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  • 1
    Digitale Medien
    Digitale Medien
    Circular dichroism studies of α-aminoisobutyric acid-containing peptides: Chain length and solvent effects in alternating Aib-L-Ala and Aib-L-Val sequences (1984)
    New York : Wiley-Blackwell
    Biopolymers 23 (1984), S. 877-886 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The CD spectra of the peptides Boc-X-(Aib-X)n-OMe (n = 1, 2, 3) and Boc-(Aib-X)5-OMe, where X = L-Ala or L-Val have been examined in several solvents. The X = Ala and Val peptides behave similarly in all solvents, suggesting that the Aib residues dominate the folding preferences of these peptides. The decapeptides adopt helical conformations in methanol and trifluoroethanol, with characteristic negative CD bands at 222 and 205 nm. In the heptapeptides, similar spectra with reduced intensities are observed. Comparison with nmr studies suggest that estimates of helical content in oligopeptides by CD methods may lead to erroneous conclusions. The pentapeptides yield solvent-dependent spectra indicative of conformational perturbations. Peptide association in dioxane results in an unusual spectrum with a single negative band at 210 nm for the decapeptides. Disaggregation is induced by the addition of methanol or water to dioxane solutions. Aggregation of the heptapeptides is less pronounced in dioxane, suggesting that a critical helix length may be necessary to promote association stabilized by helix dipole-dipole interactions.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.360230505
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  • 2
    Digitale Medien
    Digitale Medien
    Stabilization of γ-turn conformations in peptides by disulfide bridging (1985)
    New York : Wiley-Blackwell
    Biopolymers 24 (1985), S. 2041-2043 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.360241104
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  • 3
    Digitale Medien
    Digitale Medien
    Stereochemistry of α-aminoisobutyric acid peptides in solution: Conformations of decapeptides with a central triplet of contiguous L-amino acids (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 2209-2223 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The decapeptides Boc-Aib-L-Val-Aib-Aib-(L-Val)3-Aib-L-Val-Aib-OMe and Boc-Aib-L-Leu-Aib-Aib-(L-Leu)3-Aib-L-Leu-Aib-OMe have been studied in CDCl3 and (CD3)2SO solutions by 270-MHz1 H-nmr. In CDCl3, the presence of eight intramolecularly hydrogen-bonded NH groups has been established, consistent with a 310-helical conformation, for both decapeptides. In (CD3)2SO, only seven solvent-shielded NH groups are observed, supporting either an α-helical conformation or a partially unfolded 310-helix. Ir studies provided supporting evidence for intramolecularly hydrogen-bonded structures in CHCl3, while CD studies suggest helical conformation in both decapeptides in various solvents. CD studies also support helical folding in the C-terminal hexapeptides. The central triplet of L-amino acids appears to destabilize 310-helical conformations in polar solvents like (CD3)2SO.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.360251112
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  • 4
    Digitale Medien
    Digitale Medien
    Solvated helical backbones: X-ray diffraction study of Boc-Ala-Leu-Aib-Ala-Leu-Aib-OMe · H2O (1989)
    New York : Wiley-Blackwell
    Biopolymers 28 (1989), S. 773-781 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A second example of insertion of a water molecule into the helical backbone of an apolar peptide is presented here and compared to a similar occurrence in a longer peptide with the same type of sequence of residues, i.e., Boc-Aib-(Ala-Leu-Aib)3-OMe. The backbone of the title compound assumes an approximate 310-helical form with three 4 → 1 hydrogen bonds. In the place of a fourth 4 → 1 hydrogen bond, a water molecule is inserted between O(1) and N(4), and acts as a bridge by forming hydrogen bonds N(4) … W(1) (2.95 Å) and W(1) … O(1) (2.81 Å). The water molecule participates in a third hydrogen bond with a neighboring peptide molecule, W(1) … O(4) (2.91 Å). The insertion of the water molecule causes the apolar peptide to mimic an amphiphilic helix. Crystals grown from ethyl acetate/petroleum ether (reported here) or from methanol/water solution are in space group P212121 with a = 12.024(4) Å, b = 15.714(6) Å, c = 21.411(7) Å, Z = 4 and dcalc = 1.124 g/cm3 for C32H58N6O9 · H2O. The overall agreement factor R is 6.3% for 2707 reflections observed with intensities 〉 3σ(F) and the resolution is 0.90 Å.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.360280307
