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Effect of lengthening of peptide backbone by insertion of chiral β‐ homo amino acid residues: Conformational behavior of linear peptides containing alternating L ‐leucine and β‐ homo L ‐leucine residues
Author(s) -
Rossi F.,
Bucci E.,
Isernia C.,
Saviano M.,
Iacovino R.,
Romanelli A.,
Di Lello P.,
Grimaldi M.,
Montesarchio D.,
De Napoli L.,
Piccialli G.,
Benedetti E.
Publication year - 2000
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/(sici)1097-0282(200002)53:2<140::aid-bip4>3.0.co;2-g
Subject(s) - chemistry , tripeptide , conformational isomerism , stereochemistry , peptide , intramolecular force , dipeptide , residue (chemistry) , leucine , side chain , crystallography , dihedral angle , amino acid , molecule , hydrogen bond , organic chemistry , biochemistry , polymer
The synthesis and the solution behavior of the linear peptides containing a β‐ homo (β‐H) leucine residue—Boc–Leu–β‐HLeu–Leu–OMe, Boc–β‐HLeu–Leu–β‐HLeu–Leu–OMe, and Boc–Leu–β‐HLeu–Leu–β‐HLeu–Leu–OMe—as well as the solid structure of the tripeptide, are reported. The conformational behavior of the peptides was investigated in solution by two‐dimensional nmr. Our data support the existence in solution with different families of conformers in rapid interchange. The crystals of the tripeptide are orthorhombic, space group P2 1 2 1 2, with a = 15.829(1) Å, b = 29.659(1) Å, c = 6.563(1) Å, and Z = 4. The structure has been solved by direct methods and refined to final R1 and wR2 indexes of 0.0530 and 0.1436 for 2420 reflections with I > 2σ( I ). In the solid state, the tripeptide does not present intramolecular H bonds, and the peptide backbone of the two leucine residues adopts a quasi ‐extended conformation. For the β‐HLeu residue, the backbone conformation is specified by the torsion angles ϕ 2 = −120.9(4)°, μ 2 = 56.7(4)°, ψ 3 = −133.2(4)°. The side chains of the three residues assume the same conformation ( g − , g − , trans ), and all peptide bonds, except the urethane group at the N‐terminus, are in the trans conformation. Preliminary conformational energy calculations carried out on the Ac–NH–β‐HAla–NHMe underline that the conformations with μ angle equal to 180° and 60° assume lower energy with respect to the others. In addition, we found a larger conformational freedom for the ψ angle with respect to the ϕ angle. © 2000 John Wiley & Sons, Inc. Biopoly 53: 140–149, 2000