A Sustainable Approach to ε-Lys Branched GLP-1 Analogs: Integrating Green SPPS, Metal-free Alloc Removal, Waste Minimization and TFA/PFAS-free Resin Cleavage

Epsilon-lysine branched (ε-Kb) glucagon-like peptide-1 (GLP-1) analogs comprise a prominent class of peptide therapeutics, altering the outlook for illnesses such as type 2 diabetes and obesity, in turn necessitating manufacturing on up to ton scales. Nevertheless, the lack of sustainable approaches to ε-Kb GLP-1s has raised concerns about the viability of making ε-Kb GLP-1s with current manufacturing methods. We report a solid-phase peptide synthesis (SPPS) approach to ε-Kb GLP-1s demonstrated by a four-α-disubstituted unnatural amino acid (uAA) containing GLP-1 triple agonist as a substrate. Our approach to ε-Kb GLP-1s encompassed efficient DMF-free SPPS, which required addressing solvent quality issues and metal-free Lys(Alloc) removal, for which a His iodination side reaction had to be tackled. Minimizing the footprint of the synthesis was achieved by a dual strategy, eliminating postcoupling washes and recycling the SPPS waste stream, while FeCl3/AcOH cleavage of ε-Kb GLP-1 peptide resin marks the expansion of TFA-free resin cleavage from 10AA to ∼40AA peptides. Taken together, our approach constitutes the first truly sustainable SPPS route to ε-Kb GLP-1s, opening up a new frontier in the commercially viable and environmentally responsible manufacturing of this notable class of incretin peptide drugs.