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Biomedical subjects

J Thiem

Publications and source records attributed to J Thiem.

48 records · Page 3Linked to original sources
PubMed1992

Synthesis and properties of sulfated alkyl glycosides.

Alkyl glycosides were sulfated with sulfur trioxide-pyridine. Dodecyl alpha- and beta-D-glucopyranoside gave the corresponding 6-sulfates in 75 and 51% yields, respectively. Separation from polysulfated compounds was carried out by reversed-phase HPLC. Tetradecyl beta-maltopyranoside (16) gave a 88: 12 mixture of 6'- and 6-sulfates. The sulfated compounds were characterized by 1H-, 13C-, and 2-dimensional NMR spectroscopy. Surfactant and thermotropic liquid-crystalline properties of the sugar derivatives were examined. All of the glycosides show smectic phases (SA), and the clearing points rise by introduction of sulfate groups. Even glycosides having no unprotected hydroxy groups may show SA-phases when bearing sulfate groups. The mesomorphic properties cannot be explained by formation of distinct aggregates, but rather must be interpreted by an effective intramolecular contrast.

Alkylation↗
PubMed1991

Approaches to the C-B-A trisaccharide of dihydroaclacinomycin by extending the chain from either side.

Selective benzylation of L-fucal (1) under phase-transfer conditions gave the 3- and 4-monoethers 2 and 3, respectively. Two routes, the "tail" or the "head" addition are presented, both leading to the target molecule 9, a mimic of the C-B-A trisaccharide component of dihydroaclacinomycin. Addition of glycals 2 and 3 respectively, to the acetylated glycal (7) of amicetose used as glycosyl donor gave the disaccharide glycals 6 and 8. Alternatively, glucosylation of the 4-acetate (4) of 2 with the benzyl hex-2-enopyranoside derivative 10 gave the disaccharide derivative 11. In the first case, the final glycosylation step involves the addition of 10 to disaccharide glycal 8. In the second procedure, the disaccharide alcohol 12 is obtained by O-deacetylation of 11, and serves as the glycosyl acceptor for glycal derivative 7 to give the C-B-a precursor trisaccharide derivative.

Aclarubicin↗
PubMed1990

Synthesis and reactions of leucrose and its exocyclic glycal.

5-O-alpha-D-Glucopyranosyl-beta-D-fructopyranose (leucrose, 1) was transformed into 3,4-di-O-acetyl-1-O-methanesulfonyl-5-O-(2,3,4-tri-O-acetyl-6-O-methanes ulfonyl-alpha-D-glucopyranosyl)-beta-D-fructopyranosyl bromide (3) and 1,3,4-tri-O-benzoyl-5-O-(2,3,4,6-tetra-O-benzoyl-alpha-D-glucopyranosyl) -beta-D-fructopyranosyl bromide (8), which were converted into derivatives (8 and 9) of 2,6-anhydro-1-deoxy-5-O-alpha-D-glucopyranosyl-D-arabino-hex-1-enitol . Hydrogenation of 8 and 9 gave the corresponding anhydroalditol derivatives. N-Iodosuccinimide-mediated glycosylation of 9 with 1,2,3,4-tetra-O-acetyl-beta-D-glucopyranose gave 1,2,3,4-tetra-O-acetyl-6-O-[3,4-di-O-benzyl-1-deoxy-1-iodo-5-O-(2,3,4,6- tetra-O-benzoyl-alpha-D-glucopyranosyl)-beta-D-fructopyranosyl]- beta-D-glucopyranose (12). Some amino, acetylated, and isopropylidene derivatives of leucrose have been prepared and characterised.

Carbohydrate Sequence↗
PubMed1990

Purification of alpha-L-fucosidase by C-glycosylic affinity chromatography, and the enzymic synthesis of alpha-L-fucosyl disaccharides.

