bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis, Cytotoxicity, and Apoptosis Induction in Human Tumor Cells by Geiparvarin Analogues
Authors: Viola Giampietro , Vedaldi Daniela , dall'Acqua Francesco , Basso Giuseppe , Disarò Silvia , Spinelli Monica , Cosimelli Barbara , Boccalini Marco , Chimichi Stefano 
Published: September 2004

AbstractA series of geiparvarin analogues modified on the unsaturated alkenyloxy bridge, where a H‐atom replaced the 3′‐Me group, were synthesized and evaluated against a panel of human tumor cell lines in vitro. These compounds demonstrated a stronger increase in growth inhibitory activity when compared to the parent compound geiparvarin (8). In particular, the activity increased even further in the series of demethylated compounds when a Me substituent in the coumarin moiety is introduced. On the contrary, the same modifications exerted on the parent compound led to an activity reduction. Interestingly, the new derivatives proved to be fully inhibitory to drug‐resistant cell lines, thus suggesting that they are not subject to the pump‐mediating efflux of antitumor drugs. On the basis of their cytotoxic profiles, the most‐active compounds were selected for further biological evaluation. The extracellular acidification rate by the new geiparvarin analogues was measured with the CytosensorTM microphysiometer. The new derivatives significantly increased the acidification rate during the 24–48 h of incubation in a concentration‐dependent manner. Cell‐cycle analysis, evaluated by flow cytometry, revealed a strong apoptotic induction by these compounds confirmed by DNA laddering and observation by electron microscopy. Interestingly, the apoptotic pathway did not appear to be mediated by the activation of caspase‐3.
Electroreduction of Oxygen by Cytochrome c Oxidase Immobilized in Electrode‐Supported Lipid Bilayer Membranes
Authors: Su Lianyong , Hawkridge Fred M. , Rhoten Melissa C. 
Published: September 2004

AbstractCytochrome c oxidase is the terminal enzyme in mammalian respiration, and one of its main functions is to catalyze the reduction of oxygen under physiological conditions. Direct reduction of oxygen at electrodes requires application of substantial overpotentials. In this work, bovine cytochrome c oxidase has been immobilized in electrode‐supported lipid bilayer membranes to investigate the electroreduction of oxygen under flow conditions. The effect that temperature, solution pH, and solution composition have on the reduction of oxygen by this novel enzyme‐modified electrode is reported. Results indicate that the electroreduction of oxygen is most pronounced at low pH (6.4) and elevated temperature (38°). At an applied potential of −350 mV vs. Ag/AgCl (1M KCl), a current density of ca. 7 μA/cm2 was obtained. The current responses obtained at these electrodes are stable over a period of ca. 10–14 days (10–15% decrease in response). The cytochrome c oxidase‐modified electrodes described here could potentially be used for the direct electroreduction of oxygen to water in a biofuel cell.
Cholinesterase‐Inhibiting Withanolides from Ajuga bracteosa
Authors: Riaz Naheed , Malik Abdul , Aziz‐ur‐Rehman  , Nawaz Sarfraz Ahmad , Muhammad Pir , Choudhary M. Iqbal 
Published: September 2004

AbstractThree new withanolides, bracteosin A (=(22R)‐5β,6β : 22,26‐diepoxy‐4β,28‐dihydroxy‐3β‐methoxyergost‐24‐ene‐1,26‐dione; 1), bracteosin B (=(22R)‐5β,6β : 22,26‐diepoxy‐4β,28‐dihydroxy‐3β‐methoxy‐1,26‐dioxoergost‐24‐en‐19‐oic acid; 2), and bracteosin C (=(22R)‐22,26‐epoxy‐4β,6β,27‐trihydroxy‐3β‐methoxyergost‐ 24‐ene‐1,26‐dione; 3), have been isolated from the whole plants of Ajuga bracteosa. Their structures were deduced by spectral analysis, including 1D‐ and 2D‐NMR techniques. In addition, dihydroclerodin‐1, clerodinin A, lupulin A, and dihydroajugapitin have also been isolated for the first time from this species. Compounds 1–3 exhibited evident inhibitory potential against cholinesterase enzymes in a concentration‐dependent fashion.
Nine New Isoxuxuarine‐Type Triterpene Dimers from Maytenus chuchuhuasca
Authors: Shirota Osamu , Sekita Setsuko , Satake Motoyoshi , Morita Hiroshi , Takeya Koichi , Itokawa Hideji 
Published: September 2004

