bluuebunny/crossref_metadata_2025_split huggingface dataset:
The First Catalytic Highly Enantioselective Alkylation of Ketimines—A Novel Approach to Optically Active Quaternary α‐Amino Acids
Authors: Saaby Steen , Nakama Kimitaka , Lie Mette Alstrup , Hazell Rita G. , Jørgensen Karl Anker 
Published: December 2003

AbstractA series of novel ketimines with intrinsic protecting group anchoring was synthesized and allowed to react with various silylketene acetals in the presence of 5–10 mol % of a chiral Zn(OTf)2‐(R,R)‐Ph‐pybox‐aqua complex. The corresponding optically active quaternary α‐amino acid derivatives were obtained in high yields and with enantioselectivities ranging from 34 % up to 95 % ee. The catalyst was studied by 1H NMR spectroscopy and X‐ray crystallography, and a dynamic equilibrium of two species was identified in solution. These are a homo‐chiral 1:2 metal–ligand complex and a 1:1 metal–ligand complex, of which the latter is expected to be the actual catalyst of the diastereo‐ and enantioselective reaction. A strong positive nonlinear effect was observed due to the formation of a catalytically inactive 1:2 metal–ligand hetero‐chiral complex. On the basis of DFT calculations and the absolute stereochemistry of the products, simultaneous coordination of the imino electrophile and a single molecule of H2O to the chiral Lewis acid complex is proposed. Coordination of the imine‐nitrogen atom in the axial position of an octahedral complex can account for the facial selectivity as well as the diastereoselectivity observed.
The (2‐Phenyl‐2‐trimethylsilyl)ethyl‐(PTMSEL)‐Linker in the Synthesis of Glycopeptide Partial Structures of Complex Cell Surface Glycoproteins
Authors: Wagner Michael , Dziadek Sebastian , Kunz Horst 
Published: December 2003

AbstractThe (2‐phenyl‐2‐trimethylsilyl)ethyl‐(PTMSEL) linker represents a novel fluoride‐sensitive anchor for the solid‐phase synthesis of protected peptides and glycopeptides. Its cleavage is achieved under almost neutral conditions using tetrabutylammonium fluoride trihydrate in dichloromethane thus allowing the construction of complex molecules sensitive to basic and acidic media commonly required for the cleavage of standard linker systems. The advantages of the PTMSEL linker are demonstrated in the synthesis of glycopeptides from the liver intestine (LI)‐cadherin and the mucin MUC1, bearing carbohydrate moieties such as N‐linked chitobiose or O‐linked sialyl‐TN‐residues. The synthesis of these types of glycopeptides is difficult because they are prone to secondary structure formation during the synthesis on the solid phase as well as in the completely deprotected form. Using the PTMSEL linker these molecules are accessible by automated synthesis according to the Fmoc strategy without frequently observed side reactions such as aspartimide or diketopiperazine formation.
Structural Basis for Vapoluminescent Organoplatinum Materials Derived from Noncovalent Interactions as Recognition Components
Authors: Lu Wei , Chan Michael C. W. , Zhu Nianyong , Che Chi‐Ming , He Zhike , Wong Kwok‐Yin 
Published: December 2003

AbstractThe spectroscopic properties and crystal structures of a series of platinum(II) complexes bearing functionalized σ‐alkynyl groups, namely [(tBu2bpy)Pt(CCAr)2] (tBu2bpy = 4,4′‐bis‐tert‐butyl‐2,2′‐bipyridine, Ar = 4‐pyridyl, 1; 3‐pyridyl, 2; 2‐pyridyl, 3; 4‐ethynylpyridyl, 4; 2‐thienyl, 5; pentafluorophenyl, 6) have been studied. Solid‐state emissions of 1 and 6 are dependent on their crystallinity. Reversible and selective vapoluminescence was observed for 1 and 6 in the presence of chlorocarbon vapors. For solid 1, dramatic enhancement of green luminescence is observed upon sorption of CH2Cl2 or CHCl3 vapor. The excimeric orange emission for solid 6 is switched to monomeric green emission upon exposure to CH2Cl2 vapor. The luminescent responses of a thin film of 1 towards various organic vapors have also been examined. In the crystallographically determined structure of 1⋅CH2Cl2, the bis(acetylide) moiety acts as the receptor berth for a CH2Cl2 molecule through concerted CH⋅⋅⋅π(CC) interactions, while Cl⋅⋅⋅Cl interactions connect the CH2Cl2 molecules into infinite linear chains. The observed crystal lattices are arranged into scaffolds of varying porosity by weak CH⋅⋅⋅N(py) (1⋅CH2Cl2, 1⋅CH3CN, 4⋅DMF) and CH⋅⋅⋅FC (6, 6⋅CH3CN) interactions. The correlation between the crystal structures of 1⋅CH2Cl2, 1⋅CH3CN, 2, 4⋅DMF, 5, 6, and 6⋅CH3CN and their vapoluminescence suggests that weak nonconventional hydrogen‐bonding interactions preside over the reversible sensing and signalling processes.
Solvothermal Syntheses of High‐Nuclearity Vanadium(III) Clusters
Authors: Laye Rebecca H. , Murrie Mark , Ochsenbein Stefan , Bell Aidan R. , Teat Simon J. , Raftery James , Güdel Hans‐Ulrich , McInnes Eric J. L. 
Published: December 2003

