# Infrared Spectroscopy as a Probe for the Development of Secondary Structure in the Amino-Terminal Segment of Alamethicin

Rao, Pulla and Nagaraj, R and Rao, CNR and Balaram, P (1979) Infrared Spectroscopy as a Probe for the Development of Secondary Structure in the Amino-Terminal Segment of Alamethicin. In: FEBS Letters, 100 (2). pp. 244-248.

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Peptides containing \alpha-aminoisobutyryl (Aib) residues have been shown to adopt well-defined structures in solution, by 1H NMR methods [1]. Theoretical studies suggest that the presence of geminal methyl substituents at $C^{\alpha}$ imposes severe restrictions on the conformations accessible to Aib residues [2,3]. Single crystal X-ray diffraction studies of Z-Aib-Pro-NHMe[4], Z-Aib-Pro-Aib-Ala-OMe [5] and $Tosyl-{(Aib)}_5-OMe$ [6] have clearly established the tendency of Aib residues to adopt $3_{10}$ helical conformations and to initiate the formation of type III \beta bends, stabilised by 4 \rightarrow 1 intramolecular hydrogen bonds. Interest in the stereochemistry of Aib containing peptides, stems from the fact that alamethicin [7,8] and the related polypeptide ionophores antianioebin [9], emmerimicin [10], suzukacillin [11] and trichotoxin [12] contain high proportions of Aib residues. Here, we report the results of an infrared spectroscopic study of synthetic alamethicin fragments and demonstrate the development of a $3_{10}$ helical structure at the amino-terminus of the antibiotic.