title: Morpholine-based immonium and halogenoamidinium salts as coupling reagents in Peptide synthesis1.
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.
authors.affiliation: Institute for Research in Biomedicine, Barcelona Science Park, Josep Samitier 1, 08028-Barcelona, Spain. aymanel-faham@hotmail.com
authors.forename: Ayman
authors.initials: A
authors.lastname: El-Faham
authors.forename: Fernando
authors.initials: F
authors.lastname: Albericio
mesh_terms: D000578:Amidines / Q000737:chemistry*; D018360:Crystallography, X-Ray; D007097:Imines / Q000737:chemistry*; D007202:Indicators and Reagents / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009025:Morpholines / Q000737:chemistry*; D010455:Peptides / Q000138:chemical synthesis* / Q000737:chemistry; D012492:Salts / Q000737:chemistry; D012995:Solubility; D013237:Stereoisomerism
chemical_list: D000578:Amidines; D007097:Imines; D007202:Indicators and Reagents; D009025:Morpholines; D010455:Peptides; D012492:Salts; C037574:morpholine