Thomas Peters

A Monte Carlo method for conformational analysis of saccharides.

A Metropolis Monte Carlo (MMC) algorithm was applied to explore conformational spaces spanned by the exocyclic dihedral angles of four disaccharides alpha-D-Man(1-->3)-alpha-D-Man(1-->O)Me (1), alpha-D-Man(1-->2)-alpha-D-Man(1-->O)Me (2), methyl beta-cellobioside (3), and methyl beta-maltoside (4). The simulation method uses the HSEA force field and randomly samples the conformational space with an automatic preference for low-energy states. In comparison to a systematic grid search, MMC offers a much more convenient and efficient protocol for the computation of ensemble average values of experimentally accessible NMR parameters such as NOE effects or 3J coupling constants. Energy barriers of a few kcal/mol were found to be surmounted easily when running the simulations with the temperature parameter set at room temperature, whereas passing significantly higher barriers required elevated temperature parameters. Ensemble average NOE values were calculated using the MMC technique and a conventional systematic grid search showing that the MMC method adequately samples the conformational spaces of 1-4. Theoretical NOEs derived for global or local minimum conformations are different from ensemble average values, and it is shown that averaged NOEs agree significantly better with experimental data. Ensemble average NOEs for 1 derived from MMC/HSEA, and previously reported MM2CARB and AMBER calculations all showed good agreement with experimental data, with MMC/HSEA giving the closest fit.

Konformationsanalyse der verzweigten pentasaccharid-sequenz der “bisected” struktur von N-glycoproteinen

In the conformational analysis of the pentasaccharide alpha-D-Manp-(1----3)-[beta-D-GlcpNAc-(1----4)]-[alpha-D- Manp-(1----6)]-beta-D-Manp-(1----4)-D-GlcNAc, which represents the essential core structure within the bisected type of N-glycoproteins, n.m.r. experiments and GESA calculations indicated that a gg conformation is preferred for the (1----6)-glycosidic linkage. This is in contrast to the results obtained for the tetrasaccharide alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-beta-D- Manp-(1----4)- D-GlcNAc, which indicated that a gt conformation with the (1----6)-linked alpha-D-mannose group folded back is preferred. The conformations of the remaining glycosidic linkages in the tetra- and penta-saccharide are similar.

Assessing glycosidic linkage flexibility: Conformational analysis of the repeating trisaccharide unit of Aeromonas salmonicida

SummaryA detailed conformational analysis was performed for the synthetic branched trisaccharide β-d-Man-NAc-(1→4)-[α-d-Glc-(1→3)]-l-Rha 1 which represents the repeating unit of the O-antigenic polysaccharide of Aeromonas salmonicida. The study was based on 26 experimental NOE curves from 1D transient NOE experiments, employing Gaussian-shaped inversion pulses at 600 MHz. Eight of the NOE curves were interglycosidic and thus useful for an analysis of glycosidic linkage orientations. Metropolis Monte Carlo (MMC) simulations and minimum-energy calculations with the program GEGOP were used to obtain theoretical NOE curves which were compared to the experimental ones. MMC simulations with different temperature parameters of 310, 600, 900 and 2000 K allowed identification of NOEs which are sensitive towards different conformation distributions-not only different conformations-at both glycosidic linkages in 1. A comparison of trisaccharide 1 with the constituent disaccharides β-d-ManNAc-(1→4)-l-Rha 2 and α-d-Glc-(1→3)-l-Rha 3 revealed effects of branching on glycosidic linkage flexibility. A quantitative evaluation was facilitated by the introduction of entropy-related flexibility parameters. Our study indicates a notable restriction of flexibility, especially at the (1→3) linkage in 1. Although overall flexibility in 1 is reduced as compared to the constituent disaccharides 2 and 3, it cannot be neglected altogether. In summary, combined transient NOE experiments and MMC simulations provide a simple approach to analyse glycosidic linkage flexibility.

