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NMR investigations on alanyl-[15% 13C, 95% 15N]-proline: 15N chemical shifts and 13C15N coupling constants

✍ Scribed by F. Blomberg; H. Rüterjans; K. Lintner; F. Toma; S. Fermandjian

Publisher
John Wiley and Sons
Year
1978
Tongue
English
Weight
435 KB
Volume
11
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

The dipeptide alanylproline has been prepared with the proline residue both ^13^C (15%) and ^15^N (95%) enriched. ^15^N NMR spectra of alanylproline reveal signals for both possible conformations—cis and trans—of the dipeptide backbone in solution. Different p__K__ values for both conformers are obtained from the pH dependence of the ^15^N chemical shifts using a least square programme based on the Henderson–Hasselbach equation. These different values are discussed in terms of interaction between the α‐amino group and the carboxylate group and between the carboxylate oxygen and the carbonyl oxygen of the dipeptide via hydrogen bonding. Further evidence for these interactions is obtained from the pH dependence of the ratio of the ^15^N NMR signal intensities of the two conformers. One, two or three bonded ^13^C^15^N coupling constants measured in the ^13^C NMR high resolution spectra have different values in the cis and trans isomers of alanylproline and thus indicate different geometry in the pyrrolidine ring.

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