Thiol protection

The outcome of rapid radiation chemical processes in mammalian cells is to cause a variety of longer-Hved physical alterations in the DNA. Of these, double-strand breaks (DSBs) appear to be most frequently involved in cell killing if not correctly repaired. In general, thiols protect against DSB induction in proportion to their effect on cell killing (7), although there are exceptions (8). 

Acetamidoethyl)-4,S,6-trimethoxy-acetophenone, 56, 7 Acetamidoitiethyl group, for thiol protection, 59,194... 

Thiol protection, 59, 190 Thiono esters, reaction with ethyl isocyanoacetate, 59,187 Thionyl chloride, 55, 27 Thiophenol, 55, 122 58, 144 Thorium dodecanedioate, 56,110 Toluene, 56, 86 58,125 p-Toluenesulfonates, reaction with organo-cuprates, 55,112 p-Toluenesulfonic acid, 58, 57, 63 p-Toluenesulfonic acid, monohydrate, 56,44... 

Smith, J. J., Conrad, D. W., Cuneo, M. J. and Hellinga, H. W. (2005). Orthogonal site-specific protein modification by engineering reversible thiol protection mechanisms. Protein Sci. 14, 64-73. 

DF Veber, JD Milkouski, SL Varga, RG Denkewalter, R Hirschmann. Acetamidomethyl. A novel thiol protecting group for cysteine. J Am Chem Soc 94, 5456, 1972. 

Zhu M, Aikens CM, Hollander FJ (2008) Correlating the crystal structure of a thiol-protected Au25 cluster and optical properties. J Am Chem Soc 130 5883-5885... 

A reasonable mechanism for the iodine oxidation of 5-Trt cysteine peptides is given in Scheme 6. 45 Reaction of iodine with the divalent sulfur atom leads to the iodosulfonium ion 5 which is then transformed to the sulfenyl iodide 6 and the trityl cation. Sulfenyl iodides are also postulated as intermediates in the iodine oxidation of thiols to disulfides. The disulfide bond is then formed by disproportionation of two sulfenyl iodides or by reaction between the electrophilic sulfur atom of R -S-I and the nucleophilic S-atom of a second R -S-Trt molecule. The proposed mechanism suggests that any sulfur substitution (i.e., thiol protecting group) capable of forming a stabilized species on cleavage, such as the trityl cation, can be oxidatively cleaved by iodine. 

The Tmb thiol protection has also been exploited for the peptide dithiol formation on a resin by using dilute TFA.1641 The use of the mild oxidant CCLt in NMP1 061 for the oxidation of a resin-bound dithiol peptide is an interesting variation to this synthetic strategy.1641... 

A general procedure for the iodine reaction in the solid phase is shown in Scheme 9. Both Boc and Fmoc chemistry can be used to assemble the linear S-protected bis-cysteine peptides and for thiol protection the well-established Acm and Trt groups are usually used. Suitable solvents for the thiol-deprotection/oxidation step by iodine to form the disulfide are CH2C12, DMF, or aqueous AcOH. The final deblocking and cleavage from the resin is carried out under standard conditions. Modification at sensitive amino acid residues caused... 

An interesting approach based entirely on the solid-phase route has been reported for the synthesis of a-conotoxin SI (Scheme 14) where a combination of acid-labile and acid-stable thiol protecting groups are employed for the required orthogonality.[107]... 

X = thiol protecting groups Y, = Y = amino protecting groups of attachment sites Z = side-chain protecting groups... 

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