bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and In Vitro Evaluation of 2‐Aminoquinazolin‐4(3H)‐one‐Based Inhibitors for tRNA‐Guanine Transglycosylase (TGT)
Authors: Meyer Emmanuel A. , Furler Maya , Diederich François , Brenk Ruth , Klebe Gerhard 
Published: June 2004

AbstracttRNA‐Guanine transglycosylase (TGT) plays a key role in the post‐transcriptional modification of tRNA. It has been linked with the pathogenicity of shigellae, the causative agents of bacillary dysentery (shigellosis). Here, we report structureactivity relationships (SARs) for a new series of 2‐aminoquinazolin‐4(3H)‐one‐based inhibitors of TGT, resulting from structure‐based design (Fig. 2). Versatile synthetic protocols allow selective functionalization of the 2‐aminoquinazolin‐4(3H)‐one core (Schemes 1–6) with H‐bond‐donor groups in position 6 (for H‐bonding to the C=O group of Leu231) and lipophilic residues in position 8 for reaching into a shallow, newly discovered lipophilic pocket lined by Val282, Val45, and Leu68. The binding mode of several of these ligands in the active site of TGT was established by crystal structure analyses (Figs. 4 and 6). A dramatic S effect was observed, with the replacement of the S‐atom in the (phenylsulfanyl)methyl residue in position 8 of inhibitor 1c (Ki=100 nM) by the O‐atom (in 1h, Ki=5.6 μM) or CH2 (in 1i, Ki=3.6 μM), resulting in a massive loss of activity (Fig. 3). Crystal structure analysis showed that the lipophilic Me group points into a highly polar region of the active site encompassed by the side chains of Asp280 and Asp102 and collides directly (d(C⋅⋅⋅O)=3.1 Å) with one of the O‐atoms of the carboxylate of Asp102. Similarly, lipophilic linkers departing from position 8 and orienting residues in the shallow hydrophobic pocket presumably encounter analogous unfavorable contacts, accounting for the modest contribution to the binding free enthalpy upon introduction of these residues. These findings provide a valuable starting point for future structure‐based lead optimization cycles leading to TGT inhibitors with increased in vitro potency.
Four New Dibenzocyclooctene Lignans from Kadsura renchangiana
Authors: Chen Min , Liao Zhixin , Chen Daofeng 
Published: June 2004

AbstractFour new dibenzocyclooctene‐type lignans, named renchangianins A–D (1–4), were isolated from the stems of Kadsura renchangiana. Their structures and configurations were elucidated by spectroscopic methods, including 2D‐NMR techniques. Renchangianin D (4) possesses a spiro[dibenzocyclooctene‐6,2′‐oxirane] parent structure previously unknown in plants of the Schisandraceae family.
Studies on Direct Stereoselective Aldol Reactions in Aqueous Media
Authors: Wu Yin‐Su , Shao Wei‐Yan , Zheng Chuan‐Qi , Huang Zhong‐Li , Cai Jiwen , Deng Qin‐Ying 
Published: June 2004

AbstractThe direct aldol reaction of 4‐nitrobenzaldehyde catalyzed by NaHCO3, with three different ketones, Znproline, NaHCO3/Znproline, and L‐proline/Znproline in aqueous media, was studied to explore the selectivity of this environmentally benign type of reaction. Amazingly, NaHCO3 proper was found to be an efficient catalyst for the selective synthesis of β‐hydroxy ketones, showing good regio‐ and diastereoselectivity, with all reactions being completed within 9 h. Cyclopentanone and cyclohexanone were found to give rise to reversed diastereoisomer ratios, the syn and anti isomers being the major products, respectively – an unprecedented result. Also, the observed syn diastereoselectivity of aldol reactions catalyzed by L‐proline and Znproline is remarkable. The corresponding condensation products 7 and 8 were characterized by 1H‐NMR and single‐crystal X‐ray analyses. Finally, a chelate‐ vs. nonchelate‐type transition state is proposed to account for the differential diastereoselectivities.
Echinosporamicin, a New Antibiotic Produced by Micromonospora echinospora ssp. echinospora, LL‐P175
Authors: He Haiyin , Yang Hui Y. , Luckman Scott W. , Bernan Valerie S. , Tsai Gordon , Roll Deborah M. , Carter Guy T. 
Published: June 2004