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  • 5
    Digitale Medien
    Digitale Medien
    Peptide design: Influence of a guest Aib-Pro segment on the stereochemistry of an Oligo-Val sequence - solution conformations and crystal structure of Boc-(Val)2-Aib-Pro-(Val)3-OMe (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 1433-1442 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The peptide Boc-Val-Val-Aib-Pro-Val-Val-Val-OMe has been synthesized to investigate the effect of introduction of a strong β-turn promoting guest segment into an oligopeptide with a tendency to form extended structures. 1H-nmr studies in solution using analysis of NH group solvent accessibility and nuclear Overhauser effects suggest an appreciable solvent dependence of conformations. In chloroform a 310-helical structure is favored while in dimethylsulfoxide an Aib-Pro β-turn with extended arms on either side is suggested. In the crystal, the backbone forms a somewhat distorted 310-helix despite the presence of a Pro residue in the middle. Among the four possible intrahelical hydrogen bonds three are of the 4 → 1 type and one 5 → 1. Head-to-tail NH⃛O=C hydrogen bonds link the helical molecules into continuous columns. The space group is P212121 with a = 11.320(2), b = 19.889(3), and c = 21.247(3) Å.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.360291010
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  • 6
    Digitale Medien
    Digitale Medien
    Accommodation of a D-Phe residue into a right-handed 310-helix: Structure of Boc-D-Phe-(Aib)4-Gly-L-Leu-(Aib)2-Ome, an analogue of the amino terminal segment of antiamoebins and emerimicins (1993)
    New York : Wiley-Blackwell
    Biopolymers 33 (1993), S. 401-407 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The crystal structure of the nonapeptide Boc-D-Phe-Aib-Aib-Aib-Aib-Gly-Leu-Aib-AibOMe (I), which is an analogue of the N-terminal sequence of antiamoebins and emerimicins, establishes a completely 310-helical conformation with seven successive intramolecular 4 → 1 hydrogen bonds. The average, φ, ψ values for residues 1-8 are -59° and -32°, respectively. Crystal parameters are C47H77N9O12, space group P1, a = 10.636(4) Å, b = 11.239(4) Å, c = 12.227(6) Å, α = 101.17(4)°, β = 97.22(4)°, γ = 89.80(3)°, Z = 1, R = 5.95% for 3018 data with |F0| 〉 3α(F), resolution 0.93 Å. The use of the torsion angle κ = C(i - 1)N(i)Cα(i)Cβ(i), where κ = 68° for D-Phe and κ = 164° for L-Leu, confirms the opposite configurations of these residues. The φ, ψ values of -62° and -32° at D-Phe are unusual, since this region is characteristic of residues with L configurations. Peptide I possesses only two chiral residues of opposing configuration. The observed right-handed 310-helical structure suggests that helix sense has probably been determined by the stereo-chemical preferences of the Leu residue. © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.360330308
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  • 7
    Digitale Medien
    Digitale Medien
    Solid state and solution conformations of a helical peptide with a central gly-gly segment (1996)
    New York : Wiley-Blackwell
    Biopolymers 38 (1996), S. 515-526 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The influence of amino acids with contrasting conformational tendencies on the stereochemistry of oligopeptides has been investigated using an octapeptide Boc-Leu-Aib-Val-Gly-Gly-Leu-Aib-Val-OMe, which contains two helix-promoting Aib residues and a central helix-destabilizing Gly-Gly segment. Single crystal x-ray diffraction studies reveal that a 3 10-helix is formed up to the penultimate Aib residue, at which point there is a helix reversal in the backbone, reminiscent of a C-terminal 6 → I hydrogen bond. The curious feature in the crystal is the solvation of the possible 6 → 1 bond by a CH3OH molecule, where the OH is inserted between O(3) and N(8) and participates in hydrogen bonds with both. The cell parameters are as follows: space group P212121, a = 10.649(4) Å, b = 15.694(5) Å, c = 30.181(8) Å, R = 6.7% for 3427 data (| F0| 〉 3σF) observed to 0.9 Å. Nuclear magnetic resonance studies in CDCl3 using NH group solvent accessibility and nuclear Overhauser effects as probes are consistent with a 3 10-helical conformation. In contrast, in (CD3)2SO, unfolding of the central segment results in a multiple β-turn structure, with β-turn conformations populated at residues 1-2, 3-4, and 6-7. CD studies in methanol-2,2,2-trifluoroethanol (TFE) mixtures also provide evidence for a solvent-dependent structural transition. Helical conformations are populated in TFE, while type II β-turn structures are favored in methanol. © 1996 John Wiley & Sons, Inc.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Peptide design: Crystal structure of a helical peptide module attached to a potentially nonhelical amino terminal segment (1996)
