Defect peptide chemistry: perturbations in the structure of a homopentapeptide induced by a guest residue interrupting side-chain regularity.
The fully blocked pentapeptide Tfa-(Deg)2-L-Abu-(Deg)2-OtBu (Tfa: triflouroacetyl; Deg: C alpha, alpha-diethylglycine; Otbu: tert-butoxy) adopts in the crystal state a regular, right-handed 3(10)-helical structure stabilized by three N--H...O=C intramolecular 1 < 4 (or C10) H bonds, as determined by an x-ray diffraction analysis. However, a Fourier transform ir absorption and 1H-nmr study strongly supports the view that in deuterochloroform solution the four Deg residues at both termini of the peptide main chain are involved in successive, fully extended C5 forms. A comparison with the stable, fully developed, multiple C5 conformation of Tfa-(Deg)5-OtBu indicates that incorporation of an Abu guest residue, interrupting the side-chain uniformity of the host (Deg)5 homopeptide, while altering only marginally the conformation in a solvent of low polarity, is responsible for a dramatic perturbation of the crystal-state structure.
Benedetti
E
E
CNR, Department of Chemistry, University of Naples Federico II, Italy.
Pedone
C
C
Pavone
V
V
Di Blasio
B
B
Saviano
M
M
Fattorusso
R
R
Crisma
M
M
Formaggio
F
F
Bonora
G M
GM
Toniolo
C
C
D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000737:chemistry*; D011487:Protein Conformation
D009842:Oligopeptides