Going Green With Sustainable Peptide Production

Tharwat Mohy El Dine, Innovation Scientist at the PolyPeptide Group began by introducing her company as a global market leader for innovative clinical and commercial peptide drug substances. The peptide market and development of peptide drugs have become hot topics in pharmaceutical research because of their pharmacological properties and safety profiles. Over 80 peptides have been approved and marketed across the globe with over 170 in active clinical development and around 600 in preclinical evaluation. However, an increase in the complexity of peptide sequences has created a demand for the development of new formulation strategies and applications such as personalised therapy. Furthermore, there has been a recent push for more sustainable practices in peptide manufacturing. PolyPeptide has a green chemistry program that aims to reduce its environmental footprint. To guide their route to sustainability, El Dine outlined their thinking: “It is important to identify the critical process steps of solid-phase peptide synthesis, which will guide us during the search for improvement opportunities that will be further implemented in industrial applications.” As their first measure toward achieving sustainable manufacturing, PolyPeptide implemented batch washing in the standard SPPS reactor used for large-scale manufacturing. Repeated batch washing led to reduced solvent consumption attained using a lower volume of solvent per batch wash but also had a negative impact on manufacturing time. To tackle this and improve washing PolyPeptide introduced the percolation concept, which requires a continuous addition of DMF whole controlling the percolation velocity to allow continuous liquid phase draining. El Dine outlined the results: “Compared to batch wash, percolation allowed the reduction of solvent consumption by 57% and contributed to a significant reduction in washing time by more than 60%.” PolyPeptide is also committed to recycling and has extensive experience in acetonitrile recycling in downstream processes. At PolyPeptide’s manufacturing facility, 90% of the waste is recycled to secure the supply of solvent. Furthermore, PolyPeptide is trying to tackle the challenge of replacing highly hazardous reagents and solvents like DMF or additives such as piperidine. Although DMF is an effective universal solvent for SPPS it is highly toxic, resulting in the REACH Regulation amending some of their rules to restrict the manufacture and use of DMF on the European market starting at the end of 2023. Therefore, PolyPeptide is looking to find green alternatives. No single solvent mixtures were able to compete with DMF but binary solvent mixtures including DMSO/2-Me-THF, DMSO/DOL, and NBP/DOL were able to synthesise longer peptides up to 28-mer residues. Yet, the ratios of both solvents need to be further tuned based on additional considerations. The extra parameters include kinetics of pre-activation, the solubility of amino acids in green solvents, precipitation of diisopropylurea, and critical impurities assessment. In DMF, pre-activation was slow and coupling was fast and pre-activation kinetics was tested in alternative solutions like Fmoc-phenylalanine in DMF alongside different green solvents from the literature. Pre-activation kinetics is important because it will have a direct impact on synthesis time, formation of side products, and implementation at a larger scale. The results showed that optimal solubility was achieved in DMSO/ethyl acetate and DMSO/THF mixtures. Additionally, addressing the formation of diiosopropylurea (DIU), a problematic by-product during scale-up, is crucial to minimizing waste and ensuring efficiency. The identification and management of critical impurities further enhance downstream processes, improving cost-effectiveness and purification yields. Looking ahead, the PolyPeptide Group continues to explore green alternatives for DMF and is investigating mechanochemistry for solvent-free peptide synthesis.