AbstractEchinosporamicin (1), a novel antibiotic containing an aromatic polycyclic system and a piperazinone moiety, was isolated from the fermentation broth of a new strain of Micromonospora echinospora subspecies echinospora, LL‐P175. The structure of this compound was determined by spectroscopic analysis by using variable‐temperature NMR techniques. Compound 1 exhibited potent activity against methicillin‐resistant Staphylococci and vancomycin‐resistant Enterococci strains. The methyl, ethyl, and benzyl esters showed improved antibacterial activity against Streptococci.
Derivatives from Isoselenocyanates: Synthesis of 2‐Phenyl‐6H‐[5,1,3]benzoselenadiazocine
Authors: Atanassov Plamen K. , Linden Anthony , Heimgartner Heinz 
Published: June 2004

AbstractThe reaction of N‐phenylbenzimidoyl isoselenocyanates 8 with primary and secondary amines in acetone at room temperature, followed by treatment with a base, led to 6H‐[5,1,3]benzoselenadiazocine derivatives of type 10 (Scheme 3). An analogous cyclization was observed when 8a and 8b were reacted with the Na salt of diethyl malonate in EtOH at room temperature, which yielded the eight‐membered selenaheterocycles 11 (Scheme 5). The molecular structures of some of the products, as well as that of a sulfur analogue, have been established by X‐ray crystallography (Figs. 1–4). The isoselenocyanates 8 have been prepared from N‐(2‐methylphenyl)benzamides 5 in a three‐step procedure via the corresponding imidoyl chlorides 6, side‐chain chlorination to give 7, and treatment with KSeCN (Scheme 2).
Enantioselective Preparation of β2‐Amino Acids with Aspartate, Glutamate, Asparagine, and Glutamine Side Chains
Authors: Lelais Gérald , Campo Marino A. , Kopp Sascha , Seebach Dieter 
Published: June 2004

Abstract(S)‐β2‐Homoamino acids with the side chains of Asp, Glu, Asn, and Gln have been prepared and suitably protected (N‐Fmoc, CO2tBu, CONHTrt) for solid‐phase peptide syntheses. The key steps of the syntheses are: N‐acylation of 5,5‐diphenyl‐4‐isopropyl‐1,3‐oxazolidin‐2‐one (DIOZ) with succinic and glutaric anhydrides (Scheme 2), alkylation of the corresponding Li‐enolates with benzyl iodoacetate and Curtius degradation (Scheme 4), and removal of the chiral auxiliary (Scheme 5). In addition, numerous functional‐group manipulations (CO2H⇌CO2tBu, CO2Bn⇌CO2H, CbzNH→FmocNH, CO2H→CO2NH2→CONHTrt; Schemes 2, 4, 5, and 6) were necessary, in order to arrive at the four target structures. The configurational assignments were confirmed by X‐ray crystal‐structure determinations (Scheme 2 and Fig. 3). The enantiomeric purities of a β2hAsn and of a β2hGln derivative were determined by HPLC on a Chiralcel column to be 99.7 : 0.3 and >99 : 1, respectively (Fig. 4). Notably, it took up to twelve steps to prepare a suitably protected trifunctional product with a single stereogenic center (overall yield of 10% from DIOZ and succinic anhydride)!
Azo‐Coupling Reactions Used in Analytical Chemistry: The Role of Reactants, Intermediates, and Aqueous Medium
Authors: Pankratov Alexei N. 
Published: June 2004