An alpha-L-fucosidase from porcine liver was purified using the new C-glycosylic affinity adsorbent, Sepharose-epsilon-aminocaproyl-3-(alpha-L-fucopyranosyl)propylamine. The C-fucosylic linkage was synthesized by a radical reaction of 2,3,4-tri-O-acetyl-alpha-L-fucopyranosyl bromide with acrylonitrile. In transglycosylation reactions with p-nitrophenyl alpha-L-fucopyranoside or alpha-L-fucopyranosyl fluoride as donor and methyl beta-D-galactopyranoside as acceptor, the enzyme mediated the formation of (1----2)- and (1----6)-linked alpha-L-fucosyl derivatives (6.5 and 10.0%, respectively).

Animals↗
PubMed1990

Cleavage of zearalenone-glycoside, a "masked" mycotoxin, during digestion in swine.

Comparative analyses of cereal samples pretreated with or without beta-glucosidase indicate the presence of zearalenone-glycoside. To examine the stability of zearalenone-glycoside during digestion, mixed feed was artificially contaminated with synthesized zearalenone-4-beta-D-glucopyranoside (395 micrograms/kg) and fed to a pig over a period of 14 days. The metabolites detected in feces and urine samples were zearalenone and alpha-zearalenol. These results demonstrate that zearalenone-4-beta-D-glucopyranoside is decomposed during digestion and the aglucone, zearalenone, is released. Since zearalenone-glycoside is not detected during routine analysis, but hydrolysed during digestion, it seems likely that such "masked mycotoxins" are involved in cases of mycotoxicoses.

Animal Feed↗
PubMed1984

NAD[S], an NAD analogue with reduced susceptibility to phosphodiesterase. Chemical synthesis and enzymic properties.

The chemical synthesis of adenosine(5') [alpha-thio]diphospho(5')ribofuranosyl-nicotinamide (NAD[S]) is described. The product occurs as a pair of diastereomers with different configuration at the sulfur-bearing phosphorus atom. The diastereomers were separated by high-performance liquid chromatography and their absolute configuration was determined after chemical degradation to the ADP[alpha S] diastereomers and chromatographic comparison with enzymically synthesized ADP[alpha S] diastereomers of known absolute configuration. Additional support for this assignment is based on different rates in the phosphodiesterase-catalyzed hydrolysis. Furthermore the synthesis of [14C]NAD[S] is described. The coenzyme activity of NAD[S] in the reaction with alcohol dehydrogenase from baker's yeast and lactate dehydrogenase from pig heart is very similar to that of beta-NAD. Also, NAD and NAD[S] serve equally well as substrates for NAD glycohydrolase from calf spleen. In contrast, no reaction was detected with NAD pyrophosphorylase, and hydrolysis of the separated NAD[S] diastereomers with snake venom phosphodiesterase showed a 26-fold and a 33-fold slower reaction rate than that of NAD. Nucleotide pyrophosphatase was less sensitive to the S substitution, hydrolyzing NAD[S] 14-times slower than NAD. Poly(ADP-ribose) polymerase from Ehrlich ascites tumor cell nuclei accepted NAD[S] as a substrate but the reaction was significantly slower and approached saturation at much lower values than with NAD. Alkaline hydrolysis of the products insoluble in trichloroacetic acid yielded AMP[S] as the main derivative. It is concluded that with NAD[S] as a substrate the nuclear acceptors were nearly exclusively mono(ADP-ribosyl) ated .

Alcohol Dehydrogenase↗
PubMed1977

[Preparative approach to mannobiose and laminaribiose (author's transl)].

For synthetic purposes mannobiose is isolated from the polysaccharide mannan of ivory nut flower. The chain length of mannan A is determined to approximately 15 mannose units on average with a definite distribution from 5 to 25 mannose units. Acetolysis is optimized and yields 41% mannobiose. The separation on Sephadex G-15 yields pure mannobiose, and in addition its higher homologues in gram amounts. Detection of the eluates is performed using a differential refractometer. Correspondingly laminaribiose can be obtained from the polysaccharides laminaran (brown algae Laminaria hyperborea) and pachyman (fungus Poria cocos Wolf, Bukuryo) by selectively optimized acetolysis in 30% yield. Depending on the starting material separations are favourably performed on silica gel or on Sephadex G-15. Laminaribiose and its higher homologues are obtained in gram amounts.

Chemical Phenomena↗