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1.
Ferdinand Bohlmann Elena Tsankova Jasmin Jakupovic Robert M. King Harold Robinson 《Phytochemistry》1983,22(2):557-560
The investigation of Encelia canescens afforded, in addition to several known compounds, four new dimeric p-hydroxyacetophenone derivatives, two epimeric chromene dimers and two epimeric mixed dimers of euparin and encecalin. Furthermore, derivatives of tremetone and of encecalin were present. The structures were elucidated hy high field 1H NMR spectroscopy. 相似文献
2.
Silvia Pastorekova Daniela Vullo Angela Casini Andrea Scozzafava Jaromir Pastorek Isao Nishimori 《Journal of enzyme inhibition and medicinal chemistry》2013,28(3):211-217
The tumor-associated transmembrane carbonic anhydrase (CA, EC 4.2.1.1) isozymes IX (CA IX) and XII (CA XII) are involved in acidification of hypoxic tumors, a process correlated with poor prognosis and clinical outcome of patients harboring such tumors. This process may be reversed by inhibiting these enzymes with potent sulfonamide/sulfamate inhibitors. A series of such aromatic/heterocyclic sulfonamides incorporating 2,3,5,6-tetrafluorobenzoyl-, 2,3,5,6-tetrafluoro- phenylsulfonyl- and pentafluorophenylureido moieties has been investigated for its interaction with the catalytic domain of the human isozymes hCA IX and hCA XII. Some of these compounds showed excellent inhibitory properties against both isozymes IX and XII, with several subnanomolar inhibitors detected for the first time. These sulfonamides may constitute valuable candidates for the development of novel antitumor therapies based on the inhibition of such tumor-associated CA isozymes. 相似文献
3.
E.E. Mazokopakis G.E. Vrentzos J.A. Papadakis D.E. Babalis E.S. Ganotakis 《Phytomedicine》2005,12(1-2):25-27
Oral mucositis is a known complication of methotrexate (MTX) therapy, but a single efficacious intervention or agent for prophylaxis or management of this side effect has not yet been identified. We report a case of MTX-induced oral mucositis in a patient with rheumatoid arthritis, who was successfully treated with Wild chamomile mouthwashes. 相似文献
4.
川一阶导数光谱法测定猫豆中主旋多巴的含量,可以排除无关杂质吸收的干扰,省去复杂的分离提取步骤。试验结果表明:相关系数达0.9999,平均回收率101.5%,重现性较好。 相似文献
5.
Christine No Jordi Hernandez-Borrell Stephen C. Kinsky Eiji Matsuura Lee Leserman 《生物化学与生物物理学报:生物膜》1988,946(2)
We have prepared liposomes containing methotrexate-γ-dimyristoylphosphatidylethanolamine (MTX-DMPE liposomes), to which protein A was covalently coupled, permitting specific association of these liposomes in vitro with murine cells preincubated with relevant protein A-binding monoclonal antibodies. In the absence of antibody the presence of externally-oriented methotrexate (MTX) in MTX-DMPE liposomes did not result in greater binding to cells than liposomes made without MTX-γ-DMPE. Derivation of methotrexate with phospholipid permits enhanced drug-liposome association. These liposomes are more resistant than conventional liposomes to repeated cycles of freezing and thawing. MTX-DMPE liposomes are comparable to antibody-targeted liposomes made with encapsulated water-soluble methotrexate both with respect to specific binding to target cells and drug effect. The inhibitory effects off MTX-liposomes, as well as free MTX, were reversible by either thiamin pyrophosphate (Tpp) or N5-formyltetrahydrofolate (F-THF), while the effects of MTX-DMPE liposomes were reversed only by N5-formyltetrahydrofolate. This suggests that the toxicity of non-targeted MTX-liposomes may be due to leakage of the encapsulated MTX. The absence of an effect of thiamin pyrophosphate on non-targeted MTX-DMPE liposomes indicates that they do not enter into the cell via the normal folate transport system. 相似文献
6.
Bisulfite reversibly inhibits the growth of a variety of microorganisms and has been used as a preservative in foods and beverages for that reason. We have now measured macromolecule synthesis in Escherichia coli K12 after bisulfite treatment. RNA synthesis, the synthesis of total protein, and of an inducible enzyme, beta-galactosidase, stopped almost immediately upon addition of 2 mM (or higher concentrations) of bisulfite. These functions resumed after a lag whose duration depended on the concentration of bisulfite added. The synthesis of DNA was slowed upon bisulfite addition, but did not stop entirely. The inhibition of RNA synthesis by bisulfite took place in both stringent and relaxed strains of E. coli and was not relieved upon addition of chloramphenicol. Stringent control was therefore not involved in this effect. No effect on protein synthesis was observed in the cell-free system of E. coli (using poly(U) or MS2 RNA as messenger) at bisulfite concentrations up to 10 mM. Protein synthesis inhibition in vivo was apparently not due to a reaction of bisulfite with a component of this system. In additional experiments, RNA polymerase was not impaired by bisulfite, and the growth inhibition effect was shown to proceed in the presence of inhibitors of free radical chain reactions. 相似文献
7.
