OxymaPure Coupling Reagents: Beyond Solid-Phase Peptide Synthesis

Total synthesis of [β-HIle]2-nodupetide: effect of ester to amide substitution on its antimicrobial activity

The increasing prevalence of deaths due to multidrug-resistant bacteria (MDRB) in infectious disease therapy has become a global health concern. This led to the development of new antimicrobial therapeutic agents that can combat resistance to pathogenic bacteria. The utilization of natural peptide compounds as potential antimicrobial agents is very promising. Nodupetide, a cyclodepsipeptide with very strong antimicrobial activity against Pseudomonas aeruginosa was isolated from the fermentation of Nodulisporium sp. Unfortunately, one of its residues (3S,4S)-3-hydroxy-4-methylhexanoic acid (HMHA) is not commercially available and the synthesis strategies applied have not been successful. Hence, we synthesized its cyclopeptide analogue [β-HIle]2-nodupetide by replacing HMHA with isoleucine homologue. A combination of solid- and solution-phase peptide synthesis was successfully carried out to synthesize [β-HIle]2-nodupetide with an overall yield of 10.4%. The substitution of HMHA with β-homoisoleucine (β-HIle) changed the ester bond into an amide bond in nodupetide's backbone. The analogue was considerably inactive against Pseudomonas aeruginosa. It can be concluded that the ester bond is crucial for the antimicrobial activity of nodupetide.

Total wash elimination for solid phase peptide synthesis

We present a process for solid phase peptide synthesis (SPPS) that completely eliminates all solvent intensive washing steps during each amino acid addition cycle. A key breakthrough is the removal of a volatile Fmoc deprotection base through bulk evaporation at elevated temperature while preventing condensation on the vessel surfaces with a directed headspace gas flushing. This process was demonstrated at both research and production scales without any impact on product quality and when applied to a variety of challenging sequences (up to 89 amino acids in length). The overall result is an extremely fast, high purity, scalable process with a massive waste reduction (up to 95%) while only requiring 10-15% of the standard amount of base used. This transformation of SPPS represents a step-change in peptide manufacturing process efficiency, and should encourage expanded access to peptide-based therapeutics.