bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis, Structure, and Reactivity of sp Carbon Chains with Bis(phosphine) Pentafluorophenylplatinum Endgroups: Butadiynediyl (C4) through Hexadecaoctaynediyl (C16) Bridges, and Beyond
Authors: Mohr Wolfgang , Stahl Jürgen , Hampel Frank , Gladysz J. A. 
Published: July 2003

AbstractThe reaction of trans‐[(C6F5)(p‐tol3P)2PtCl] (PtCl) and butadiyne (cat. CuI, HNEt2) gives trans‐[(C6F5)(p‐tol3P)2Pt(CC)2H] (PtC4H, 81 %), which reacts with excess HCCSiEt3 under Hay coupling conditions (O2, cat. CuCl/TMEDA, acetone) to yield PtC6Si (53 %). A solution of PtC6Si in acetone is treated with wet nBu4NF to generate PtC6H. The addition of ClSiMe3 (F− scavenger) and then excess HCCSiEt3 under Hay conditions gives PtC8Si (39 %). Hay homocouplings of PtC4H, PtC6H, and PtC8H (generated in situ analogously to PtC6H) yield PtC8Pt, PtC12Pt, and PtC16Pt (97–92 %). Reactions of PtC4H and PtC6H with PtCl (cat. CuCl, HNEt2) give PtC4Pt and PtC6Pt (69 %, 34 %). The attempted conversion of PtC8H to PtC10Si affords mainly PtC16Pt, with traces of PtC20Pt and PtC24Pt. The complexes PtCxPt are exceedingly stable (dec pts 234 to 288 °C), and Et3P displaces p‐tol3P to give the corresponding compounds Pt′C8Pt′ and Pt′C12Pt′ (94–90 %). The effect of carbon chain lengths upon IR νCC patterns (progressively more bands), UV/Vis spectra (progressively red‐shifted and more intense bands with ε>600 000 M−1 cm−1), redox properties (progressively more difficult and less reversible oxidations), and NMR values are studied, and analyzed with respect to the polymeric sp carbon allotrope “carbyne”. The crystal structure of PtC12Pt shows a dramatic, unprecedented degree of chain bending, whereas the chains in PtC8Pt, Pt′C12Pt′, and PtC16Pt are nearly linear.
Useful Dual Diels–Alder Behavior of 2‐Azetidinone‐Tethered Aryl Imines as Azadienophiles or Azadienes: A β‐Lactam‐Based Stereocontrolled Access to Optically Pure Highly Functionalized Indolizidine Systems
Authors: Alcaide Benito , Almendros Pedro , Alonso Jose M. , Aly Moustafa F. 
Published: July 2003

AbstractImines derived from 4‐oxoazetidine‐2‐carbaldehydes have been found to be versatile Diels–Alder reagents in that they exhibit two reactivity patterns. 2‐Azetidinone‐tethered imines undergo diastereoselective reaction with Danishefsky's diene in the presence of different Lewis acids. The effect of the amount of catalyst on the conversion rate as well as on the product ratio has been studied. Under standard reaction conditions, indium(III) chloride and zinc(II) iodide provided the best yields, and indium(III) triflate the highest diastereoselectivity in the Lewis acid promoted aza‐Diels–Alder cycloaddition. Treatment of the aforementioned imines with cyclopentadiene, 2,3‐dimethyl‐1,3‐butadiene or 3,4‐dihydro‐2 H‐pyran led to cycloadducts arising from inverse electron‐demand condensation involving the β‐lactam‐tethered aryl imine as the heterodiene component. In addition, the first methodology for preparing indolizidines from β‐lactams has been developed. This process involves amide bond cleavage of the β‐lactam ring in the aza‐Diels–Alder cycloadducts with concomitant cyclization. Full chirality transfer occurs when the reaction is performed with an enantiomerically pure substrate.
CCα Insertion: Insertion of an Alkyne into the CC Single Bond between the Carbene‐Carbon Atom and the α‐Carbon Atom of a Fischer Carbene Complex by an Unprecedented Metalla(di‐π‐methane) Skeletal Rearrangement
Authors: Ünaldi Seda , Aumann Rudolf , Fröhlich Roland 
Published: July 2003

