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861.
S. Chandrasekhar M. Srinivasa Reddy G.S. Kiranbabu A. Sai Krishna Murthy 《Tetrahedron letters》2006,47(41):7307-7309
An efficient synthesis of protected (2R,3R,4S)-4,7-diamino-2,3-dihydroxy heptanoic acid, a constituent of the depsipeptides, callipeltins A and D from l-ascorbic acid is described. 相似文献
862.
Nitrite can be determined by its reaction with 2-aminobiphenyl in acidic medium to produce 2-phenylphenol which is quantified by gas chromatography with flame ionisation detection using biphenyl as an internal standard. The hydrolysis of the intermediate diazonium ion avoids many of the problems encountered in the conventional determination of nitrite by the diazotization of an aromatic amine (usually sulphanilamide) and coupling with N-(1-napthyl)ethylenediamine dihydrochloride to yield an azo dye followed by spectrophotometry. Unlike this method, the proposed reaction is rapid and does not suffer from interferences by copper(II), iron(III) and lead(II). The calibration graph was linear over the range 5–1000 μg/l NO2-N and the limit of detection found to be 0.5 μg/l NO2-N. A single analysis can be completed within 20 min. The method was not affected by coloured or turbid analyte solutions and has been used to determine nitrite in natural waters. 相似文献
863.
V. Panduranga Rao P. V. Krishna Rao G. Gopala Rao 《Fresenius' Journal of Analytical Chemistry》1960,176(5):333-336
Summary A method has been developed for the titration of cerium(IV) sulphate with sodium oxalate at the room temperature, using ferroin as internal indicator. A new principle has been utilised for facilitating the indicator action at the equivalence point. This involves the use of a photochemical reaction between the oxalate and iron(III) which is deliberately added to the mixture containing cerium(IV) sulphate and ferriin. When the mixture is titrated with the sodium oxalate solution under exposure to the light from a Philips Repro lamp, the addition of a very slight excess of sodium oxalate solution, after all the cerium(IV) sulphate has reacted, produces a vivid red colour. The slight excess of sodium oxalate added reacts with the iron(III) salt photochemically producing a trace of iron(II) salt which reduces the ferriin to the red ferroin. In titrations with 0.1 and 0.05 N solutions of sodium oxalate, the error is negligible. In titrations with sodium oxalate solution of lower strengths, the error amounts to 0.02 ml of 0.01 N oxalate which has to be subtracted from the titre. 相似文献
864.
The first diastereoselective intramolecular Baylis-Hillman reaction of chiral substrates is reported wherein both aldehyde and activated olefin coexist as substituents to afford alpha-methylene-beta-hydroxylactones in good yields exclusively as single isomers under the standard base-catalyzed reaction conditions in CH(2)Cl(2). Formation of alkoxylactones by an in situ derivatization of adducts was also observed. 相似文献
865.
A simple method for the iodination of aromatic compounds using NH4I as the iodine source and Oxone® as the oxidant is described. 相似文献
866.
N7-substituted guanine (N7G) has been introduced into aminoethylglycyl bisPNA (7) as a C(+) mimic to achieve pH-independent triplex formation with complementary DNA sequences. The introduction of chiral, cationic aminoethylprolyl units with C(+) and C(+) mimic N7G in the backbone of bisPNAs (8, 9) influenced the recognition of complementary DNA in an orientation-selective manner. A simple fluorescence assay is developed to examine the process of strand invasion of target DNA duplex by these modified bisPNAs and comparative results of the study employing triplex forming polypyrimidine (C/T) (6, 8) and purine-pyrimidine (N7G/T) mixmer-bisPNAs (7, 9) are presented. 相似文献
867.
Ivan R. Corrêa Jr. Dr. Andrea Nören‐Müller Horst‐Dieter Ambrosi Dr. Sven Jakupovic Krishna Saxena Dr. Harald Schwalbe Prof. Dr. Markus Kaiser Dr. Herbert Waldmann Prof. 《化学:亚洲杂志》2007,2(9):1109-1126
Protein phosphatases have recently emerged as important targets for research in chemical biology and medicinal chemistry, and new classes of phosphatase inhibitors are in high demand. BIOS (biology‐oriented synthesis) employs the criteria of relevance to nature and biological prevalidation for the design and synthesis of compound collections. In an application of the BIOS principle, an efficient solid‐phase synthesis of highly substituted indolo[2,3‐a]quinolizidines by using a vinylogous Mannich–Michael reaction in combination with phosgene‐ or acid‐mediated ring closure was developed. Screening of this library for phosphatase inhibitors yielded a new inhibitor class for the Mycobacterium tuberculosis phosphatase MptpB. 相似文献
868.
Conversion of nitrate into a nitro-phenol derivative by reaction with 2-methylphenol or 2,6-dimethylphenol allowed at least 100-fold enrichment of the derivative on Lichrolut EN polymeric cartridge, and it is stable for up to 1 month on the cartridge. The derivative could be eluted with ammonia-methanol mixture. This reaction for nitrate determination has permitted a choice of final measurement by UV-Vis spectrophotometry, liquid chromatography or gas chromatography-mass spectrometry when the limits of detection were 10, 6 and 3 μg l−1, respectively, and the calibration range 20 μg to 10 mg l−1 nitrate. The method has been validated by spiking natural water samples, when the recovery of nitrate was 98.5-108.4% (relative standard deviation 2.5-6.1%). 相似文献
869.
Chiral 2,3-epoxy aldehydes have been effectively utilized for the first time as novel electrophiles in Baylis-Hillman reactions with activated alkenes to result in densely functionalized adducts in good yields (61-80%) and in moderate to good diastereoselectivities (40-72% de). 相似文献
870.
E. García-Pérez J. B. Parra C. O. Ania A. García-Sánchez J. M. van Baten R. Krishna D. Dubbeldam S. Calero 《Adsorption》2007,13(5-6):469-476
The adsorption properties of CO2, N2 and CH4 in all-silica zeolites were studied using molecular simulations. Adsorption isotherms for single components in MFI were both
measured and computed showing good agreement. In addition simulations in other all silica structures were performed for a
wide range of pressures and temperatures and for single components as well as binary and ternary mixtures with varying bulk
compositions. The adsorption selectivity was analyzed for mixtures with bulk composition of 50:50 CO2/CH4, 50:50 CO2/N2, 10:90 CO2/N2 and 5:90:5 CO2/N2/CH4 in MFI, MOR, ISV, ITE, CHA and DDR showing high selectivity of adsorption of CO2 over N2 and CH4 that varies with the type of crystal and with the mixture bulk composition. 相似文献