S-Protective group

Conversion of Conventional S-Protective Groups into the NpysSR Derivative ... 

Wuts PGM, Greene TW (2007) Greene s protective groups in organic synthesis, 4th edn. Wiley, Hoboken, NJ, Chapter 7... 

E Wtinsch, R Spangenburg. A new S-protecting group for cysteine, (in German) (5-terf-butyl) in E Scoffone, ed. Peptides 1969. Proceedings of the 10th European Peptide Symposium, North-Holland, Amsterdam, 1971, pp 30-34. 

Table 2 Reagents for Oxidative Cleavage of S-Protecting Groups 45-48 66 67 72 89 90 93-96 ...

Disulfide formation using a mixture of chlorosilanes and sulfoxides is a novel oxidation procedure developed independently by Akaji et al. 94-95 and Koide et al. 96 The reagents oxidatively cleave almost all types of S-protecting groups including those which are not oxidatively cleaved by iodine. Therefore, this procedure offers an additional dimension to the strategies of regioselective multiple-disulfide formation (see Section 6.1.4.2). 

The proposed mechanism of the oxidative cleavage of S-protecting groups by the chlorosilane/sulfoxide procedure is outlined in Scheme 8. 95 The first reaction is considered to be formation of the sulfonium cation 9 from diphenyl sulfoxide (7) and the oxygenophilic silyl compound 8. The formation of a sulfonium ion of this type is known and has been utilized for the reduction of sulfoxides. 97 Subsequent electrophilic attack of 9 on the sulfur atom of the S-protected cysteine residue leads to the formation of intermediate 10, whereby the nature of the silyl chloride employed should be the main factor that influences the electrophilicity of 9. The postulated intermediate 10 may then act as the electrophile and react with another S-protected cysteine residue to generate the disulfide 11 and the inert byproduct diphenyl sulfide (12). This final step is analogous to the reaction of a sulfenyl iodide as discussed in Section 6.1.1.2.1. 

By a combination of acid-labile S-protecting groups, such as Trt or Mob, with the acid-stable 5-Acm protection consecutive formation of two disulfide bonds can be achieved by two very mild oxidation procedures namely air oxidation followed by acid-catalyzed DMSO oxidation... 

R1 s protecting group R2 R3s amino acid side chains R4 = H, alkyl, substituted alkyl... 

R1 s protecting group, N-protected peptide R2sR3 = amino acid side chains R5 = H R6 = alkyl, substituted alkyl X1 =H X2 = OH X1 = X2 = CH2, n2... 

Fig. 2.6 The hypermonomer method (C=coupling unit, F=functional group, S= protective group)...

Butyl chloroformate reacts with cysteine to protect both the amine and thiol groups as with N,S-bis(benzyloxycarbonyl)cysteine, selective or simultaneous removal of the N- or S-protective groups can be effected.1... 

Greene s Protective Groups in Organic Synthesis, 4th ed., ed. T. W. Greene and P. G. M. Wuts, Wiley-Interscience, 2006. 

In Table 1, the most common S-protecting groups of cysteine are compiled according to their compatibility with either of the two major strategies used in stepwise solid-phase peptide synthesis the Boc/Bzl schemes based on acidolyzable A -Boc derivatives for temporary... 

Scheme 7 p-Elimination of an S-Protecting Group with Formation of Dehydroalanine, Followed by the Formation of the Corresponding Piperidine Adduct, 3-(l-Piperidyl)alanine.P l... 

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