Accelerated Synthesis of Protected Peptides in a Continuous-Flow Fixed-Bed Reactor

Amide Bonds Meet Flow Chemistry: A Journey into Methodologies and Sustainable Evolution

Formation of amide bonds is of immanent importance in organic and synthetic medicinal chemistry. Its presence in "traditional" small-molecule active pharmaceutical ingredients, in linear or cyclic oligo- and polypeptidic actives, including pseudopeptides, has led to the development of dedicated synthetic approaches for the formation of amide bonds starting from, if necessary, suitably protected amino acids. While the use of solid supported reagents is common in traditional peptide synthesis, similar approaches targeting amide bond formation in continuous-flow mode took off more significantly, after a first publication in 2006, only a couple of years ago. Most efforts rely upon the transition of traditional approaches in flow mode, or the combination of solid-phase peptide synthesis principles with flow chemistry, and advantages are mainly seen in improving space-time yields. This Review summarizes and compares the various approaches in terms of basic amide formation, peptide synthesis, and pseudopeptide generation, describing the technological approaches and the advantages that were generated by the specific flow approaches. A final discussion highlights potential future needs and perspectives in terms of greener and more sustainable syntheses.

The renascence of continuous-flow peptide synthesis - an abridged account of solid and solution-based approaches

Within a decade of Merrifield's seminal description of solid-phase peptide synthesis, the synergies between solid-phase approaches and flow synthesis were noted by a number of groups. However, despite the various advantages flow brings to peptide synthesis, throughout the 1990s and 2000s, interest in the technique was overshadowed by microwave assisted approaches. However, the current expansion of flow technologies has reinvigorated interest in both solid-phase and solution-phase continuous-flow approaches for assembling peptides. This perspective traces the introduction and evolution of continuous-flow solid-phase synthesis from a practical aspect with a particular focus on solid supports, acylation protocols, and racemisation suppression. Practical aspects of solution-phase continuous-flow peptide synthesis are also considered with an evaluation of microreactor systems, coupling protocols, and fragment-based approaches for assembly of extended peptide units.

A continuous flow protocol to generate, regenerate, load, and recycle chlorotrityl functionalised resins

From a screen of chlorinating agent concentration, flow rates, and reagent addition methodologies, a continuous flow protocol to activate, reactivate, and recycle both 2-chlorotrityl chloride functionalised polystyrene and trityl-hydroxy ChemMatrix functionalised resins was established.

An optimised approach for continuous-flow solid-phase peptide synthesis utilising a rudimentary flow reactor

From the repurposing of used HPLC components, a chromatography column, a Rheodyne,® and a heater stirrer, a simple, cost-effective system to conveniently conduct continuous flow solid-phase peptide construction was assembled.