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Development of a Backbone Cyclic Peptide Library as Potential Antiparasitic Therapeutics Using Microwave Irradiation

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New 21- and 24-atom Aib-containing cyclopeptides.

Tatjana Jeremic¹, Anthony Linden, Heinz Heimgartner

¹Institute of Organic Chemistry, University of Zürich, Winterthurerstrasse 190, Zürich, Switzerland.

Journal of Peptide Science : an Official Publication of the European Peptide Society

|June 5, 2008

Summary

Researchers synthesized cyclic peptides containing alpha-aminoisobutyric acid (Aib). Peptide cyclization success and yield depended on coupling reagents, with octapeptides yielding better than heptapeptides.

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Area of Science:

Peptide Chemistry
Organic Synthesis
Structural Biology

Background:

Cyclic peptides offer unique structural and functional properties.
Alpha-aminoisobutyric acid (Aib) residues induce specific conformational preferences in peptides.

Purpose of the Study:

To synthesize novel Aib-containing cyclic octapeptides and a cyclic heptapeptide.
To evaluate the efficiency of different coupling reagents in the macrolactamization step.
To perform conformational analysis of the synthesized cyclic octapeptide.

Main Methods:

Solution-phase synthesis of linear peptide precursors.
Solution-phase cyclization using various coupling reagents (PyAOP, HATU, DEPC/DEPBT).
X-ray crystallography for crystal-state conformational analysis.

Main Results:

Successful synthesis of two cyclic octapeptides and one cyclic heptapeptide.
Cyclization efficiency was highly dependent on the coupling reagent used.
Octapeptides (1 and 2) were obtained in higher yields (up to 63%) compared to the heptapeptide (3, 30-37%).
X-ray crystallography revealed a stable structure for octapeptide 2, stabilized by six intramolecular hydrogen bonds and multiple beta- and gamma-turns.

Conclusions:

The choice of coupling reagent is critical for efficient synthesis of Aib-containing cyclic peptides.
Cyclic octapeptides were synthesized more effectively than the cyclic heptapeptide.
The conformational analysis provides insights into the structural features of Aib-rich cyclic peptides.