AbstractThe first examples of insertion of a CC bond of an alkyne into a CcarbeneCα single bond of a carbene complex (CCα insertion) are reported. (prim‐Alkyl)carbene complexes [(OC)5MC(OEt)CH2R] (1 a–f; M=Cr, W; R=nPr, C7H7, Ph) undergo CCα insertion of electron‐deficient alkynes [PhCCC(XEt)NMe2]BF4 (5 a,b; X=O, S) to give zwitterionic carbiminium carbonylmetalates 3 a–g, which are thermally transformed into (CO)4M chelate carbene complexes 4 a–g by elimination of CO. The overall reaction is highly regio‐ and stereoselective. It involves an unprecedented metalla(di‐π‐methane) rearrangement as the key step.
Through‐Space Delocalized Water‐Soluble Paracyclophane Bichromophores: New Fluorescent Optical Reporters
Authors: Hong Janice W. , Benmansour Hadjar , Bazan Guillermo C. 
Published: July 2003

AbstractConjugated polymers and oligomers can serve as highly responsive fluorescent reporters for biosensor applications. However, their optical properties in aqueous media are highly dependent upon environmental conditions. The structure of the paracyclophane framework provides a platform for designing optical reporters that show little sensitivity to surfactants, and thus is well‐suited for fluorescent assays. The permanent intramolecular delocalization through the paracyclophane core dominates intermolecular perturbations in spontaneously formed aggregates.
Template Effect Where 1‐3 Molecules Drive Formation of a Trimer Carceplex
Authors: Makeiff Darren A. , Sherman John C. 
Published: July 2003

AbstractThe template effect in the formation of a trimer carceplex using 1‐3 molecules as templates is explored. Thirteen different templates were studied and template ratios were measured for templates of like and unlike molecularity. Five transition‐state models were studied for their binding abilities to see if these mirror the template ratios. The chemical shifts of the guests and the thermodynamic and kinetic values for templation suggest that binding is key, often tight, and that the guest determining step is formation of the last covalent bond. The molecular dynamics of guests as well as the conformational dynamics of both hosts and guests further addresses nature of the recognition between host and guest. Finally, we were surprised to discover that water can bind reversibly to the trimer carceplexes, which will have ramifications to any inner phase reactions conducted inside the cage.
Optimization of Hydrolase Efficiency in Organic Solvents
Authors: Secundo Francesco , Carrea Giacomo 
Published: July 2003

AbstractThe application of hydrolases in organic solvents for synthetic purposes is a procedure routinely adopted in organic chemistry, especially for the preparation of chiral building blocks. Numerous studies have shed light on several aspects of the mechanism of hydrolase action in low‐water environments. Procedures suitable to improve the catalytic efficiency of enzymes and productivity of the synthetic processes have been reported. These fundamental and applied investigations have made hydrolase‐catalyzed reactions in organic solvents of industrial interest. In this article we describe and discuss various approaches adopted to optimize the performance of hydrolases in organic media, with special emphasis on the formulation of the biocatalysts which, under proper conditions, can display an activity equal to that displayed in aqueous buffers.
Development of the Traceless Phenylhydrazide Linker for Solid‐Phase Synthesis
Authors: Stieber Frank , Grether Uwe , Waldmann Herbert 
Published: July 2003

AbstractThe hydrazide group is a new oxidatively cleavable traceless linker for solid‐phase chemistry. It can be readily introduced by hydrazide formation between a carboxy‐functionalized resin and different substituted hydrazines. In order to achieve high yields in this step, new carboxylic acid resins were developed that are not prone to undesired imide formation upon activation of the carboxylic acid. The polymer‐bound acyl hydrazides were successfully employed in various transformations, namely Heck, Suzuki, Sonogashira, and Stille couplings, as well as Wittig and Grignard reactions. Traceless release of the coupling products from the solid support is achieved selectively under mild conditions and in high purity by oxidation of the aryl hydrazides to acyl diazenes with CuII salts or N‐bromosuccinimide (NBS) and subsequent nucleophilic attack of the acyl diazene intermediates. Traceless cleavage by oxidation with NBS can be carried out as a two‐step process in which stable acyl diazenes are first generated by treatment with NBS in the absence of a nucleophile. After removal of the reagents by simple resin washing, the traceless release is effected by the addition of methanol, which leads to products of high purity without any additional separation steps.
Multistep Solid‐Phase Synthesis of an Antibiotic and Receptor Tyrosine Kinase Inhibitors Using the Traceless Phenylhydrazide Linker
Authors: Stieber Frank , Grether Uwe , Mazitschek Ralph , Soric Natascha , Giannis Athanassios , Waldmann Herbert 
Published: July 2003

