1,720,973 research outputs found
Synthesis and Conformational Characterisation of Hexameric beta-Peptide Foldamers by Using Double POAC Spin Labelling and cw-EPR
No full textA selected set of terminally protected beta-hexapeptides, each containing two nitroxide-based (3R,4R)-4-amino-1-oxyl-2,2,5,5-tetramethylpyrrolidine-3-carboxylic acid (POAC) residues combined with four (1S,2S)-2-aminocyclopentane-1-carboxylic acid (ACPC) residues, was synthesised by using solution methods and was fully characterised. The two POAC residues are separated in the sequences by different numbers of intervening ACPC residues. The conformational features of the doubly spin-labelled beta-hexapeptides were examined in chloroform by FTIR absorption and continuous-wave electron paramagnetic resonance spectroscopic techniques. In particular, the biradical exchange coupling (I) between two POAC residues within each peptide indicates unambiguously that the secondary structure overwhelmingly adopted is the 12-helix. Taken together, these results support the view that POAC is an excellent beta-amino acid for exploring this type of helical conformation in doubly labelled beta-peptides
New tools for the control of peptide conformation and supramolecular chemistry: Crown-carrier, C-alpha-methyl L-DOPA amino acids
No full textThe preferred conformation of five, terminally protected, model peptide series to the hexamer level, based on three novel crowned, Cα-methyl L-DOPA amino acids combined with either L-Ala/Aib or Gly/Aib, were assessed in structure supporting solvents using FT-IR absorption, 1H NMR, and CD techniques. The FT-IR absorption spectra strongly suggest that the contribution of the crowned Cα-tetrasubstituted residue to intramolecular H-bonding is equivalent to that of Aib and is much more significant than that of either L-Ala or Gly. In addition, the 1H NMR titrations and the CD patterns resemble those typically exhibited by (right-handed) 310-helical structures
A new tool for photoaffinity labeling studies: a partially constrained, benzophenone based, alpha-amino acid
No full textThe novel alpha-amino acid BpAib, a partially conformationally restricted analogue of the currently extensively used 3-(4-benzoylphenyl)alanine (Bpa) photoaffinity label, was synthesized, optically resolved, fully characterized, and appropriately derivatized. An intermolecular photocrosslinking experiment highlighted its regioselective reactivity towards the S-methyl side-chain group of a Met-based dipeptide, which is closely comparable to that of Bpa
Evidence for the 3(10)-helical structure of peptides based on antAib, a fluorophoric, anthracene-fused, 1-aminocyclopentane-1-carbocylic acid
No full textPeptides based on 2-amino-2,3-dihydro-1H-cyclopenta[b]anthracene-2-carboxylic acid (antAib), a fluorescent, achiral, α-amino acid belonging to the class of C→C cyclized, Cα,α-disubstituted glycines, combined with L-Ala, up to the hexamer level, were synthesized by solution methods and chemically characterized. A conformational analysis by FTIR absorption and NMR techniques suggests that the highest oligomers of this series tend to fold into β-turns/310-helices. The UV absorption, CD, and fluorescence properties of these antAib/L-Ala model peptides are also described
Synthesis, resolution and assignment of absolute configuration of trans 3-amino-1-oxyl-2,2,5,5-tetramethylpyrrolidine-4-carboxylic acid (POAC), a cyclic, spin-labelled beta-amino acid
No full textRacemic trans 3-(9-fluorenylmethyloxycarbonylamino)-1-oxyl-2,2,5,5-tetramethylpyrrolidine-4-carboxylic acid (Fmoc-POAC-OH), prepared by conventional methods, was resolved upon esterification with (aR)-2,2'-dihydroxy-1,1'-binaphthyl. Separation of the obtained diastereomeric monoesters Fmoc-(+/-)-trans-POAC-O-(aR)-binaphthol by crystallization/chromatography, and removal of the chiral auxiliary by saponification of the aryl ester function furnished both enantiomers (+)-(3R,4R)-Fmoc-POAC-OH and (-)-(3S,4S)-Fmoc-POAC-OH. The absolute configuration of the asymmetric C(3), C(4) carbons of POAC were assigned from the induced circular dichroism of a flexible biphenyl probe present in the terminally protected dipeptide derivatives Boc-Bip-(+)-POAC-OMe and Boc-Bip-(-)-POAC-OMe (Bip, 2',1':1,2;1 '',2 '':3,4-dibenzcyclohepta-1,3-diene-6-amino-6-carboxylic acid). This assignment was confirmed by X-ray diffraction analysis of the diastereomeric monoester Fmoc-(+)-trans-POAC-O-(aR)-binaphthol, shown to be (aR,3R,4R). Solution synthesis of peptides to the hexamer level, based on the (3RAR)-POAC enantiomer combined with (1S,2S)-2-aminocyclopentane-l-carboxylic acid, was carried out to examine coupling conditions at both C- and N-termini of the POAC residue, in view of further syntheses and 3D-structural investigations
The "BIP METHOD" for spectroscopic assignment of the absolute configuration of the spin-labelled, cyclic beta(2,3) amino acids beta-TOAC and POAC
No full textEPR distance measurement in a doubly nitroxide-labelled helical beta-peptide
No full textA terminally protected β-hexapeptide, based on trans-(3R,4S)-β-TOAC and trans-(1S,2S)-ACHC, synthesized using classical solution methods, was found by FT-IR
absorption and CD techniques to adopt the 3-14-helical conformation.