    New York : Wiley-Blackwell
    Biopolymers 39 (1996), S. 75-83 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The peptide Boc-Gly-Dpg-Gly-Val-Ala-Leu-Aib-Val-Ala-Leu-OMe has been designed to examine the structural consequences of placing a short segment with a low helix propensity at the amino terminus of a helical heptapeptide module. The Gly-Dpg-Gly segment is a potential connecting element in the synthetic construction of a helix-linker-helix motif. Crystal parameters for the peptide are P21, a = 8.651(3) Å, b = 46.826(13) Å, c = 16.245 Å, β = 90.13(3)*, Z = 4; 2 independent molecules/asymmetric unit. The structure reveals almost identical conformations for the two independent molecules. The backbone is completely helical for residues 2-9, with one 4 → 1 hydrogen bond and six 5 → 1 hydrogen bonds. The α,α-di-n-propylglycine residue adopts a helical conformation. Gly(1) adopts an extended conformation resulting in a nonhelical N-terminus, with the Boc group swinging away from the helix. The lateral association of helices in the b axis direction is unusual in that the helix axes are directed up or down (parallel or antiparallel) by pairs: ↓↓↑↑↓↓, etc. © 1996 John Wiley & Sons, Inc.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Polymyxin B nonapeptide: Conformations in water and in the lipopolysaccharide-bound state determined by two-dimensional NMR and molecular dynamics (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 251-265 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Polymyxin B nonapeptide (PMN) is a derivative of polymyxin B, an α, γ-diaminobutyric acid-rich decapeptide from Bacillus polymyxa that displays antimicrobial and lipopolysaccharide (LPS)-antagonistic activities. The conformations of PMN in aqueous solution as well as in the LPS-bound state have been studied by 1H two-dimensional nmr methods in conjunction with molecular dynamics techniques. The aqueous structure of the free peptide is characterized by a type II′ β-turn centered around D-Phe5 and Leu6, and an inverse γ-turn at Thr9. The LPS-bound conformation of PMN was studied by transferred nuclear Overhauser effect experiments. The essential features of the cyclic portion of free aqueous PMN are mostly preserved when the peptide is bound to LPS; however, the linear dipeptide fragment as well as the side chains of the heptatpeptide ring show a conformational change and a reduction in mobility. The LPS-bound PMN structure was used to construct a model of the lipid A-polymyxin B (decapeptide) complex, which allows the rationalization of several experimental observations concerning the binding of polymyxin to, and consequent neutralization of, the toxicity of LPS, and may be of value in the rational therapeutic targeting of endotoxin. © 1997 John Wiley & Sons, Inc.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Crystal and molecular structure of benzyloxycarbonyl-α-aminoisobutyryl-L-prolyl methylamide: The observation of an X2-Pro3 Type III β-TurnContribution No. 127 from Molecular Biophysics Unit, Indian Institute of Science, Bangalore. (1979)
    New York : Wiley-Blackwell
    Biopolymers 18 (1979), S. 1635-1646 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The crystal and molecular structure of N-benzyloxycarbonyl-α-aminoisobutyryl-L-prolyl methylamide, the amino terminal dipeptide fragment of alamethicin, has been determined using direct methods. The compound crystallizes in the orthorhombic system with the space group P212121. Cell dimensions are a = 7.705 Å, b = 11.365 Å, and c = 21.904 Å. The structure has been refined using conventional procedures to a final R factor of 0.054. The molecular structure possesses a 4 → 1 intramolecular N-H - O hydrogen bond formed between the CO group of the urethane moiety and the NH group of the methylamide function. The peptide backbone adopts the type III β-turn conformation, with φ2 = -51.0°, ψ2 = -39.7°, φ3 = -65.0°, ψ3 = -25.4°. An unusual feature is the occurrence of the proline residue at position 3 of the β-turn. The observed structure supports the view that Aib residues initiate the formation of type III β-turn conformations. The pyrrolidine ring is puckered in Cγ-exo fashion.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1979.360180704
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