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A Bischoff

Publications and source records attributed to A Bischoff.

At least 19 recordsLinked to original sources
PubMed2001

Stereoselective synthesis of pseudopeptide microbial agent AI-77-B.

[structure: see text]. An efficient and highly stereoselective synthesis of the gastroprotective natural product AI-77-B is described. The stereocenters of the hydroxy amino acid moiety were generated by an ester-derived titanium-enolate-mediated syn-aldol reaction, a Curtius rearrangement, and application of Dondoni's aldehyde homologation. Condensation with the dihydroisocoumarin fragment and subsequent deprotecting transformations furnished optically active AI-77-B.

Anti-Bacterial Agents↗
PubMed2001

Retraction.

Explore the source record for details and available documents.

Retraction Notice↗
PubMed2001

Nifedipine inhibits sphinogosine-1-phosphate-induced renovascular contraction in vitro and in vivo.

Sphingosine-1-phosphate (SPP) can constrict isolated intrarenal blood vessels in vitro and reduce renal blood flow in vivo. The present study has investigated the role of extracellular Ca2+ and dihydropyridine-sensitive Ca2+ channels in SPP-induced renovascular contraction. In isolated intrarenal microvessels, cumulative addition of SPP (0.1-100 microM) caused concentration-dependent vasoconstriction (maximum effect 5.0 +/- 1.1 mN). In the presence of nifedipine (300 nM, added 30 min before SPP) or EGTA (5 mM, added 1 min before SPP), SPP-induced vasoconstriction was almost completely abolished. In thiobutabarbitone-anaesthetized rats, i.v. bolus injections of SPP (1-100 microg/kg) dose-dependently lowered renal blood flow from basal values of approximately 4.8 ml/min by up to 2.2 +/- 0.2 ml/min but had only little effect on mean arterial pressure. Pretreatment with nifedipine (10-100 microg/kg per min, i.v.) dose-dependently attenuated SPP-induced renal blood flow reductions. We conclude that SPP-induced renovascular contraction requires the influx of extracellular Ca2+ which may occur largely via nifedipine-sensitive L-type Ca2+ channels.

Animals↗
PubMed2001

Limited signal transduction repertoire of human Y(5) neuropeptide Y receptors expressed in HEC-1B cells.

In HEC-1B cells transfected with human Y(5) neuropeptide Y (NPY) receptors (but not in non-transfected cells) NPY inhibited forskolin-stimulated cAMP accumulation in a pertussis toxin-sensitive manner (-log EC(50) 8.88 +/- 0.25). Elevations of intracellular Ca(2+) were largely restricted to very high NPY concentrations and similar in transfected and nontransfected cells. NPY did not increase inositol phosphate accumulation and did not activate a variety of isoforms of protein kinase C or mitogen-activated protein kinases. We conclude that at least upon expression in HEC-1B cells the signal transduction of Y(5) NPY receptors is limited to inhibition of cAMP accumulation.

Analysis of Variance↗
PubMed2001

Lysosphingolipid receptor-mediated diuresis and natriuresis in anaesthetized rats.

Lysosphingolipids such as sphingosine-1-phosphate (SPP) and sphingosylphosphorylcholine (SPPC) can act on specific G-protein-coupled receptors. Since SPP and SPPC cause renal vasoconstriction, we have investigated their effects on urine and electrolyte excretion in anaesthetized rats. Infusion of SPP (1 - 30 microg kg(-1) min(-1)) for up to 120 min dose-dependently but transiently (peak after 15 min, disappearance after 60 min) reduced renal blood flow without altering endogenous creatinine clearance. Nevertheless, infusion of SPP increased diuresis, natriuresis and calciuresis and, to a lesser extent, kaliuresis. These tubular lysosphingolipid effects developed more slowly (maximum after 60 - 90 min) and also abated more slowly upon lysosphingolipid washout than the renovascular effects. Infusion of SPPC, sphingosine and glucopsychosine (3 - 30 microg kg(-1) min(-1) each) caused little if any alterations in renal blood flow but also increased diuresis, natriuresis and calciuresis and, to a lesser extent, kaliuresis. Pretreatment with pertussis toxin (10 microg kg(-1) 3 days before the acute experiment) abolished the renovascular and tubular effects of 30 microg kg(-1) min(-1) SPP. These findings suggest that lysosphingolipids are a hitherto unrecognized class of endogenous modulators of renal function. SPP affects renovascular tone and tubular function via receptors coupled to G(i)-type G-proteins. SPPC, sphingosine and glucopsychosine mimic only the tubular effects of SPP, and hence may act on distinct sites.

