N‐Butylpyrrolidinone for Solid‐Phase Peptide Synthesis is Environmentally Friendlier and Synthetically Better than DMF

Abstract

Solid-phase peptide synthesis (SPPS) is the method of choice for the preparation of peptides in both laboratory scale and large production. Although the methodology has been improved during the last decades allowing the achievement of long peptides and challenging sequences in good yields and purities, the process was not revised from an environmental point of view. One of the main problems in this regard is the large amount of solvents used, and therefore the tons of generated waste. Moreover, the solvent of choice for the SPPS is N,N-dimethylformamide (DMF), which is considered as reprotoxic; thus, there is an urgent necessity to replace it with safer solvents. The DMF substitution by a green solvent is not a trivial task, because it should solubilize all the reagents and byproducts involved in the process, and, in addition to facilitating the coupling of the different amino acids, it should not favor the formation of side-reactions compared with DMF. Herein, it was demonstrated that the use of the green solvent N-butylpyrrolidinone (NBP) as a replacement of DMF was beneficial in two well-documented side reactions in peptide synthesis, racemization and aspartimide formation. The use of NBP rendered a lower or equal level of racemization in the amino acids more prone to this side reaction than DMF, whilst the aspartimide formation was clearly lower when NBP was used as solvent. Our findings demonstrate that the use of a green solvent does not hamper the synthetic process and could even improve it, making it environmentally friendlier and synthetically better.

Fmoc-Removal with Pyrrolidine Expands the Available Solvent Space in Green Solid-Phase Peptide Synthesis

“…In addition to DMF, three neat solvents and three binary solvent mixtures that have previously 22 been demonstrated to achieve good resin swelling and overall fast coupling reactions were initially included (Figure 2). Moreover, the neat solvent NBP, which has recently been promoted as a suitable alternative solvent for SPPS, 28,38,39 was included despite displaying a viscosity (3.3 mPa × s) well outside the range we have found acceptable (typically 0.5−1.1 mPa × s at room temperature). 22 Fmoc-Ala-Phe-Phe-Ala linked to the 2-chlorotrityl-PS resin was used as a model peptide for Fmoc-removal.…”

Replacing DMF in solid-phase peptide synthesis: varying the composition of green binary solvent mixtures as a tool to mitigate common side-reactions

“…41 However, the polarity of the solvent is also believed to play a central role, and a recent report showed that aspartimide formation was reduced when switching from DMF to the less polar green solvent NBP. 42 To shed more light on this finding, we investigated aspartimide formation in binary solvent mixtures of different polarity. To this end, we synthesised scorpion toxin II (Fmoc-Val-Lys(Boc)-Asp(OtBu)-Gly-Tyr(tBu)-Ile) on a Wang-PS resin, a wellstudied model peptide that readily undergoes aspartimide formation.…”

Rhodiasolv PolarClean – a greener alternative in solid-phase peptide synthesis

“…Maximum swelling was observed at 12 h at RT and at 3 h at 45°C. The polystyrene (PS) and ChemMatrix showed swelling values of (8,25,26) (Figure 2 and Table 3). We next tested the efficiency of PolarClean (also compared with DMF) for SPPS.…”