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H Röper

Publications and source records attributed to H Röper.

18 recordsLinked to original sources
PubMed1992

Antitumour and immunological activity of a beta 1----3/1----6 glucan from Glomerella cingulata.

The in vivo antitumour activity of a beta 1----3/1----6 glucan from the fungus Glomerella cingulata was investigated in vivo. The glucan exhibited a strong inhibition of tumour growth of the allogeneic Sarcoma-180 as well as the syngeneic DBA/2-MC.SC-1 fibrosarcoma with inhibition ratios up to 100%. Against the hormone sensitive Noble-Nb-R prostate carcinoma the glucan alone showed a moderate antitumour effect, whereas in combination with diethylstilbestrol an almost complete regression of the tumour could be achieved. It could be demonstrated that a highly ordered structure of the glucan is not essential for the antitumour activity. Since the glucan expressed no direct cytotoxic effects, the immunomodulating activity was investigated in vitro in order to get an indication for a possible mode of action. In the lymphocyte transformation assay the glucan at a dose of 100 micrograms/ml caused a fourfold increase in the proliferation of murine spleen lymphocytes. Moreover, the glucan stimulated the phagocytosis of zymosan by bone marrow macrophages up to 100%. However, the glucan was not able to render macrophages cytotoxic against P-815 mastocytoma cells.

Animals↗
PubMed1991

Structural investigations of glucans from cultures of Glomerella cingulata Spaulding & von Schrenck.

Methylation analysis, enzymic digestion, n.m.r. spectroscopy, and Smith degradation showed that the major extracellular polysaccharide, isolated from cultures of the fungus Glomerella cingulata, was a (1----3)-beta-D-glucan with side chains of 1-4 (1----3)-linked beta-D-glucose residues attached to position 6. A (1----6)-beta-D-glucan was produced by the fungus in small proportions. Treatment of the (1----3,1----6)-beta-D-glucan (890,315) with greater than 0.05M NaOH at greater than 150 degrees, or Me2SO-H2O with a concentration of dimethyl sulfoxide of greater than 80%, irreversibly destroyed the highly ordered structure responsible for the high viscosity of aqueous solutions. The strong shift of the lambda max of aqueous solutions of Congo Red by the degraded glucan, the fact that the mol. wt. of the original glucan was approximately 4 times higher than that of the degraded polymer, and the suppression of the n.m.r. signals for C-3 indicated that the original glucan had a highly ordered structure, probably built up from single helices.

Ascomycota↗
PubMed1984

Mutagenicity studies on N-nitrosated products of the Maillard browning reaction: N-nitroso-fructose-amino acids.

The N-nitroso derivatives of D-fructose-L-glycine, D-fructose-L-alanine, D-fructose-L-phenylalanine, D-fructose-L-serine, Dfructose-L-aspartic acid and D-fructose-L-tryptophan (a mixture of alpha-N-nitroso-D-fructose-L-tryptophan and 'indolyl-nitrosamine'-D-fructose-L-tryptophan) were tested for mutagenicity in five auxotrophic strains of Salmonella typhimurium with and without metabolic activation (S-9 mix). The alanine, phenylalanine and aspartic acid compounds were not mutagenic. The glycine and serine compounds showed a very low but reproducible increase in the numbers of his+ revertants in strain TA1535 without S-9 mix. The mixture containing both nitrosated D-fructose-L-tryptophan compounds was mutagenic in all five strains, with or without metabolic activation. The alpha-N-nitroso-D-fructose-L-tryptophan component of the mixture, which is nitrosated at the amino group, was isolated and tested without S-9 mix. It was mutagenic in three strains. Unnitrosated D-fructose-L-amino acids, D-fructose, and the individual L-amino acids were non-mutagenic when tested under those conditions for which a positive response had been obtained with the corresponding nitrosated compounds. These results indicate the potential value of developing analytical methods to identify alpha-N-nitroso-D-fructose-L-tryptophan in food or food extracts that are to be screened for mutagenic components.

Amino Acids↗
PubMed1984

Amadori- and N-nitroso-Amadori compounds and their pyrolysis products. Chemical, analytical and biological aspects.

N-(1-Deoxy-D-fructos-1-yl)-L-amino acids (fructose amino acids), Amadori compounds, are formed by reaction of D-glucose and L-amino acids and Amadori rearrangement. They are detected in heat-processed natural products and various foodstuffs and are key products of the Maillard-Browning reaction. N-Nitroso-N-(1-deoxy-D-fructos-1-yl)-L-amino acids (N-NO-fructose amino acids), N-NO-Amadori compounds, are formed in high yields by reacting fructose amino acids with sodium nitrite in acidic aqueous solution. They constitute a new class of non-volatile, bis-beta-oxidized nitrosamine derivatives with unknown biological (mutagenic and/or carcinogenic) activity. N-NO-Fructose amino acids may be formed in nitrite-containing Maillard systems (e.g., cured-meat products, tobacco) or in the human stomach after ingestion of food containing fructose amino acids and nitrite in food or saliva. Thirteen fructose amino acids and 13 N-NO-fructose amino acids (-gly, -ala, -val, -leu, -ileu, -ser, -thr, -met, -asp, -pheala, -tyr, -his, -trp) were prepared and investigated by high-resolution 1H-nuclear magnetic resonance (NMR) and 13C-NMR spectroscopy. The percentage amounts of the sugar ring forms (beta-pyranose, beta-furanose, alpha-furanose and alpha-pyranose) of these compounds in D2O mutarotation equilibrium were determined by 13C-NMR spectroscopy, together with the amounts (%) of E/Z isomers in the case of N-NO-compounds. The nitrosation products of D-fru-L-tyr, D-fru-L-his and D-fru-L-trp were isolated and identified by spectroscopic methods (NMR, infra-red). The N-NO-fructose amino acids can be separated by reversed-phase, ion-pairing, high-performance liquid chromatography. In some case the E/Z isomers are separated.

