Regarding galactofuranose-containing glycoconjugates.
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Databases, Factual↗
Biomedical subjects
K Bock
Publications and source records attributed to K Bock.
Transferred nuclear Overhauser enhancement experiments show that the monoclonal antibody strep 9 selects a local minimum conformation of a Streptococcus group A trisaccharide-hapten.
Transferred nuclear Overhauser enhancement (TRNOE) experiments have been performed to investigate the bound conformation of the trisaccharide repeating unit of the Streptococcus Group A cell-wall polysaccharide. Thus, the conformations of propyl 3-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-2-O-(alpha-L-rhamnopyran osyl)- alpha-L-rhamnopyranoside [C(A')B] (1) as a free ligand and when complexed to the monoclonal antibody Strep 9 were examined. Improved insights about the conformational preferences of the glycosidic linkages of the trisaccharide ligand showed that the free ligand populates various conformations in aqueous solution, thus displaying relatively flexible behavior. The NOE HNAc-H2A', which was not detected in previous work, accounts for a conformation at the beta-(1-->3) linkage with a phi angle of approximately 180 degrees. Observed TRNOEs for the complex are weak, and their analysis was further complicated by spin diffusion. With the use of transferred rotating-frame Overhauser enhancement (TRROE) experiments, the amount of spin diffusion was assessed experimentally, proving that all of the observed long-range TRNOEs arose through spin diffusion. Four interglycosidic distances, derived from the remaining TRNOEs and TRROEs, together with repulsive constraints, derived from the absence of TRROE effects, were used as input parameters in simulated annealing and molecular mechanics calculations to determine the bound conformation of the trisaccharide. Complexation by the antibody results in the selection of one defined conformation of the carbohydrate hapten. This bound conformation, which is a local energy minimum on the energy maps calculated for the trisaccharide ligand, shows only a change from a +gauche to a -gauche orientation at the psi angle of the alpha-(1-->2) linkage when compared to the global minimum conformation. The results infer that the bound conformation of the Streptococcus Group A cell-wall polysaccharide is different from its previously proposed solution structure (Kreis et al., 1995).
Antibodies, Monoclonal↗
The structure of the lipid A-core region of the lipopolysaccharides from Vibrio cholerae O1 smooth strain 569B (Inaba) and rough mutant strain 95R (Ogawa).
The lipopolysaccharides (LPS) from Vibrio cholerae 95R, a rough mutant strain of O1 V. cholerae 162 (Ogawa), and from smooth O1 V. cholerae 569B (Inaba) were de-O-acylated. In each case, one part of the products was treated with 48% aqueous HF which removed the phosphoryl and fructose residues, then reduced, de-N-acylated, and N-acetylated. Another part was de-N-acylated by treatment with hot KOH. The products of both degradation pathways were separated by high-performance anion-exchange chromatography. The major dephosphorylated and defructosylated product 1 was obtained in pure form, whereas the minor products 2 and 3 were eluted as a mixture, as were, from the second degradation, the phosphorylated oligosaccharides 4 (major product) and 5 (minor product). No phosphorylated component corresponding to oligosaccharide 3 could be identified by NMR spectroscopy in the latter mixture. The following structures of oligosaccharides 1-5 were established on the basis of monosaccharide and methylation analyses, Smith degradation, and 1H- and 13C-NMR investigations (correlated, total correlated, NOE and heteronuclear correlation spectroscopy; all sugars are present as alpha-D-pyranoses except where indicated otherwise; Hep, L-glycero-D-manno-heptose; Kdo, 3-deoxy-D-manno-2-octulosonic acid). [formula: see text] In the untreated lipopolysaccharide, the amino group of the non-reducing terminal glucosamine residue is not substituted.
Carbohydrate Sequence↗
The structures of oligosaccharide bisphosphates isolated from the lipopolysaccharide of a recombinant Escherichia coli strain expressing the gene gseA [3-deoxy-D-manno-octulopyranosonic acid (Kdo) transferase] of Chlamydia psittaci 6BC.
