𝔖 Bobbio Scriptorium
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Experimental conformational study of two peptides containing α-aminoisobutyric acid. Crystal structure of N-acetyl-α-aminoisobutyric acid methylamide

✍ Scribed by A. Aubry; J. Protas; G. Boussard; M. Marraud; J. Neel

Publisher
Wiley (John Wiley & Sons)
Year
1978
Tongue
English
Weight
789 KB
Volume
17
Category
Article
ISSN
0006-3525

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✦ Synopsis

Some theoretical studies have predicted that the conformational freedom of the cy-aminoisobutyric acid (H-Aib-OH) residue is restricted to the a-helical region of the Ramachandran map. In order to obtain conformational experimental data, two model peptide derivatives, MeCO-Aib-NHMe 1 and Bu'CO-LPro-Aib-NHMe 2, have been investigated. The Aib dipeptide 1 crystallizes in the monoclinic system (a = 12.71 A, b = 10.19 A, c = 7.29 A, p = 110.02°, Cc space group) and its crystal structure was elucidated by x-ray diffraction analysis.

The azimuthal angles depicting the molecular conformation (4 = -55.5", 11. = -39.3') fall in the a-helical region of the Ramachandran map and molecules are hydrogen-bonded in a three-dimensional network. In CC1, solution, ir spectroscopy provides evidence for the occurrence of the so-called C g and C7 conformers stabilized by the intramolecular ii and i + 2i hydrogen bonds, respectively, The tripeptide 2 was studied in various solvents [CCld, CD2C12, CDC13, (CD&SO, and D20] by ir and pmr spectroscopies. I t was shown to accommodate predominantly the PI1 folded state stabilized by the i + 3i hydrogen bond. All these experimental findings indicate that the Aib residue displays the same conformational behavior as the other natural chiral amino acid residues. * Supplementary material listing observed and calculated structure factors for N-acetyla-aminoisobutyric acid methylamide, space group Cc, a = 12.71, b = 10.19, c = 7.

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