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Updated: Jul 6, 2026

Constructing Cyclic Peptides Using an On-Tether Sulfonium Center
Published on: September 28, 2022
Morpholine-based immonium and halogenoamidinium salts as coupling reagents in Peptide synthesis1
Ayman El-Faham1, Fernando Albericio
1Institute for Research in Biomedicine, Barcelona Science Park, Josep Samitier 1, 08028-Barcelona, Spain. aymanel-faham@hotmail.com
Abstract:
Here we describe a new family of N-form immonium-type coupling reagents that differ in their carbocation skeleton structure. The N-methylpiperazine derivative failed to form immonium salts, while the thiomorpholine derivative did not give better results than the coupling reagents currently used. The presence of the morpholine had a marked influence on the solubility and stability as well as the reactivity of the reagent. Finally, the fluoroamidinium salt performed extremely well in the presence of only 1 equiv of base, thereby confirming the effect of the proton acceptor in the reaction.
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