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11.
买麻藤化学成分的研究 总被引:2,自引:0,他引:2
从买麻藤(Gnetum montanum Markgr)的藤茎中分离鉴定出4个新化合物:2-羟基(?)甲氧基-4-甲氧羰基吡咯(1),2-羟基-3-甲氧甲基-4-甲氧羰基吡咯(2),3,4-二羟基-4-(?)氧基二苄醚(3)和3,3',4'-三羟基-4-甲氧基二苄醚(4)以及两个已知化合物2,3-二苯基吡咯(5)和胺甲基甲醇(6)。化合物(1)、(2)和(6)是以盐酸盐形式分离得到。 相似文献
12.
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
13.
A chemically reactive analog of the phytotropin N-1-naphthylphthalamic acid (NPA) was synthesized and evaluated as a site-directed irreversible ligand for the NPA receptor. The NPA analog (5-isothiocyanato-N-1-naphthylphthalamic acid; NCS-NPA) was synthesized in two steps. Pretreatment of etiolated Helianthus hypocotyl segments with NCS-NPA at concentrations in excess of 1 M resulted in a dose-dependent inhibition of basipetal [14C]IAA transport. Net uptake of IAA by hypocotyl segments was stimulated by NCS-NPA at concentrations of 1 M or greater. NCS-NPA inhibited the saturable binding of [3H]NPA in Helianthus microsomes in a dose-dependent fashion with 50% inhibition occurring at NCS-NPA concentrations of 3 to 10 nM. The binding affinity of [3H]NPA in microsomes pretreated with NCS-NPA followed by extensive washing was substantially reduced. These results demonstrate that NCS-NPA is a site-directed irreversible ligand for the NPA receptor and suggest that it may be of use in the purification and characterization of this biologically important receptor.Abbreviations ANPA
5-amino-naphthylphthalamic acid
- IAA
indole-3-acetic acid
- NCS-NPA
5-isothiocyanato-N-1-naphthylphthalamic acid
- NPA
N-1-naphthylphthalamic acid
- TLC
thin-layer chromatography 相似文献
14.
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
15.
An enantioselective HPLC bioassay has been developed relying on extraction of (R)- and (S)-atenolol from alkalinized plasma or serum (pH > 12) into dichloromethane containing 5% (v/v) 1-butanol followed by an achiral derivatization of the drug with phosgene leading to (R)- and (S)-oxazolidine-2-one derivatives. Under these conditions there was quantitative conversion of the acetamido group to the corresponding nitrile. These stable derivatives were separated on a (R,R)-diaminocylohexane-dinitrobenzoyl chiral stationary phase [(R,R)-DACH-DNB] using dichloromethane/methanol 98/2 as mobile phase. Determination limits of 0.5 ng for (R)- and 0.6 ng for (S)-atenolol could be achieved using fluorimetric detection. The assay was applied to a human pharmacokinetic study which was performed in a randomized cross-over, double-blind fashion in 12 healthy volunteers, administering single oral doses of 100 mg (R,S)-, 50 mg (R)-, and 50 mg (S)-atenolol AUC0–24 and Cmax values of (R)-atenolol were slightly but significant higher than those of (S)-atenolol. The R/S ratios were 1.09 for AUC(R)/AUC(S) and 1.03 for Cmax (R)/Cmax(S) (P < 0.01) respectively after administration of the racemic drug. However, there were no differences between AUC, Cmax, and t½ values of each enantiomer, whether they were administered as single enantiometers or in the form of its racemic mixture. © 1993 Wiley-Liss, Inc. 相似文献
16.
This study describes the enantioseparation of three chiral amines as naphthaldimine derivatives, using normal phase HPLC with amylose and cellulose tris(3,5-dimethylphenylcarbamate) chiral stationary phases (CSPs). Three chiral amines were derivatized using three structurally similar naphthaldehyde derivatizing agents, and the enantioselectivity of the CSPs toward the derivatives was examined. The degree of enantioseparation and resolution was affected by the amylose or cellulose-derived CSPs and aromatic moieties as well as a kind of chiral amine. Especially, efficient enantiomer separation was observed for 2-hydroxynapthaldimine derivatives on cellulose-derived CSPs. Molecular docking studies of three naphthaldimine derivatives of leucinol on cellulose tris(3,5-dimethylphenylcarbamate) were performed to estimate the binding energies and conformations of the CSP–analyte complexes. The obtained binding energies were in good agreement with the experimentally determined enantioseparation and elution order. 相似文献
17.
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
18.
Summary In continuation of a previous work (Pecci et al., 1993), dedicated to the detection of the autoxidation products of S-aminoethylcysteine ketimine (AECK), we give here data for the identification of 2,3,6,7-tetrahydro-4H-[1,4]thiazino[2,3-b]thiazine, thiomorpholine-3-one and 5,5, 6,6-tetrahydro-2,2-dihydroxy-3,3-bi-2H-thiazine among the products of AECK autoxidation. Identification has been done on the basis of mass spectrometry and NMR spectral analyses of the isolated products.Abbreviations TLC
thin layer chromatography
- HPLC
High performance liquid chromatography
- AECK
S-aminoethylcysteine ketimine 相似文献
19.
M. Kukhanova A. Krayevsky N. Terentyeva V. Rasskazov 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1984,783(3):221-226
2′,3′-Dideoxy-3′-aminonucleoside 5′-triphosphates have been shown to be inhibitors of replicative DNA synthesis in isolated nuclei of sea urchin embryo. These compounds inhibit the Okazaki fragment synthesis. The effect of 2′,3′-dideoxy-3′-aminothymidine 5′-triphosphate and arabinothymidine 5′-triphosphate is reversible when adding the corresponding substrate for DNA synthesis, 2′-deoxythymidine 5′-triphosphate. 相似文献
20.
Sergio Grinstein Wendy Furuya 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1984,803(4):221-228
The site and mechanism of accumulation of acridine derivatives into platelets and their isolated organelles were investigated. In addition, their suitability as indicators of cytoplasmic pH was analysed. Direct microscopic observation showed that quinacrine and 9-aminoacridine are concentrated inside organelles in platelets. Using fractionation studies, the acridine derivatives were found to accumulate particularly in dense and α-granules. Uptake into these organelles is driven by a pH differential across their membrane (acidic inside). Because of their cellular distribution, acridine derivatives were found to be poor indicators of cytoplasmic pH. In contrast, a poorly permeant dicarboxylated fluorescein derivative, generated in situ by cytosolic enzymes, is shown to be a more reliable probe of intracellular pH. The results are compared with previous reports of the use of 9-aminoacridine as a cytoplasmic pH probe in platelets and of quinacrine as a selective dense-granule marker. 相似文献