Cyclo‐β‐peptides: Structure and tubular stacking of cyclic tetramers of 3‐aminobutanoic acid as determined from powder diffraction data

Abstract

Dedicated to Professor Hans Paulsen on the occasion of his 75th birthday (23.XII. 1996) The solid-state structures of three stereoisomers, 1-3, of the cyclic tetramer of 3-aminobutanoic acid are presented. These cyclo-p-peptides were found to be highly insoluble materials, and it proved to be impossible to grow crystals of suficient quality for X-ray single-crystal analysis. The samples of 1-3 were, however, suitable candidates for structure determination from powder diffraction data (Fig. Z), and the application of this method is described. All three isomers have been found to adopt tubular structures (Figs. 2-4) in a fashion similar to those already observed for certain cyclo-a-peptides. The stacks of 16-membered rings are held together by four nonlinear C=O ...H-N H-bonds between pairs of molecules (Fig. 5 ) .

(S)-β3-Homolysine- and (S)-β3-Homoserine-Containingβ-Peptides: CD Spectra in Aqueous Solution

“…Changes of the CD spectra in the range 195 ± 200 nm are not discussed. 12 ) When measured in TFE, the CD spectra exhibit a stronger negative Cotton effect (Fig. 2).…”

“…More recently, further structural diversity has been achieved with the successful design and synthesis of parallel [4] [10] and antiparallel [11] pleated-sheet-type structures based on b With respect to potential applications of b-peptides in biological systems, the current challenge is to design, based on secondary structural elements, b-peptides with a given secondary structure and with specific biological functions. For example, cyclob 3 -tetrapeptides that have been found to form nanotubes in the solid state [12], have recently been used as transmembrane ion channels [13]. The elucidation of structural propensities of linear b-peptides in aqueous environment represents a further important issue that still needs to be addressed for future developments in bioorganic chemistry.…”

Using a structure envelope to facilitate structure solution from powder diffraction data

“…In this way, periodic nodal lines (PNL), which are the two-dimensional equivalents of PNS, can be generated within the centrosymmetric planes. The PNL for a cyclic tetramer of a /3 peptide (Seebach et al, 1997), generated from the {220} and {310} reflections in the noncentrosymmetric space group 14 is shown in Fig. 3.…”

Effect of lengthening of peptide backbone by insertion of chiral ?-homo amino acid residues: Conformational behavior of linear peptides containing alternatingL-leucine and ?-homoL-leucine residues

“…In addition to the linear peptides, Seebach and co-workers have synthesized and studied the conformations of cyclic ␤-peptides. 8 In the solid state, these cyclopeptides stack one on top of the other in a cylindrical array stabilized by hydrogen bonds. These cylindrical array display structural similarities with the nanotubules investigated by Hartgerink et al 9 and by Sun and Lorenzi.…”

“…The name "␤-homo" is utilized to designate the intercalation of a CH 2 unit between the ␣-carbon and the carboxylic group of a proteinogenic ␣-amino acid according to Spatola. 12 The nomenclature proposed by Seebach et al 8 for the description of the peptide sequences is also used.…”