1,721,060 research outputs found
Synthesis of the Protected Glycotetrapeptide Corresponding To the N-terminal Amino-acid Sequence of [thr3-o-alpha-d-galactopyranosyl]-vespulakinin-1
No full textOn the Role of Basic Residues of Head-to-Tail Cyclic Bradykinin Analogues on Rat Duodenum Relaxation
No full textConformational investigations on glycosylated threonine-oligopeptides of increasing chain length
No full textStepwise solution syntheses are described of the homo-oligomers Z-(Thr)(n)-NHCH3 (n=1-4, I1-4), Z- ([Gal(Ac)(4) beta]Thr](n)-NHCH3 (n=1-5, II1-5] and Z[(Gal beta)Thr]n-NHCH3 (n=1-5, III1-5). Members of the III1-5 series were obtained by de-acetylation of the corresponding oligomers of the II1-5 series. The conformational preferences of the terminally protected homo-peptides of the three series were investigated by FT-IR absorption spectroscopy both in the solid state and in CDCl3 solution, at various concentrations. Proton NMR measurements in CDCl3 and in DMSO-d(6) were also carried out and the effect of temperature variation on the chemical shifts of amide protons was determined in DMSO-d(6) (range 298-335 K) and in CDCl3 (range 298- 320 K). CD spectra were recorded in water and in TFE. Solubility problems prevented measurements in CDCl3 solution for Z(Thr)(4)-NHCH3 and for the entire III1-5 series. The existence of unordered structures in the carbohydrate-free oligomers and of more or less extended, organized structures in the glycosylated derivatives is indicated by the NMR and IR measurements. The sugar moieties apparently show a structure-inducing effect on the peptide chain. (C) 1998 European Peptide Society and John Wiley Br Sons, Ltd
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Conformational Investigations on Glycosylated Asparagine-Oligopeptides of Increasing Chain Length
No full textStepwise solution syntheses of the homo-oligomers Boc-(Asn)(n)-NHCH3 (n= 1-5: I1-5), Boc([GlcNAc(Ac)3(beta)]Asn)(n)-NHCH3 (n=1-8: II1-8). and Boc-[(GlcNAcbeta)Asn](n)-NHCH3 (n=1-8: III1-8) are described. Members of the series III were obtained by deacetylation of the corresponding members of the series II. The conformational preferences of the N-protected homo-peptides of the three series were investigated by spectroscopic techniques. H-1-NMR measurements were carried out in various solvents: the CD spectra were recorded in water. aqueous SDS and TFE. The poor solubility of the oligomers of the three series prevented FT-IR measurements in solution. NMR and IR measurements indicate the existence of unordered structures containing some gamma-turns in the carbohydrate-free oligomers and the presence of beta-turns in the glycosylated oligopeptides. whether acetylated or not. The CD spectra do not indicate the presence of organized structures. The sugar moieties apparently do not have a structure-inducing effect on the asparagine homo-oligomer main chain
Synthesis and Biological-activity of Some Linear and Cyclic Kinin Analogs
No full textSyntheses are described of some linear and cyclic kinin analogues. Cyclization, by the diphenyl-phosphorazide method, of linear peptides prepared by the solid-phase procedure based on Fmoc chemistry, was used for preparing cyclo-bradykinin and cyclo-kallidin (cyclo-Lys-bradykinin). Removal of the protecting group from the lysine side chain of cyclo-kallidin followed by acylation with the N-terminal sequence of vespulakinin 1 (VSK 1), Fmoc-Thr(tBu)-Ala-Thr(tBu)-Thr(tBu)-Arg(Pmc)-Arg(Pmc)-Arg(Pmc)-Gly-OH, by the Bop-HOBt procedure, yielded the protected N-epsilon-(1-8 VSK 1)-cyclo-N-alpha-kallidin, which was deblocked by acid treatment and purified by semi-preparative HPLC. The diglycosylated 1-8 VSK 1 sequence Boc-Thr(tBu)-Ala-(Gal beta)Thr-(Gal beta)Thr-Arg(Pmc)-Arg(Pmc)-Agr(Pmc)-Gly-OH was also synthesized by the solid-phase procedure and used to prepare the N-epsilon-[(Gal beta)Thr(3), (Gal beta)Thr(4), 1-8 VSK 1]-cyclo-N-alpha-kallidin. Peptides and glycopeptides were characterized by amino acid analysis, optical rotation, analytical HPLC and FAB-MS. Preliminary pharmacological experiments showed that the cyclic kinin analogues are much less potent than bradykinin but still show specific bradykinin-like actions that support the hypothesis of the presence of a pharmacophore in the centre of the (brady)kinin molecule. (C) Munksgaard 1994