The lipopolysaccharide from the recombinant strain Escherichia coli F515-140 containing the cloned gene gseA [3-deoxy-D-manno-octulopyranosonic acid (Kdo) transferase] from Chlamydia psittaci 6BC was isolated and sequentially de-O-acylated and de-N-acylated. The products were separated by high-performance anion-exchange chromatography into three fractions, two of which contained a single compound. Their structures were elucidated by high-field NMR spectroscopy as alpha-Kdo-(2-->4)-alpha-Kdo-(2-->6)-beta-D-GlcN-(1-->6)-alpha-D-GlcN 1,4'-P2 (compound 1) (tetrasaccharide bisphosphate) [Holst, O., Broer, W., Thomas-Oates, J. E., Mamat, U. & Brade, H. (1993) Eur. J. Biochem. 214, 703-710] and alpha-Kdo-(2-->4)-[alpha-Kdo-(2-->8)-]-alpha-Kdo-(2-->4)-alpha-Kdo- (2-->6)-beta-D-GlcN-(1-->6)-alpha-D-GlcN 1,4'-P2 (compound 4) (hexasaccharide bisphosphate). The third fraction comprised two pentasaccharide bisphosphates, which could be separated by affinity chromatography using an immobilized monoclonal antibody specific for the trisaccharide alpha-Kdo-(2-->8)-alpha-Kdo-(2-->4)-alpha-Kdo. The bound fraction was identified as alpha-Kdo-(2-->8)-alpha-Kdo-(2-->4)-alpha-Kdo-(2-->6)-beta-D- GlcN-(1-->6)-alpha-D-GlcN 1,4'-P2 (compound 2) [Holst, O., Broer, W., Thomas-Oates, J. E., Mamat, U. & Brade, H. (1993) Eur. J. Biochem. 214, 703-710], whereas the unbound fraction was identified as alpha-Kdo-(2-->4)-alpha-Kdo-(2-->4)-alpha-Kdo-(2-->6)-beta-D-GlcN-(1-->6 )- alpha-D-GlcN 1,4'-P2 (compound 3). This novel Kdo tetrasaccharide extends our knowledge on multifunctional Kdo transferases.
Carbohydrate Sequence↗
Synthesis of the glycosyl amino acids N alpha-Fmoc-Ser[Ac4-beta-D-Galp-(1-->3)-Ac2-alpha-D-GalN3p]-OPfp and N alpha-Fmoc-Thr[Ac4-beta-D-Galp-(1-->3)-Ac2-alpha-D-GalN3p]-OPfp and the application in the solid-phase peptide synthesis of multiply glycosylated mucin peptides with Tn and T antigenic structures.
Two new glycosyl amino acids N alpha-Fmoc-Ser[Ac4-beta-D-Galp-(1-->3)-Ac2-alpha-D-GalN3p]-+ ++OPfp and N alpha-Fmoc-Thr[Ac4-beta-D-Galp-(1-->3)-Ac2-alpha-D-GalN3p]-+ ++OPfp were synthesized. Glycosylation of N alpha-Fmoc-Ser-OPfp or N alpha-Fmoc-Thr-OPfp with protected beta-D-Gal-(1-->3)-D-GalN3 donors afforded the glycosyl amino acids containing an activated C-terminus which could be utilized directly for solid-phase glycopeptide synthesis. The transformation of the 2-azido group into the acetamido derivative was achieved quantitatively at the end of the synthesis by treatment of the polymer-bound glycopeptide with thioacetic acid. The versatility of this strategy was demonstrated by the assembly of eight triply glycosylated mucin peptides which were synthesized simultaneously by multiple column techniques. The glycopeptides were prepared in order to investigate the substrate specificity of a galactosyltransferase.
Amino Acid Sequence↗
[Standardization and quality assurance exemplified by tinnitus].