AbstractThe hydrazide group is an oxidatively cleavable traceless linker for solid‐phase chemistry. This linker technology was used to develop a multistep solid‐phase synthesis of an antibiotic that is active against Mycobacterium tuberculosis. Furthermore, we describe an efficient method for the traceless synthesis of 2‐aminothiazoles that display dual inhibitory activity against the receptor tyrosine kinases VEGFR‐2 and Tie‐2. The synthesis method proceeds through 9 steps on the solid phase and should give access to a much larger library of 2‐aminothiazoles, from which a new class of anti‐angiogenesis drugs may be developed.
The Solution Structure of (Me3Si)3CSiBr—An Ab Initio/NMR Study
Authors: Flock Michaela , Dransfeld Alk 
Published: July 2003

AbstractThe first halosilylene stable in solution was investigated by ab initio/NMR calculations (IGLO SOS‐DFPT PW91/B2//B3LYP/6‐31+G(d)). The δ 29Sicalc of (Me3Si)3CSiBr (446 ppm) does not agree with the measured NMR signal at 106 ppm assigned to the free halosilylene. From the possible silylene complexes in the reaction solution, two structures agree with the observed NMR signal: the (Me3Si)3CSiBr2 anion (δ 29Sicalc=124 ppm) and the unsolvated and solvated complex of the anion with two Li+ (δ 29Sicalc=117 and estimated 134 ppm). Additionally the δ 29Sicalc of alkylsilylenes, R‐Si‐X, ranging from 200 to 900 ppm are presented to guide NMR identification in future silylene synthesis.
Routes to Metallodendrimers: Synthesis of Isomeric Neutral Metallomacromolecules Based on Bis(2,2′:6′,2″‐terpyridine)ruthenium(II) Connectivity
Authors: Newkome George R. , Yoo Kyung Soo , Kim Hyung Jin , Moorefield Charles N. 
Published: July 2003

AbstractRoutes for the syntheses of isomeric, zwitterionic, bisterpyridine–RuII‐based macromolecules are described. Access to these novel architectures is facilitated by the construction of terpyridine‐modified, 1→3 C‐branched, ester‐terminated building blocks. Constitutional isomers result from the interchangable placement of methyl and tert‐butyl ester groups on both the branched framework near the RuII centers and the termini of the branched construct. Water solubility is imparted to each isomer through selective transformation of the tert‐butyl esters to their corresponding carboxylates. Along with the standard characterization techniques, electrochemical and spectroscopic data also support the structural formation.
The suprachiasmatic nucleus balances sympathetic and parasympathetic output to peripheral organs through separate preautonomic neurons
Authors: Buijs Ruud M. , la Fleur Susanne E. , Wortel Joke , van Heyningen Caroline , Zuiddam Laura , Mettenleiter Thomas C. , Kalsbeek Andries , Nagai Katsuya , Niijima Akira 
Published: July 2003

AbstractOpposing parasympathetic and sympathetic signals determine the autonomic output of the brain to the body and the change in balance over the sleep‐wake cycle. The suprachiasmatic nucleus (SCN) organizes the activity/inactivity cycle and the behaviors that go along with it, but it is unclear how the hypothalamus, in particular the SCN, with its high daytime electrical activity, influences this differentiated autonomic balance. In a first series of experiments, we visualized hypothalamic pre‐sympathetic neurons by injecting the retrograde tracer Fluoro‐Gold into the thoracic sympathetic nuclei of the spinal cord. Pre‐parasympathetic neurons were revealed by injection of the retrograde trans‐synaptic tracer pseudorabies virus (PRV) into the liver and by sympathetic liver denervation, forcing the virus to infect via the vagus nerve only. This approach revealed separate pre‐sympathetic and pre‐parasympathetic neurons in the brainstem and hypothalamus. Next, selective retrograde tracing with two unique reporter PRV strains, one injected into the adrenal and the other into the sympathetic denervated liver, demonstrated that there are two separate populations of pre‐sympathetic and pre‐parasympathetic neurons within the paraventricular nucleus of the hypothalamus. Interestingly, this segregation persists into the SCN, where, as a result, the day‐night balance in autonomic function of the organs is affected by specialized pre‐sympathetic or pre‐parasympathetic SCN neurons. These separate preautonomic SCN neurons provide the anatomical basis for the circadian‐driven regulation of the parasympathetic and sympathetic autonomic output. J. Comp. Neurol. 464:36–48, 2003. © 2003 Wiley‐Liss, Inc.
Ontogeny of γ‐aminobutyric acid–immunoreactive neurons in the rhombencephalon and spinal cord of the sea lamprey
Authors: Meléndez‐Ferro Miguel , Pérez‐Costas Emma , Villar‐Cheda Begoña , Rodríguez‐Muñoz Rolando , Anadón Ramón , Rodicio María Celina 
Published: July 2003