Synthesis of Glycosylated Tuftsins and Tuftsin-containing IGg Fragment Undecapeptide
No full textSyntheses are described of two new tuftsin derivatives containing a 2-acetamido-2-deoxy-D-galactopyranosyl unit alpha- or beta-glycosidically linked to the threonine's hydroxy side chain function and of the glycosylated undecapeptide corresponding to the tuftsin region of the heavy chain of IgG (amino acid sequence 289-299). The glycosylated tuftsins were synthesized by the solution procedure. Fmoc-[Gal NAc(Ac)3-alpha]Thr-OH and Fmoc-[GalNAc(Ac)3-beta]Thr-OH were allowed to react with H-Lys(Z)-Pro-Arg(NO2)-OBzl by the mixed anhydride procedure and the resulting glycosylated tetrapeptides were fully deblocked by catalytic hydrogenation followed by treatment with potassium cyanide, purified by ion exchange chromatography and characterized by analytical HPLC, elemental and amino acid analyses, optical rotation, and proton NMR spectroscopy. Synthesis of the glycosylated undecapeptide was achieved by the continuous flow solid phase procedure on 4-hydroxymethylphenoxyacetyl-norleucyl derivatized Kieselguhr-supported resin. Fmoc-amino acid symmetrical anhydrides or pentafluorophenyl esters, in the presence of N-hydroxybenzotriazole, were used as the acylating agents. To mimic the native sequence of the tuftsin region at the Fc-domain of immunoglobulin G a 2-acetamido-2-deoxy-beta-D-glucopyranosyl unit was N-glycosidically linked to the amide side chain of Asn 297. The glycosylated asparagine residue was introduced as N2-fluorenylmethyloxycarbonyl-N4-(2-acetamido-3,4, 6-tri-O-acetyl-2-deoxy-beta-D-glucopyranosyl)-asparagine pentafluorophenyl ester. After cleavage from the resin the glycopeptide was deprotected, purified by ion exchange chromatography, and characterized by analytical HPLC, amino acid analysis, high voltage electrophoresis, and proton NMR. The conformational features of the glyco-undecapeptide were determined by circular dichroism measurements both in water and in 98% trifluoroethanol. Results of biological assays will be published elsewhere
Solution Synthesis of the Glyco-hexapeptide Sequence of the Human Oncofetal Fibronectin Defined By Monoclonal-antibody Fdc-6
No full textThe glyco-hexapeptide sequence H-Val-(GalNAc-alpha)Thr-His-Pro-Gly-Tyr-OH, was synthesized in solution by the segment condensation procedure and the stepwise procedure. A peracetylated, O-galactosaminyl threonine derivative was used for incorporating the glycosylated amino acid residue into the peptide chain. A consistent racemization occurred during the acylation of H-His-Pro-Gly-Tyr(Bzl)-OBzl with Z-Val-[GalNAc(Ac)3-alpha]Thr-OH by the BOP-HOBt procedure and the D-allothreonine containing glyco-hexapeptide was isolated in about 20% yield. Stepwise elongation of the C-terminal tetrapeptide with Fmoc-[GalNAc(Ac)3-alpha]Thr-OH and Z-Val-OH, in the presence of the same coupling reagents, yielded the L-threonine containing diastereoisomer without detectable racemization. A side product, the N(im)-ethoxy-carbonylated hexapeptide derivative, formed during the EEDQ-mediated condensation of Fmoc-[GalNAc(Ac)3-alpha]Thr-OH with the C-terminal tetrapeptide, was isolated and characterized. Preliminary studies showed that the synthetic glycohexapeptide is a good competitive inhibitor of the binding of the FDC-6 monoclonal antibody to the oncofetal fibronectin, supporting the idea that it should represent the minimum essential structure required for the FDC-6 activity
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