Amino Acids↗
PubMed1980

Synthesis of monosaccharide nitrosamines.

This paper describes the chemical synthesis of a chain-branched, monosaccharide nitrosamine: 3-[N-nitroso-N-ethyl]-aminomethyl-D-allose. Nitrosamines with alpha-carbon-carbon-bonded carbohydrate residues (hydrophilic carrier) could be interesting for experimental cancer research; specifically, in biological experiments (testing for carcinogenic, mutagenic or teratogenic effects), biochemical experiments (enzymatic activation, metabolites) and physiological experiments (resorption studies).

Hexoses↗
PubMed1978

Possible nitrosodimethylamine formation in comparative in vitro nitrosation experiments with six different tetracycline antibiotics.

The hydrochlorides of tetracycline, minocycline, chlorotetracycline, anhydrochlorotetracycline, desmethylchlorotetracycline, oxytetracycline and doxycycline were reacted with sodium nitrite for two hours at 37 degrees C in aqueous buffer solutions at pH 2 and 4 under simulated stomach conditions. NDMA formation was detected from minocycline, doxycycline, oxytetracycline and anhydrochlorotetracycline by GLC and GLC-MS analysis. NDMA formation from minocycline and dodxycycline was blocked by ascorbic acid. The catalytic effect of sodium thiocyanate for NDMA formation from minocycline and nitrite was investigated. The different reactivities of the tested tetracyclines towards nitrite in acidic solutions (NDMA formation from minocycline, doxycycline, oxytetracycline and no NDMA formation from tetracycline, chlorotetracycline and desmethylchlorotetracycline) may be understood from stereochemical considerations. The failure of dealkylative nitrosation reactions in the latter tetracyclines is explained by the formation of intramolecular hydrogen bridge linkages between epidimethylamino groups at C-4 and OH groups at C-6. This hypothesis was proved by the observations of NDMA formation from anhydrochlortetracycline and sodium nitrite at pH 2.

Ascorbic Acid↗
PubMed1976

Mass spectrometry of nitrosamines: rearrangement of nitrosobenzylmethylamine molecular ions with loss of OH-radicals investigated by deuterated derivatives.

Nitrosamines (R1R2NO) containing a certain R groups yield mass spectra with M+-OH fragments which can be accounted for by intramolecular hydrogen shift with subsequent cleavage of OH-radicals. As can be shown with mass spectra of specifically deuterated derivatives of nitrosobenzylmethylamine - nitrosobenzyltrideuteriomethylamine, alpha,alpha-nitrosodideuteriobenzylmethylamine and o,o',p-nitrosotrideuteri0-benzylmethylamine - hydrogen transfer within the molecular ion of nitrosobenzylmethylamine occurs selectively onto the oxygen of the nitroso group from the benzylethylene group, probably via a five-membered cyclic transition state. Cleavage of OH radicals leads to formation of M+-17 ions, the stability of which can be explained by mesomerically stabilized cyclic diazirinium ions.

Chemical Phenomena↗
PubMedDate not supplied

[On the problem of dimethylnitrosamine formation from tetracycline-derivatives by nitrosation reaction in acidic medium (author's transl)].

The hydrochlorides from tetracycline and six tetracycline derivatives -- 7-dimethylamino-6-des-methyl-6-desoxytetracycline [minocycline], 7-chlorotetracycline [chlorotetracycline], 7-chloro-anhydrotetracycline [anhydrochlorotetracycline, 7-chloro-6-desmethyltetracycline [demethylchlorotetracycline], 5-hydroxytetracycline [oxytetracycline] and 6-desoxy-5-hydroxytetracycline [doxycycline] -- were reacted with different amounts of sodium nitrite at 37 degrees C for two hours in aqueous buffer solutions at pH 2 and 4. Dimethylnitrosamine formation was confirmed by gas-liquid chromatography and by combined gas-liquid chromatography/mass-spectrometry from minocycline, doxycycline, oxytetracycline and anhydrochlorotetracycline. Dimethylnitrosamine formation from minocycline and doxycycline was blocked by ascorbic acid. The catalytic effect of sodium thiocyanate for the dimethylnitrosamine formation from minocycline and nitrite was investigated. The different reactivity of the investigated tetracycline derivatives towards nitrite in acidic solutions is discussed by stereochemical considerations in connection with the formation of hydrogen bridge linkages. This hypothesis was confirmed by dimethylnitrosamine formation from anhydrochlorotetracycline and sodium nitrite at pH 2.

Ascorbic Acid↗