EPR measurements of 1 in MeOH and HFIP (at 1.0 and 0.1 mM concentrations) were performed in the temperature range 120 K - 318 K. The spectra show
three sharp lines with separations of about 1.5 mT (the same at all temperatures) superimposed on two broad signals, the separation of which increases as the
temperature is lowered. The solvent and concentration effects are of minor significance. The spectra of the polycrystalline solid samples at low temperature extend over about 30 mT and their shape is mainly governed by the electron dipolar interaction. The intramolecular distance (6.1 ± 0.1 Å) between the
nitroxide labels of the two β-TOAC residues at positions i and i+3, obtained from the analysis of the low temperature spectra, allowed us to confirm the
expected ternary helical structure
Synthesis of linear and cyclic homo-beta-peptides based on a binaphthylic beta-amino acid with only axial chirality
No full textThe terminally protected, linear, homo-b-peptides Boc-[(R)-b2,2-HBin]n-OMe (n = 2–6) as well as the cyclic homo-b-peptides
c[(R)-b2,2-HBin]3 and c[(S)-b2,2-HBin]4, all derived from the 20,10:1,2;100,200:3,4-dinaphthcyclohepta-1,3-diene-6-aminomethyl-6-
carboxylic acid residue b2,2-HBin possessing only axial chirality, have been synthesized in solution by the EDC/AtOH coupling
method for chain elongation, and by cyclization of pentafluorophenyl esters. A conformational analysis suggested the concomitant
occurrence of different intramolecularly H-bonded forms for the linear oligomers in solutio
Central-to-axial chirality transfer and induced circular dichroism in 6,7-dihydro-5H-dibenz[c,e]azepine derivatives of alpha- and beta-amino esters
No full textDAZ-Xaa∗-OMe amino ester derivatives with Xaa∗ = d/l-Ala, d/l-Val, l-Leu, l-Ile, l-Ser, l-β3-HAla, l-β3-HVal, l-β3-HLeu, (1S,2S)/(1R,2R)-ACHC (2-aminocyclohexanecarboxylic acid) and (1S,2S)/(1R,2R)-ACPC (2-aminocyclopentanecarboxylic acid), N-blocked as 6,7-dihydro-5H-dibenz[c,e]azepines (DAZ), have been synthesized and evaluated for the determination of the absolute configuration of α- and β-amino esters through the induced circular dichroism of the biphenyl chromophor
An extension of the 'Bip method': induced axial chirality in a series of dipeptides based on Bip/beta(2,2)-HBip combined with Ala/beta(3)-HAla
No full textIn the search for an extension of the ‘Bip method’ for determining the absolute configuration of b-amino acids and bpeptides,
dipeptides based on b2,2-HBip/L(D)-Ala, Bip/L-b3-HAla, and b2,2-HBip/L-b3-HAla were synthesized in solution and the
induced circular dichroism (ICD) in their biphenyl core evaluated in comparison with the previously investigated Bip/L(D)-Ala series.
Weak, poorly informative ICDs were observed in MeOH solution for the linear N-Boc protected dipeptide methyl esters based
on b2,2-HBip, as well as for those with Ala/b3-HAla at the N-terminus of Bip/b2,2-HBip. However, a significant ICD was recorded
for Boc-Bip-L-b3-HAla-OMe. These results were confirmed by low-temperature 1H NMR spectroscopy studies of the dipeptides in
CDCl3 and CD3OD solutions, showing two diastereoisomeric conformers in significantly different populations for Boc-Bip-L-b3-
HAla-OMe in CD3OD. In general, ICDs were found to be weaker for dipeptides containing b-amino acids as compared to those
of their a-amino acid counterparts
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