AbstractThe development of neurons expressing γ‐aminobutyric acid (GABA) in the rhombencephalon and spinal cord of the sea lamprey (Petromyzon marinus) was studied for the first time with an anti‐GABA antibody. The earliest GABA‐immunoreactive (GABAir) neurons appear in late embryos in the basal plate of the isthmus, caudal rhombencephalon, and rostral spinal cord. In prolarvae, the GABAir neurons of the rhombencephalon appear to be distributed in spatially restricted cellular domains that, at the end of the prolarval period, form four longitudinal GABAir bands (alar dorsal, alar ventral, dorsal basal, and ventral basal). In the spinal cord, we observed only three GABAir longitudinal bands (dorsal, intermediate, and ventral). The larval pattern of GABAir neuronal populations was established by the 30‐mm stage, and the same populations were observed in premetamorphic and adult lampreys. The ontogeny of GABAergic populations in the lamprey rhombencephalon and spinal cord is, in general, similar to that previously described in mouse and Xenopus. J. Comp. Neurol. 464:17–35, 2003. © 2003 Wiley‐Liss, Inc.
Cytoarchitecture and efferent projections of the nucleus incertus of the rat
Authors: Olucha‐Bordonau Francisco E. , Teruel Vicent , Barcia‐González Jorge , Ruiz‐Torner Amparo , Valverde‐Navarro Alfonso A. , Martínez‐Soriano Francisco 
Published: July 2003

AbstractThe nucleus incertus is located caudal to the dorsal raphe and medial to the dorsal tegmentum. It is composed of a pars compacta and a pars dissipata and contains acetylcholinesterase, glutamic acid decarboxylase, and cholecystokinin‐positive somata. In the present study, anterograde tracer injections in the nucleus incertus resulted in terminal‐like labeling in the perirhinal cortex and the dorsal endopyriform nucleus, the hippocampus, the medial septum diagonal band complex, lateral and triangular septum medial amygdala, the intralaminar thalamic nuclei, and the lateral habenula. The hypothalamus contained dense plexuses of fibers in the medial forebrain bundle that spread in nearly all nuclei. Labeling in the suprachiasmatic nucleus filled specifically the ventral half. In the midbrain, labeled fibers were observed in the interpeduncular nuclei, ventral tegmental area, periaqueductal gray, superior colliculus, pericentral inferior colliculus, pretectal area, the raphe nuclei, and the nucleus reticularis pontis oralis. Retrograde tracer injections were made in areas reached by anterogradely labeled fibers including the medial prefrontal cortex, hippocampus, amygdala, habenula, nucleus reuniens, superior colliculus, periaqueductal gray, and interpeduncular nuclei. All these injections gave rise to retrograde labeling in the nucleus incertus but not in the dorsal tegmental nucleus. These data led us to conclude that there is a system of ascending projections arising from the nucleus incertus to the median raphe, mammillary complex, hypothalamus, lateral habenula, nucleus reuniens, amygdala, entorhinal cortex, medial septum, and hippocampus. Many of the targets of the nucleus incertus were involved in arousal mechanisms including the synchronization and desynchronization of the theta rhythm. J. Comp. Neurol. 464:62–97, 2003. © 2003 Wiley‐Liss, Inc.
Identification of a cone bipolar cell in cat retina which has input from both rod and cone photoreceptors
Authors: Fyk‐Kolodziej Bozena , Qin Pu , Pourcho Roberta G. 
Published: July 2003

AbstractIt has been generally accepted that rod photoreceptor cells in the mammalian retina make synaptic contact with only a single population of rod bipolar cells, whereas cone photoreceptors contact a variety of cone bipolar cells. This assumption has been challenged in rodents by reports of a type of cone bipolar cell which receives input from both rods and cones. Questions remained as to whether similar pathways are present in other mammals. We have used an antiserum against the glutamate transporter GLT1‐B to visualize a population of cone bipolar cells in the cat retina which make flat contacts with axon terminals of both rod and cone photoreceptor cells. These cells are identified as OFF‐cone bipolar cells and correspond morphologically to type cb1 (CBa2) cone bipolar cells which are a major source of input to OFF‐beta ganglion cells in the cat retina. The GLT1‐B transporter was also localized to processes making flat contacts with photoreceptor terminals in rat and rabbit retinas. Examination of tissue processed for the GluR1 glutamate receptor subunit showed that cb1 cone bipolar cells, like their rodent counterparts, express this α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA)‐selective receptor at their contacts with rod spherules. Thus, a direct excitatory pathway from rod photoreceptors to OFF‐cone bipolar cells appears to be a common feature of mammalian retinas. J. Comp. Neurol. 464:104–113, 2003. © 2003 Wiley‐Liss, Inc.
Notch‐associated gene expression in embryonic and adult taste papillae and taste buds suggests a role in taste cell lineage decisions
Authors: Seta Yuji , Seta Chihiro , Barlow Linda A. 
Published: July 2003

