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Biomedical subjects

A Krebs

Publications and source records attributed to A Krebs.

At least 19 recordsLinked to original sources
PubMed1992

Synthesis and characterization of 6-O-beta-lactosyl-alpha,beta-lactoses, 1-O-(6-O-beta-lactosyl-beta-lactosyl)-(R,S)-glycerols, and 4,6-di-O-beta-D-galactopyranosyl-alpha,beta-D-glucoses.

1,2,3,2',3',4',6'-Hepta-O-acetyl-beta-lactose (4) was coupled with 2,3,6,2',3',4',6'-hepta-O-acetyl-alpha-lactosyl bromide (7) in the presence of Hg(CN)2 to afford 1,2,3,2',3',4',6'-hepta-O-acetyl-6-O-(2,3,6,2',3',4',6'-hepta-O-acetyl-b eta- lactosyl)-beta-lactose (11) which, upon O-deacetylation, gave 6-O-beta-lactosyl-alpha,beta-lactoses (64% from 4). In contrast, the reaction of 7 with benzyl 2,3,2',3',4',6'-hexa-O-acetyl-beta-lactoside in the presence of Hg(CN)2 produced 3,6,2',3',4',6'-hexa-O-acetyl-1,2-O- (2,3,2',3',4',6'-hexa-O-acetyl-1-O-benzyl-beta-lactos-6-yl orthoacetyl)-alpha-lactose (63%) and 3,6,2',3',4',6'-hexa-O-acetyl-1,2-O-(1- cyanoethylidene)-alpha-lactose (27%). The glycosidation of 4 using 2,3,4,6-tetra-O-acetyl-alpha-D-galactopyranosyl bromide in the presence of Hg(CN)2 afforded, after deprotection, 4,6-di-O-beta-D-galactopyranosyl-alpha,beta-D-glucoses (66%). The reaction of 11 with 1,2-di-O-benzyl-(R,S)-glycerols and trimethylsilyl trifluoromethanesulfonate yielded, after deprotection, 1-O-(6-O-beta-lactosyl-beta-lactosyl)-(R,S)-glycerols (18%). Under the same coupling conditions 11 reacted with 2-O-benzylglycerol to form 3-O-acetyl-2-O-benzyl-1-O-[2',3',4',6'-hexa-O-acetyl-6-O-(2,3,6,2',3',4' ,6'- hepta-O-acetyl-beta-lactosyl)-beta-lactosyl]-(R,S)-glycerols (16%).

Asialoglycoprotein Receptor↗
PubMed1991

Synthesis and characterization of 2-O-beta-lactosylglycerol, 1,2-di-O-beta-lactosyl-(R,S)-glycerols, and 1,2,3,-tri-O-beta-lactosylglycerol.

The reaction of 2,3,6,2',3',4',6'-hepta-O-acetyl-alpha-lactosyl bromide (5) and 1,3-di-O-benzylglycerol in the presence of mercury(II) cyanide in benzene-nitromethane afforded 1,3-di-O-benzyl-2-O-(2,3,6,2',3',4',6'-hepta-O-acetyl-beta-lactosyl)glyc erol (70%), which was converted into 2-O-beta-lactosylglycerol. 1,2-Di-O-beta-lactosyl-(R,S)-glycerols were obtained by way of the coupling of 5 to either 1-O-benzyl-(R,S)-glycerol or 1-O-benzyl-2-O-(2,3,6,2',3',4',6'-hepta-O-acetyl-beta-lactosyl)-(R,S)-gl ycerols. The most efficient route to 1,2, 3-tri-O-beta-lactosylglycerol (17) involved treatment of 2-O-(2,3,6,2',3',4',6'-hepta-O-acetyl-beta-lactosyl)glycerol with 3 mol. equiv. of 5 followed by removal of the blocking groups, to give 17 (47%).

Carbohydrate Sequence↗
PubMed1991

Synthesis and characterization of 6-O-beta-lactosyl-alpha,beta-D-mannopyranoses and 2,6-di-O-beta-lactosyl-alpha,beta-D-mannopyranoses.