AbstractA quantum‐chemical study of the analytically important azo‐coupling reactions of naphthalen‐1‐amine (1) with naphthalene‐1‐diazonium (2) and 4‐sulphobenzenediazonium (8) cations has been carried out. The reactions have been found to be frontier‐controlled, and their regioselectivity is unequivocally determined by the thermodynamics of the intermediate σ‐complexes, as well as by the aqueous medium. The latter defines high positional selectivity, providing the decision between two possible reaction routes predicted on the basis of quantum‐chemical computations for separate molecular systems. As a result, azo coupling occurs at the 4‐ rather than at the 2‐position of 1. Furthermore, the aqueous medium makes the selection of analytical forms – protonated azo‐coupling products with a quinonehydrazone‐type structure.
Cyclic mechanical strain alters tissue‐factor activity in rat osteosarcoma cells cultured on a titanium substrate
Authors: Bledsoe J. Gary , Slack Steven M. , Turitto Vincent T. 
Published: June 2004

AbstractTissue factor (TF), a transmembrane glycoprotein, plays a role in the initiation of blood coagulation at sites of vascular injury. Activated products of coagulation may then enhance inflammatory responses. The present investigation assesses the ability of rat osteosarcoma (UMR‐106) cells cultured on titanium alloy (Ti6Al4V) to express differential surface TF activity in response to cyclic mechanical strain. Strains ranged from −2000 μ‐strain to +2000 μ‐strain, and durations from 5, 10, and 20 min per day over 5 days to 24 h continuous stimulation. ROS cells exhibited significant TF activity as demonstrated by the conversion of Factor X to Factor Xa. Strains of +2000 μ‐strain with 5–20‐min duration exhibited decreased TF activity with duration from 1.4E‐04 nM/cell to 8.7E‐05 nM/cell. Additionally, ROS cells stimulated with calcium ionophore (A23187) exhibited at least twice the activity of nonstimulated cells. Strains of +1340 μ‐strain with 5–20‐min duration exhibited an increasing trend with 4.15E‐05 nM/cell to 7.38E‐05 nM/cell. Strain direction had no significant effect on TF activity. Thus, both mechanical and chemical stimuli induce differential expression of TF activity by ROS cells cultured on Ti6Al4V, a phenomenon that may potentiate or regulate the inflammatory responses associated with the implantation of orthopedic biomaterials. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 70A: 490–496, 2004
Comparative biology of the ubiquitous Na+/H+ exchanger, NHE1: Lessons from erythrocytes
Authors: Pedersen Stine Falsig , Cala Peter Michael 
Published: June 2004

AbstractBy virtue of their electroneutral exchange of intracellular H+ for extracellular Na+, the Na+/H+ exchangers (NHE1‐NHE8) play a pivotal role in many physiological processes. This review focuses on the ubiquitous plasma membrane isoform, NHE1. Particular attention is given to the roles and regulation of NHE1 in erythrocytes, in their own right and as model systems, but pertinent findings from non‐erythroid cells are also discussed. NHE1 plays a key role in the regulation of cell volume and pH, and consequently in the control of such diverse processes as blood O2/CO2 transport, and cell proliferation, motility, and survival. Disturbances in NHE1 function are involved in important pathological states such as hypoxic cell damage and cancer development. NHE1 has a predicted topology of 12 transmembrane domains, and a hydrophilic C‐terminus thought to be the major site for NHE1 regulation. NHE1 is highly conserved throughout the vertebrate phylum, particularly in the transmembrane region and the proximal part of the C‐terminus. In non‐erythroid, and probably also in erythroid cells, this part of the hydrophilic C‐terminus interacts with multiple binding partners important for NHE1 function. Erythrocyte NHE1s from mammalian, amphibian, and teleost species are activated by cell shrinkage, decreased pHi, inhibition of Ser/Thr protein phosphatases, and activation of Ser/Thr protein kinases, i.e., many of the stimuli activating NHE1 in non‐erythroid cells. In erythrocytes of many lower vertebrates, NHE1 is activated during hypoxia and is an important modulator of hemoglobin oxygen affinity. Sensitivity of NHE1 to oxygenation status has recently been described also in non‐erythroid mammalian cells. J. Exp. Zool. 301A:569–578, 2004. © 2004 Wiley‐Liss, Inc.
Simultaneous production of triploid and haploid eggs by triploid Squalius alburnoides (Teleostei: Cyprinidae)
Authors: Alves M. Judite , Gromicho Marta , Collares‐Pereira M. João , Crespo‐López Elena , Coelho M. Manuela 
Published: June 2004

