Horst Friebolin

1H-NMR studies at N-acetyl-D-neuraminic acid ketosides for the determination of the anomeric configuration II.

Abstract In D 2 O solution the 1 H-nmr signal of the equatorially orientated protons at C-3 of N-acetyl-D-neuraminic acid and its derivatives shows a quite characteristic dependence on the anomeric configurations: δ [H(3e)] = 2.72 ± 0.05; δ [H(3a)] = 2.32 ± 0.08.

1H-NMR-Spektroskopische untersuchungen zur mutarotation der N-acetyl-D-neuraminsäure-ph-abhängigkeit der mutarotationsgeschwindigkeit

Abstract The pD-dependence of the mutarotation of N-acetyl-D-neuraminic acid was studied by 1 H-nmr spectroscopy. The rate constant has a minimum at pD 5.4. At pD 1.3 and pD 11.7 the establishment of the equilibrium of mutarotation was found to be so fast, that it cannot be measured.

1H-NMR-untersuchungen an sialinsäuren markierung von N-acetyl-D-neuraminsäure mit deuterium☆

Abstract An efficient method for the deuteration of N-acetyl-D-neuraminic-acid (NeuAc) at C-3 is described. In alkaline D2O solution both protons of NeuAc (H3a and H3e) will be substituted by deuterium, whereby the substitution effect was found to be faster for H3a than for H3e. The rate of this exchange depends strongly on the pD value: the rate increases with increasing pD value. In acidic solution no effect could be observed. The process of H-D-exchange is reversible.

1H-NMR-Untersuchungen an Sialinsäuren, V1 N-Acetyl-α-D-Neuraminsäure: Chemische Verschiebungen und Kopplungskonstanten; Konfiguration und Konformation in Lösung

Abstract The enzymatic cleavage of N-acetyl-2-azido-2-deoxy-α-d-neuraminic acid in the probe of the NMR spectrometer allows the accumulation of 1H NMR spectra of the released a anomer of the N-acetyl-d-neuraminic acid before it mutarotates to the β anomer. The analysis and computer simulation of the spectra yield the 1H NMR data set of chemical shifts and coupling constants of N-acetyl-α- d-neuraminic acid. Using this data set, configuration and conformation in solution are discussed by comparing it with the 1H NMR data set of the β anomer, the structure of which is known from an X-ray study.

1H-NMR-Untersuchungen an Sialinsäuren, IV1 Kinetik und Mechanismus des Austauschs von Protonen an C-3 der N-Acetyl-D-Neuraminsäure Gegen Deuterium Oder Tritium

Abstract Kinetic data for the deuteration of N-acetyl-d-neuraminic acid at C-3 in basic solution at different pD values are given and discussed. With the same method Tritium has been introduced. A mechanism is proposed for the exchange reaction.

1H-NMR-Untersuchungen zur Spaltspezifität von α- und β-d-Glucosidasen gegenäber Disacchariden. II☆

Abstract 1H NMR spectroscopy was used to determine the rate of enzymic hydrolysis of six disaccharides having D-glucose units, i.e., cellobiose, laminarabiose, gentiobiose, maltose, nigerose, and isomaltose. β- d -Glucosidase from sweet almonds was used to hydrolyze the three β- d -glucosidic-linked disaccharides, and the three α- d -glucosidic-linked disaccharides were hydrolyzed by maltase from bakers yeast. The results showed that the rate of hydrolysis depends strongly on the position of OH-1. The kinetic investigation directly yielded the quotient of the first order velocity constants for the enzymic hydrolysis of the two anomers at low substrate concentrations (substrate conc.

Isolation and identification of sialylcompounds from hemofiltrate

SummaryHemofiltrate of patients with end stage renal disease is a source of sialyl compounds of unusual composition which accumulate in uremia. The large volumes involved (20–30l), are concentrated and desalted by modified reverse osmosis using membranes with a nominal cut-off of 500 D. The transport of the individual solutes during this process is monitored by reversed-phase HPLC of the permeates and retentates, respectively. By a combination of size-exclusion and ion-exchange chromatography 11 sialyl compounds are isolated preparatively. All structures have been determined using one and two dimensional NMR spectroscopy, enzymatic degradation and FAB mass spectrometry.

Isolation of Sialylcompounds from Hemofiltrate of Chronic Uremic Patients and Identification by Nuclear Magnetic Resonance

Sialylcompounds in the molecular weight range between 500 and 2000 D (sialyloligosaccharides, -glycopeptides) are structurally related to the carbohydrate components of serum- and tissue glycoconjugates, which are involved in numerous biological processes1. Many of them occur in cow colostrum, human milk and urine; structures and amount of excreted compounds vary under different physiological and pathological conditions. In serum they are usually not detectable. Since they are proposed to originate from biosynthesis and degradation of sialoglycoconjugates, their identification in uremic body fluids may contribute to a better knowledge of their metabolism.