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- Title
Helix-Forming Oligoureas: Temperature-Dependent NMR, Structure Determination, and Circular Dichroism of a Nonamer with Functionalized Side Chains.
- Authors
Hemmerlin, Christine; Marraud, Michel; Rognan, Didier; Graff, Roland; Semetey, Vincent; Briand, Jean-Paul; Guichard, Gilles
- Abstract
To further investigate the degree of structural homology between γ-peptides A and N, N′-linked oligoureas B, we prepared oligourea nonamer 2 containing Ala, Val, Leu, Phe, Tyr and Lys side chains. Oligomer 2 was synthesized on solid support from activated monomers, i.e., from enantiomerically pure succinimidyl {2-{[(9 H-fluoren-9-ylmethoxy)carbonyl]amino}ethyl}carbamates 3a- f that are further substituted at C(2) of the ethyl moiety. These precursors were conveniently prepared from N-Fmoc-protected β3-amino acids with corresponding side chains. Detailed NMR studies (DQF-COSY, TOCSY, and ROESY) in (D5)pyridine revealed that 2 adopts a regular ( P)- 2.5 helical secondary structure very similar to that previously determined for oligourea heptamer 1 and closely related to the ( P)- 2.614 helix of γ-peptides. Temperature-dependent NMR further demonstrated the conformational homogeneity and remarkable stability of the structure of 2 in pyridine. The CD spectrum of 2 (0.2 m M) was recorded in MeOH with the aim to gain more information about the conformation of oligoureas. In contrast to 2.6-helical γ-peptides, which display only a weak or no Cotton effect, oligourea 2 exhibits an intense positive Cotton effect at ca. 203 nm ([ Θ]=+373000 deg cm2 dmol−1) that decreases only slowly upon increasing the temperature.
- Publication
Helvetica Chimica Acta, 2002, Vol 85, Issue 11, p3692
- ISSN
0018-019X
- Publication type
Article
- DOI
10.1002/1522-2675(200211)85:11<3692::AID-HLCA3692>3.0.CO;2-W