Novel, efficient and mild preparation of 7- and 8-membered cyclic di- and 10-membered cyclic tripeptides containing α-, β- or γ-amino acid residues is effected by a Staudinger-mediated ring closure. Medium-sized cyclic di- and tripeptides – recognized as difficult targets – were obtained in moderate to good yields according to a straightforward sequence. Empirical force-field calculations were undertaken to determine their conformational behaviors and showed high levels of similarity with X-ray results. A computational study at the B3LYP/6-31+G** level of theory afforded information regarding the impact of the sequence, ring-size and substitution on the activation barriers for the cyclization of azido peptide thioesters.
Organic & Biomolecular Chemistry
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