AbstractThe hybrid minnow Squalius alburnoides comprises diploid and polyploid forms with altered modes of reproduction. In the present paper, we report a cross where a triploid female generated both large, triploid and small, haploid eggs simultaneously, which were fertilized with S. pyrenaicus sperm. Although the large eggs were rarer (15%), they originated offspring with higher survivorship, so that tetraploids were dominant among the surviving siblings. The cross yielded apparently all female progeny. Inheritance patterns were inferred using four microsatellite markers and NORs (Nucleolus Organizer Regions) phenotypes, and suggested that haploid eggs were probably produced by an atypical hybridogenesis, in which the elimination of the unmatched genome permitted random segregation and recombination between the homospecific genomes, while the triploid eggs were clonal. The present results suggest that the occurrence of triploid unreduced eggs may be a new route for the natural tetraploidization in the complex. J. Exp. Zool. 301A:552–558, 2004. © 2004 Wiley‐Liss, Inc.
Oviductal sperm storage in the ground skink Scincella laterale holbrook (Reptilia: Scincidae)
Authors: Sever David M. , Hopkins William A. 
Published: June 2004

AbstractThe reproductive tracts of female ground skinks, Scincella laterale, collected at various times throughout their reproductive cycle were examined by light and transmission electron microscopy. Examination of the tracts revealed that sperm are retained in the posterior vagina after mating but prior to the ovulation of oocytes. The sperm are not sequestered in specialized glands but occur in scattered clusters in the lumen or among the deep, narrow rugae. The simple columnar lining of the vagina consists mostly of ciliated cells interspersed with occasional secretory cells. After ovulation, as indicated by the presence of eggs in the uterus, sperm are not found in the vagina. No sperm or sperm storage tubules occur in the infundibulum, the characteristic location for sperm storage in scleroglossid squamates that have been studied. Our results are a further indication that too few species have been examined to construct a rigorous phylogenetic hypothesis about the occurrence of sperm storage tubules in lizards. J. Exp. Zool. 301A:599–611, 2004. © 2004 Wiley‐Liss, Inc.
Protein location and elemental composition of urine spheres in different avian species
Authors: Casotti Giovanni , Braun Eldon J. 
Published: June 2004

AbstractWe examined the internal morphology, location of protein, and identity and location of elements, in avian urate‐containing spheres in 9 species of birds. The urine spheres were collected from voided samples. The spheres ranged in size from 0.5–5.0 µm, except in the domestic fowl, where they ranged up to 10 µm in diameter. The internal morphology of the spheres was examined using freeze‐fracture microscopy. Protein location within the spheres was identified using fluorescein isothiocyanate (FITC). The urine spheres were analyzed for content and internal location of elements using Energy Dispersal System Analysis (EDS). Internally, the spheres consisted of a central nidus surrounded by 3–4 concentric narrow rings of protein. Elements found within the spheres included nitrogen, potassium, calcium, sodium, phosphorus, chloride and sulfur; however, only nitrogen, potassium and chloride were common in the spheres of all species. Nitrogen comprised the majority of the elemental content of the spheres (77–90%) followed by potassium (8–45%), with all other ions present in trace amounts. Unlike protein, the location of elements was random within the spheres. Protein and urate are both negatively charged and known to associate to form the spheres and as potassium is the only cation common to all spheres, it too may play a role in their formation. J. Exp. Zool. 301A:579–587, 2004. © 2004 Wiley‐Liss, Inc.
Advances in membrane receptor screening and analysis
Authors: Cooper Matthew A. 
Published: June 2004

