Deprotection thiol groups

Hi) Synthesis of S-prenylated peptides Various syntheses of S-prenylated peptides " have relied on the assembly of the peptide backbone on the solid phase, using standard protocols, and subsequent S-prenylation in solution. As a consequence, any final deprotection steps of other amino acids after the S-prenylation cannot be performed under strongly acidic conditions due to the acid lability of the prenyl group. The prenylation reactions themselves can he carried out under basic or mildly acidic conditions. Typical synthesis problems that arise during the S-alkylation are (1) incomplete conversion because of solubility problems, (2) oxidation of the thiol group to disulfides under basic conditions, (3) formation of the sulfonium... 

Reaction of (34) with the bidentate sulfur ligand isotrithionedithiol (H2dmit, (278)) produced a dianionic complex. The reaction of (278) in which the thiol groups were deprotected in situ prior to the substitution reaction with [TcNClJ in acetonitrile gave a 45% yield of [TcN(dmit)2] ... 

The simplest approach is offered by parallel homodimers which require only two orthogonal protecting groups. After deprotection of one thiol group mild oxidation by one of the methods discussed in Section 6.1.1.1 or following direct selective oxidative cleavage of one S-protected cysteine residue by the methods described in Section 6.1.1.2, the second disulfide bond has to be produced by selective procedures compatible with the presence of a disulfide as described in Section 6.1.2. 

The simplest approach to disulfide bond formation of chemically synthesized peptides and proteins involves (i) complete deprotection including that of the cysteine thiol functions, and (ii) mild oxidation of the thiol groups to form the folded product with the native cystine connectivity. With careful attention to experimental conditions, the native-type folding of the peptide can be accomplished however, misfolded disulfide isomers are often produced as the main products in spite of efforts to optimize the reaction conditions. 

Due to the S—N acyl shift, the stepwise synthesis using a S-palmitoylated cysteine derivative is not advisable. A more convenient approach is to assemble the peptide sequence and to acylate the cysteine thiol group upon its selective deprotection, retaining, however, the protection of other reactive groups. For this purpose the Cys(StBu) and Cys(Acm) deriv-... 

Ethanedithiol is added in the sulfating step to prevent oxidation of the methionine residues and in the deprotection step with TBAF to quench the dibenzofulvene, although thiol groups are expected to be sulfated at higher rates than phenolic groups. 

The acetylsulfanyl alkanoic acids can also be prepared by thioacetylation of the corresponding bromo derivatives,[101 acrylic add derivatives, 1516 or lactones.133 A fluorescent sulfanylalkanoyl fluorescein derivative was prepared by reaction of acetylsulfanylalkanoyl amine with fluorescein isothiocyanate, followed by deprotection of the thiol group. 1 ... 

To deprotect C4 thiol group and make it available for SH-directed modification, incubate 0.1 mM scVEGF with 0.1 mM DTT in a buffer containing 0.1 M Tris-HCl pH 8.0 for 30 min at room temperature. 

Protection of thiol groups is a substantive issue in peptide chemistry where protection and deprotection of cysteine and the attendant problem of disulfide bond formation is a major challenge. An authoritative review of the subject by Moroder and co-workers can be found in Synthesis of Peptides and Peptidomi-metics (Houben-Weyl), Vol E22a. ... 

Photochemical oxidation of cyclo-DL-Pro-Gly gives peroxide 372 (78CB361). Deprotection of the thiol group of 373 gives the perhydro-pyrrolo[l,2-a]pyrazin-l,4-dione (374) (85TL5481). 

As illustrated in Fig. 1, our approach is based on the maleimide group linked to the synthetic peptide and the thiol group placed on the protein partner. For this purpose sufficient stability of the maleimide function in the course of the peptide synthesis as well as in the final deprotection and purification step is required. A detailed analysis of these critical aspects revealed full stability of the maleimide function under the normal conditions of peptide synthesis (56.57). On the other hand, thiolated carrier proteins are readily prepared by reduction of cystine-containing proteins, by mercaptosuccinylation of carrier proteins (66,67) or by the choice of natural mono- or poly-cysteine-containing proteins (68). 

Cysteine protection. For masking the thiol group of cysteine, the reagent is applied in trifluoroacetic acid/dichloromethane. Deprotection is achieved by palladium-catalyzed reductive deallylation. 

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