AbstractNine new isoxuxuarine‐type triterpene dimers, named isoxuxuarines Bα (1), Bβ (2), 7,8‐dihydro‐Bα (3), Cα (4), Cβ (5), 7,8‐dihydro‐Cα (6), Dα (7), Dβ (8), and 7,8‐dihydro‐Dα (9), were isolated from the South American medicinal plant ‘xuxuá’ (Maytenus chuchuhuasca). The structures were elucidated on the basis of several spectroscopic analyses, including 2D‐NMR experiments, MS spectra, and CD spectral studies. The isolations and structure elucidations of the new triterpene dimers are presented, and a rationale for the divergent formation of the regiochemical and stereochemical isomers of triterpene dimers is discussed.
From Earth's Primitive Atmosphere to Chiral Peptides – The Origin of Precursors for Life
Authors: Plankensteiner Kristof , Reiner Hannes , Rode Bernd M. 
Published: September 2004

AbstractTo re‐enact the long way to the origin of life with today's chemical methods, many steps have to be investigated in the light of a primordial scenario deduced from geochemical research. After the formation of our planet and its atmosphere, prebiotic chemical evolution started its course with the formation of the first building blocks for the formation of biomolecules. In the case of proteins, those building blocks were amino acids that had to be formed in the primitive atmosphere, and then had to react to peptides and proteins as the main pillar of first life. In this paper, we describe the processes in the primordial atmosphere according to contemporary geochemical knowledge leading to the synthesis of amino acids until the formation of homochiral peptides, and, thus, show a plausible pathway towards the origin of life.
Bimetallic Complexes of Spiro‐Azacrown Ligands as Catalysts of Phosphoester and Phosphoric Anhydride Cleavage
Authors: Wang Qi , Mikkola Satu , Lönnberg Harri 
Published: September 2004

AbstractThe ability of bimetallic homo‐ and heteronuclear complexes of two spiro‐linked ligands, viz. a biazacrown (i.e., 2,6,10,14,18,22‐hexaazaspiro[11.11]tricosane (1)) and an azacrowncrown ether (i.e., 14,17,20,23,26‐pentaoxa‐2,6,10‐triaza‐spiro[11.15]heptacosane (2)), to promote the cleavage of the phosphoester linkage of dinucleoside 3′,5′‐phosphates and the phosphoric anhydride bridge of dinucleoside 5′,5′‐triphosphates was studied. In both reactions, the bimetallic homonuclear Cu2+ and Zn2+ complexes were better catalysts than their monometallic counterparts. The acceleration was two‐ to five‐fold with the phosphoester cleavage and 3‐ to 20‐fold with the phosphoric anhydride cleavage. Interestingly, the most‐efficient catalyst of the phosphoester cleavage was the heterodinuclear Ni2+,Zn2+ complex of 1, the catalytic activity of which was up to 5‐ and 100‐fold that of the homodinuclear Zn2+ and Ni2+ complexes, respectively. Moreover, this cooperative acceleration was observed to depend on the identity of the 5′‐linked nucleoside: 3′,5′‐UpU and 3′,5′‐ApU were cleaved much faster than 3′,5′‐UpA, and no cooperative acceleration was observed with 3′,5′‐ApA. The reaction was second‐order in hydroxide ion concentration, suggesting that a double deprotonation took place on going from the initial to the transition state. Evidently, in addition to deprotonation of the attacking 2′‐OH group, N(3)H of the 5′‐linked uridine was displaced by one of the metal ions of the cleaving agent. With the phosphoric anhydride cleavage, no similar cooperativity of two different metal ions was observed, but the greatest rate‐acceleration was achieved with the homodinuclear Cu2+ complexes.
Resolution of Binary Mixtures of Rifamycin SV and Rifampicin by UV/VIS Spectroscopy and Partial Least‐Squares Method (PLS)
Authors: Lomillo M. Asunción Alonso , Domínguez Renedo Olga , Arcos Martínez M. Julia 
Published: September 2004

