Deblocking s. Protective groups

N-Debenzylation of ammonium salts, quaternary 14,404 O-Debenzylation 24, 723 -, selective 24, 8, 17, 43 Deblocking s. Protective groups, removal... 

Debenzylation 16, 172 S-Debenzylation 16, 172 Deblocking s. Protective groups, removal Decarbalkoxylation (s. a. Replacement of carbalkoxy groups by hydrogen)... 

Deblocking cysteine protecting groups. The common S-protecting groups can be cleaved by reaction with 2-nitrophenylsulfenyl chloride in acetic acid followed by reduction of the S-(2-nitrophenylsulfenyl)cysteine residues (equation I). 

Allylic bromination of the S,0-protected compound 159 was effected with A -bromosuccinimide in the presence of azobisisobutyronitrile in refluxing carbon tetrachloride, and the bromomethyl compound 160 was isolated in 86% yield. Deblocking of protective groups was accomplished with aluminum chloride to give the thiol (161). The attempted purification of the crude thiol on silica gel resulted in cyclization to the desired 7-phthalimido-3-hydroxy-3-cephem (162). This compound was isolated in crystalline form, and it was identical to that prepared earlier by Kukolja and co-workers (1976a). 

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... 

Use of CISCO2CH2 as a protecting group for SH groups in protein and peptide chemistry. Stable to many of the conditions employed for deblocking and coupling operations used in peptide synthesis also cleaves S-trityl and S-acetamidomethy1 derivatives. 

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