E. Benedetti et al., DEFECT PEPTIDE CHEMISTRY - PERTURBATIONS IN THE STRUCTURE OF A HOMOPENTAPEPTIDE INDUCED BY A GUEST RESIDUE INTERRUPTING SIDE-CHAIN REGULARITY, Biopolymers, 34(10), 1994, pp. 1409-1418
The fully blocked pentapeptide Tfa-(Deg),(2)-L-Abu-(Deg)(2)-OtBu (Tfa:
triflouroacetyl; Deg: C-alpha,C-alpha-diethylglycine; OtBu: tert-butox
y) adopts in the crystal state a regular, right-handed 3(10)-helical s
tructure stabilized by three N-H...O=C intramolecular 1 <-- 4 (or Clo)
H bonds, as determined by an x-ray diffraction analysis. However, a F
ourier transform ir absorption and H-1-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 e
xtended C-5 forms. A comparison with the stable, fully developed, mult
iple Cg conformation of Tfa-(Deg)(5)-OtBu indicates that incorporation
of an Abu guest residue, interrupting the side-chain uniformity of th
e host (Deg)(5) homopeptide, while altering only marginally the confor
mation in a solvent of low polarity, is responsible for a dramatic per
turbation of the crystal-state structure. (C) 1994 John Wiley and Sons
, Inc.