AbstractA procedure is proposed for the joint determination of rifamycin SV and rifampicin by UV/VIS spectroscopy. A partial least‐squares regression (PLS) was used for the resolution of the overlapping spectrophotometric signals from mixtures of the two drugs. The application of a genetic algorithm to select some of the predictor variables allows one to considerably reduce the number of experimental variables, as well as to improve the prediction capacity of the PLS model constructed with these selected potentials. Finally, the methods were applied to the determination of these drugs in biological samples.
13C‐CPMAS and 1H‐NMR Study of the Inclusion Complexes of β‐Cyclodextrin with Carvacrol, Thymol, and Eugenol Prepared in Supercritical Carbon Dioxide
Authors: Locci Emanuela , Lai Simona , Piras Alessandra , Marongiu Bruno , Lai Adolfo 
Published: September 2004

Abstractβ‐Cyclodextrin (β‐CD) inclusion complexes with carvacrol (1), thymol (2), and eugenol (3) (components of essential oils of vegetable origin) were prepared by the supercritical CO2 technique, and their structural characterization was achieved by means of 1H‐NMR in aqueous solution and 13C‐CPMAS NMR in the solid state. Evidence of the formation of the inclusion complexes for all the examined systems was obtained by 1H‐NMR in solution, while 2D‐ROESY‐NMR experiments were used to investigate the geometry of inclusion. In addition, the dynamics of these inclusion complexes in the kHz timescale was investigated by analysis of the 1H and 13C spin‐lattice relaxation times in the rotating frame.
A Novel Carbazole Derivative, BMVC: a Potential Antitumor Agent and Fluorescence Marker of Cancer Cells
Authors: Chang Cheng‐Chung , Kuo I‐Chun , Lin Jing‐Jer , Lu Yu‐Cheng , Chen Chin‐Tin , Back Hong‐Tsun , Lou Pei‐Jen , Chang Ta‐Chau 
Published: September 2004

AbstractWe have investigated a novel compound, 3,6‐bis[2‐(1‐methylpyridinium)vinyl]carbazole diiodide (BMVC), for inhibiting telomerase activity and distinguishing human lung H1299 and oral Ca9‐22 cancer cells from lung IMR90 and skin Detroit‐551 normal fibroblast cells. The telomeric repeat amplification protocol (TRAP) assay shows that the concentration of BMVC that inhibits 50% of the telomerase activity (IC50) is ca. 0.05 μM. On the other hand, the cell‐viability assay indicates that the cytotoxicity was less than 15% to the H1299 and Ca9‐22 cancer cells, and almost negligible to the MRC‐5 and Detroit‐551 normal cells after incubation with 0.5 μM BMVC for 72 h. The low concentration of 0.05 μM of BMVC can inhibit telomerase activity but does not have general toxic effects to normal cells, implying that BMVC is a promising telomerase inhibitor. Moreover, wide‐field fluorescence images of 0.1 μM BMVC‐treated cells show bright fluorescence spots in the nuclei of the most H1299 and Ca9‐22 cancer cells. Interestingly, similar fluorescence spots are hardly observed in the nuclei of the IMR90 and Detroit‐551 normal cells, implying that BMVC might be a useful marker to distinguish tumor cells and normal cells.
Antimicrobial Activity of Hydrophobic Xanthones from Cudrania cochinchinensis against Bacillus subtilis and Methicillin‐Resistant Staphylococcus aureus
Authors: Fukai Toshio , Oku Yukio , Hou Ai‐Jun , Yonekawa Makiko , Terada Sumio 
Published: September 2004