Jacques Ricard Jacques Vergne Jean-Luc Decout Marie-Christine Maurell 《Journal of molecular evolution》1996,43(4):315-325
A polyallylamine carrying long hydrophobic dodecyl groups and adenine residues as side chains (PALAD C12) may be able to catalyze the hydrolysis ofN-carbobenzoxy-l-alaninep-nitrophenyl ester (N-Cbz-Ala) as well asp-nitrophenyl acetate (pNPA). The progress curve of hydrolysis of the former displays a long lag and apparently no steady state.
After this transient the rate falls off due to the accumulation of the products. Conversely, the hydrolysis ofp-nitrophenyl acetate displays classical burst kinetics followed by a slow decline of the reaction rate.
Theoretical considerations show that a steady state may be expected to occur only if the concentration of the free catalyst
is very small during the reaction. This condition is sufficient to allow the rate of disappearance of the substrate to be
equal to the rate of appearance of the products, which is precisely a condition for the existence of a steady state. If the
catalyst is poorly active and has a loose affinity for its substrate and product, the measurement of a significant reaction
rate will require a much larger concentration of the catalyst. Therefore, under these conditions, one cannot expect a steady
state to occur. The mathematical expression of the error made in the steady-state assumption has been derived. This error
increases with the catalyst concentration and decreases if the affinity of the substrate for the catalyst is high. Therefore
the lack of steady state is associated with the affinity (or the dissociation) of the substrate and the product for the catalyst.
When this affinity is low, the free concentration of the catalyst during the reaction is high and one cannot expect a steady
state to occur. This is precisely what takes place with N-Cbz-Ala.
A mathematical expression of the rate of hydrolysis of N-Cbz-Ala and of any reactant that displays this type of kinetics may
be derived at the end of the transient when the rate is close to its maximum value. Under these conditions the rate cannot
follow classical Michaelis-Menten kinetics and displays positive cooperativity.
It may therefore be speculated that primordial template-like catalysts that were displaying a poor affinity for their substrates
and products were already exhibiting apparent positive cooperativity in the kinetic reactions they were able to catalyze.
Correspondence to: J. Ricard 相似文献
8.
An Aedes albopictus dihydrofolate reductase gene was used to construct two chimeric DNA vectors that functioned as dominant selectable markers in transfected, wild type mosquito cells. Stably transformed clones were recovered after 10–15 days in the presence of selective medium containing 1 μM methotrexate. The transformed clones contained an estimated 100–500 copies of transfected DNA per nucleus. Combined data from Southern blots and in situ hybridization to metaphase chromosomes indicated that transfected DNA was likely integrated into chromosomes both as repeated structures and as randomly integrated single copy molecules, with minimal rearrangement of coding sequences. Transfected DNA was stably maintained under selective conditions, but in some cases was lost when cells were maintained for prolonged periods in the absence of methotrexate. These observations provide a general framework for further development of stable gene transfer systems for mosquito cells in culture. 相似文献
9.
Olga V. Beluzhenko Galina V. Bogdanova Vitalii A. Tumenev Yurii A. Zhdanov 《Chirality》1993,5(6):455-463
To control stereoselectivity in aldol-like reactions with chiral carbohydrate templates, we studied the interaction between completely protected dialdo compounds and magnesium enediolates of arylacetic acids. Diastereomeric mixtures of the highly functionalized acids obtained were esterified to isolate individual methyl uronates. It was found that all the diastereomeric esters exhibit Cotton effects of the same positive sign in the 220–230 nm region and so possess the same S configuration of the aryl chiral center C(6). Chiral center C(5) configurational assignments were performed using IR and ORD spectroscopy. We separated and specified four pairs of diastereomeric methyl uronates. It follows that the precursory acids have the same 5R*, 6S (major isomers) and 5S*, 6S (minor isomers) configurations. A tentative mechanism for complexation and possible models of Mg2+ -protected dialdose intermediate complexes has been proposed. We have concluded that a kind of orbital steering is realized, accompanied by some “tuning” of molecular assembly conditioned by two-point coordination between Mg2+ and potential cation-binding sites in the substrate molecules. Thus it has been demonstrated that reasonable diastereo-selectivity can be achieved even through the use of small matrix molecules using rather small functional groups, which do not impose any stringent steric requirements. © 1993 Wiley-Liss, Inc. 相似文献
10.
Cotton ovules collected during late September with prevalent night cool temperature (15°C), cultured at 30°C/15°C i.e. cycling temperatures in Beasley and Ting medium had very few epidermal cells showing bulging. Supplementing cultures with guaianolide derivative I (E-13 methyldehydrocostus lactone) promoted fibre initiation. At—1 day preanthesis (DPA), IAA oxidase activity declined in guaianolide-treated cultures but increased during the elongation phase and was enhanced during the secondary wall thickening phase. However, o-diphenol oxidase activity was adversely affected during the fibre initiation phase. The activities of all the other enzymes studied viz. acid invertase, phenylalanine ammonia lyase, -glucosidase and IAA oxidase increased, except -galactosidase, during the later phase in comparison with the controls. The present study indicates that guaianolide derivative I triggers early initiation and promotes fibre elongation by regulatin o-diphenols and IAA-oxidation levels, which in turn check wall loosening. Considerable enhancement in the soluble acid invertase activity by this compound suggests its role in apoplastic sucrose hydrolysis, thereby preventing its accumulation.Abbreviations DPA
days pre anthesis
- DAC
days after culturing
- DAA
days after anthesis 相似文献