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141.
The high-yield synthesis of 2-trimcthylsilylbenzothiazole is described, and the labile nature of this silicon-helerocyclic bond is proved when cleavage is affected by aldehydes, acid halides, chloro-formates and anhydrides. Justification for this unusual reactivity and further insight into the reaction mechanism is offered. 相似文献
142.
RAMAN and IR spectroscopic investigation of alkyl derivatives of arsenic acid. II. Vibrational spectra of some alkanearsonic acid dialkylesters RAMAN and IR spectra of CH3AsO(OCH3)2, CH3AsO(OC2H5)2, C2H5AsO(OCH3)2, and C2H5AsO(OC2H5)2, are communicated and discussed. Their skeleton CAsO(OC)2 has very probably Cs symmetry. 相似文献
143.
The oligonucleotide building blocks 4b–d derived from 7-bromo-, 7-chloro-, and 7-methyl-substituted 7-deaza-2′-deoxyadenosines 3b–d were prepared. They were employed in the solid-phase synthesis of the oligonucleotides 7–25 . The dA residues of the homomer d(A12), the alternating d[(A-T)6], and the palindromic d(G-T-A-G-A-A-T-T-C-T-A-C) were replaced by 3b–d as well as by the parent 7-deaza-2′-deoxyadenosine ( 3a ). The melting profiles and CD spectra of oligonucleotide duplexes, showing this major groove modification, were measured, and the Tm values as well as the thermodynamic data were determined. It was found that small substituents such as Br, Cl, or Me introduced in the 7-position of a 7-deazaadenine residue increase the duplex stability compared to oligonucleotides containing adenine. 相似文献
144.
Reaction of the Reissert anion with the carbonyl group of 1,3,4,6,7,11b-hexahydro-9,10-dimethoxybenzo[a]quinolizin-2-one and with 3-ethyl-1,2,3,4,6,7-hexahydro-9,10-dimethoxy-11bH-benzo[a]quinolizin-2-carboxaldehyde give emetine analogs. This anion does not react with the carbonyl group of 3-aIkyl-1,3,4,6,7,11b-hexahydro-9,10-dimethoxybenzo[a]quinolizin-2-one but instead gives a rearrangement product and the benzoquinolizinone cyanohydrin. 相似文献
145.
Infrared multiple-photon dissociation of CTCl3 was investigated using a pulsed CO2 laser-pumped NH3 laser at 12.08 μm. No evidence of any CDCl3 depletion or decomposition product was observed in photolyzed CTCl3/CDCl3 mixtures. A lower limit of the single-step T/D enrichment factor, β, was found to be ≈ 165, based on the sensitivity in measuring CDCl3 depletion. The low-fluene CTCl3/CDCl3 optical selectivity in absorptions is > 9000 at the 835 cm?1 CTCl3 ν4 peak. 相似文献
146.
Described are the photophysical properties of the mononuclear copper(I) complexes CuL(4)(+) (L = pyridine (py), 4-methylpyridine, 4-phenylpyridine, or acetonitrile), Cu(lut)(3)(+) (lut = 2,6-lutidine), and Cu(lut)(2)(+). Each of these compounds as their solid PF(6)(-) salts display a relatively long-lived (>1 &mgr;s), visible range emission at both ambient temperature and at 77 K but not in fluid solutions. Also reported are the results for ab initio calculations at the restricted Hartree-Fock self-consistent field level to probe the natures of lower energy excited states of the hypothetical species CuL(n)()(+) (L = NH(3), CH(3)CN, or py; n = 1-4). These results point to an assignment of the lowest energy, luminactive excited states as being largely metal centered, d --> s in character for each of the above complexes with the possible exception of the CuL(4)(+) species where L is py or a substituted analogue. In the case of Cu(py)(4)(+) the ab initiocalculations indicate a metal-to-ligand charge transfer to be the lowest energy Franck-Condon state, although the similarities of emission band shapes, energies, and lifetimes among the various complexes suggest a common d --> s assignment. 相似文献
147.
Heering HA Wiertz FG Dekker C de Vries S 《Journal of the American Chemical Society》2004,126(35):11103-11112
Cyclic voltammetry shows that yeast iso-1-cytochrome c (YCC), chemisorbed on a bare gold electrode via Cys102, exhibits fast, reversible interfacial electron transfer (k(0) = 1.8 x 10(3) s(-1)) and retains its native functionality. Vectorially immobilized YCC relays electrons to yeast cytochrome c peroxidase, and to both cytochrome cd(1) nitrite reductase (NIR) and nitric oxide reductase from Paracoccus denitrificans, thereby revealing the mechanistic properties of these enzymes. On a microelectrode, we measured nitrite turnover by approximately 80 zmol (49 000 molecules) of NIR, coadsorbed on 0.65 amol (390 000 molecules) of YCC. 相似文献
148.