AbstractDuring the last decade there has been significant progress in the development of analytical techniques for the screening of ligand binding to membranes and membrane receptors. This review focuses on developments using label‐free assays that facilitate ligand–membrane–receptor screening without the need for chemical‐, biological‐ or radiological‐labelled reagents. These assays include acoustic, optical surface plasmon resonance biosensing, sedimentation (analytical ultracentrifugation), chromatographic assays, isothermal titration calorimetry and differential scanning calorimetry. The merits and applications of cell‐based screening systems and of different model membrane systems, including planar supported lipid layers, bead‐supported membranes and lipid micro‐arrays, are discussed. Recent advances involving more established techniques including intrinsic fluorescence, FRET spectroscopy, scintillation proximity assays and automated patch clamping are presented along with applications to peripheral membrane proteins, ion channels and G protein‐coupled receptors. Novel high‐throughput assays for determination of drug‐ and protein‐partitioning in membranes are also highlighted. To aid the experimenter, a brief synopsis of the techniques commonly employed to purify and reconstitute membranes and membrane receptors is included. Copyright © 2004 John Wiley & Sons, Ltd
De novo adipose formation in a vascularized engineered construct
Authors: Walton Robert L. , Beahm Elisabeth K. , Wu Liza 
Published: June 2004

AbstractWhile the field of tissue engineering is a burgeoning one, progress with fat engineering has lagged, due in large part to problems associated with nurturing and sustaining this unique tissue in vivo. In a pilot study using an experimental rat model, we induced liponeogenesis with a combination of Matrigel and basic fibroblast growth factor in an fibrovascular scaffold, isolating the construct to a pedicled blood supply (the superficial inferior epigastric vessels) via a silicone housing, creating an engineered three‐dimensional adipose tissue construct. Adipose tissue and vascular ingrowth were assessed histologically and followed by serial study at 4‐week intervals for 16 weeks. We demonstrated persistence of shaped adipose tissue constructs over time, and postulate that incorporating a vascular supply may enhance the durability of experimentally induced fat constructs and potentially provide a means for microsurgical transfer of the construct. © 2004 Wiley‐Liss, Inc.
Identification and analysis of stage‐specific expression of lysosome‐associated protein transmembrane 4α gene during development of preimplantation rabbit nuclear transfer embryo
Authors: Yu Weidong , He Xin , Liu Guisheng , Chen Qingxuan 
Published: June 2004

AbstractThe stage‐specific expression of Lysosome‐associated protein transmembrane 4α (LAPTM4α) in preimplantation rabbit nuclear transfer (NT) embryo was identified with the DDRT‐PCR and reverse Northern Blot. The full length (1,364 bp) cDNA of LAPTM4α was screened out from cDNA library constructed with rabbit ovary and in situ hybridization (ISH) was used to trace the distribution of the LAPTM4α mRNA in intra‐ovary, especially the follicle which proved that the LAPTM4α gene expression is involved in the follicles development, maturation, ovulation, luteinization, and preimplantation development in the rabbit (Oryctolagus cuniculus domestica). To our knowledge, this is the first characterization of LAPTM4α gene expression and mRNA distribution in the rabbit ovary and first evidence for this gene involving in follicle development and rabbit preimplantation development. Mol. Reprod. Dev. 68: 415–421, 2004. © 2004 Wiley‐Liss, Inc.
Carbohydrates and glycoproteins involved in bovine fertilization in vitro
Authors: Tanghe S. , Van Soom Ann , Duchateau L. , Nauwynck H. , de Kruif A. 
Published: June 2004

