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.
Described herein is a comparative study of immobilised triphenylphosphine (PS-PPh 3 ) and 1-hydroxybenzotriazole (PS-HOBt) to mediate amide couplings under continuous flow. Compared to Appel-type amidations (PS-PPh 3 ), the developed 'catch-and-release' approach (PS-HOBt) afforded near-quantitative amide conversions. Utilising this strategy, sulfonyl chloride amenability enabled facile access to an expanded library of sulfonate and sulfonamides. Postconstructional peptide modification was also demonstrated, affording two N β -functionalised pentapeptides in high yields and purities. In contrast to frequently utilised coupling agents, the PS-HOBt resin could be recycled six times without a reduction in efficacy or regeneration requirements.
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