AbstractSuperheating alcohol solutions of simple trimetallic vanadium(III) precursors gives the octa‐ and decametallic vanadium(III) clusters [V8(OEt)8(OH)4(O2CPh)12] (1) and [V10(OMe)20(O2CMe)10] (2). Cluster 2 is the largest vanadium(III) cluster synthesised to date. Thus solvothermal synthetic techniques are an excellent route to high‐nuclearity vanadium(III) clusters. Both 1 and 2 consist of a planar or near‐planar array of VIII ions. The metal ions in 1 are bridged by either a μ2‐hydroxide and two μ2‐benzoate groups or two μ2‐ethoxides and a μ2‐benzoate groups, the two bridging arrangements alternating around the ring. In 2 each pair of neighbouring metal ions is bridged by two μ2‐methoxides and a μ2‐acetate, and this molecule is the VIII analogue of Lippard's famous “ferric wheel”. Preliminary magnetic susceptibility studies show the exchange coupling in both complexes to be antiferromagnetic in nature, with the coupling stronger in 1 than in 2.
Mouse strain‐specific nicotinic acetylcholine receptor expression by inhibitory interneurons and astrocytes in the dorsal hippocampus
Authors: Gahring Lorise C. , Persiyanov Karina , Dunn Diane , Weiss Robert , Meyer Erin L. , Rogers Scott W. 
Published: December 2003

AbstractThe response by individuals to nicotine is likely to reflect the interaction of this compound with target nAChRs. However, resolving how different genetic backgrounds contribute to unique mouse strain‐specific responses to this compound remains an important and unresolved issue. To examine this question in detail, expression of the nicotine acetylcholine receptor (nAChR) subunits α3, α4, α5, α7, β2, and β4 was measured in the dorsal hippocampus using immunohistochemistry in mouse strains or lines BALB/c, C3H/J, C57BL/6, CBA/J, DBA/2, Long Sleep (LS), Short Sleep (SS), and CF1. The nAChRs in all mice colocalized with glutamic acid decarboxylase (GAD)‐positive interneurons that were subclassified into at least four groups based on nAChR subunit heterogeneity. A notable difference between mouse strains was the expression of nAChRs by astrocyte subpopulations in CA1 subregions whose numbers vary inversely with nAChR‐immunostained neurons. This novel relationship also correlated with published parameters of strain sensitivity to nicotine. Attempts to identify the origin of this significant difference in nAChR expression among strains included comparison of the entire nAChRα4 gene sequence. Although multiple polymorphisms were identified, including two that changed nAChRα4 amino acid coding, none of these clearly correlate with strain‐related differences in cell type‐specific nAChR expression. These findings suggest that mouse strain‐specific behavioral and physiological responses to nicotine are likely to be a reflection of a complex interplay between genetic factors that shape differences in expression and cellular architecture of this modulatory neurotransmitter system in the mammalian nervous system. J. Comp. Neurol. 468:334–346, 2004. © 2003 Wiley‐Liss, Inc.
Morphologic characterization of rat taste receptor cells that express components of the phospholipase C signaling pathway
Authors: Clapp Tod R. , Yang Ruibiao , Stoick Cristi L. , Kinnamon Sue C. , Kinnamon John C. 
Published: December 2003

