Green Solvent Mixtures for Solid-Phase Peptide Synthesis: A Dimethylformamide-Free Highly Efficient Synthesis of Pharmaceutical-Grade Peptides

Abstract

To replace dimethylformamide (DMF) in fluorenylmethoxycarbonyl (Fmoc) solid-phase peptide synthesis, we explored the application of mixtures of green solvents (green solvents mixtures for solid-phase peptide synthesis (GM-SPPS)) as combinations of Cyrene (dihydrolevoglucosenone), sulfolane, or anisole with dimethyl carbonate or diethyl carbonate, in different proportions. Their ability to swell differently functionalized polystyrene and polyethylene glycol resins was explored, and solubility of amino acids and coupling reagents was studied. Moreover, the synthesis of the model peptide Aib-enkephalin was performed in the new green mixtures, confirming the possibility to fully replace DMF all over SPPS. The two established best green protocols were then successfully applied to the synthesis of a longer peptide (Aib-ACP). Finally, the green solvent-based procedure was applied to the synthesis of the reduced form of the active pharmaceutical ingredient (API) Octreotide. After oxidative cyclization and a single high-pressure column chromatography, the pharmaceutical-grade compound was isolated in comparable high yield to that obtained with the standard procedures.

Scope and Limitations of γ-Valerolactone (GVL) as a Green Solvent to be Used with Base for Fmoc Removal in Solid Phase Peptide Synthesis

“…Several attempts have been made to replace DMF with a green solvent, according to the solvent selection guide [14]. Our group and others have proposed the use of less hazardous and green solvents such as water [15], acetonitrile (ACN), tetrahydrofuran (THF) [16], 2-methyltetrahydrofuran (2-MeTHF) [17,18], N -formylmorpholine (NFM) [19], γ-valerolactone (GVL) [12,19,20], N -butylpyrrolidone (NBP) [21], and propylene carbonate [22], and even mixtures of green solvents [23]. In order to be used in SPPS, solvents must have the capacity to swell the resins to allow the reagents to reach the active functional groups, and they must also be efficient during the coupling and deprotection steps, both of which are crucial [11].…”

Assessing the correlation of microscopy‐based and volumetry‐based measurements for resin swelling in a range of potential greener solvents for SPPS

“…We have also reported the use of GVL and another green solvent Cyrene (dihydrolevoglucosenone) 49 as part of our previous studies involving the critical initial loading stage of SPPS 50 . Studies involving mixtures of greener solvent systems, in the context of GSPPS, have been applied by Přibylka et al, 51 Ran et al, 52 Pawlas et al 53 and Ferrazzan et al 54 Recently, Ran et al also reported highly detailed swelling and peptide synthesis study involving mixed solvent systems, including mixed green solvents 52 . Ran et al found that, in general, the swelling properties of Hypogel 200 and Merrifield resins in certain binary solvent systems do not vary linearly relative to the composition of the mixture 52 .…”

Greening the synthesis of peptide therapeutics: an industrial perspective

“…Ferrazzano et al reported the combinations of Cyrene™ or sulfolane with DEC, and anisole with DMC in varying ratios as green alternatives for SPPS (Table 4), 41 although sulfolane is undesired in waste water and suspected of reproductive toxicity, and anisole is suspected of causing genetic defects (see Table 1). 14 The swelling properties of Merrield, ChemMatrix® and Tentagel™ resins in combination with either Wang or Rink Amide linkers were evaluated.…”

“…Next, DIC/Oxyma Pure in the three different solvent systems was evaluated for its ability to solubilise 18 representative Fmoc-protected amino acid building blocks. In all cases, the activated Fmoc-amino acid was fully soluble at a concentration of 0.2 M. 41 In another study, Lopez et al studied the swelling and solubilisation properties of a wide range of solvents, including many environmentally problematic or poorly characterised ones (e.g. DMPU, tetramethyl urea and sulfolane), using an aminomethylpolystyrene resin (Table 5).…”