Conformational analysis of α-d-Fuc-(1→4)-β-d-GlcNAc-OMe. One-dimensional transient NOE experiments and metropolis Monte Carlo simulations

SummaryOne-dimensional transient NOE build-up curves were measured for the synthetic disaccharide α-d-Fuc-(1→4)-β-d-GlcNAc 1 utilizing Gaussian shaped pulses. Simulated build-up curves from Metropolis Monte Carlo simulations were compared to the experimental data. Disaccharide 1 is structurally related to methyl β-d-maltoside in that it also contains an α-(1→4) linkage, and it has the same configuration of groups around the glycosidic linkage. Analysis of NOEs in methyl β-d-maltoside is restricted to those observed upon selective excitation of H1′ because of severe spectral overlap. The situation is different in 1 where 1H-NMR signals are well separated. Several interglycosidic NOEs were observed. The corresponding build-up curves allowed an accurate determination of the conformational preferences at the glycosidic linkage in 1. Comparison of experimental and theoretical NOE build-up curves showed clearly that rigid minimum-energy models cannot account for the experimental data. The best fit of experimental NOE build-up curves was obtained with theoretical curves from a 2×106 step Metropolis Monte Carlo simulation with the temperature parameter set at 1000 K. Finally, it was observed that only the interglycosidic NOE H5′/H6-pro-S significantly depends upon varying conformation distributions at the α-(1→4)-glycosidic linkage, induced by choosing different temperature parameters for the Metropolis Monte Carlo simulations.

Synthesis and conformational and NMR studies of α-d-mannopyranosyl and α-d-mannopyranosyl-(1 → 2)-α-d-mannopyranosyl linked to l-serine and l-threonine

Abstract α- d -Mannopyranosyl and α- d -mannopyranosyl-(1 → 2)-α- d -mannopyranosyl linked to l -serine and l -threonine have been synthesised as model substances for the linkage region in certain O-linked glycoproteins. Metropolis Monte Carlo simulations were performed with a modified version of the GESA program, to yield theoretical NOEs and interatomic distances as ensemble-average values, and these were compared with results from steady-state NOE experiments. The NOEs were determined as ensemble-average and as global minimum values. NMR chemical shift differences, obtained for signals of the glycopeptides relative to those of the respective monomers, were interpreted in terms of short inter-residue atomic distances as found within the global minima, and on the basis of averaged distances derived from Monte Carlo simulations.

Drug abuse emergencies in Hamburg 1990/91

During a 30-month investigation of the prevalence and structure of drug emergencies in Hamburg, data from all ambulances were analysed. From January 1991 to June 1992 there were 1565 drug-related emergency patients suffering a life-threatening event in Hamburg (1097 male, 350 female, 118 without information concerning the sex) to whom medical care was given by an emergency team. The number of cases grew strongly from 538 in 1990 to 720 in 1991. The place where the patients were found was very often in the region around the main railway station and near to the Reeperbahn, but we could also observe a scene south of the river Elbe.

Konformationsanalyse modifizierter tetrasaccharid-sequenzen vom type der N-glycoproteine — zum problem der α-(1→6)-glycosidischen bindung☆

The conformational analysis of the recently synthesized tetrasaccharides alpha-D-Manp (1----3)-[alpha-D-Manp-(1----6)]-4-deoxy-beta-D-lyx-hexp+ ++-(1----4)-D-GlcNAc (2) and alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-beta-D-Talp -(1----4)-D-GlcNAc (3) will be described. The preferred solution conformation of 2 and 3 is a gt-conformation, which is nearly identical with the preferred conformation of the naturally occurring tetrasaccharide alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-beta-D-Manp -(1----4)-D-GlcNAc (1). The main structural feature is the backfolding of the alpha-(1----6)-linked D-Man to the reducing D-GlcNAc unit. Conformational analysis of the tetrasaccharides alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-beta-D-Manp -(1----4)-1,6- anhydro-beta-D-GlcNAc (4), alpha-D-Manp-(1----3)-alpha-D-Manp-(1----6)]-4-deoxy-beta-D- lyx-hexp-(1----4)- 1,6-anhydro-beta-D-GlcNAc (5), and alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-beta-D-Talp -(1----4)- 1,6-anhydro-beta-D-GlcNAc (6) gave additional proof for this backfolding. The substitution of the reducing unit leads to a smaller amount of gt- and a greater amount of gg-conformers. The method used for conformational analysis of 2-6 is a combination of n.m.r.-experiments and HSEA-calculations with the program GESA. Concerning the application of new 2D-techniques, the COLOC-experiment turned out to be extremely useful in sequencing oligosaccharides.

Comparison of drug abuse fatalities and emergencies

During a 9-month period, drug abuse emergencies were investigated prospectively and compared with drug-related fatalities of the same period. The emergency patients were of younger age, the proportion of women and the prevalence of infections with HIV, HBV and HCV was higher than in drug-related deaths. Additional alcohol consumption was similar in both groups but more frequent in drug-addict emergencies where the patients were 20-30 years of age. It is suggested that the emergency patients might characterise a special risk group of drug addicts and might be a target for interventional help to prevent fatalities.