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131.
T. Sudhakar Rao Ganapathi R. Revankar Ravi S. Vinayak Roland K. Robins 《Journal of heterocyclic chemistry》1991,28(7):1779-1788
Several disubstituted pyrazolo[3,4-d]pyrimidine, pyrazolo[1,5-a]pyrimidine and thiazolo[4,5-d]pyrimidine ribonucleosides have been prepared as congeners of uridine and cytidine. Glycosylation of the trimethylsilyl (TMS) derivative of pyrazolo[3,4-d]pyrimidine-4,6(1H,5H,7H)-dione ( 4 ) with 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribofuranose ( 5 ) in the presence of TMS triflate afforded 7-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)pyrazolo-[3,4-d]pyrimidine-4,6(1H,5H)-dione ( 6 ). Debenzoylation of 6 gave the uridine analog 7-β-D-ribofuranosylpyrazolo[3,4-d]pyrimidine-4,6(1H,5H)-dione ( 3 ), identical with 7-ribofuranosyloxoallopurinol reported earlier. Thiation of 6 gave 7 , which on debenzoylation afforded 7-β-D-ribofuranosyl-6-oxopyrazolo[3,4-d]pyrimidine-4(1H,5H)-thione ( 8 ). Ammonolysis of 7 at elevated temperature gave a low yield of the cytidine analog 4-amino-7-β-D-ribofuranosylpyrazolo[3,4-d]pyrimidin-6(1H)-one ( 11 ). Chlorination of 6 , followed by ammonolysis, furnished an alternate route to 11 . A similar glycosylation of TMS-4 with 2,3,5-tri-O-benzyl-α-D-arabinofuranosyl chloride ( 12 ) gave mainly the N7-glycosylated product 13 , which on debenzylation provided 7-β-D-arabinofuranosylpyrazolo[3,4-d]pyrimidine-4,6(1H,5H)-dione ( 14 ). 4-Amino-7-β-D-arabinofuranosyl-pyrazolo[3,4-d]pyrimidin-6(1H)-one ( 19 ) was prepared from 13 via the C4-pyridinium chloride intermediate 17 . Condensation of the TMS derivatives of 7-hydroxy- ( 20 ) or 7-aminopyrazolo[1,5-a]pyrimidin-5(4H)-one ( 23 ) with 5 in the presence of TMS triflate gave the corresponding blocked nucleosides 21 and 24 , respectively, which on deprotection afforded 7-hydroxy- 22 and 7-amino-4-β-D-ribofuranosylpyrazolo[1,5-a]pyrimidin-5-one ( 25 ), respectively. Similarly, starting either from 2-chloro ( 26 ) or 2-aminothiazolo[4,5-d]pyrimidine-5,7-(4H,6H)-dione ( 29 ), 2-amino-4-β-D-ribofuranosylthiazolo[4,5-d]pyrimidine-5,7(6H)-dione ( 28 ) has been prepared. The structure of 25 was confirmed by single crystal X-ray diffraction studies. 相似文献
132.
Jayachander Rao B Mahapatra S Köppel H Jungen M 《The Journal of chemical physics》2005,123(13):134325
The static and dynamic aspects of the Jahn-Teller (JT) interactions in the 3p(E') and 3d(E") Rydberg electronic states of H3 are analyzed theoretically. The static aspects are discussed based on recent ab initio quantum chemistry results, and the dynamic aspects are examined in terms of the vibronic spectra and nonradiative decay behavior of these states. The adiabatic potential-energy surfaces of these degenerate electronic states are derived from extensive ab initio calculations. The calculated adiabatic potential-energy surfaces are diabatized following our earlier study on this system in its 2p(E') ground electronic state. The nuclear dynamics on the resulting conically intersecting manifold of electronic states is studied by a time-dependent wave-packet approach. Calculations are performed both for the uncoupled and coupled state situations in order to understand the importance of nonadiabatic interactions due to the JT conical intersections in these excited Rydberg electronic states. 相似文献
133.
McArdle CP Jennings MC Vittal JJ Puddephatt RJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(16):3572-3583
Reaction of the flexible dialkynyldigold(I) precursors X(4-C6H4OCH2C-CAu)2 with 1,4-bis(diphenylphosphino)butane gave complexes of formula [[[mu-X(4-C6H4OCH2CCAu)2[mu-(Ph2PCH2CH2CH2CH2PPh2)]]n]. The complexes exist as 25-membered ring compounds with n = 1 when X = O or S, as [2]catenanes with n = 2 when X = CH2 or CMe2, and as a unique doubly braided [2]catenane, containing interlocked 50-membered rings with n = 4 when X = cyclohexylidene. These compounds form easily and selectively by self-assembly; reasons for the selectivity are also discussed. 相似文献
134.