Quality management will become another discipline for intensive care and research for the physician. Therefore, the first step in this process will be the need for standardised evaluation criteria and case record forms for documentation, leading to effective quality assessment and control. Only this approach may promote our attempts to improve the quality of patient care. Tinnitus is, due to the lack of objective measurable parameters and a missing rational basis of therapy, up to now a "crux medicorum" for every involved person. In this paper we reproduce a case record form and a patient's questionnaire for patients suffering from tinnitus. The presented forms are based on a consensus conference concerning the evaluation of treatment regimens held at the Fourth International Tinnitus Seminar in Bordeaux in August 1991. Epidemiological data, collected with this questionnaire, are presented and analysed. In conclusion, the presented case record form will lead to a standardised evaluation of symptoms according to tinnitus and improve our understanding of concomitant disturbances in tinnitus sufferers. Furthermore, this form of evaluation and documentation will produce comparable data in different centres allowing a pooling of patients data and history. A comparison of clinical trials in which the items are collected by the procedure shown here will be facilitated and lead us to a new understanding in determining the causes of the disease and the outcome of different therapeutic regimens.
Adolescent↗
Bile acid derived HMG-CoA reductase inhibitors.
The target organ for HMG-CoA reductase inhibitors to decrease cholesterol biosynthesis in hypercholesterolemic patients is the liver. Since bile acids undergo an enterohepatic circulation showing a strict organotropism for the liver and the small intestine, the structural elements of an inhibitor for HMG-CoA reductase were combined with those for specific molecular recognition of a bile acid molecule for selective uptake by hepatocytes. Either, the HMG-CoA reductase inhibitors HR 780 and mevinolin were covalently attached to 3 xi-(omega-aminoalkoxy)-7 alpha, 12 alpha-dihydroxy-5 beta-cholan-24-oic acids to obtain bile acid prodrugs, or the side chain of bile acids at C-17 was replaced by 3,5-dihydroxy-heptanoic acid--a structural element essential for inhibition of HMG-CoA reductase--to obtain hybrid bile acid: HMG-CoA reductase inhibitors. The prodrugs could, as expected, not inhibit rat liver HMG-CoA reductase to a significant extent, whereas the hybrid inhibitors showed a stereospecific inhibition of HMG-CoA reductase from rat liver microsomes with an IC50-value of 0.7 microM for the most potent compound S 2467 and 6 microM for its diastereomere S 2468. Uptake measurements with isolated rat hepatocytes and ileal brush-border membrane vesicles from rabbit small intestine revealed a specific interaction of both classes of bile acid-derived HMG-CoA reductase inhibitors with the hepatocyte and ileocyte bile acid uptake systems. Photoaffinity labeling studies using 3-azi- or 7-azi-derivatives of taurocholate with freshly isolated rat hepatocytes or rabbit ileal brush-border membrane vesicles revealed a specific interaction of bile acid derived HMG-CoA reductase inhibitors with the respective putative bile acid transporters in the liver and the ileum demonstrating the bile acid character of these derivatives, both for the prodrugs and the hybrids. Cholesterol biosynthesis in Hep G2 cells was inhibited by the bile acid prodrugs with IC50-values in the range of 68 nM to 600 nM compared to 13 nM for HR 780 and 130 nM for mevinolin. Among the hybrid inhibitors, S 2467 was the most active compound with an IC50-value of 16 microM compared to 55 microM for its diastereomere S 2468. Preliminary in vivo experiments showed an inhibition of hepatic cholesterol biosynthesis after oral dosage only with prodrugs such as S 3554, whereas the hybrid molecules were inactive after oral application.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
Isolation and structural analysis of oligosaccharide phosphates containing the complete carbohydrate chain of the lipopolysaccharide from Vibrio cholerae strain H11 (non-O1).