AbstractTen xanthones with one or two isoprenoid groups and a prenylated benzophenone isolated from roots of Cudrania cochinchinensis (Moraceae) were tested for their antimicrobial activities against Bacillus subtilis and methicillin‐resistant Staphylococcus aureus (MRSA). Among these compounds, gerontoxanthone H exhibited considerable antibacterial activity against B. subtilis (MIC=1.56 μg/ml). Four xanthones, gerontoxanthone I, toxyloxanthone C, cudraxanthone S, and 1,3,7‐trihydroxy‐2‐prenylxanthone, showed weak antibacterial activity against the bacterium (MICs=3.13–6.25 μg/ml). These compounds also exhibited similar MIC values against methicillin‐sensitive S. aureus, MRSAs, and Micrococcus luteus.
Comparative Metabolism of α‐ and β‐Peptides in the Insect Heliothis virescens and in Plant Cells of Black Mexican Sweet Maize
Authors: Lind Rob , Greenhow Daren , Perry Simon , Kimmerlin Thierry , Seebach Dieter 
Published: September 2004

AbstractThe tripeptide H‐Val‐Ala‐Leu‐OH and the N‐Ac‐tetrapeptide amide Ac‐Thr‐Lys‐Trp‐Phe‐NH2, and their β‐peptidic counterparts H‐β3hVal‐β3hAla‐β3hLeu‐OH and Ac‐β3hThr‐(S)β2hLys‐β3hTrp‐β3hPhe‐NH2, respectively, have been injected into Heliothis virescens larvae and added to cell cultures of black mexican sweet maize. The body liquids of the larvae and the supernatant of the plant cell cultures were sampled 0, 2, 3, 6, 17, and/or 24 h after application and analyzed by LC/MS. While the two α‐peptides were degraded rapidly in these environments, the concentration of the β‐peptides was found to decrease very slowly. Thus, ca. 60% of the original amount of the β‐tetrapeptide was detected in the liquids of the insect after 24 h. The plant cells did not seem to make use of the β‐peptides at all, whereas, the α‐tripeptide completely disappeared from the supernatant after 3 h. Thus, we have demonstrated, for the first time, the high stability of β‐peptides against degradation and metabolism in an insect and a plant. Especially remarkable is the persistence of the β‐tetrapeptide with its functionalised and, thus, ‘metabolisable’ side chains of Thr, Lys, Trp, and Phe in the insect larvae, which are known to have a high level of activity of oxidizing enzymes. The results described here match those of ADME investigations with radioactively labeled β‐peptides in rats, where essentially complete stability has been observed, while environmental microorganisms have been found to biodegrade β‐peptides, albeit slowly. Possible implications of these findings for biomedical and pest‐control applications are proposed.
CO2 in Supramolecular Chemistry: Preparation of Switchable Supramolecular Polymers
Authors: Xu Heng , Rudkevich Dmitry M. 
Published: September 2004

