RESUMEN

Herein we report for the first time the diastereoselective synthesis of (2R,3aR,7aS)- and (2S,3aS,7aR)-octahydroindole-2-phosphonic acid (OicP trans-fused stereoisomers) from diethyl (R)- and (S)-phosphopyroglutamate derivative. The key steps of this procedure are the ruthenium tetroxide oxidation of enantiomerically pure diethyl (R)- and (S)-phosphoprolinate obtained through Katritzky's benzotriazole-oxazolidine methodology, a highly diastereoselective successive double 4,5-diallylation of diethyl (R)- and (S)-phosphopyroglutamate with allyl bromide and allyltrimethylsilane with a trans-addition mode, and a ring-closing metathesis with Grubbs' first-generation ruthenium catalyst.

RESUMEN

Enantiopure 3-((R)- and 3-((S)-1-phenylethyl)-4-oxazoline-2-ones were evaluated as chiral building blocks for the divergent construction of heterocycles with stereogenic quaternary centers. The N-(R)- or N-(S)-1-phenylethyl group of these compounds proved to be an efficient chiral auxiliary for the asymmetric induction of the 4- and 5-positions of the 4-oxazolin-2-one ring through thermal and MW-promoted nucleophilic conjugated addition to Michael acceptors and alkyl halides. The resulting adducts were transformed via a cascade process into fused six-membered carbo- and heterocycles. The structure of the reaction products depended on the electrophiles and reaction conditions used. Alternative isomeric 4-methylene-2-oxazolidinones served as chiral precursors for a versatile and divergent approach to highly substituted cyclic carbamates. DFT quantum calculations showed that the formation of bicyclic pyranyl compounds was generated by a diastereoselective concerted hetero-Diels-Alder cycloaddition.

RESUMEN

Thrombin effect increasing swelling-induced glutamate efflux was examined in cultured cortical astrocytes, cerebellar granule neurons (CGN), hippocampal and cortical neurons. Hypotonic glutamate efflux (monitored by D-[(3)H]aspartate) from cortical astrocytes was increased by thrombin (5 U/mL) to reach 16% of the cell pool in 5 min. Thrombin had lower effects in CGN, and marginal effects in hippocampal and cortical neurons. These differences were related to the magnitude of thrombin-evoked cytosolic calcium rise. The protease-activated receptor 1 is expressed in astrocytes and neurons. In astrocytes exposed to chemical ischemia (sodium iodoacetate plus sodium azide) D-[(3)H]aspartate release showed a first phase (20-40 min) of initial low efflux which progressively increases; and a second phase (40-60 min) of larger efflux coincident with cell swelling. Efflux at the first phase was 52% inhibited by the glutamate transporter blocker DL-threo-ß-benzyloxyaspartic-acid (TBOA) and 11% by the volume-sensitive pathway blocker phloretin. At the second phase, efflux was reduced 52 and 38% respectively, by these blockers. In CGN D-[(3)H]aspartate efflux increased sharply and then decreased. This efflux was 32% reduced by calcium omission, 46% by TBOA and 32% by 4-[(2-butyl-6,7dichloro-2-cyclopentyl-2,3-dihydro-1oxo-1H-inden-5-yl)oxy] butanoic-acid. Thrombin enhanced this release by 32%. Ischemic treatment increased astrocyte mortality from 4% in controls to 39 and 61% in ischemia and ischemia plus thrombin, respectively. Cell death was prevented by phloretin. CGN viability was unaffected by the treatment. These results suggest that coincidence of swelling and thrombin during ischemia elevates extracellular glutamate prominently from astrocyte efflux, which may endanger neurons in vivo.

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RESUMEN

Activation of protein-activated receptor (PAR-1) by thrombin potentiates the hyposmotic efflux of (3)H-D-aspartate and (3)H-taurine from cultured cerebellar astrocytes. This effect is mediated by a thrombin-elicited increase in cytosolic Ca(2+) levels [Ca(2+)](i) and the activation of phosphoinositide-3-kinase (PI3K). These signalling pathways operate independently showing additive effects if prevented simultaneously. The contribution of the Ca(2+)-mediated pathway to thrombin-increased D-aspartate or taurine efflux, evaluated by the inhibitory effect of preventing [Ca(2+)](i) rise, was higher for D-aspartate (64% efflux decrease) than for taurine (40% decrease). The PI3K blocker decreased 48% and 36% D-aspartate and taurine efflux, respectively. Hyposmolarity increases phosphorylation of EGFR and c-src, but thrombin did not enhance this effect. Blockade of EGFR/src phosphorylation marginally reduced (11-14%) the hyposmolarity plus thrombin efflux of D-aspartate; taurine efflux was more sensitive to these blockers (18-26%). Since thrombin has no effect increasing EGFR/src phosphorylation in astrocytes, the contribution of this transactivation pathway may represent the inhibition of the hyposmotic efflux solely.

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