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Carbon Units (carbon + unit)
Selected AbstractsStereoselective Construction of a Highly Functionalized Taxoid ABC-Ring System: the C2,C9 Oxa-Bridge ApproachEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2005Sylvain Hamon Abstract The goal of this investigation is to assemble the 20-carbon unit 1 of the taxoid diterpene skeleton with a high level of stereocontrol by means of a three-reaction sequence developed in this laboratory. The strategy involves seven C,C bond-forming operations together with eighteen functional group transformations, circumventing the stereoselectivity issue altogether. Furthermore, there is no isomer formation and hence no need for chromatographic separation. A temporary oxa-bridge (C2/C9) was used as a problem-solving approach. The key step in the planned sequence was based on achieving the last C,C bonding between C11 and C12, following a successful C11 functionalization. X-ray analyses of 8b, 17, 18, 19, 20, and 21, together with extensive use of 800 MHz 1H (200 MHz 13C) NMR spectra, support the suggested structures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] The glutamate/GABA-glutamine cycle: aspects of transport, neurotransmitter homeostasis and ammonia transferJOURNAL OF NEUROCHEMISTRY, Issue 3 2006Lasse K. Bak Abstract Neurons are metabolically handicapped in the sense that they are not able to perform de novo synthesis of neurotransmitter glutamate and ,-aminobutyric acid (GABA) from glucose. A metabolite shuttle known as the glutamate/GABA-glutamine cycle describes the release of neurotransmitter glutamate or GABA from neurons and subsequent uptake into astrocytes. In return, astrocytes release glutamine to be taken up into neurons for use as neurotransmitter precursor. In this review, the basic properties of the glutamate/GABA-glutamine cycle will be discussed, including aspects of transport and metabolism. Discussions of stoichiometry, the relative role of glutamate vs. GABA and pathological conditions affecting the glutamate/GABA-glutamine cycling are presented. Furthermore, a section is devoted to the accompanying ammonia homeostasis of the glutamate/GABA-glutamine cycle, examining the possible means of intercellular transfer of ammonia produced in neurons (when glutamine is deamidated to glutamate) and utilized in astrocytes (for amidation of glutamate) when the glutamate/GABA-glutamine cycle is operating. A main objective of this review is to endorse the view that the glutamate/GABA-glutamine cycle must be seen as a bi-directional transfer of not only carbon units but also nitrogen units. [source] Case study of ex situ remediation and conversion to a combined in situ/ex situ bioremediation approach at an oxygenated gasoline release siteREMEDIATION, Issue 2 2007Armand A. Juneau Jr. In response to an oxygenated gasoline release at a gas station site in New Hampshire, a temporary treatment system consisting of a single bedrock extraction well, a product recovery pump, an air stripper, and carbon polishing units was installed. However, this system was ineffective at removing tertiary butyl alcohol from groundwater. The subsequent remedial system design featured multiple bedrock extraction wells and an ex situ treatment system that included an air stripper, a fluidized bed bioreactor, and carbon polishing units. Treated effluent was initially discharged to surface water. Periodic evaluation of the remediation system performance led to system modifications, which included installing an additional extraction well to draw contaminated groundwater away from an on-site water supply well, adding an iron and manganese pretreatment system, and discharge of treated effluent to an on-site drywell. Later, the air stripper and carbon units were eliminated, and an infiltration gallery was installed to receive treated, oxygenated effluent in order to promote flushing of the smear zone and in situ bioremediation in the source area. This article discusses the design, operation, performance, and modifications to the remediation system over time, and provides recommendations for similar sites. © 2007 Wiley Periodicals, Inc. [source] Synthesis of Conformationally Constrained Glutamic Acid Homologues and Investigation of Their Pharmacological ProfilesCHEMMEDCHEM, Issue 11 2007Paola Conti Prof. Abstract Homologation of the glutamic acid chain together with conformational constraint is a commonly used strategy to achieve selectivity towards different types of glutamate receptors. We investigated the effects of a further increase in the distance between the amino acid moiety and the distal carboxylate group of model compounds (±)- 1 and (±)- 2 on their activity/selectivity profiles. We therefore synthesized new derivatives (±)- 3,(±)- 6, which are homologues of glutamic acid containing three additional carbon units. Moreover, because the potency of NMDA antagonists can be markedly increased by replacing the distal carboxylate with the bioisosteric phosphonate group, we also prepared the corresponding phosphonate derivatives (±)- 7,(±)- 10. All new compounds were submitted to binding assays with iGluRs, and derivatives (±)- 3,(±)- 6 were also tested in second messenger assays at representative mGluR subtypes. All the applied structural modifications were detrimental to the interaction with NMDA receptors. Conversely, structural variation of the nonselective mGluR ligand (±)- 2 led to derivative (±)- 5, which behaved as a selective group,I metabotropic receptor antagonist. Notably, upon i.c.v. administration in DBA/2 mice, amino acid (±)- 5 produced a significant protection against audiogenic seizures, whereas it was inactive after i.p. administration. 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