AbstractCO2 gas was used to construct novel types of supramolecular polymers. Self‐assembling nanostructures 11 and 13 were prepared, which employ both hydrogen bonding and dynamic, thermally reversible carbamate bonds. As precursors, calixarene ureas 1 and 2 were synthesized, which strongly aggregate/dimerize (KD≥106 M−1 per capsule) in apolar solution with the formation of self‐assembling capsules 7 and linear polymeric chains 8, respectively, and also possess “CO2‐philic” primary amino groups on the periphery. CO2 effectively reacts with molecules 7 and 8 in apolar solvents and cross‐links them with the formation of multiple carbamate salt bridges. Oligomeric aggregate 11 and three‐dimensional polymeric network 13 were prepared and characterized by 1H and 13C NMR spectroscopy. The morphology of supramolecular gel 13 was studied by scanning electron microscopy. Addition of a competitive solvent destroyed the hydrogen bonding in assembling structures 11 and 13, but did not influence the carbamate linkers; carbamate salts 12 and 14, respectively, were obtained. On the other hand, thermal release of CO2 from 11 and 13 was easily accomplished (1 h, 100 °C) while retaining the hydrogen‐bonding capsules. Thus, three‐dimensional polymeric network 13 was transformed back to linear polymeric chain 8 without breaking up. Encapsulation and storage of solvent molecules by 11 and 13 was demonstrated. This opens the way for switchable materials, which reversibly trap, store, and then release guest molecules. A two‐parameter switch and control over hydrogen bonding and CO2–amine adducts was established.
Polymeric Nanoparticles from Rapid Expansion of Supercritical Fluid Solution
Authors: Sun Ya‐Ping , Meziani Mohammed J. , Pathak Pankaj , Qu Liangwei 
Published: September 2004

AbstractIn this concept paper we highlight applications of supercritical fluid technology in particle formation and production, especially some recent advances in the rapid expansion of supercritical solutions (RESS) processing technique. We also highlight the simple but significant modification to the traditional RESS by using a liquid solvent or solution at the receiving end of the supercritical solution expansion, or the rapid expansion of a supercritical solution into a liquid solvent (RESOLV), and applications of the technique to the preparation of nanoparticles. In particular, successes and challenges in the use of RESOLV for nanoscale (<100 nm) polymeric particles and the subsequent protection of the suspended nanoparticles from agglomeration are discussed.
Vinyl Sulfoxides as Stereochemical Controllers in Intermolecular Pauson–Khand Reactions: Applications to the Enantioselective Synthesis of Natural Cyclopentanoids
Authors: Rodríguez Rivero Marta , Alonso Inés , Carretero Juan C. 
Published: September 2004

AbstractThe use of sulfoxides as chiral auxiliaries in asymmetric intermolecular Pauson–Khand reactions is described. After screening a wide variety of substituents on the sulfur atom in α,β‐unsaturated sulfoxides, the readily available o‐(N,N‐dimethylamino)phenyl vinyl sulfoxide (1 i) has proved to be highly reactive with substituted terminal alkynes under N‐oxide‐promoted conditions (CH3CN, 0 °C). In addition, these Pauson–Khand reactions occurred with complete regioselectivity and very high diastereoselectivity (de=86–>96 %, (S,RS) diastereomer). Experimental studies suggest that the high reactivity exhibited by the vinyl sulfoxide 1 i relies on the ability of the amine group to act as a soft ligand on the alkyne dicobalt complex prior to the generation of the cobaltacycle intermediate. On the other hand, both theoretical and experimental studies show that the high stereoselectivity of the process is due to the easy thermodynamic epimerization at the C5 center in the resulting 5‐sulfinyl‐2‐cyclopentenone adducts. When it is taken into account that the known asymmetric intermolecular Pauson–Khand reactions are limited to the use of highly reactive bicyclic alkenes, mainly norbornene and norbornadiene, this novel procedure constitutes the first asymmetric version with unstrained acyclic alkenes. As a demonstration of the synthetic interest of this sulfoxide‐based methodology in the enantioselective preparation of stereochemically complex cyclopentanoids, we have developed very short and efficient syntheses of the antibiotic (−)‐pentenomycin I and the (−)‐aminocyclopentitol moiety of a hopane triterpenoid.
Insights into the Reaction of Transplatin with DNA and Proteins: Methionine‐Mediated Formation of Histidine–Guanine trans‐Pt(NH3)2 Cross‐Links
Authors: Marchán Vicente , Pedroso Enrique , Grandas Anna 
Published: September 2004

