.beta.-Helical structure of D,L-alternating oligophenylalanines with terminal butyloxycarbonyl and methoxy groups in chloroform: comparison with oligovalines

Abstract

Tancredi, T.; Temussi, P. A.; Trivellone, E.; Bradbury, E. M.; Crane-Robinson, C., J. Chem. Soc., Chem.ABSTRACT: This paper reports on a 'H NMR study of the members 11-X (n = 2-10) and XV ( n = 15) of the series Boc-(L-Phe),-(D-Phe-L-Phe)c,-,,,z-OMe (n = number of residues in the oligopeptide; m = 0 or 1) in chloroform solution a t 25 'C. It is shown that there is a species that is strongly preferred by the oligophenylalanines with seven or more residues and that this species is a dimer with the structure of a right-handedt&@6,6-helix with 2(n -1) interstrand H bonds. In the case of XV this species is virtually the only one occurring. The preference of these D,L-alternating oligophenylalanines for a t J@5.6-helix contrasts with the behavior of the corresponding oligovalines, which, as it has been observed in earlier studies, form preferentially P4.*-helices in chloroform. The role of the nature of the side chains in determining this different behavior is discussed.ABSTRACT: The structure and conformational energies of polysilane, H-(SiH&,-H, and poly(dimethylsilylene), Me-(SiMe&,,-Me, have been investigated by using full relaxation empirical force field (EFF) techniques. Gauche conformational states are calculated to be lowest in energy for both polymers. These results contrast with polyethylene hydrocarbon polymers which typically adopt trans conformations in the ground state. Both polysilane and poly(dimethylsily1ene) are calculated to be conformationally more flexible than polyethylene.

Self-Assembling Organic Nanotubes

“…[52] Mirroring the findings with other b-sheet model systems, [53±55] Lorenzi and co-workers indicated that linear stereocooligopeptides (that is, peptides of alternating d,lconfiguration) containing b-or g-branched side chains strongly favor b-helical conformations. [56] In contrast, the less sterically demanding syndiotactic oligonorleucines between 8 and 15 residues in length did not form b-helices and proved much less soluble in chloroform than related branched species. [57] The reduced steric bulk presumably results in a lesser degree of b-helical preorganziation in the backbone, allowing precipitation through the formation of a-pleatedsheet aggregates.…”

Sequestration of connexin43 in the early endosomes: An early event of Leydig cell tumor progression

“…Diese und weitere Ergebnisse an anderen β ‐Faltblattmodellen53–55 führten Lorenzi et al zu dem Schluss, dass lineare Stereocooligopeptide (d. h. Peptide mit alternierender D , L ‐Konfiguration der Aminosäurereste) mit β ‐ oder γ ‐verzweigten Seitenketten β ‐helicale Konformationen stark bevorzugen 56. Demgegenüber bilden die sterisch weniger anspruchsvollen syndiotaktischen Oligonorleucine mit 8–15 Aminosäureeinheiten keine β ‐Helices und sind in Chloroform weit weniger löslich als entsprechende verzweigte Verbindungen 57.…”

12/10-Helical β-Peptide with Dynamic Folding Propensity: Coexistence of Right- and Left-Handed Helices in an Enantiomeric Foldamer

“…A number of heterochiral α-peptides that consist of alternating d - and l -α-amino acid residues are known to display β-helical conformations with either handedness, which is dependent on various factors such as side chain groups, solvent polarity, hydrogen bonding patterns, and backbone constraints. − Lorenzi and co-workers have reported the crystal structures of two d , l -alternating peptide octamers, Boc-( l -Val- d -Val) 4 -OMe and Boc-( l -Phe- d -Phe) 4 -OMe, displaying double-stranded, antiparallel β-helical conformations with left and right handedness, respectively . NMR analysis of related d , l -alternating peptides suggested that multiple forms of β-helices may exist in solution, although the major conformers are consistent with those in the crystal state . In contrast, Clark and co-workers have reported that a cyclic analogue with two β-turn motifs and two alternating d , l -oligovaline fragments displays a single type of double-stranded, antiparallel β-helical conformations with right handedness …”