Sustainable Peptide Synthesis Enabled by a Transient Protecting Group

Abstract

The growing interest in synthetic peptides has prompted the development of viable methods for their sustainable production. Currently, large amounts of toxic solvents are required for peptide assembly from protected building blocks, and switching to water as a reaction medium remains a major hurdle in peptide chemistry. We report an aqueous solid‐phase peptide synthesis strategy that is based on a water‐compatible 2,7‐disulfo‐9‐fluorenylmethoxycarbonyl (Smoc) protecting group. This approach enables peptide assembly under aqueous conditions, real‐time monitoring of building block coupling, and efficient postsynthetic purification. The procedure for the synthesis of all natural and several non‐natural Smoc‐protected amino acids is described, as well as the assembly of 22 peptide sequences and the fundamental issues of SPPS, including the protecting group strategy, coupling and cleavage efficiency, stability under aqueous conditions, and crucial side reactions.

Greening the synthesis of peptide therapeutics: an industrial perspective

“…6). 95,96 The Fmoc-analogue Smoc is removed under basic conditions (e.g. aqueous ammonia, ethanolamine or ethylenediamine, or piperidine), whereas the SBoc, tBuS, StBuS, sulfo-Trt and BOMS are removed under acidic conditions (e.g.…”

“…Furthermore, they determined epimerisation to be <0.5% for most studied amino acids in model peptides (up to 2% for Asp/Asn) and showed that side reactions such as aspartimide formation were sequence and temperature dependent. 96 Overall, ASPPS is an interesting technology which requires further development. It is currently not clear if the approach would be generally successful when applied to longer and more complex peptide sequences.…”

“…95 In line with the work described above, better aqueous solubility and easier purication by ion exchange chromatography can be expected but no data on their efficiency as coupling reagents has been disclosed making it unclear how well this technology works in practice, and for their recently published protocol, EDC-HCl and Oxyma was used. 96 A water-based SPPS strategy using N-carboxyanhydride (NCA) derivatives on a ChemMatrix® resin was reported by Gentilucci and co-workers. 98 The NCA amino acids for coupling were synthesised by microwave irradiation of the amino acid in the presence of triphosgene under solvent free conditions.…”

“…6 Sulfonate-derived protecting groups developed by Kolmar and co-workers and commercialised by the company Sulfotools. 95,96 This journal is © The Royal Society of Chemistry 2020 RSC Adv., 2020, 10, 42457-42492 | 42479 acid imide (HONB) the most effective in water and MTBE respectively. Several peptide sequences ranging from di-to pentapeptides were synthesized in water using TBTU/HOBt, typically affording the target peptides in high purities (94-100%).…”

Flow‐based SPPS for protein synthesis: A perspective

“…To further improve the properties of water‐compatible protecting groups, SO 3 − ‐functionalized protecting groups, so‐called 9‐(2‐sulfo)fluorenylmethyloxycarbonyl (Smoc) amino acid derivatives, [ 116 ] as well as additional solvation strategies, additional compatible activators and microwave irradiation were successfully implemented. [ 108,117–123 ]…”