Peptide Synthesis, Peptide Array, HATU, Fmoc ..
Solid phase synthesis of a β-dodecapeptide with seven functionalized side chains and cd-spectroscopic evidence for a dramatic structural switch when going from water to methanol solution.
Solid Phase Peptide Synthesis : The Basics - YouTube
This is a complex task in the case of the synthesis of peptides because of the complexity and the number of operations involved in the production process.
Certain groups of chemical functionality have exceptional affinities for selective reaction, particularly in the formation of small rings. Recent developments have led to the synthesis of large peptide fragments by solid-phase synthesis, removal from the polymeric support and of most, if not all, side-chain protecting groups, and then selective coupling of the unprotected fragments based on chemical ligation. The most developed strategy for this approach is the use of an N-terminal cysteine residue with a special reactive C-terminal group on the other peptide. This approach was initially conceived by Kemp in his thiol capture strategy (7) and was reduced to a practically successful general approach by the groups of Kent (8-10) and Tam (11-13). For illustrative purposes, the native chemical ligation procedure of Dawson et al. (9) is described (Fig. 4), because it seems to have had the most practical impact. In this case, solid-phase synthesis is used to prepare two unprotected peptide segments that are combined in aqueous solution. The C-terminal fragment contains an N-terminal cysteine residue, and the C-terminal peptide fragment is prepared as the thioester. The thioester is displaced by the thiolate anion of a Cys residue. If the Cys is N-terminal, an acyl migration through formation of a five-membered ring occurs to generate the desired stable amide bond. If the sulfur atom of a Cys residue within the peptide chain is involved, then the thioether formed is capable of being displaced by other thiols, until the fragment migrates to the N-terminal Cys, when the stable rearrangement can occur. An alternative strategy, using an N-terminal b-bromoalanine of fragment two and the C-terminal thioester of fragment one to give the same covalent thioester intermediate by thioesterification, has been explored by Tam et al. (12)
It has been replaced in most labs by solid-phase synthesis ..
Illustrative are the solid-phase protocols for the two strategies (Boc and Fmoc) commonly used for the synthesis of peptides. The Boc strategy (Fig. 1) is often combined with a 1% to 2% cross-linked polystyrene support and a benzyl ester linkage to the polymer, requiring strong acid such as hydrogen fluoride for deprotection. The procedure favored by most synthetic laboratories uses an acid-labile linkage similar to the p-methoxybenzyl ester linkage of the Wang resin and a base-labile amino protecting group, the fluorenylmethyloxycarbonyl (Fmoc), on the added amino acids (Fig. 2). One can use side-chain protection with similar acid lability to the Wang linkage to give free peptide upon cleavage, or use more stable side-chain protection to give the protected peptide for fragment condensation after purification and characterization. In the latter case, a final deprotection with strong acid such as HF is required.
TentaGel Resins for the Synthesis of PEG Attached Peptides:
The other approach is to introduce backbone protecting groups which will prevent the formation of hydrogen bonds. Such protection is made by the introduction of the Hmb group on the αnitrogen . It has been shown that the presence of a Hmb unit every 6-7 residues is sufficient to disrupt the peptide aggregation . The Hmb protected amino acid is introduced under the form of N,O-bis-Fmoc-N-(2hydroxy-4-methoxybenzyl) derivative, the O-Fmoc protection being cleaved during the following piperidine treatment. At the end of the synthesis the Hmb group is cleaved in the final TFA cleavage.
ChemPep: One stop for peptide synthesis
In peptide synthesis diketopiperazine formation is a notorious side-reaction at the dipeptide stage and is particularly prone to occur in Fmoc based SPPS because of its mechanism.