135.
V. R. S. Rao G. Erdtmann H. Petri 《Journal of Radioanalytical and Nuclear Chemistry》1989,135(4):257-264
The extent of exchange of bromine-82 with bromamine-T in strong acid medium is low due to the formation of
at lower acid concentrations and bromine at higher acidities.
formation occurs over a narrow acid concentration range and is less stable than
. 相似文献
136.
A simple potentiometric method is presented for successive determination of iron(III) and cobalt(II) by complexometric titration of the iron(III) with EDTA at pH 2 and 40 degrees , followed by redox titration of the cobalt(II) complex with 1,10-phenanthroline or 2,2'-bipyridyl at pH 4-5 and 40 degrees , with gold(III). There is no interference in either determination from common metal ions other than copper(II), which severely affects the cobalt determination but can be removed by electrolysis. The method has been successfully applied to determination of iron and cobalt in Kovar and Alnico magnet alloys. 相似文献
137.
Maciej Adamczyk Srinivasa Rao AkireddyPhillip G Mattingly Rajarathnam E Reddy 《Tetrahedron》2003,59(30):5749-5761
A total of 11 novel phosphoramidites, 3a-d, 4a-d and 14a-c were prepared from 2′-deoxyuridine functionalized at 5 and 6-position of the pyrimidine ring with hapten reporter groups, e.g. adamantane, carbazole, dansyl and dabsyl, suitable for use in immunodetection nucleic acid testing assays. 相似文献
138.
D. Maitraie V.V.V.N.S. Rama Rao B. Narsaiah P. Shanthan Rao B. Sridhar 《Tetrahedron》2005,61(16):3999-4008
Synthesis of novel-2,3-bifunctionalised indole regioisomers (2/3 and 6/7) from unsymmetrical dicyanoanilines 1 by regioselective cyclization in two independent ways. Regioisomers 6 are further utilized in synthesis of novel 4,5-dihydro[1,3]oxazino[5,4-b] indole-6-carbonitriles 9. 相似文献
139.
Alex. G. Harrison R. Krishna Mohan Rao Kallury 《Journal of mass spectrometry : JMS》1980,15(6):284-288
The H2 and CH4 chemical ionization mass spectra of a selection of substituted nitrobenzenes have been determined. It is shown that reduction of the nitro group to the amine is favoured by high source temperatures and the presence of water in the ion source. The H2 chemical ionization mass spectra are much more useful for distinguishing between isomeric compounds than the CH4 CI mass spectra because of the more extensive fragmentation. For ortho substituents bearing a labile hydrogen abundant [MH ? H2O]+ fragments are observed. When the substituent is electron-releasing both ortho and para substituted nitrobenzenes show abundant [MH? OH]+ fragment ions while meta substituted compounds show abundant loss of NO and NO2 from [MH]+. The latter fragmentation is interpreted in terms of protonation para to the substituent or ortho to the vitro function, while the first two fragmentation routes arise from protonation at the nitro group. When the substituent is electron-attracting the chemical ionization mass spectra of isomers are very similar except for the H2O loss reaction for ortho compounds. 相似文献
140.
Sai Chodavarapu Seshatalpa Hela Pamidipati Gayatri Sridhar Yeleswarapu Anipindi Nageswara Rao 《Transition Metal Chemistry》1998,23(3):249-252
The reaction of the Cr(xx)2(H2O)2
− (xx = oxalate, malonate and methylmalonate) complexes with dissolved CO2 was studied by stopped-flow spectrophotometry in the 7 < pH < 9 range and between 20 to 30°C at an ionic strength of 0.5
mol dm−3 (NaCl). Under the experimental conditions the aqua complex ion consists of a pH-dependent mixture of Cr(xx)2(H2O)2
−, Cr(xx)2(OH) (H2O)2− and Cr(xx)2(OH)2
3−. The monohydroxo and dihydroxo species undergo CO2 uptake and subsequent intramolecular carbonate ligand chelation independently, at rates which are readily distinguishable
and are governed by the uptake rate constants k
1 and k
2 and chelation rate constants k
3 and k
4, respectively. Only the k
1 values for oxalato, malonato and methylmalonato complexes could be calculated; k
1 = 1084 and 1333 and 1650 mol−1 dm3 s−1, respectively. The results obtained were compared with those obtained from other systems that have either cobalt(III), iridium(III)
or rhodium(III) as central atoms.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献