AbstractRat taste buds contain three morphologically distinct cell types that are candidates for taste transduction. The physiologic roles of these cells are, however, not clear. Inositol 1,4,5‐triphosphate (IP3) has been implicated as an important second messenger in bitter, sweet, and umami taste transductions. Previously, we identified the type III IP3 receptor (IP3R3) as the dominant isoform in taste receptor cells. In addition, a recent study showed that phospholipase Cβ2 (PLCβ2) is essential for the transduction of bitter, sweet, and umami stimuli. IP3R3 and PLCβ2 are expressed in the same subset of cells. To identify the taste cell types that express proteins involved in PLC signal transduction, we used 3,3′diaminobenzidine tetrahydrochloride immunoelectron microscopy and fluorescence microscopy to identify cells with IP3R3. Confocal microscopy was used to compare IP3R3 or PLCβ2 immunoreactivity with that of some known cell type markers such as serotonin, protein gene‐regulated product 9.5, and neural cell adhesion molecule. Here we show that a large subset of type II cells and a small subset of type III cells display IP3R3 immunoreactivity within their cytoplasm. These data suggest that type II cells are the principal transducers of bitter, sweet, and umami taste transduction. However, we did not observe synapses between type II taste cells and nerve fibers. Interestingly, we observed subsurface cisternae of smooth endoplasmic reticulum at the close appositions between the plasma membrane of type II taste cells and nerve processes. We speculate that some type II cells may communicate to the nervous system via subsurface cisternae of smooth endoplasmic reticulum in lieu of conventional synapses. J. Comp. Neurol. 468:311–321, 2004. © 2003 Wiley‐Liss, Inc.
Definition and connections of the entopallium in the zebra finch (Taeniopygia guttata)
Authors: Krützfeldt Nils O.E. , Wild J. Martin 
Published: December 2003

AbstractIn birds the entopallium (formerly known as the core region of ectostriatum) is the major thalamorecipient zone, within the telencephalon, of the tectofugal visual system. Here we sought to redefine the entopallium in the zebra finch, particularly with respect to a laterally adjacent zone, known as the perientopallium (formerly known as the periectostriatal belt), and to determine its projections. We show that the entopallium can be defined by the almost complete overlap of dense terminations of thalamic rotundal afferents and intense cytochrome oxidase activity and parvalbumin immunoreactivity. The perientopallium, on the other hand, can be defined by relatively sparse projections from nucleus rotundus, a calretinin‐positive plexus of nerve fibers, and weak cytochrome oxidase activity and parvalbumin immunoreactivity. Within the entopallium, medial and lateral parts can be distinguished on the basis of cell packing density, differential patterns of parvalbumin immunoreactivity and cytochrome oxidase activity, and different projections. We show that the entopallium projects laterally and diffusely to the perientopallium and nidopallium (formerly the neostriatum) and specifically and densely to a teardrop‐shaped nucleus in the ventrolateral mesopallium (formerly known as the hyperstriatum ventrale), here called MVL (abbreviation used as a proper name). This latter projection arises predominantly from medial parts of the entopallium, which also receives a reciprocal projection from MVL, and projects to the lateral striatum. These findings suggest that the entopallium can be divided into medial and lateral parts having different functions, one of which is to provide for an extratelencephalic outflow from the medial part, via the lateral striatum. The findings also challenge the idea that informational flow through the various stations of the telencephalic tectofugal visual system is largely sequential and, together with findings in the chicken (Alpar and Tömböl [2000] Ann Anat 182:101–110), suggest instead that further substantial projections to telencephalic visual areas in birds can arise independently from both E (entopallium) and Ep (perientopallial belt). J. Comp. Neurol. 468:452–465, 2004. © 2003 Wiley‐Liss, Inc.
Rostral agranular insular cortex and pain areas of the central nervous system: A tract‐tracing study in the rat
Authors: Jasmin Luc , Granato Alberto , Ohara Peter T. 
Published: December 2003

