The synthesis qf the ABCD ring system of wmnudne A has been achieved using the oli$n naadmis cy&mtion reocdon for the cm&l atamcyclic ring Djiamahn a&p.
Smooth operation: C‐terminal peptide activation with full stereointegrity was accomplished using a copper(II) ‐mediated coupling reaction of carboxylic acids with arylboroxines (see scheme, NCL = native chemical ligation, Boc = tert‐butoxycarbonyl). This method allows epimerization‐free activation and ligation of peptides with racemization‐prone phenylglycine at the C terminus.
Durch intramolekulare Staudinger‐Reaktion sind Lactame mittlerer Ringgröße aus ω‐Aminosäuren zugänglich, die sich herkömmlichen Ringschlussstrategien widersetzen. Ein unerwünschter vorzeitiger Ringschluss wird durch Schützen der Phosphanylgruppe als Borankomplex verhindert (siehe Schema, dabco=1,4‐Diazabicyclo[2.2.2]octan).
A new method to cyclise peptides is reported based on insertion of a salicylaldehyde derived pincer auxiliary in the linear precursor sequence. H-betaAla-Phe-OH and H-Phe-betaAla-OH were chosen as representative model peptides.
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