Anesthesia↗
PubMed2001

Anaphylactoid reactions after cisatracurium administration in six patients.

IMPLICATIONS: We report six cases of anaphylactoid reaction after the administration of the muscle relaxant cisatracurium. They include two first-time documented anaphylactoid reactions after a precurarising dose. These incidents challenge existing views of a substantially reduced anaphylactoid potential of cisatracurium relative to other muscle relaxants.

Adult↗
PubMed2001

Expression, gene cloning, and characterization of five novel phytases from four basidiomycete fungi: Peniophora lycii, Agrocybe pediades, a Ceriporia sp., and Trametes pubescens.

Phytases catalyze the hydrolysis of phosphomonoester bonds of phytate (myo-inositol hexakisphosphate), thereby creating lower forms of myo-inositol phosphates and inorganic phosphate. In this study, cDNA expression libraries were constructed from four basidiomycete fungi (Peniophora lycii, Agrocybe pediades, a Ceriporia sp., and Trametes pubescens) and screened for phytase activity in yeast. One full-length phytase-encoding cDNA was isolated from each library, except for the Ceriporia sp. library where two different phytase-encoding cDNAs were found. All five phytases were expressed in Aspergillus oryzae, purified, and characterized. The phytases revealed temperature optima between 40 and 60 degrees C and pH optima at 5.0 to 6.0, except for the P. lycii phytase, which has a pH optimum at 4.0 to 5.0. They exhibited specific activities in the range of 400 to 1,200 U. mg, of protein(-1) and were capable of hydrolyzing phytate down to myo-inositol monophosphate. Surprisingly, (1)H nuclear magnetic resonance analysis of the hydrolysis of phytate by all five basidiomycete phytases showed a preference for initial attack at the 6-phosphate group of phytic acid, a characteristic that was believed so far not to be seen with fungal phytases. Accordingly, the basidiomycete phytases described here should be grouped as 6-phytases (EC 3.1.3.26).

6-Phytase↗
PubMed2000

92Nb-(92)Zr and the Early Differentiation History of Planetary Bodies.

The niobium-92-zirconium-92 ((92)Nb-(92)Zr) extinct radioactive decay system (half-life of about 36 million years) can place new time constraints on early differentiation processes in the silicate portion of planets and meteorites. Zirconium isotope data show that Earth and the oldest lunar crust have the same relative abundances of (92)Zr as chondrites. (92)Zr deficits in calcium-aluminum-rich inclusions from the Allende meteorite constrain the minimum value for the initial (92)Nb/(93)Nb ratio of the solar system to 0.001. The absence of (92)Zr anomalies in terrestrial and lunar samples indicates that large silicate reservoirs on Earth and the moon (such as a magma ocean residue, a depleted mantle, or a crust) formed more than 50 million years after the oldest meteorites formed.

Journal Article↗
PubMed2000

A convergent synthesis of (+)-cryptophycin B, a potent antitumor macrolide from Nostoc sp. cyanobacteria.

[structure--see text] An efficient and highly stereoselective synthesis of cryptophycin B (2), a potent cytotoxic agent, is described. The ester-derived titanium-enolate-mediated syn-aldol reaction was employed to generate the stereocenters C(5) and C(6). The route is convergent and provides a convenient access to the synthesis of structural variants of cryptophycin B as well as members of its family.

Antifungal Agents↗