Alkylation sulfhydryls

Half-lives of derivatives are the same as for those obtained with the tetrahydrophthalic anhydride. This reagent does not alkylate sulfhydryl groups... 

Both a- and t-NH2 groups are modified. Acyl derivatives of tyrosine formed by these reagents hydrolyze spontaneously under mild alkaline conditions. Small amounts of stable acyl derivatives of serine and threonine are formed. These can be quantitatively decomposed by treatment with 1 M NHjOH at pH 8.2 at 25°C for 2 hr. The olefmic reagents alkylate sulfhydryl groups with the formation of stable derivatives. 

The general expression of aniline alkyl sulfhydryl can be given as follows ... 

It was reported that aniline alkyl sulfhydryl was applied in the flotation of zinc ore of New Brocken Hill in Australia [27]. Under the condition of pH 8.2, reagent dosage 102 g/t, and no addition of CUSO4, the recovery rate of zinc and concentrate grade are, respectively, 96 and 46 %. When the concentrate grade is 50.1 %, the recovery rate of zinc becomes 80 %. The flotation performance of aniline alkyl sulfhydryl is similar to that of xanthate. 

Aniline alkyl sulfhydryl can be synthesized by adopting aniline and vinyl episulfide as raw materials. The synthetic reaction can be given by the following ... 

Examples of alkyl sulfhydryl-bearing compounds that can covalently attach to a chitosan backbone are cysteine, A-acetylcysteine, thioglycolic acid, and glutathione. These molecules become linked to the chitosan primary amino group via an amide bond. 

As seen in Figure 1, the organo sulfur compounds are methylated at the boiling point (90°C) of dimethyl carbonate, whereas methylation (or alkylation with other alkyl groups) of other functional groups requites higher temperatures. This has resulted in the selective methylation of sulfhydryl groups of compounds that contain other substituents that can be alkylated. The other substituents can then be alkylated at elevated temperatures (63). 

Warfarin, diphenacoum, bromodiolone, flocoumafen, and brodiphacoum are examples Both alkyl and aryl mercury compounds can bind to sulfhydryl groups Have caused population declines in certain mollusks... 

These gold exchange reactions are prevented by prior alkylation of this protein thiol. Because of its lower affinity for gold when Cys-34 exists as a disulfide species, gold-to-sulfhydryl and gold-to-total albumin ratios are considered when analyzing data. Albumin with the Cys-34 blocked by alkylation is often used. 

Red cells provide a useful model for studying the likely movement of gold into and out of cells. Itwas shown that Et3PAuCl moving into red cells binds to glutathione and hemoglobin [84, 85] providing ancillary evidence for the sulfhydryl shuttle. Similarly, [Au(CN)2] has been shown to enter red cells by the sulfhydryl shuttle and its uptake can be blocked by alkylation of membrane thiols [32]. 

Cysteine sulfhydryls and cystine disulfides may undergo a variety of reactions, including alkylation to form stable thioether derivatives, acylation to form relatively unstable thioesters, and a number of oxidation and reduction processes (Figure 1.10). Derivatization of the side chain sulfhydryl of cysteine is one of the most important reactions of modification and conjugation techniques for proteins. 

Figure 1.10 Sulfhydryl groups may undergo a number of additional reactions, including acylation and alkylation. Thiols also may participate in redox reactions, which generate reversible disulfide linkages.

Maleic acid imides (maleimides) are derivatives of the reaction of maleic anhydride and ammonia or primary amine compounds. The double bond of a maleimide may undergo an alkylation reaction with a sulfhydryl group to form a stable thioether bond (Chapter 2, Section 2.2). Maleic anhydride may presumably undergo the same reaction with cysteine residues and other sulfhydryl compounds. 

Most of the bis-alkyl halides referenced in the literature are unavailable commercially, and therefore must be synthesized. Some key references to the preparation and use of these compounds for the crosslinking of sulfhydryl-containing proteins and other molecules include Goodlad (1957), Segal and Hurwitz (1976), Ewig and Kohn (1977), Wilchek and Givol (1977), Prestayko et al. (1981), Luduena et al. (1982), Hiratsuka (1988), and Aliosman et al. (1989). 

Coupling of affinity molecules to surfaces also can be enhanced by the use of discrete PEG linkers. Nishimura et al. (2005) modified an amino surface with a NHS-PEG -maleimide crosslinker to create a hydrophilic self-assembled monolayer (SAM) surface that was thiol reactive for the conjugation of sulfhydryl-modified RNAs. This array then was used to investigate the binding specificity of synthetic kanamycins with selected RNA sequences to prove the specific interaction of ribosomal RNA with this molecule. The PEG linkers on surfaces provide lower nonspecific binding character than alkyl linkers, when preparing SAM surfaces for affinity interactions. 

Another approach uses reactive alkyl halogen compounds containing a terminal carboxylate group on the other end to form spacer arms off the dextran polymer from each available hydroxyl. In this manner, Brunswick et al. (1988) used chloroacetic acid to modify the hydroxyl groups to form the carboxymethyl derivative. The carboxylates then were aminated with ethylene diamine to create an amine-terminal derivative (Inman, 1985). Finally, the amines were modified with iodoacetate to form a sulfhydryl-reactive polymer (Figure 25.14). 

PROTECTION OF CARBOXYL, HYDROXYL, AND SULFHYDRYL GROUPS BY TFRT-BUTYLATION AND ALKYLATION... 

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