270575-69-4Relevant articles and documents
Helix-forming oligoureas: Temperature-dependent NMR, structure determination, and circular dichroism of a nonamer with functionalized side chains
Hemmerlin, Christine,Marraud, Michel,Rognan, Didier,Graff, Roland,Semetey, Vincent,Briand, Jean-Paul,Guichard, Gilles
, p. 3692 - 3711 (2002)
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-{[(9H-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 mm) 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 ([O] = +373000 deg cm2 dmol-1) that decreases only slowly upon increasing the temperature.
