1,721,260 research outputs found
An oxazol-5(4H)-one from benzyloxycarbonyl-(Aib)4-OH
No full textBenzyl N-[8-(4,4-dimethyl-5-oxo-4,5-dihydrooxazol-2-yl)-2,5,5,8-tetramethyl-3,6-dioxo-4,7-diazanon-2-yl]carbamate, C24H34N4O6, an oxazol-5(4H)-one from N-alpha-benzyloxycarbonyl-(Aib)(4)-OH (Aib = alpha-aminoisobutyryl) represents the longest peptide oxazolone so far characterized by X-ray diffraction. The overall geometry of the oxazolone ring compares well with literature data. The Aib(1) and Aib(2) residues are folded into a type III beta-bend, while the conformation adopted by Aib(3), preceding the oxazolone moiety, is semi-extended. The disposition of the oxazolone ring relative to the preceding residue is stabilized by C-H ... N and C-H ... O intramolecular interactions
Understanding alpha-amino acid chemistry from x-ray diffraction structures
No full textThe geometry and conformation for a variety of reactive or-amino acid and peptide derivatives, as obtained from x-ray diffraction analyses, are reviewed in detail. The derivatives are (a) carboxylic acid halides, (b) anhydrides, (c) esters, (d) azides, and (e) amides. The contribution of this information to our understanding of amino acid reactivity, regiospecificity, and tendency to racemization is discussed. (C) 1997 John Wiley & Sons, Inc
TOAC, a nitroxide spin-labeled, achiral C(alpha)-tetrasubstituted alpha-amino acid, is an excellent tool in material science and biochemistry
No full textThe 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid is a nitroxide spin-labeled, achiral C(alpha)-tetmsubstituted alpha-amino acid that has recently been shown to be an effective beta-turn and 3(10)/alpha-helix inducer in peptides and an excellent and relatively rigid electron spin resonance probe and fluorescence quencher. (C) 1998 John Wiley & Sons, Inc
Linear oligopeptides. 401. In search of a peptide 3(10)-helix in water
No full textThe terminally blocked, sequential oligopeptides of general formula Ac-[L-Lys-(Aib)(2)](n)-OtBu (n = 1-4) have been synthesized by segment condensation in solution and fully characterized. Using CD technique we determined the preferred solution conformation of these hydrosoluble oligomers under a variety of experimental conditions. Low populations of alpha-helical structure are shown by the nonamer and dodecamer in water. The amount of alpha-helix can be increased by increasing the pH to 12, adding 2,2,2-trifluoroethanol up to 50%, and decreasing the temperature to 3 degrees C. The effect of peptide concentration on conformation is negligible. Under membrane-mimetic conditions the two highest oligomers appear to fold largely into a 3(10)-helix. The observation of a peptide 3(10)-helix in water remains elusive. Only the dodecamer shows antibacterial activity, although modest
Linear Oligopeptides .292. 1st Characterization At Atomic-resolution of the C-activating Groups In A Peptide-synthesis Acid Chloride, Acid Azide and Carboxylic Carboxylic Mixed Anhydride
No full textThe X-ray diffraction structures of three N(alpha)-protected, C(alpha)-activated MeAib derivatives are reported. They are Tos-MeAib-Cl, Tos-MeAib-N3 and Tos-MeAib-O-Piv. The geometry and conformation of these classical carboxyl activating groups, which have been characterized at atomic resolution for the first time, are discussed
Geometry and Conformation of the Alpha-aminoisobutyric-acid Residue In Simple Derivatives and Dipeptides - 4 New X-ray Structural-analyses and A Statistical-analysis From Known Crystal Data
No full textIle/allo-Ile Dyad: Lack of Screw-Sense Control of the 310-Helical Structure by β-Carbon Configuration.
No full textK. Rolka, P. Rekowski, and J. Silberring Eds., Kenes Int., Geneva, Switzerland, 2007, pp. 24-25
Reactive Intermediates in Peptide Synthesis. Molecular and Crystal Structures of Reactive Carboxylic Amides
No full textThe molecular and crystal structures of N-para-toluenesulphonyl-N-methyl-alpha-aminoisobutyric acyl imidazole (1), and 3-(N-para-toluenesulphonyl-alpha-aminoisobutyric acyl)-1,3-thiazolidine-2-thione (2) have been determined by X-ray diffraction. Crystal parameters: (1) orthorhombic, space group P2(1)2(1)2(1), a = 11.735(2) Angstrom, b = 19.990(3) Angstrom, c = 6.925(1) Angstrom, and Z = 4; (2) orthorhombic, space group Pnc2, a = 9.507(2) Angstrom, b = 16.902(2) Angstrom, c = 10.347(2) Angstrom, and Z = 4. The structures were solved by direct methods. The least-squares refinements led to conventional R factors of 0.036 and 0.031 for (1) and (2), respectively. This is the first geometrical and conformational characterization at atomic resolution of N-alpha-protected alpha-aminoacids containing the elusive acyl imidazole and 3-acyl-1,3-thiazolidine-2-thione C-activating groups. Only the reactive carboxylic amide of (2) deviates significantly from planarity
High-resolution Solid-state C-13-nmr of Peptides - A Study of Chain-length Dependence For 310-helix Formation
No full textMembrane modifying properties of the lipopeptaibols trikoningins and their analogues with modifications in the fatty acid chain and in position 1
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