Efficient route to (S)-azetidine-2-carboxylic acid.
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A new and efficient route to (S)-azetidine-2-carboxylic acid (>99.9% ee) in five steps and total yield of 48% via malonic ester intermediates was established. As the key step, efficient four-membered ring formation (99%) was achieved from dimethyl (S)-(1'-methyl)benzylaminomalonate by treating with 1,2-dibromoethane (1.5 eq) and cesium carbonate (2 eq) in DMF. Krapcho dealkoxycarbonylation of dimethyl (1'S)-1-(1'-methyl)benzylazetidine-2,2-dicarboxylate, the product of this cyclization procedure, proceeded with preferential formation (2.7:1, 78% total yield) of the desired (2S,1'S)-monoester, with the help of a chiral auxiliary which was introduced on the nitrogen atom. The undesired (2R,1'S)-isomer could be converted to that with proper stereochemistry, by a deprotonation and subsequent re-protonation step. Finally, lipase-catalyzed preferential hydrolysis of the (2S,1'S)-monoester and subsequent deprotection provided enantiomerically pure (S)-azetidine-2-carboxylic acid in a 91% yield from the mixture of (2S,1'S)- and (2R,1'S)-isomers. (+info)
Effects of calcium channel blockade on angiotensin II-induced peritubular ischemia in rats.
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Recent studies have indicated that derangement of peritubular capillary (PTC) circulation with consequent tubulointerstitial hypoxia plays a pivotal role in the pathogenesis of renal injury. The present study was performed to determine whether azelnidipine, a new dihydropyridine calcium channel blocker, attenuates angiotensin II (AngII)-induced peritubular ischemia in anesthetized rats. The superficial PTCs were visualized directly using an intravital fluorescence videomicroscope system, and the PTC blood flow was evaluated by analyzing the velocity of fluorescein isothiocyanate-labeled erythrocytes. Intravenous infusion of AngII (50 ng/kg/min, 10 min) significantly increased mean arterial pressure (MAP) and renal vascular resistance (RVR) (by 35 +/- 3% and 110 +/- 32%, respectively), and decreased total renal blood flow (RBF) and PTC erythrocyte velocity (by -34 +/- 4 and -37 +/- 1%, respectively). Treatment with azelnidipine (5 microg/kg/min i.v., 10 min) had no effect on basal MAP, RBF, RVR, or PTC erythrocyte velocity. However, azelnidipine markedly attenuated the AngII-induced increases in MAP (7 +/- 3%) and RVR (40 +/- 4%) and decreases in RBF (-24 +/- 1%) and PTC erythrocyte velocity (-22 +/- 1%). Similar attenuation in the AngII-induced responses of MAP, RBF, RVR, and PTC erythrocyte velocity were observed in rats treated with a higher dose of azelnidipine (20 microg/kg/min i.v., 10 min), which significantly decreased basal MAP and RVR and increased RBF and PTC erythrocyte velocity. These data suggest that calcium channel blockade attenuates AngII-induced peritubular ischemia, which may be involved in its beneficial effects on renal injury. (+info)
Up-regulation of the clusterin gene after proteotoxic stress: implication of HSF1-HSF2 heterocomplexes.
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Clusterin is a secreted protein chaperone up-regulated in several pathologies, including cancer and neurodegenerative diseases. The present study shows that accumulation of aberrant proteins, caused by the proteasome inhibitor MG132 or the incorporation of the amino acid analogue AZC (L-azetidine-2-carboxylic acid), increased both clusterin protein and mRNA levels in the human glial cell line U-251 MG. Consistently, MG132 treatment was capable of stimulating a 1.3 kb clusterin gene promoter. Promoter deletion and mutation studies revealed a critical MG132-responsive region between -218 and -106 bp, which contains a particular heat-shock element, named CLE for 'clusterin element'. Gel mobility-shift assays demonstrated that MG132 and AZC treatments induced the formation of a protein complex that bound to CLE. As shown by supershift and chromatin-immunoprecipitation experiments, CLE is bound by HSF1 (heat-shock factor 1) and HSF2 upon proteasome inhibition. Furthermore, co-immunoprecipitation assays indicated that these two transcription factors interact. Gel-filtration analyses revealed that the HSF1-HSF2 heterocomplexes bound to CLE after proteasome inhibition have the same apparent mass as HSF1 homotrimers after heat shock, suggesting that HSF1 and HSF2 could heterotrimerize. Therefore these studies indicate that the clusterin is a good candidate to be part of a cellular defence mechanism against neurodegenerative diseases associated with misfolded protein accumulation or decrease in proteasome activity. (+info)
Protein synthesis upon acute nutrient restriction relies on proteasome function.