The reaction of 2,3,6,2',3',4',6'-hepta-O-acetyl-alpha-lactosyl bromide (4) and benzyl 3,4-di-O-benzyl-alpha-D-mannopyranoside (3) in the presence of mercury(II) cyanide in benzene-nitromethane produced benzyl 3,4-di-O-benzyl-2,6-bis-O-(2,3,6,2',3',4',6'-hepta-O-acetyl-beta-lact osy l)-alph a D-mannopyranoside (5) and benzyl 3,4-di-O-benzyl-6-O-(2,3,6,2',3',4',6'-hepta-O-acetyl-beta-lactosyl)-alp ha-D- mannopyranoside (6), as part of a complex mixture. Column chromatography, followed by acetylation of the fraction containing 5 and 6, gave a sample of 5 and benzyl 2-O-acetyl-3,4-di-O-benzyl-6-O (2,3,6,2',3',4',6'-hepta-O-acetyl-beta-lactosyl)-alpha-D-mannopyranoside (7) in approximately 35% and 17% yields (based on 4), respectively. Deprotection of 5 and 7 afforded the target compounds, namely 2,6-di-O-beta-lactosyl-alpha,beta-D-mannopyranoses and 6-O-beta-lactosyl-alpha,beta-D-mannopyranoses, respectively. If the coupling of 4 with 3 were performed in the presence of silver trifluoromethanesulfonate and 2,4,6-trimethylpyridine, only a mixture of 3,6,2',3',4',6'-hexa-O-acetyl- alpha-lactose-1,2-[( 3,6,2',3',4',6'-hexa-O-acetyl-alpha-lactose 1,2-(benzyl 3,4-di-O-benzyl-alpha-D-mannopyranosid-6-yl orthoacetyl)-2-yl]orthoacetate) and 3,6,2',3',4',6'-hexa-O-acetyl-alpha-lactose 1,2-(benzyl 3,4-di-O-benzyl-alpha-D-mannopyranosid-6-yl orthoacetate) was obtained. The orthoacetates were characterized by n.m.r. spectroscopy. The two target materials are useful in the assessment of the binding properties of galactose-terminated ligands to the asialoglycoprotein receptor of normal rabbit and human hepatocytes.

Carbohydrate Sequence↗
PubMed1991

Elevated serum neopterin levels in atherosclerosis.

Plasma levels of neopterin were determined in patients with different clinical stages of atherosclerosis. Non-hospitalized patients with atherosclerosis had serum and plasma neopterin levels within the normal range of the assay (6 +/- 2 nM). These values were not significantly different from those reported for healthy blood donors (5 +/- 2 nM). In contrast, about 50% (29 out of 61) of hospitalized patients undergoing conservative or surgical therapy had neopterin plasma levels, which exceeded the normal range (greater than 10 nM) up to 10-fold. The two groups differ on a significance level of P less than 0.01. For further evaluation hospitalized patients were subgrouped according to neopterin levels. In the subgroup with elevated neopterin levels patients with higher Frederickson types of atherosclerosis were overrepresented compared to patients with normal neopterin levels. Type 4 differed significantly from patients without pathological changes of lipoprotein (P less than 0.05). Only 3 patients suffered from minimal skin necrosis, two of them had elevated neopterin levels. Significantly more patients with peripheral artery occlusions had elevated neopterin levels than patients with occlusions of central arteries (P less than 0.05). All other criteria used for comparison (sex, age, smoking, antioxidant status, diabetes, hypertension, adipositas, hyperuricemia) did not vary significantly in both subgroups. These data indicate that neopterin plasma levels might be a valuable parameter in activity staging and therapeutic follow up of atherosclerotic patients. Additionally, an involvement of the nonspecific immune system in atherogenesis is suggested by the increased plasma neopterin concentrations.

Aged↗
PubMed1990

Synthesis and characterization of new 10-acylderivatives of the antipsoriatic agent dithranol: coupling products of dithranol with all-trans-retinoic acid, 13-cis-retinoid acid and an aromatic analogue of retinoic acid: all-trans-9-(4-methoxy-2,3,6-trimethylphenyl)-3,7-dimethyl- nona-2,4,6,8-tetraenoate.

The synthesis of new 10-acylderivatives of dithranol 1 is described. Compound 1 was reacted with the acid chlorides of all-trans retinoic acid 5, 13-cis-retinoic acid 6 and all-trans-9-(4-methoxy-2,3,6-trimethylphenyl)-3,7-dimethyl-nona-2,4,6,8- tetraenoate 7 in toluene and collidin as a base to give the coupling products 2, 3 and 4. The different structures were confirmed by high resolution 1H- and 13C-NMR spectroscopy. Initial investigations with the enzyme glucose-6-phosphate dehydrogenase indicate that all of them are inhibitors of the protein and therefore might have antipsoriatic activity.

Acitretin↗
PubMed1990

[Synthesis and biochemical properties of new 10-acyl derivatives of dithranols: acetylsalicyldithranol and 1-acetyllactyldithranol].

