Advancing Sustainable Solid-Phase Peptide Synthesis: The Role of 1-(3-(Dimethylamino)propyl)-3-ethylcarbodiimide Methotosylate (EDC·MeTos) in Green Solvents

Abstract

Carbodiimides are essential reagents in peptide synthesis due to their ability to activate carboxylic acids toward amide bond formation. In this study, we investigated the coupling efficiency and racemization propensity of 1-(3-(Dimethylamino)propyl)-3-ethylcarbodiimide methotosylate (EDC·MeTos), both alone and in combination with ethyl 2-cyano-2-(hydroxyimino)acetate (OxymaPure), under green solvent conditions as alternatives to the conventional use of N,N-dimethylformamide (DMF). Using Fmoc-based solid-phase peptide synthesis (SPPS), we synthesized several model peptides to assess the coupling efficiency, side-product formation, and epimerization levels across different reaction media. Our results demonstrate that the binary green solvent system EtOAc/DMSO (ethyl acetate/dimethyl sulfoxide, 9:1) supports highly efficient peptide couplings when used with quaternary carbodiimides (QCD), producing peptides of comparable purity to those synthesized in DMF. Remarkably, the use of QCD alone in this green medium led to lower racemization levels than in DMF, highlighting a dual advantage in terms of both environmental impact and stereochemical integrity. The additive OxymaPure was beneficial for sterically hindered sequences such as Aib-ACP (α-aminoisobutyric acid-ACP), but not essential for less demanding peptides. Overall, the findings support the viability of green solvent systems in high-fidelity peptide synthesis, enabling more sustainable manufacturing practices.