Peptides benzyloxycarbonyl protecting group

BW Erickson, RB Merrifield. Use of chlorinated benzyloxycarbonyl protecting groups to eliminate Ne-branching at lysine during solid-phase peptide synthesis. J Am Chem Soc 95, 3757, 1973. 

The first solid-phase peptide synthesis reported by Merrifield had some disadvantages, which were corrected in later versions of this synthesis. The main improvements were the replacement of benzyloxycarbonyl protective groups by the TFA-labile Boc protection, and the use of TFA-resistant linkers cleavable by HF. 

The benzyloxycarbonyl protecting group, commonly used in peptide synthesis, has also been used in the preparation of azamacrocycles. Sutherland and co-workers <76CC639> prepared a benzodiaza-15-crown-4 derivative from a,a -dibromo-/w-xylene <79JCS(P1)1089>. Although not specified in the report, deprotection was presumably accomplished using standard conditions (HBr/HOAc). 

Show the steps involved in the synthesis of Ala-Leu from alanine and leucine using benzyloxycarbonyl and benzyl ester protecting groups and DCCI-promoted peptide bond formation. 

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