Chemical ligation, SPPS

CHO Chinese hamster ovary NCL native chemical ligation SPPS solid-phase peptide synthesis... 

In contrast to the use of self-assembly reactions and metal ion coordination preferences to direct the construction of mixed cofactor systems, the use of SPPS or selective chemical ligation allows for the direct covalent attachment of cofactors for the construction of mixed cofactor systems within de novo design. Figure 11 shows the flavocy-tochrome maquette constructed by Dutton and co-workers (149) using a flavin moiety covalently attached to a unique cysteine residue inside a four helix bundle with bis-histidine binding sites for heme... 

C-terminal peptide a-thioester, mUdly activated peptide ester acting as a valuable key intermediate for the synthesis/semi-synthesis of polypeptides and proteins by both chemical ligation and the Aimoto thioester approach. The synthesis of the peptide a-thioester (—r thioester) can be performed by standard SPPS using Boc- or Fmoc-based chemistry or, for larger target polypeptides, by application of intein-based bacterial expression systems. Peptide a-thioester synthesis can also be carried out based on an N-S acyl shift reaction mediated by a thiol ligation auxiliary [F. B. Perler, E. Adams, Curr. Opin. Biotechnol. 2000, 377 D. Swinnen, D. Hilvert, Org. Lett. 2000, 2, 2439 R. Quaderer, D. Hilvert, Org. Lett. 2001, 3, 3181 T. W. Muir, Annu. Rev. Biochem. 2003, 72, 249 T. Kawakami et al.. Tetrahedron Lett. 2005, 46, 8805 J. A. Camarero, A. R. Mitchell, Prot. Pept. Lett. 2005, 12, 723]. 

Despite the potential for diverse post-ligation modifications at Sec residues. Sec-mediated ligation chemistry has not been widely adopted for the routine construction of target peptides and proteins which do not contain Sec residues in the final product [147]. The lack of commercially available Sec building blocks for direct incorporation into peptides using standard SPPS and the ability to modify readily the side-chain of Cys residues [54, 66, 148] have generally favored the use of standard native chemical ligation at Cys. 

Blanco-Canosa JB, Dawson PE (2008) An efficient Fmoc-SPPS approach for the generation of thioester peptide precursors for use in native chemical ligation. Angew Chem Int Ed 47 6851-6855... 

OCH2CONH2 (75), and H3(96-135) (76), which were sequentially ligated by the native chemical ligation and thioester methods (Scheme 23). These segments were prepared by Fmoc SPPS. Peptides 75 and 76 were first ligated under NCL... 

Keywords Acyl migration Acyl transfer Chemical ligation Computational studies Cyclic peptides Glycopeptides Neoglycoconjugates SPPS... 

In our laboratory we use two different SPPS-based approaches to synthesize cyclic disulfide-rich peptides. Most commonly we use the intramolecular native chemical ligation (NCL) reaction between a thioester group at the C-terminus and a cysteine residue at the N-terminus [16, 26-29]. For this approach the coupling of the thioester linker requires Boc-SPPS protection chemistry as the thioester is unstable in the basic conditions used for Fmoc chemistry. The first amino acid coupled after the thioester linker could be any residue however, Gly, Cys, and His are most favorable, and Leu, Thr, Val, He, and Pro are the least favorable amino acids, as reflected in their ligation rates with the N-terminal cysteine [26]. The second SPPS approach used in our laboratory to synthesize the cyclic disulfide-rich peptides involves an Fmoc-based method, in... 

C-terminal peptide tiiioesters are used extensively in synthetic protein chemistry, especially for native chemical ligation (NCL) and other chemoselective reactions, which has inspired a search for robust synthetic strategies. Initially, peptide thioesters were mainly prepared using solid-phase peptide synthesis with amino acids N -protected with Boc (Boc-SPPS) [1-3], see Chapter 4. However, this technique requires specialized equipment for handling of hydrofluoric acid (HP) for release of the peptide from the resin, and it is therefore currently not used in many laboratories. Furthermore, the HP treatment is incompatible with many post-translational modiflcations such as glycosylations or phosphorylations [4]. Boc-SPPS is described thoroughly in Chapter 4. 

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