Several new dinitritochromium(III) complexes of the type trans-[Cr(L)(ONO)(2)]BF(4), where L is a derivative of the macrocyclic ligand cyclam having pendant aromatic chromophores attached (L = 5,7-dimethyl-6-(substituted)-1,4,8,11-tetraazacyclotetradecane), have been prepared and characterized. Photoexcitation of aqueous solutions containing these complexes at wavelengths corresponding to the pendant chromophore absorption bands led to the generation of NO as detected by an electrochemical sensor. Photophysical data show that the expected fluorescence of the pendant chromophores is largely quenched when the macrocyclic ligand is coordinated to these Cr(III) centers, and this is interpreted in terms of fast energy transfer processes from the ligand-centered pipi states to the Cr(III)-centered ligand field states leading to subsequent cleavage of the Cr(III)-coordinated nitrito ligand. Thus, the chromophores tethered to the coordinated cyclam serve as light-gathering antennae for the intramolecular sensitization of the NO-generating photoreactions at the metal center. 相似文献
149.
Two syntheses of some optically active 2-benzyl-2,3-dihydro-4H-benzopyrans and benzopyran-4-ones are presented. An asymmetric synthesis starting from D- and L-phenylalanine was used to provide both enantiomers of 2-benzyl-6-(methoxycarbonyl)-2,3-dihydro-4H-benzopyran-4-one 19. Phenylalanine was diazotized in aqueous sulfuric acid to 2-hydroxy-3-phenylpropionic acid 6 which was converted in four steps to 1-bromo-2-(4-methoxycarbonylphenoxy)-3-phenylpropane 11. (4R,S)-Benzamido-2-benzyl-2,3-dihydro-6-(methoxycarbonyl)-4H-1-benzopyran-4-carboxylic acid 16 was prepared from 11 by amidoalkylation with α-hydroxyhippuric acid in methanesulfonic acid solution followed by spiroalkylation to (4R,S)-2-benzyl-2,3-dihydro-6-(methoxycarbonyl)spiro[4H-benzopyran-4,4′-2′-phenyloxazolidin]-5′-one 15. After the phenyloxazolidin-5-one 15 was hydrolyzed to the spirobenzamido carboxylic acid 16 , oxidative decarboxylation with sodium hypochlorite yielded optically active 2-benzyl-6-(methoxycarbonyl)-2,3-dihydro-4H-benzopyran-4-one 19. The ketone in 19 was reduced by hydrogenation over palladium on carbon to a methylene group and the ester was converted to the aldehyde to give both isomers of the desired intermediate 2-benzyl-6-(formyl)-2,3-dihydro-4H-benzopyran 25. The second synthesis relied on an enzymatic hydrolysis of ethyl 2,3-dihydrobenzopyran-2-carboxylate 27 with the lipase from P. fluorescens to provide the desired 2R-ester. The ester group in (R)- 27 was converted to the triflate (R)- 29. Displacement of the triflate group with phenylmagnesium bromide and cuprous bromide as catalyst gave 2R-benzyl-2,3-dihydro-4H-benzopyran (R)- 30. Formylation of (R)- 30 provided 2R-benzyl-6-(formyl)-2,3-dihydro-4H-benzopyran (R)- 25 identical with that from the first synthesis. These optically active intermediates are used in the preparation of the hypoglycemic agent englitazone. 相似文献
150.
The structure of 1-hydroxy-1,2,3-benzotriazolium diphenyl phosphate (HOBt/DPP) has been investigated by X-ray analysis. The compound crystallizes in the monoclinic space group P21/n with Z = 4 and the following lattice parameters: a = 11.711(2), b = 12.727(2) and c = 12.794(3) Å, β = 105.12(2)°, V = 1840.9(6) Å3. The structure was solved by direct methods and refined on F2 to R values of wR2 = 0.084 and R1 = 0.034 for 1985 observed reflections. HOBt/DPP has an ionic structure with very short OHO and NHO hydrogen bonds linking the different ions. Owing to these hydrogen bonds, infinite screw-shaped chains which are twisted parallel to the y-axis are formed. 相似文献