AbstractSimultaneous exposure of transplatin to polypeptides and DNA was mimicked by using a model peptide–oligonucleotide conjugate. Initially formed methionine–guanine chelates evolved into adducts with histidine–guanine trans‐Pt(NH3)2 cross‐links that differed in constitution and stability from those formed by reaction of the same conjugate with the anticancer drug cisplatin. This finding may be due to different capacities of the two diamminedichloroplatinum(II) complexes to interfere with biological processes and may explain their differing cytotoxicities.
CC Bond Insertion of a Complexed Phosphinidene into 1,6‐Methano[10]annulene
Authors: Bulo Rosa E. , Trion Linda , Ehlers Andreas W. , de Kanter Fransiscus J. J. , Schakel Marius , Lutz Martin , Spek Anthony L. , Lammertsma Koop 
Published: September 2004

AbstractReaction of electrophilic phosphinidene complex [MePW(CO)5] with 1,6‐methano‐[10]annulene results in the sole formation of the isomeric CC insertion products 6 c (main) and 6 d (minor). The single‐crystal X‐ray structure of the complexed 1,7‐methano‐3‐phospha[11]annulene (6 c) shows a syn‐W(CO)5 group at the exo bent phosphorus. The structure displays CC bond alternation without bonding between the bridgehead carbon atoms. Density functional theory calculations indicate 6 c to result from a concerted disrotatory ring opening of an undetected tricyclic exo–syn phosphirane intermediate. The endo–anti phosphirane cannot undergo ring expansion, due to the high barrier that is associated with an intramolecular antara–antara retro Diels–Alder reaction. The stabilizing effect of transition‐metal coordination is discussed.
Towards Organo‐Click Chemistry: Development of Organocatalytic Multicomponent Reactions Through Combinations of Aldol, Wittig, Knoevenagel, Michael, Diels–Alder and Huisgen Cycloaddition Reactions
Authors: Ramachary Dhevalapally B. , Barbas Carlos F. 
Published: September 2004

AbstractHere we report on our studies on combinations of amino acids and copper(I) for catalyzing multicomponent reactions (MCRs). We aimed to prepare both diene and dienophiles simultaneously, under very mild and environmentally friendly conditions, thus giving the constituents for a stereocontrolled Diels–Alder reaction, which in turn yields compounds 4 to 8. A diversity‐oriented synthesis of polysubstituted spirotriones 4 to 6 were assembled from simple substrates like 1‐(triphenylphosphanylidene)‐propan‐2‐one, two aldehydes, and cyclic‐1,3‐diketones through Wittig/Knoevenagel/Diels–Alder and aldol/Knoevenagel/Diels–Alder reaction sequences in one pot under stereospecific organocatalysis. Chemical diversity libraries of polysubstituted spirotrione‐1,2,3‐traizoles 8 were assembled from simple substrates by means of Wittig/Knoevenagel/Diels–Alder/Huisgen cycloaddition reaction sequences in one pot under stereospecific organo/CuI catalysis. Functionalized dispirolactones such as 6 are biologically active antioxidants and radical scavengers, and spirotrione‐1,2,3‐traizoles 8 have found wide applications in chemistry, biology, and materials science. Experimentally simple and environmentally friendly, organocatalytic, asymmetric four‐component Diels–Alder (AFCDA) reactions of 1‐(triphenylphosphanylidene)‐ propan‐2‐one, two different aldehydes, and cyclic‐1,3‐diketones produced diastereospecific and highly enantioselective substituted spirotriones 4 by means of a Wittig/Knoevenagel/Diels–Alder reaction sequence in one pot. Additionally we have developed an organocatalytic, asymmetric three‐component Michael (ATCM) reaction of 1‐(triphenylphosphanylidene)‐propan‐2‐one, aldehyde, and cyclic‐1,3‐diketones that produced Michael adducts 15, 16 through a Wittig/Michael reaction sequence in a highly enantioselective one‐pot process.