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71.
When 7-oxodesacetamidothiocolchicine (1) was treated with various peroxides in order to afford a Baeyer-Villiger rearrangement, a complex mixture of products was formed, which included the sulfoxide, (2) and sulfone, (3). When peracetic acid was used two additional products were formed; a C-ring lactone (4) and a ring-contracted allocolchicine derivative (5). The sulfoxide (2) was semi-preparatively resolved into enantiomers by chromatography on microcrystalline triacetylcellulose. Rotational barriers around the A-C pivot bond of, and were determined by dynamic 1H NMR analysis. The compounds, and exhibit moderate inhibition of tubulin polymerization, according to in vitro turbidity studies, whereas was inactive.  相似文献   
72.
The novel promoter system IX/AgOTf (X = Cl or Br) has been evaluated in the synthesis of two bislactam analogues of GD3. We have carried out two high-yielding galactosylations in 97% and 98% yield, respectively, using ICl/AgOTf, and four sialylations in 93%, 59%, 40%, and 44% yield, using IBr/AgOTf. The choice of interhalogen (IX) is determined by the donor type used in the glycosylation. We also report some mechanistic investigations leading to further optimization of the IX/AgOTf promoter system.  相似文献   
73.
Rhodium-MonoPhos was successfully immobilised by ionic interactions on aluminosilicate AlTUD-1. The resulting new heterogeneous catalyst can be used in water and showed excellent enantioselectivity and activity in the asymmetric hydrogenation of methyl-2-acetamidoacrylate.  相似文献   
74.
The formylated spirobyclic alcohol was computer modeled to be a mimetic of paclitaxel. In this model, the formyl group was used as a truncated paclitaxel side chain in order to reduce the computational work. Compound , carrying the paclitaxel side chain, was synthesized in six steps from optically active 1,3-diketone . Microtubule stabilization was not observed for , indicating that the model needs to be adjusted.  相似文献   
75.
We report on the shear induced transition from the L3- to the L-phase studied by means of flow birefringence using the system pentaethyleneglycol monododecylether (C12E5), decane, water. The dependence of the critical shear rate, at which the transition from the isotropic state to the anisotropic takes place, on membrane volume fraction was studied in temperature ramp experiments at different constant shear rates and in isothermal shear ramp experiments. These results are compared with relaxation experiments from the shear aligned state back to the isotropic. For all these experiments power law exponents in the membrane volume fraction between 1.6 and 2.8 were found, which are rather low compared to values of current theories. The values found for the inverse critical shear rate and the decay times from the relaxation experiments differ by four orders of magnitude.  相似文献   
76.
A member of a new class of novel macrocycles possessing both polyether and phenolic functionalities, forms dimers in both the solid-state and in solution when exposed to chloroform, dichloromethane or toluene, but does not self-associate in the presence of dimethyl sulfoxide.  相似文献   
77.
Structural isomers of [UO(2)(oxalate)(3)](4-), [UO(2)(oxalate)F(3)](3-), [UO(2)(oxalate)(2)F](3-), and [UO(2)(oxalate)(2)(H(2)O)](2-) have been studied by using EXAFS and quantum chemical ab initio methods. Theoretical structures and their relative energies were determined in the gas phase and in water using the CPCM model. The most stable isomers according to the quantum chemical calculations have geometries consistent with the EXAFS data, and the difference between measured and calculated bond distances is generally less than 0.05 A. The complex [UO(2)(oxalate)(3)](4-) contains two oxalate ligands forming five-membered chelate rings, while the third is bonded end-on to a single carboxylate oxygen. The most stable isomer of the other two complexes also contains the same type of chelate-bonded oxalate ligands. The activation energy for ring opening in [UO(2)(oxalate)F(3)](3-), deltaU++ = 63 kJ/mol, is in fair agreement with the experimental activation enthalpy, deltaH++ = 45 +/- 5 kJ/mol, for different [UO(2)(picolinate)F(3)](2-) complexes, indicating similar ring-opening mechanisms. No direct experimental information is available on intramolecular exchange in [UO(3)(oxalate)(3)](4-). The theoretical results indicate that it takes place via the tris-chelated intermediate with an activation energy of deltaU++ = 38 kJ/mol; the other pathways involve multiple steps and have much higher activation energies. The geometries and energies of dioxouranium(VI) complexes in the gas phase and solvent models differ slightly, with differences in bond distance and energy of typically less than 0.06 A and 10 kJ/mol, respectively. However, there might be a significant difference in the distance between uranium and the leaving/entering group in the transition state, resulting in a systematic error when the gas-phase geometry is used to estimate the activation energy in solution. This systematic error is about 10 kJ/mol and tends to cancel when comparing different pathways.  相似文献   
78.
[reaction: see text] Aryl alpha,beta-unsaturated ketones and aldehydes were synthesized, in moderate to excellent yields, with use of dimethylammonium dimethyl carbamate (DIMCARB) as a recyclable reaction medium and as a catalyst.  相似文献   
79.
A chiral non-aqueous CE system with UV and mass spectrometric detection has been developed. The enantioseparation was promoted by diastereomeric complex (ion-pair) formation between the amines (e.g. salbutamol, atenolol) and the chiral selector, (-)-2,3:4,6-di-O-isopropylidene-2-keto-L-gulonic acid [(-)-DIKGA]. Different solvent mixtures were studied, as well as different concentrations of (-)-DIKGA and ammonium acetate in the background electrolyte. A partial filling technique was developed with a selector plug composed of (-)-DIKGA and ammonium acetate in a solvent mixture of methanol and 2-propanol. The separated enantiomers of pronethalol were detected by a Q-TOF MS system equipped with a sheath-flow electrospray ionization interface.  相似文献   
80.
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