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991.
Eggen M Mossman CJ Buck SB Nair SK Bhat L Ali SM Reiff EA Boge TC Georg GI 《The Journal of organic chemistry》2000,65(23):7792-7799
Two efficient protocols for the synthesis of tert-butyl (5S,6R,2E, 7E)-5-[(tert-butyldimethylsilyl)oxy]-6-methyl-8-phenyl-2, 7-octadienoate, a major component of the cryptophycins, are reported. The first utilized the Noyori reduction and Frater alkylation of methyl 5-benzyloxy-3-oxopentanoate to set two stereogenic centers, which became the C16 hydroxyl and C1' methyl of the cryptophycins. The second approach started from 3-p-methoxybenzyloxypropanal and a crotyl borane reagent derived from (-)-alpha-pinene to set both stereocenters in a single step and provided the dephenyl analogue, tert-butyl (5S,6R,2E)-5-[(tert-butyldimethylsilyl)oxy]-6-methyl-2, 7-octadienoate, in five steps. This compound was readily converted to the 8-phenyl compound via Heck coupling. The silanyloxy esters were efficiently deprotected and coupled to the C2-C10 amino acid fragment to provide desepoxyarenastatin A and its dephenyl analogue. The terminal olefin of the latter was further elaborated via Heck coupling. Epoxidation provided cryptophycin-24 (arenastatin A). 相似文献
992.
B. Muralidhara Rao B. Narayana Biju Mathew K. Subrahmanya Bhat 《Mikrochimica acta》1995,118(1-2):63-68
A selective complexometric method is described for the determination of palladium, sodium nitrite being used as masking reagent. Palladium(II) in a given sample solution is initially cornplexed with an excess of EDTA and the surplus EDTA is titrated with zinc sulfate solution at pH 4.5–5.5 (acetic acid-sodium acetate buffer), using xylenol orange as indicator. An excess of sodium nitrite is then added, the mixture is shaken well and the EDTA released from the Pd-EDTA complex is titrated with a standard zinc sulfate solution. Results are obtained for 2.5–27.5 mg of Pd with relative errors 0.5% and standard deviations 0.05 mg. The interferences of various ions are studied. The method is applied for the determination of palladium(II) in alloys and complexes. 相似文献
993.
Determination of scandium in wolframite and in the residues obtained after the extraction of tungsten 总被引:1,自引:0,他引:1
The separation of scandium from iron and manganese by extraction with TBP from hydrochloric acid was studied in detail and this method was applied to the estimation of scandium in wolframite and its residues. The method consists of the extraction of tungsten from the wolframite with sodium carbonate, dissolution of the residue in hydrochloric acid and preferential extraction of iron and scandium from hydrochloric acid, stripping of the scandium with 8 M hydrochloric acid and re-extraction of accompanying iron with fresh TBP, precipitation of scandium with ammonia in presence of ammonium chloride, and final purification of the scandium by TBP extraction. 相似文献
994.
The stability constants of complexes of Mn++, Fe++, Co++, Ni++, Cu++, Zn++, Cd++ and UO with 5,7-dichloro-, 5,7-dibromo- and 5,7-dinitro-8-hydroxyquinoline and their corresponding N-oxides have been determined in 75 + 25 v/v dioxan + water medium at 35°C in presence of 0.20 M sodium perchlorate by pH-titration technique as given by IRVING and Rossotti. A possible explanation for the observed orders of the stability constants of the metal complex with the different ligands, and of the complexes of a particular ligand with different metal ions is also proposed. 相似文献
995.
A simple, selective, rapid, precise and accurate reverse phase high pressure liquid chromatographic method has been developed for the simultaneous estimation of diclofenac sodium and rabeprazole sodium from pharmaceutical formulations. The method was developed using a HiQ SiL C18 (250 mm × 4.6 mm i.d.) column with a mobile phase consisting of methanol:water, (80:20 v/v), at a flow rate of 1.25 mL min?1. Detection was carried out at 284 nm. Indapamide was used as an internal standard. The developed method was validated for linearity, accuracy, precision, limit of detection and limit of quantitation. The proposed method can be used for the estimation of these drugs in combined dosage forms. 相似文献
996.
Abhijit Bandyopadhyay Mousumi de Sarkar Anil K. Bhowmick 《Journal of Polymer Science.Polymer Physics》2005,43(17):2399-2412
The effect of polymer–filler interaction on solvent swelling and dynamic mechanical properties of the sol–gel derived acrylic rubber (ACM)/silica, epoxidized natural rubber (ENR)/silica, and poly (vinyl alcohol) (PVA)/silica hybrid nanocomposites has been described for the first time. Tetraethoxysilane (TEOS) at three different concentrations (10, 30, and 50 wt %) was used as the precursor for in situ silica generation. Equilibrium swelling of the hybrid nanocomposites in respective solvents at ambient condition showed highest volume fraction of the polymer in the swollen gel in PVA/silica system and least in ACM/silica, with ENR/silica recording an intermediate value. The Kraus constant (C) also followed a similar trend. In dynamic mechanical analysis, the storage modulus dropped at higher strain (>1%), which indicated disengagement of polymer segments from the filler surfaces. This drop was maximum in ACM/silica, intermediate in ENR/silica, and minimum in PVA/silica, both at 50 and 70 °C. The drop in modulus with theoretical volume fraction of silica (ϕ) was interpreted with the help of a Power law model ΔE′ = a1ϕ, where a1 was a constant and b1 was primarily a filler attachment parameter. Strain dependence of loss modulus was observed in ACM/silica hybrid nanocomposites, while ENR/silica and PVA/silica nanocomposites showed almost strain‐independent behavior. The storage modulus showed sharp increase with increasing frequency in ACM/silica system, while that was lower in both ENR/silica (at higher frequency) and PVA/silica systems (in the entire frequency spectrum). The increase in modulus with ϕ also followed similar model ΔE′ = a2ϕ proposed in the strain sweep mode. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2399–2412, 2005 相似文献
997.
Abachi S Abbott B Abolins M Acharya BS Adam I Adams DL Adams M Ahn S Aihara H Álvarez G Alves GA Amidi E Amos N Anderson EW Aronson SH Astur R Avery RE Baden A Balamurali V Balderston J Baldin B Bantly J Bartlett JF Bazizi K Behnke T Bendich J Beri SB Bertram I Bezzubov VA Bhat PC Bhatnagar V Bhattacharjee M Bischoff A Biswas N Blazey G Blessing S Boehnlein A Bojko NI Borcherding F Borders J Boswell C Brandt A Brock R Bross A Buchholz D Burtovoi VS Butler JM Callot O Casey D Castilla-Valdez H 《Physical review letters》1995,74(18):3548-3552
998.
999.
Alexopoulos T Allen C Anderson EW Balamurali V Banerjee S Beery PD Bhat P Bishop JM Biswas NN Bujak A Carmony DD Carter T Choi Y Cole P DeBonte R DeCarlo V Erwin AR Findeisen C Goshaw AT Gutay LJ Hirsch AS Hojvat C Jennings JR Kenney VP Lindsey CS Loomis C LoSecco JM McMahon T McManus AP Morgan NK Nelson K Oh SH Porile NT Reeves D Rimai A Robertson WR Scharenberg RP Stampke SR Stringfellow BC Thompson MA Turkot F Walker WD Wang CH Warchol J Wesson DK Zhan YH 《Physical review D: Particles and fields》1993,48(5):1931-1942
1000.