For the first time, an oligosaccharide has been prepared comprising the lipid A backbone, the core oligosaccharide and one repeating unit of the O-specific polysaccharide (O-chain) of a lipopolysaccharide. Lipopolysaccharide from Vibrio cholerae strain H11 (non-O1) was deacylated and the products were separated by high-performance anion-exchange chromatography. Major fractions were a hexadecasaccharide trisphosphate 1, representing the core-lipid A oligosaccharide substituted by one modified repeating unit of the O-antigenic polysaccharide, a dodecasaccharide trisphosphate 2 and an undecasaccharide trisphosphate 3, representing the core-lipid A region. Oligosaccharide 1 originated from beta-elimination upon alkaline hydrolysis of alpha-galacturonic acid of the O-chain; oligosaccharides 2 and 3 were most likely obtained from naturally occurring lipopolysaccharide species carrying no O-chain. The structures of these compounds were elucidated on the basis of monosaccharide composition, and NMR investigations comprising correlation spectroscopy, total correlation spectroscopy and nuclear Overhauser enhancement spectroscopy experiments, as well as heteronuclear 13C, 1H correlation spectroscopy. The structures are as follows: [formula: see text] where R is beta-L-threo-hex-4-enuronopyranosyl-(1-4)-alpha-Neu-(2-3)-beta-Gal A-(1-3)- beta-QuiN-(1-4)-beta-Sedf-(2- in 1, beta-Sedf-(2- in 2, and H in 3. Where not stated otherwise, sugars are pyranoses of the D-series. Hep is L-glycero-D-manno-heptose, QuiN is 2-amino-2,6-dideoxy-glucose, Kdo is 3-deoxy-D-manno-2-octulosonic acid, Sed is D-altro-heptulose and GalA is galacturonic acid.
Carbohydrate Sequence↗
Synthesis and biological activity of bile acid-derived HMG-CoA reductase inhibitors. The role of 21-methyl in recognition of HMG-CoA reductase and the ileal bile acid transport system.
To increase hepatoselectivity of HMG-CoA reductase inhibitors by using the specific bile acid transport systems, deoxycholic acid-derived inhibitors 9 and 11 have been synthesized, on the basis of the concept of combining in one molecule structural requirements for specific inhibition of the HMG-CoA reductase and specific recognition by the ileal bile acid transport system. The 1-methyl-3-carboxylpropyl subunit of deoxycholic acid was replaced by the 3,5-dihydroxyheptanoic acid lactone of lovastatin, and position 12-OH was esterified with 2-methylbutyric acid. Compounds 9 and 11 were evaluated for their inhibitory activity on rat liver HMG-CoA reductase, cholesterol biosynthesis in HEP G2 cells, and [3H]taurocholate uptake in rabbit brush border membrane vesicles and compared with methyl derivatives 8 and 10. The steroidal 21-CH3 group affects both activity on HMG-CoA reductase and recognition by the ileal bile acid transport system.
Androstanols↗
Gram-scale synthesis of alpha,alpha-trehalose 6-monophosphate and alpha,alpha-trehalose 6,6'-diphosphate.
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Carbohydrate Conformation↗
Nuclear magnetic resonance and conformational investigations of the pentasaccharide of the Forssman antigen and overlapping di-, tri-, and tetra-saccharide sequences.
The 1H and 13C NMR parameters, i.e., chemical shifts and coupling constants, for the pentasaccharide of the Forssman antigen and overlapping di-, tri-, and tetra-saccharide sequences thereof have been measured and assigned completely using 1D and 2D techniques, and the oligosaccharide structures have thereby been confirmed. Nuclear Overhauser effect (NOE) experiments have been carried out at three different temperatures to assess the preferred conformations of the pentasaccharide and the component oligosaccharides. The conformational preferences of the compounds mentioned above have subsequently been investigated by theoretical calculations. The flexibility and dynamics of the molecules have been studied by Metropolis Monte Carlo simulations using a modified HSEA force field, and ensemble average data have been generated and compared to data obtained experimentally.
Calorimetry↗
Specific inhibitors of ileal bile acid transport.
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Animals↗
Primary structure of the O-glycosidically linked glycan chain of the crystalline surface layer glycoprotein of Thermoanaerobacter thermohydrosulfuricus L111-69. Galactosyl tyrosine as a novel linkage unit.
