Bachem and Novo Nordisk find greener SPPS peptide synthesis alternatives

Bubendorf, Switzerland: – Bachem AG has partnered with Danish-based Novo Nordisk in studies to find alternative solvents to make solid phase peptide synthesis (SPPS) a significantly greener technology.

The studies propose solvent alternatives to replace the reprotoxic N, N-dimethylformamide (DMF), dichloromethane (DCM) and N-methyl-2-pyrrolidone (NMP). These solvents are currently the gold standards in SPPS processes for academic research and industrial production facilities, with excellent solubilization and stability properties for reagents and are the best choice in terms of resin swelling.

However, both solvents are to be restricted by the European Chemicals Agency (ECHA) due to their hazardous nature. While replacing DMF, DCM and NMP for a greener alternative presents a huge technical challenge, it will deliver significant gains in sustainability and reduced environmental footprint for peptide synthesis processes.

Screening solvents

Screening solvents and mixtures of solvents is required for achieving the best physiochemical properties in large scale SPPS.

The first study focused on the combination of solvent viscosity and polarity as key physicochemical parameters for SPPS, which consists of several steps requiring different optimum conditions. The use of binary solvent mixtures enabled the team to reach the desired solvent properties in a way otherwise impossible to achieve with neat solvents. In the search for a DMF substitute in large-scale SPPS, the study partners therefore decided to focus on environmental and safety aspects based on guidelines defined by REACH and the European Chemicals Agency (ECHA).

The study selected 19 ‘green’ solvents with acceptable environmental profiles that could be used neat or as mixtures and evaluated them for reagent solubility, solvent stability and resin swelling. In a series of reagent dissolution, resin swelling, peptide coupling and Fmoc-removal experiments, Study 1 showed that combining solvents offered unprecedented opportunities to predict and fine-tune overall solvent properties for different aspects of SPPS.

In particular, the Bachem/Novo Nordisk team found that binary mixtures of green solvents, such as dimethyl sulfoxide (DMSO)/ethyl acetate (EtOAc), DMSO/1,3-dioxolane (DOL), and DMSO/2-methyl tetrahydrofuran (2-Me-THF), displaying similar polarity and viscosity profiles to DMF presented viable, less toxic solvent alternatives for SPPS.

Binary solvent alternatives

The second study systematically investigated how the composition of green binary solvent mixtures influences Fmoc-removal, peptide coupling and common side reactions in SPPS, showing that the purity profile is not impacted adversely in binary solvent mixtures when compared to DMF.

Ultimately, the identified green binary solvent mixtures could be employed for the synthesis of a range of challenging model peptides and peptide therapeutics on meaningful scale, demonstrating that binary solvent mixtures are viable green alternatives to DMF in SPPS. The team demonstrated that the polarity and viscosity profile of a binary solvent mixture could be used to predict its usability in SPPS.

Furthermore, the researchers showed that the sole variation of the composition of the binary solvent mixture during synthesis represents a novel and simple tool to mitigate certain side-reactions in SPPS. Adjusting the ratio of binary solvent mixtures enables the reduction of Arg-lactamization and aspartimide formation. When applied to the synthesis of the peptide therapeutic Bivalirudin on a 7.5 mmol scale, the team found that simply adjusting the solvent ratio in a single step of the synthesis significantly suppressed a problematic Arg-lactamization side reaction. These results underline that green binary solvent mixtures not only can replace DMF in SPPS, but also provide novel solutions for mitigating common side-reactions in SPPS.

Sustainability commitment

As a leading company in the development and manufacture of peptide and oligonucleotide APIs, SPPS plays an important role in Bachem production processes. Therefore any innovation that reduces solvent consumption or created more sustainable alternatives has huge efficiency as well as environmental advantages for API production processes.

The studies with Novo Nordisk not only show ways to make current state-of-the-art manufacturing technologies more sustainable, but also identify new technologies that have intrinsic potential to minimize environmental impact. They succeeded in identifying environmentally benign solvents suitable for large-scale SPPS of peptide therapeutics at ambient temperature by assessing reagent solubility, resin swelling, amino acid coupling and Fmoc-removal efficiency in a collection of REACH compatible neat solvents and selected binary solvent mixtures. These studies further showed that binary solvent mixtures present viable alternatives to DMF for the synthesis of therapeutically relevant peptides, paving the way towards greener peptide synthesis.

About Bachem

Bachem is a leading, innovation-driven company specializing in the development and manufacture of peptides and oligonucleotides.

With 50 years of experience and expertise Bachem provides products for research, clinical development and commercial application to pharmaceutical and biotechnology companies worldwide and offers a comprehensive range of services.

Bachem operates internationally with headquarters in Switzerland and locations in Europe, the US and Asia.

The company is listed on the SIX Swiss Exchange. For further information, visit the Bachem website.

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