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Updated: Sep 13, 2025

Synthesis and Structure Determination of µ-Conotoxin PIIIA Isomers with Different Disulfide Connectivities
Published on: October 2, 2018
Synthesis of Fusahexin and Characterization of a Natural β-Turn Dipeptide
Carmen Bäuerlein1, Armin Geyer1
1Philipps-University Marburg, Department of Chemistry, Hans-Meerwein-Straße 4, 35043 Marburg, Germany.
Abstract:
We describe the first synthesis of the natural cyclic hexapeptide Fusahexin cyclo(-ala-Leu-ehr=Pro-leu-Leu) (1) containing the bicyclic dipeptide ehr=Pro, a tetrahydro-1,3-oxazin-4-one formed from erythronine and proline. Fusahexin and several other peptides were obtained either by using the bicyclic dipeptide Fmoc-ehr=Pro-OH (2) in SPPS or by late-stage oxidation of a precursor peptide aldehyde. In all cases studied, the bicyclic dipeptide ehr=Pro cyclizes by acid-promoted condensation, forming the bridge head of the fused bicyclic ring exclusively in R configuration. The conformational behavior of Fusahexin and several stereochemical variants was characterized by NMR and modeling. Its convenient accessibility and its transferability make the β-turn dipeptide ehr=Pro a useful general reverse-turn dipeptide.
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