AbstractThe Notch signaling pathway is involved in cell fate decisions during development. To explore the role of this signaling cascade in the taste system, we investigated the expression patterns of Notch signaling genes in fetal and adult mouse tongues using in situ hybridization. Three of the four murine Notch receptors, their ligands, Delta‐like 1 (Dll‐1), Jagged1, and Jagged2, as well as three transcription factors, Hes1, Hes6, and Mash1, are expressed in the embryonic taste epithelium. Expression is first detected in the circumvallate papilla at embryonic day E14.5, when Notch1, Jagged1, and Jagged2 are expressed broadly in the papilla and general lingual epithelium. In contrast, Mash1 and Hes6 are restricted to only a few epithelial cells in the apical region of the developing papilla. By E18.5, many of the genes now exhibit a bimodal expression pattern in the papillary epithelium: apically and dorsally they are expressed in sparse clusters of cells, while more ventrally expression typically occurs throughout the lower regions of the trenches. The extent of papilla innervation was compared with Mash1 and Hes6 expression. At E14.5, when Hes6 and Mash1 are already expressed in small numbers of epithelial cells, PGP9.5 immunoreactive fibers have not yet invaded the epithelium, consistent with the specification of taste bud primordia prior to nerve contact. All of the genes examined (except Notch2) are also expressed in subsets of cells within circumvallate taste buds in adult mice, although Notch1 is restricted to basal cells adjacent to taste buds. The onset of embryonic Notch associated gene expression after the morphological differentiation of the circumvallate papilla argues that this signaling cascade may specify taste receptor cell lineages within an already specified taste papilla. Similarly, Notch gene expression in adult taste buds suggests continued roles in cell lineage determination and cell turnover. J. Comp. Neurol. 464:49–61, 2003. © 2003 Wiley‐Liss, Inc.
Centrosomal abnormality is common in and a potential biomarker for bladder cancer
Authors: Jiang Feng , Caraway Nancy P. , Sabichi Anita L. , Zhang Hua Z. , Ruitrok Arnout , Grossman H. Barton , Gu Jun , Lerner Seth P. , Lippman Scott , Katz Ruth L. 
Published: July 2003

AbstractCentrosomal abnormalities have been implicated in chromosomal segregation aberrations that result from the formation of multipolar mitotic spindles and lead to aneuploidy. Aneuploidy is a characteristic of neoplasia and underlies the development and progression of bladder cancer. Therefore, centrosomal abnormality may play a key role in urothelial tumor transformation. The purpose of our investigation was to determine whether centrosomal abnormalities are present in malignant urothelial cells, define the relationship between centrosomal abnormalities and aneuploidy and determine whether the presence of centrosomal abnormalities might be a potential diagnostic marker for bladder cancer. Bladder wash specimens obtained from patients with and without a history of urothelial carcinoma were analyzed for centrosomal abnormalities using an immunoassay with a γ‐tubulin antibody. FISH with centromeric probes for chromosomes 4 and 9 and DNA ploidy image analysis were performed to detect aneuploidy. Defective centrosomes were found in 40 of 45 bladder wash specimens from patients with bladder cancer but in none of the 10 samples from patients without it. A large percentage (69%) of grade 1 tumors were positive for centrosomal abnormalities, and these abnormalities were increasing in numbers and size in grade 2 (93%) and grade 3 (100%) specimens. Centrosomal abnormalities and numerical chromosomal aberrations frequently appeared concomitantly in the same malignant cells. All of the specimens showing aneuploidy also exhibited centrosomal abnormalities: centrosomal defects and aneuploidy occurred together in 80% of malignant bladder tumors, with an especially high percentage in higher‐grade tumors. The overall positivity of centrosomal abnormalities was higher than that of aneuploidy (88% vs. 80%), especially in grade 1 tumors (69% vs. 46%), whereas aneuploidy was strongly associated with grade 2 and grade 3 tumors. Centrosomal abnormalities are common in bladder cancer, even in low‐grade tumors, and strongly associated with cancer grade and aneuploidy, especially in high‐grade neoplasms. Centrosomal abnormalities appear to be intrinsic to aneuploidy and tumorigenesis and may be potential markers for early detection of bladder cancer. © 2003 Wiley‐Liss, Inc.