AbstractThe rostral agranular insular cortex (RAIC) has recently been identified as a site where local changes in GABA and dopamine levels, or application of opioids, can alter nociceptive thresholds in awake animals (Jasmin et al. [2003] Nature 424:316–320). The connections of the cortex dorsal to the rhinal fissure that includes the RAIC have been examined previously, with emphasis on visceral and gustatory functions but not nociception. Here we examined the afferent and efferent connections of the RAIC with sites implicated in nociceptive processing. Sensory information from the thalamus reaches the RAIC via the submedius and central lateral nuclei and the parvicellular part of the ventral posterior nucleus. The RAIC has extensive reciprocal cortico‐cortical connections with the orbital, infralimbic, and anterior cingulate cortices and with the contralateral RAIC. The amygdala, particularly the basal complex, and the nucleus accumbens are important targets of RAIC efferent fibers. Other connections include projections to lateral hypothalamus, dorsal raphe, periaqueductal gray matter, pericerulear region, rostroventral medulla, and parabrachial nuclei. The connectivity of the RAIC suggests it is involved in multiple aspects of pain behavior. Projections to the RAIC from medial thalamic nuclei are associated with motivational/affective components of pain. RAIC projections to mesolimbic/mesocortical ventral forebrain circuits are likely to participate in the sensorimotor integration of nociceptive processing, while its brainstem projections are most likely to contribute to descending pain inhibitory control. J. Comp. Neurol. 468:425–440, 2004. © 2003 Wiley‐Liss, Inc.
Regional and subcellular compartmentation of the dopamine transporter and tyrosine hydroxylase in the rat ventral pallidum
Authors: Mengual Elisa , Pickel Virginia M. 
Published: December 2003

AbstractThe ventral pallidum (VP) is a major intermediary in the prefrontal cortical circuitry regulating sensorimotor gating and locomotor behavior, both of which are potently modulated by catecholamines. The VP catecholaminergic innervation is derived from midbrain dopaminergic neurons that differ in expression levels of the dopamine transporter (DAT) and from brainstem noradrenergic neurons without DAT. The preferentially low level of DAT in dopaminergic terminals in the prefrontal cortex and in striatal regions projecting more extensively to the VP medial (VPm) compared with VP lateral (VPl) compartment suggests possible region‐specific differences in VP axonal distribution of DAT. To test this hypothesis, we examined the electron microscopic localization of DAT and the catecholamine‐synthesizing enzyme, tyrosine hydroxylase (TH), in the VPm and VPl of rat brain. In both regions, DAT and TH were localized primarily in small unmyelinated axons and morphologically heterogeneous axon terminals. DAT‐immunogold particles were few in number, but mostly located on the plasma membrane. In contrast, TH immunoreactivity was distributed in the cytoplasm of individual profiles, many of which were without detectable DAT. In comparison with TH, the mean area density of DAT‐labeled axons was low throughout the VP. The mean area density of DAT‐immunogold axon terminals, however, was significantly higher in VPl than in VPm, whereas that of TH‐labeled axons was higher in VPm than in VPl. This dissociation suggests that, compared to the VPl, the VPm receives the greatest input from catecholaminergic afferents that are either nondopaminergic or characterized by having low levels or less terminal distributions of DAT. J. Comp. Neurol. 468:395–409, 2004. © 2003 Wiley‐Liss, Inc.
Connection from the dorsal column nuclei to the superior colliculus in the rat: Topographical organization and somatotopic specific plasticity in response to neonatal enucleation
Authors: García Del Caño Gontzal , Uria Iñigo , Gerrikagoitia Inmaculada , Martínez‐Millán Luis 
Published: December 2003

AbstractSomatosensory stimuli from the body to deep and intermediate strata of the superior colliculus (SC) are relayed from the dorsal column nuclei (DCN), gracile (GrN) and cuneate (CuN). Electrophysiological studies have shown that the somatosensory representation in SC is arranged into a map‐like pattern. However, there is a lack of studies confirming a morphological correlate of such an organization. On the other hand, after neonatal enucleation in rodents, somatosensory inputs ascend from their normal termination territory in intermediate and deep collicular strata to invade the more dorsally located visual strata. However, the origin of these reactive afferents has not been specified. By using anterograde (biotinylated dextran amine 10,000; BDA) and retrograde (Fluoro‐Gold; FG) tracers, we studied separately the connection from GrN and CuN to the intact and neonatally deafferented SC. GrN‐collicular afferents were found to terminate mainly within the periphery of the caudomedial SC quadrant, whereas CuN‐collicular fibers innervated primarily the lateral part of the rostrolateral and caudolateral collicular quadrants, in a way consistent with previously described functional data. Retrograde tracing experiments using FG injected in SC confirmed this topographical arrangement. Injections of BDA in GrN or CuN of neonatally enucleated rats showed that reactive fibers reaching superficial strata are only those CuN‐collicular fibers innervating the caudolateral SC quadrant, where the forelimb is represented. The present results provide an anatomical substrate for the known somatotopic organization of tactile representation in SC and further reinforce the previous proposal that the plastic reorganization of DCN‐collicular afferents following neonatal enucleation constitutes a functional compensatory response. J. Comp. Neurol. 468:410–424, 2004. © 2003 Wiley‐Liss, Inc.
Expression of vesicular glutamate transporters in rat lumbar spinal cord, with a note on dorsal root ganglia
Authors: Landry Marc , Bouali‐Benazzouz Rabia , El Mestikawy Salah , Ravassard Philippe , Nagy Frédéric 
Published: December 2003

