Deblocking s. Protective

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)... 

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... 

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). 

Boc-Cys-Tyr[Z(Br)]-Ile-Gln-Asn-Cys-Pro-Leu-Gly-MBHA-resin [prepared from the corresponding S-Fm-protected resin-linked peptide (50-60mg, 0.35mmol/g, 19 nmol) by treatment with piperidine/ DMF/[5-ME (10 10 0.7) at 25 °C for 3 h] was suspended in pH 8 buffered DMF (3 mL) in an open vessel at 25 °C for 1 h, washed, deblocked with TFA/CH2C12, and cleaved with HF/anisole (9 1) at 0 °C for 1 h to provide the crude peptide yield 16 xmol (88%). This material was purified by MPLC on a Lobar RP-8 column yield 8.5 xmol (53%) the product was characterized by amino acid analysis and HPLC. 

A characteristic feature is the construction of the open-chain octapeptide intermediates 12 from two molecules of the tetrapeptides 9 that have been deblocked at their N-terminus (—> 11) and at the C-terminus (—> 10), respectively. In the synthesis of the octapeptide (S,R)-Amhn-12, one molecule of (S)-Amhn-ll and of (/ )-Amhn-10, each, is used. The tetra-peptide (5)-Amhn-9 is prepared by a 2+2 condensation of Boc-Lys(Z)-(5)-Amhn-OH with HCl-H-Lys(Z)-Gly-OMe. The synthetic strategy uses Na-Boc protection and DCC/HOBt... 

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