Beta-turn mimic in tripeptide with Phe(1)-Aib(2) as corner residues and beta-strand structure in an isomeric tripeptide: an X-ray diffraction study |
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Authors: | Dutt Anita Fröhlich Roland Pramanik Animesh |
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Institution: | Department of Chemistry, University of Calcutta, 92, A. P. C. Road, Kolkata 700 009, India. |
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Abstract: | A single crystal X-ray diffraction study of the tripeptide Boc-Phe-Aib-Leu-OMe (Aib = alpha-aminoisobutyric acid) reveals that it forms structurally one of the best type II beta-turns so far reported in tripeptides, stabilized by 10 atom intramolecular hydrogen bonding. In contrast, the isomeric tripeptide Boc-Phe-Leu-Aib-OMe adopts a beta-strand like conformation. Interestingly, a previously reported structure of another isomeric tripeptide, Boc-Leu-Aib-Phe-OMe, shows a double bend conformation without any intramolecular hydrogen bonding. These results demonstrate an example of the creation of structural diversities in the backbone of small peptides depending upon the co-operative steric interactions amongst the amino acid residues. |
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