AbstractThree vesicular glutamate transporters (VGLUTs) have been recently identified and their distribution has been mapped in various brain areas. In the present study, we used morphological approaches to investigate their expression in the rat lumbar spinal cord and dorsal root ganglia. Our results show a complementary distribution of VGLUT‐expressing fibers in the spinal cord, with no overlapping in nerve endings. In the dorsal horn, VGLUT1 is most abundant in mechanosensory/proprioceptive deep afferent fibers. VGLUT2 and VGLUT3 are expressed only at moderate levels in primary sensory afferent fibers and are not used by central projections of nociceptive neurons. VGLUT1 and VGLUT2 mRNAs are mainly segregated in superficial laminae but colocalized in deeper laminae. Weak expression of VGLUT3 mRNA is only detected in deep laminae. The colocalization of VGLUT1 and VGLUT2 transcripts in most sensory neurons of the dorsal root ganglia is not in agreement with the clear segregation between the proteins in their spinal projections. Such a discrepancy suggests targeting mechanisms specific for each transporter and/or a distinct regulation of their translation. In the ventral horn, the expression of VGLUT1 and VGLUT2 mRNAs in motoneuron perikarya suggests the possible unexpected role of glutamate in the vertebrate neuromuscular junction. These results demonstrate the existence of different subpopulations of glutamate nerve terminals in the rat lumbar spinal cord and suggest that functionally distinct subsets of excitatory glutamatergic neuronal networks are involved in sensory processing and motor control. J. Comp. Neurol. 468:380–394, 2004. © 2003 Wiley‐Liss, Inc.
Organization of suprachiasmatic nucleus projections in Syrian hamsters (Mesocricetus auratus): An anterograde and retrograde analysis
Authors: Kriegsfeld Lance J. , Leak Rehana K. , Yackulic Charles B. , LeSauter Joseph , Silver Rae 
Published: December 2003

AbstractCircadian rhythms in physiology and behavior are controlled by pacemaker cells located in the suprachiasmatic nucleus (SCN) of the hypothalamus. The mammalian SCN can be classified into two subdivisions (core and shell) based on the organization of neuroactive substances, inputs, and outputs. Recent studies in our laboratory indicate that these subdivisions are associated with functional specialization in Syrian hamsters. The core region, marked by calbindin‐D28K (CalB)‐containing cells, expresses light‐induced, but not rhythmic, clock genes. In the shell compartment, marked by vasopressinergic cells and fibers, clock gene expression is rhythmic. Given these findings, an important question is how photic and rhythmic information are integrated and communicated from each of these regions to effector areas. The present study used localized, intra‐SCN iontophoretic injections of the anterograde tracer biotinylated dextran amine (BDA) to investigate intra‐SCN connectivity and the neural pathways by which information is communicated from SCN subregions to targets. Intra‐SCN connections project from the core to the shell compartment of the SCN, but not from the shell to the CalB region of the SCN. Retrograde tracing experiments were performed using cholera toxin‐β (CTB) to determine more specifically whether SCN efferents originated in the core or shell using neurochemical markers for the rhythmic (vasopressin) and light‐induced (CalB) SCN subregions. The combined results from anterograde and retrograde experiments suggest that all SCN targets receive information from both the light‐induced and rhythmic regions of the SCN (albeit to varying degrees) and indicate that light and rhythmic information may be integrated both within the SCN and at target effector areas. J. Comp. Neurol. 468:361–379, 2004. © 2003 Wiley‐Liss, Inc.