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The mechanisms that protect mammalian cells against amino acid deprivation are only partially understood. We found that during an acute decrease in external amino acid supply, before up-regulation of the autophagosomal-lysosomal pathway, efficient translation was ensured by proteasomal protein degradation. Amino acids for the synthesis of new proteins were supplied by the degradation of preexisting proteins, whereas nascent and newly formed polypeptides remained largely protected from proteolysis. Proteasome inhibition during nutrient deprivation caused rapid amino acid depletion and marked impairment of translation. Thus, the proteasome plays a crucial role in cell survival after acute disruption of amino acid supply. (+info)
Regulation of herpesvirus macromolecular synthesis: sequential transition of polypeptide synthesis requires functional viral polypeptides.
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It was previously shown that virus-specific polypeptides made in HEp-2 cells infected with herpes simplex 1 form three groups designated alpha, beta, and gamma whose synthesis is coordinately regulated and sequentially ordered. This report shows that one or more functional alpha polypeptides are necessary to turn on the synthesis of beta and gamma groups, and conversely, one or more polypeptides in the latter groups turn off the synthesis of alpha polypeptides. Specifically, infected cells maintained in medium containing either canavanine, an analogue of arginine, or azetidine-2-carboxylic acid an analogue of proline and hydroxyproline, synthesized alpha polypeptide at rates comparable to maximal rates in untreated infected cells but did not undergo the normal transition to beta and gamma polypeptide synthesis. The transition to gamma polypeptide synthesis and shut-off of synthesis of earlier polypeptide groups proceeded normally if addition of canavanine was delayed until at least 4-5 hr after infection. Addition of canavanine after the onset of beta and gamma polypeptide synthesis, i.e., between 2 and 3.5 hr after infection, resulted in sustained, simultaneous synthesis of all three polypeptide groups, a phenomenon not seen in untreated infected cells. Canavanine-treated infected cells, synthesizing alpha polypeptides, recovered the capacity to make beta and gamma polypeptides after removal of the analogue, but only after a 1-to 2-hr delay compared with infected untreated cells. The data indicate that the on and off controls inherent in the cascade regulation of viral polypeptide synthesis are mediated by one or more polypeptides in each group at transcriptional or post-transcriptional levels. (+info)
The transition metal chelator nicotianamine is synthesized by filamentous fungi.
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Nicotianamine is an important metal ligand in plants. Surprisingly, recent genome sequencing revealed that ascomycetes encode proteins with similarity to plant nicotianamine synthases (NAS). By expression in a Zn2+-hypersensitive fission yeast mutant we show for a protein from Neurospora crassa that it indeed possesses NAS activity. Using electrospray-ionization-quadrupole-time-of-flight mass spectrometry we prove the formation of nicotianamine in N. crassa. Transcript level is strongly upregulated under Zn deficiency as shown by real-time PCR. These findings demonstrate that nicotianamine is more widespread in nature than anticipated and provide further evidence for a function of nicotianamine as a cytosolic chelator of Zn2+ ions. (+info)
Metabolic engineering of Saccharomyces cerevisiae producing nicotianamine: potential for industrial biosynthesis of a novel antihypertensive substrate.
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Nicotianamine (NA), a metal chelator, is ubiquitous in higher plants. In humans, NA inhibits angiotensin I-converting enzyme (ACE), and consequently reduces high blood pressure. Nicotianamine is synthesized from the trimerization of S-adenosylmethionine (SAM) by NA synthase (NAS). Here, we aimed to produce large amounts of NA fermentatively by introducing the Arabidopsis AtNAS2 gene into Saccharomyces cerevisiae strain SCY4. This strain can accumulate up to 100 times the usual amount of SAM, and this is considered desirable for overproduction of NA. Nicotianamine was produced in the engineered yeast, and the NA level increased with incubation time until the stationary phase. The maximum concentration of intracellular NA obtained was 766+/-33 microg/g wet weight. Successful production of NA in S. cerevisiae should pave the way for industrial production of this novel antihypertensive substrate. (+info)
Genetically modified cyanobacterium Nostoc muscorum overproducing proline in response to salinity and osmotic stresses.
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In the parent Nostoc muscorum an active proline oxidase enzyme is required to assimilate exogenous proline as a fixed nitrogen source. Cyanobacterial mutants, resistant to growth inhibitory action of proline analogue L-azetidine-2-carboxylate (Ac-R), were deficient in proline oxidase activity, and were over-accumulators of proline. Proline over-accumulation, resulting either from mutational acquisition of the Ac-R phenotype, or from salinity-induced uptake of exogenous proline, confirmed enhanced salinity/osmotic tolerance in the mutant strain. The nitrogenase activity and photosynthetic O 2 evolution of the parent were sensitive to both salinity as well as osmotic stresses than of Ac-R mutant strain. In addition, the mutation to Ac-resistant phenotype showed no alteration in salinity inducible potassium transport system in the cyanobacterium. (+info)