X‐ray crystallography of peptides: The contributions of the Italian laboratories

Abstract

The review article summarizes the most relevant solid state structural and conformational results obtained in the laboratories involved in Italy in the studies of synthetic and natural peptides by x‐ray diffraction analyses. Some of the topics will include research studies carried out in other European countries, whereas in other cases studies carried out in Italy will be included in other review articles included in this volume. The review deals with peptides containing symmetrically achiral and unsymmetrically chiral Cα,α‐dialkylated glycine residues, peptides containing β‐alanine residues, α,β‐dehydroamino acid residues, and aminosuccinyl residues, peptides containing the thioamide surrogate, heterochiral peptides and several bioactive peptides systems with the proposed relationships between function and structure. © 1996 John Wiley & Sons, Inc.

Design and Synthesis of Chiral .ALPHA.,.ALPHA.-Disubstituted Amino Acids and Conformational Study of Their Oligopeptides

“…5,[8][9][10][11] Homopeptides composed of Aib assume a 3 10 -helical structure both in solution and in the crystal state. There are both enantiomeric right-handed (P) and left-handed (M) 3 10 -helices in the ratio of 1 to 1 because Aib is an achiral amino acid.…”

“…The author prepared homopeptides, Cbz-{(S,S)-Ac 5 c dOM } n -OMe (nϭ2, 4,6,8,10), by coupling between the N-terminal free peptide H-{(S,S)-Ac 5 c dOM } n -OMe and C-terminal free dipeptide acid Cbz-{(S,S)-Ac 5 c dOM } 2 -OH using EDC as a coupling reagent. The coupling reaction proceeded without problem, and homopeptides, up to the decapeptide, were prepared.…”

Stabilization of a novel β-turn-like motif by nonconventional intramolecular hydrogen-bonding interactions in a model peptide incorporating β-alanine

“…The de novo design of compact folded secondary structures of peptides incorporating flexible, unsubstituted β‐amino acid (β‐Ala; NHCH 2 CH 2 CO) continues to receive considerable attention 1–18. Identification and characterization of unique conformational preferences in short linear peptides incorporating this noncoding amino acid has demonstrated its potential as stereocontrolling element 1, 2, 7–17. Extensive x‐ray crystallographic investigations of β‐Ala peptides have revealed that the critical μ‐torsion angle of the β‐Ala residue exhibits pronounced preference for an energetically favorable, extended trans conformation (μ ≈ ±180° ± 20°) in short linear peptides and for a folded gauche conformation (μ ≈ ±60° ± 20°) in cyclic peptides 17.…”

Effect of methylene group insertions on the structural rigidity of Aib containing helices

“…Cyclic as well as acyclic β‐amino acids are accommodated well into helices, strands, and turn like secondary structures when these amino acids are incorporated in α‐amino acid peptide sequences . The simplest β‐amino acid, β‐alanine is capable of adopting different secondary structures like helix, turns, and extended conformations . After these observations, there was considerable interest in investigating conformations of the peptides containing β‐, γ‐, δ‐, and ε‐amino acids .…”