The products of Pronase digestion of the crystalline surface layer (S-layer) glycoproteins of Thermoanaerobacter thermohydrosulfuricus strains L111-69 and L110-69 were isolated by gel permeation chromatography, cation exchange chromatography, chromatofocusing, and reversed phase high performance liquid chromatography. Four compounds were obtained which were analyzed by monosaccharide analysis, one- and two-dimensional 500 and 600 MHz 1H and 13C NMR spectroscopy, methylation analysis, gas-liquid chromatography/mass spectrometry, and matrix-assisted laser desorption ionization mass spectrometry. For all glycopeptides we propose the following glycan structure with galactose as the linkage sugar. [formula: see text] The isolated glycopeptides resulted from Pronase cleavage at the glycosylated tyrosine residues. Tyrosine was found as the linkage amino acid in all fractions but the remaining amino acid sequences varied, indicating the presence of different glycosylation sites in the intact S-layer glycoprotein.
Bacterial Proteins↗
Conformational equilibria of 4-thiomaltose and nitrogen analogues of maltose in aqueous solutions.
The 1H and 13C NMR data at neutral pH are presented for methyl 4-thio-beta- and alpha-maltoside (1 and 2) together with methyl 1-thio-alpha-D-glucopyranoside (3) and methyl 4-thio-alpha-D-glucopyranoside (4) as reference compounds. Furthermore, the NMR data at high and low pH are presented for the 4-amino-4-deoxy analogues of methyl alpha-maltoside (5 and 6) and the 5-amino-5-deoxy analogue (8) together with reference compounds methyl 4-amino-4-deoxy-alpha-D-glucopyranoside (7) and 1-deoxynojirimycin (9). The experimental NMR data are assigned by 1- and 2-dimensional spectroscopy at 500 and 600 MHz. The conformational preferences of the maltose analogues 1, 2, 5, 6 and 8 are evaluated by difference NOE experiments, 13C-1H long-range coupling constants, chemical-shift comparison with model compounds and hard-sphere force field calculations for 1 using Monte Carlo simulations. Additionally, the results are compared with extensive experimental NOE data for methyl alpha- and beta-maltoside and the results discussed in light of earlier studies.
Carbohydrate Conformation↗
An NMR spectroscopic and conformational study of 12 pseudo-disaccharides (D-glucopyranosyl-5a-carba-D- and -L-glucopyranoses).
NMR spectroscopic data for 12 pseudo-disaccharides of the general structure: (alpha or beta)-D-glucopyranosyl-(1-->chi)-5a-carba-(D or L)-glucopyranose, representing analogues of laminaribiose (beta-D-Glc p, chi = 3), cellobiose (beta-D-Glc p, chi = 4), and maltose (alpha-D-Glc p, chi = 4) are presented. The assigned NMR chemical shifts together with NOE difference measurements in association with calculations applying the HSEA force field combined with Monte Carlo simulations have been used to assess the conformational preferences of the investigated compounds. The results are correlated with general structural features involved in the interactions between monosaccharide units of oligosaccharides.
Carbohydrate Conformation↗
Ergot induced peripheral vascular insufficiency, non-interventional treatment.
We report a case of ergotamine tartrate induced severe vasospasm in the renal arteries and the arteries of the lower extremities. Classic features seen on peripheral angiography make the diagnosis. Anticoagulation, thrombolysis, vasodilation, steroids, and prostaglandin inhibitors all have been successfully used to treat symptomatic ergot induced arterial vasospasm. Although balloon angioplasty of ergot induced vasospasm has been described in case reports, ergot vasospasm is a self limited and medically treatable condition that does not require peripheral mechanical intervention, unless the immediate threat of necrosis and gangrene exists.
Adult↗
A general approach to the synthesis of O- and N-linked glycopeptides.
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Acylation↗
Silyl protection in the solid-phase synthesis of N-linked glycopeptides. Preparation of glycosylated fluorogenic substrates for subtilisins.
The trimethylsilyl (TMS) group was used for protection of the hydroxy groups of three disaccharide 1-amino-alditols and of the glycosylamines of glucose, maltotriose and maltoheptose. The per-O-trimethylsilylated derivatives were coupled with N alpha-Fmoc-Asp(Cl)-OPfp 7 to give six glycosylated building blocks for the solid-phase synthesis of N-linked glycopeptides. Building block 8 was used in the synthesis of five internally quenched fluorescent substrates which were studied by enzymatic hydrolysis with savinase, a subtilisin-type enzyme.
Amino Acid Sequence↗