Solid phase peptide synthesis: new resin and new protecting group.

Masters Degree. University of KwaZulu- Natal, Durban.Solid phase peptide synthesis is the common approach used today in synthesizing peptides in a research scale and production. Success in this approach are governed by several factors. These are; (1) the solid support on which synthesis is to be carried out, (2) linker/spacer on which the first amino acid is linked to the support to allow stepwise growth of the peptide chain, (3) protecting groups of amino acids to allow a clean synthesis without disruption of the growing peptide chain and (4) coupling reagents for improved amide bond formation yielding peptides in the shortest amount of time and with the highest quality. The following thesis shows work conducted on some of these aspects. Chapter two is based on the application of a novel resin Fmoc-Rink-Amide PEG Octagel surface resin. Chapter three describes the development of a novel protecting group for histidine amino acid. A new PEG-PS based resin called Octagel has been developed by Aapptec. Fmoc-Rink-Amide Octagel PEG surface resin is a unique highly uniform surface-active resin. To study the resin’s performance, two peptides Aib-enkephalin pentapeptide and Aib-ACP decapeptide were synthesized and results were compared to Polystyrene and ChemMatrix resins. Swelling and microscope imaging studies were also conducted on each of the resins to highlight their performance associated with Solid Phase Peptide Synthesis. Results have demonstrated that Octagel resin has the potential to synthesize peptide sequences with high purity and therefore to be a good alternative to those currently in the market. Histidine is an important amino acid used in SPPS. It contains a reactive imidazole side group that can cause side reactions in SPPS if left unprotected. Fmoc-based SPPS is the most commonly used strategy in synthesizing peptides today. A protecting group was created for Fmoc-Histidine. SPPS was carried out on the protected histidine and results show that the group is stable in acidic conditions

Refractive Index: The Ultimate Tool for Real-Time Monitoring of Solid-Phase Peptide Synthesis. Greening the Process

Peptides are the basis of many drugs currently in the market and much more entering clinical trials, as well as in preclinical studies. The most part of peptides in both research and industrial modes are synthesized using Solid-Phase Peptide Synthesis (SPPS) processes. A characteristic of this strategy is that the synthetic intermediates are not isolated and not characterized. In this context, the development of a real-time monitoring method would assure an optimal synthetic process. Refractive index (RI) of a liquid has important information about its physical properties and makes it possible to know the composition of any solution. Herein, RI is demonstrated for the first time as a Process Analytical Tool (PAT) that can be used for real-time monitoring of SPPS. The three basic steps involved in this process can be followed up on line: coupling, deprotection and washes. This has consequences for the determination of the end-point of the reactions and the optimization of all synthetic steps. This will impact directly into the consumption of reagents, solvents, and time, making SPPS greener

Scope and Limitations of Barbituric and Thiobarbituric Amino Acid Derivatives as Protecting Groups for Solid-Phase Peptide Synthesis: Towards a Green Protecting Group

DMB (Dimethylbarbituric) and DETB (Diethylthiobarbituric) are both barbituric and thiobarbituric acid derivatives respectively, that forms enamines with the Nα amine of amino acids. These compounds were found to be stable crystalline solids and show stability in the standard acidic and basic conditions used for solid-phase peptide synthesis (SPPS) strategies. These protecting groups are cleaved by a mild solution of 2 % hydrazine hydrate in DMF and 2 % hydroxylamine in DMF, both at short reaction times. Their use in SPPS showed that DMB-protected amino acids allow the preparation of peptides and therefore could be an alternative to the Fmoc strategy currently used. A further advantage of these protecting groups is that their preparation does not involve the concourse of phosgene derivatives and therefore they could be considered greener protecting groups than the carbamate-based one.This work was funded in part by the National Research Foundation (NRF) (#105892 and Blue Sky's Research Programme#120386). The authors thank the Deanship of Scientific Research at King Saud University for funding this work through research group no. (RG-1441-365, Saudi Arabia). Special thanks go to Merck-Millipore-Sigma Aldrich for financial support and Dr. Peter White for continuous advice.Peer reviewe