10.57. They also indicated that the covalent adduct Ar — N2 — SC6H5 is formed as an intermediate, which then undergoes homolytic dissociation to produce the aryl radical (Scheme 10-83). Following the bimolecular addition of the aryl radical to a thiolate ion (Scheme 10-84), the chain propagation reaction (Scheme 10-85) yielding the arylphenylsulfide is in competition with an alternative route leading to the uncyclized product 10.57. 

According to reaction conditions, formation of either the sulfinic acid or the a-thiolated sulfone could be observed (up to 80%) the intermediate a-sulfonylamino sulfone proved to be unstable. 

In this classic41 and general method, an acylated glycosyl halide reacts with a thiolate anion to produce a 1-thioglycoside, usually with 1,2-trans configuration. With alkyl thiolates, re-acylation is normally required following this treatment. 

If the Fe-Ni center is not redox active, at least during catalysis, then the process must be ligand-based (92). Maroney and co-workers have argued that the paramagnetic Ni-C state could be generated by the interaction of a thyil radical with a Ni(II) ion. This species is isoelectronic with a thiolate-bound Ni(III) according to the reaction... 

A tridentate SNO ligand coordinates with a bipyridine to give ((2,2 -bipyridine)[2-(2-mercapto-phenyl)iminophenoxy])zinc. The monomeric complex has a distorted trigonal bipyramidal geometry with a phenolate and a thiolate coordinated. The synthesis was carried out electrochemically from anodic zinc in the presence of a disulfide-linked ligand precursor.867... 

A comprehensive compilation of data derived from feeding and other biosynthetic studies performed by Kirby [21], Sammes [22], and Taylor [23], genomic studies conducted by Howlett [lc, 24], as well as our own synthetic studies probing the innate reactivity of various intermediates (vide infra) culminated in our formulation of the biosynthetic hypothesis delineated below (Scheme 9.1). The biosynthesis features two distinct phases an oxidative dimerization phase and a thiolation phase in which diketopiperazine structures are elaborated to afford the defining epipolysulfide motifs (Scheme 9.1) [25, 26]. 

PDPH also may be used as a thiolation reagent to add sulfhydryl functional groups to carbohydrate molecules. The reagent can be used in this sense similar to the protocol described for AMBH (Chapter 1, Section 4.1). After modification of an oxidized polysaccharide with the hydrazide end of PDPH, the pyridyl group is removed by treatment with DTT, leaving the exposed sulfhydryl (Figure 5.15). 

Add 1-10 mg of a protein or antibody containing an available thiol group to the particle suspension. Alternatively, add the protein to be coupled to the particle suspension in an amount equal to 1-10 X molar excess over the calculated monolayer for the protein type to be coupled. The optimal amount of protein to be added should be determined experimentally. Creating thiol groups on proteins or peptides may be done from disulfides by reduction. Alternatively, a thiolation reagent may be used to add thiols to the protein surface for coupling (see the protocols in Chapter 1, Section 4.1). 

Collect the peak containing the activated antibody (eluting first) and concentrate to 10 mg/ml using centrifugal concentrators. Use immediately for conjugating to a thiolated toxin. 

A variation of the above method can be used, wherein the enzyme is first activated with SMCC and conjugated to a thiolated (strept)avidin molecule. This approach probably is the most common way of preparing (strept)avidin-enzyme conjugates, and since the preactivated enzymes are readily available (Thermo Fisher), it also may be the easiest. 

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