AbstractIn the present study, efforts were made towards identifying carbohydrates and glycoproteins involved in bovine in vitro fertilization (IVF). In vitro matured cumulus–oocyte complexes (COCs) were inseminated in the presence of a variety of carbohydrates and glycoproteins to determine which glycoconjugates act as competitive inhibitors of oocyte penetration. Among the carbohydrates and glycoproteins tested, D‐mannose, fucoidan, dextran sulfate, and fibronectin were the most potent inhibitors of oocyte penetration (90% or more inhibition), while L‐fucose and vitronectin inhibited the penetration rate to a lesser extent (around 50% inhibition). Other carbohydrates caused less than 40% inhibition (i.e., D‐galactose, N‐acetyl‐D‐galactosamine, D‐fucose, and sialic acid) or were not effective as inhibitors of oocyte penetration (i.e., mannan, N‐acetyl‐D‐glucosamine, dextran, and heparan sulfate). Heparin was the only carbohydrate that significantly increased the penetration rate. To exclude a possible toxic effect on spermatozoa, sperm motility was evaluated over time by means of computer‐assisted sperm analysis in the presence of carbohydrates and/or glycoproteins that inhibited the penetration rate with 40% or more. L‐fucose, dextran sulfate, and vitronectin did not significantly influence total and progressive sperm motility, whereas D‐mannose, fucoidan, and fibronectin caused a significant, but slight reduction in both motility parameters. These results are indicative for the involvement of D‐mannose, L‐fucose, fucoidan, dextran sulfate, fibronectin, and vitronectin in bovine IVF. Mol. Reprod. Dev. 68: 492–499, 2004. © 2004 Wiley‐Liss, Inc.
Relationship between the morphological changes of somatic compartment and the kinetics of nuclear and cytoplasmic maturation of oocytes during in vitro maturation of porcine follicular oocytes
Authors: Somfai Tamás , Kikuchi Kazuhiro , Onishi Akira , Iwamoto Masaki , Fuchimoto Dai‐ichiro , Papp Ágnes Bali , Sato Eimei , Nagai Takashi 
Published: June 2004

AbstractBased on the morphology and expansion of the cumulus cells, several different classes of porcine cumulus‐oocyte complexes (COCs) can be distinguished, during their maturation in vitro. The goal of the present study was to find out the rate of each morphologic category in case of COCs and granulosa‐cumulus‐oocyte complexes (GCOCs), the characteristics of their nuclear progression, cytoplasmic maturation, and the frequency of monospermy after IVF. It was found that the frequency of cumulus expansion is higher in case of GCOCs than that of COCs. Nuclear progression of COCs was more accelerated than that of GCOCs. Oocytes attached to the bottom of culture dish with dark, compact cumulus underwent nuclear and acquired their ability to be activated earlier than that of oocytes showing normal cumulus expansion. The rate of monospermic fertilization after IVF of normal COCs showing normal cumulus expansion was higher than that of COCs attached to the dish. These results suggest that diverse behavior of cumulus cells during in vitro culture affects nuclear and cytoplasmic maturation of porcine oocytes, which also affects IVF results. It can be concluded that granulosa cells promote normal cumulus expansion thus decrease heterogeneity in nuclear and cytoplasmic maturation amongst oocytes. Mol. Reprod. Dev. 68: 484–491, 2004. © 2004 Wiley‐Liss, Inc.
Germ cells enter meiosis in a rostro‐caudal wave during development of the mouse ovary
Authors: Bullejos Monica , Koopman Peter 
Published: June 2004

AbstractGerm cells in the mouse embryo remain undifferentiated until about 13.5 days post‐coitum (dpc), when male germ cells enter mitotic arrest and female germ cells enter meiosis. The molecular signals and transcriptional control mechanisms governing the differential fate of germ cells in males and females remain largely unknown. In order to gain insights into the behavior of germ cells around this period and into likely mechanisms controlling entry into meiosis, we have studied by wholemount in situ hybridization the expression pattern of two germ cell‐specific markers, Oct4 and Sycp3, during mouse fetal gonad development. We observed a dynamic wave of expression of both genes in developing ovaries, with Oct4 expression being extinguished in a rostro‐caudal wave and Sycp3 being upregulated in a corresponding wave, during the period 13.5–15.5 dpc. These results indicate that entry into meiosis proceeds in a rostro‐caudal progression, in turn suggesting that somatically derived signals may contribute to the control of germ cell entry into meiosis in developing ovaries. Mol. Reprod. Dev. 68: 422–428, 2004. © 2004 Wiley‐Liss, Inc.