By reaction of the corresponding acid chlorides of acetylsalicylic acid (8) and L-acetyllactic acid (5) with dithranol (1) in toluene and collidin or pyridine as a base two new 10-acylderivatives of (1) were prepared: L-acetyllactyldithranol (2) and acetylsalicyldithranol (3). Both derivatives strongly inhibited the enzyme glucose-6-phosphate dehydrogenase, indicating possible antipsoriatic activity.

Anthralin↗
PubMed1990

[Synthesis, characterization, racemation and biochemical studies on 10-acylderivatives of chrysarobin: sorbylchrysarobin, beta-carbethoxypropionylchrysarobin and senecioylchrysarobin].

The racemic synthesis of three 10-acylderivatives of chrysarobin (1) is described. Senecioylchrysarobin (3), beta-carbethoxypropionylchrysarobin (4) and sorbylchrysarobin (5) were prepared by reaction of (1) with the corresponding carboxylic acid chlorides and collidine as a base in toluene. The separation of the racemates of (3) and (5) on a chiral stationary phase is demonstrated for the first time. All of the new compounds showed an increased potency of inhibition of the enzyme glucose-6-phosphate dehydrogenase, an indication for possible antipsoriatic activity.

Anthracenes↗
PubMed1990

[Chemical instability of the antipsoriatic dithranol and chrysarobin in aqueous systems: oxidation behavior].

Decomposition of dithranol (1) and chrysarobin (4) in homogeneous and heterogeneous buffer solutions (pH 7.5) were studied by means of HPLC-chromatography. Half lives of (1) under homogeneous conditions were 1 h 15 min., under heterogeneous conditions 2 h 45 min., whereas in the case of (4) 3 h and 30 min. respectively were measured. (1) was degraded to dihydroxyanthrachinon (2) and dimeric dithranol (3), the amount of (2) and (3) depending of the chosen conditions, whereas degradation of (4) under heterogeneous conditions revealed no oxidation products. On the other hand two metabolites of (4) were detected in homogeneous buffer solutions. The presenting studies clearly show the different ways of decomposition of (1) and (4) in homogeneous and heterogeneous solutions.

Anthracenes↗
PubMed1990

[10-Acyldithranol dimers; new derivatives of the antipsoriatic dithranol; synthesis, characterization and biochemical properties].

With regard to the synthesis of 10-(omega-carboxyacyl)-derivatives dithranol 1 was reacted with the carboxylic acid dichlorides of succinic acid, glutaric acid, adipic acid and pimelic acid in toluene and collidin as a base. Instead of the expected derivatives the 10-acyldithranol dimers 5-7 were isolated as main products except for the reaction of succinyl chloride where only lactone 2 was formed. Moreover the 6-ring lactone 3 as a side product and traces of the 7-ring lactone 4 could also be isolated and characterized. All compounds revealed to be inhibitors of the enzyme glucose-6-phosphate dehydrogenase, indicating antipsoriatic activity.

Anthralin↗
PubMed1987

Interaction of hepatic asialoglycoprotein receptor with dimyristoyl phosphatidylcholine vesicles.

The hepatocyte membrane asialoglycoprotein receptor (ASGP-R) was extracted from rabbit liver, purified, and then incubated with preformed vesicles of dimyristoyl phosphatidylcholine. The association of protein with lipid was dependent on vesicle size and the best results were achieved with small vesicles of about 20 nm diameter. The ligand binding capacity of ASGP-R-vesicle complexes was also measured and found to be approximately sevenfold greater than free receptor in aqueous buffer and twofold greater than receptor solubilized in Triton X-100. Most likely, the reconstitution procedure used in these experiments does not result in transmembrane insertion of the receptor. ASGP-R probably resides on the surface of the vesicle, held there primarily by weak hydrophobic forces.

Animals↗
PubMed1987

Dithranol: further investigations on the structure-activity-relationship. The new series of the 10-mono-alkyldithranol derivatives.

The in vitro stability of 10-ethyldithranol (1,8-dihydroxy-10-ethyl-9(10H)-anthracenone) and its effects on healthy and psoriatic skin is investigated. 10-Ethyl-dithranol as a representative of the new class of 10-alkyldithranol derivatives neither stains nor irritates and has no antipsoriatic activity at all. This is due to the relatively stable substituent at carbon 10 which enables the fast oxidation processes necessary for the antipsoriatic effect. Therefore, antipsoriatically active dithranol derivatives require a free or easily liberated 10-position and hence the so-called 'minimum structure of antipsoriatic anthrones' keeps its validity.

Anthralin↗