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991.
El-Barbary A. A. El-Brollosy N. R. Pedersen E. B. Nielsen C. 《Monatshefte für Chemie / Chemical Monthly》1995,126(5):593-600
Summary Thieno[2,3-d]pyrimidine-2,4(1H,3H)-dione (4) was silylated and condensed with methyl 5-azido-2,5-dideoxy-3-O-(4-methylbenzoyl)-D-erythro-pentofuranoside (2) in the presence ofTMS triflate to afford the corresponding protected nucleoside6 and acyclic nucleoside7. Deprotection of6 with MeONa/MeOH at room temperature gave 1-(5-azido-2,5-dideoxy--D-erythro-pentofuranosyl)-thieno[2,3-d]pyrimidine-2,4(1H,3H)-dione (8) and the corresponding anomer9, whereas compound7 yielded 5-azido-2,5-dideoxy-1-(2,4-dioxo-1,2,3,4-tetrahydrothieno[2,3-d]pyrimidin-1-yl)-1-O-methyl-D-erythro-pentitol (10) under the same reaction conditions. 1-(5-Amino-2,5-dideoxy--D-erythro-pentofuranosyl)thieno[2,3-d]pyrimidine-2,4(1H,3H)-dione (11) was obtained on treating9 with Ph3P in pyridine followed by hyrolysis with NH4OH. The anomeric nucleosides14 and15 and the corresponding acyclic nucleoside16 were obtained when4 was trimethylsilylated and condensed with methyl 2-deoxy-3,5-di-O-(4-methylbenzoyl)-D-erythro-pentofuranoside (3) followed by deprotection with MeONa in MeOH. Compounds8 and9 were also obtained when the anomeric mixture14/15 was treated with a mixture of NaN3, Ph3P, and CBr4 in dryDMF at room temperature.On leave from Chemistry Department, Faculty of Science, Tanta University, Tanta, Egypt 相似文献
992.
Salting effects of metal chelate electrolytes Fe(phen)3Br2, Fe(bpy)3Br2, Co(phen)3Br2, Co(phen)3Br3, Co(en)3Br3, and Co(pn)3Br3 (where phen=1,10-phenanthroline, bpy=2,2-bipyridyl, en=ethylenediamine, and pn=1,2-propylenediamine) on the solubilities of nitrobenzene,o-,m-,and p-dinitrobenzenes (DNB), and toluene were studied in water at 25°C and compared to the results for sodium bromide and tetrabutylammonium bromide (Bu4NBr). The Co(phen)
3
3+
, Fe(phen)
3
2+
, and Fe(bpy)
3
2+
ions showed much stronger salting-in effects than did the Bu4N+ ion, while the effects of the Co(en)
3
3+
and Co(pn)
3
3+
ions are comparable with those of Bu4N+. A great dependence of salting-in on the polarity of dinitrobenzene isomers was found for Co(phen)
3
3+
and Fe(phen)
3
2+
. The results were related to the partial molal volume of the respective cations. The very strong salting-in was considered to be mainly due to hydrophobic hydrations of the metal chelate cations and partly due to van der Waals interactions between the aromatic ligands and the nonelectrolytes. The small salting-in effects by Co(en)
3
3+
and Co(en)
3
3+
were interpreted in terms of hydrogen bonding between oxygen atoms of the nitro compounds or the solvent water molecules and hydrogen atoms attached to nitrogens in the complexes. 相似文献
993.
994.
Gregory Gutin 《Journal of Graph Theory》2016,82(3):233-235
A spanning subgraph F of a graph G is called perfect if F is a forest, the degree of each vertex x in F is odd, and each tree of F is an induced subgraph of G. We provide a short linear‐algebraic proof of the following theorem of A. D. Scott (Graphs Combin 17 (2001), 539–553): A connected graph G contains a perfect forest if and only if G has an even number of vertices. 相似文献
995.
Let R be a unital *-ring with the unit I.Assume that R contains a symmetric idempotent P which satisfies ARP = 0 implies A = 0 and AR(I-P) = 0 implies A = 0.In this paper,it is shown that a surjective map Φ:R→R is strong skew commutativity preserving(that is,satisfiesΦ(A)Φ(B)-Φ(B)Φ(A)~w= AB-BA~w for all A,B∈R) if and only if there exist a map f:R→Z_s(R)and an element Z∈Z_s(R) with Z~2=I such that Φ(A)=ZA +f(A) for all A∈R,where Z_s(R) is the symmetric center of R.As applications,the strong skew commutativity preserving maps on unital prime *-rings and von Neumann algebras with no central summands of type I_1 are characterized. 相似文献
996.
Driss AIAT HADJ AHMED 《数学研究及应用》2016,36(2):162-170
Let $R$ and $S$ be rings with identity, $M$ be a unitary $(R,S)$-bimodule and $T=\left(\begin{array}{cc}R & M \\ 0 & S\end{array}\right) $ be the upper triangular matrix ring determined by $R$, $S$ and $M$. In this paper we prove that under certain conditions a Jordan biderivation of an upper triangular matrix ring $T$ is a biderivation of $T$. 相似文献
997.
998.
The main purpose of this paper is to prove the following result. Let H be a complex Hilbert space, let (H) be the algebra of all bounded linear operators on H, and let (H) ⊂ (H) be a standard operator algebra which is closed under the adjoint operation. Suppose that T: (H) → (H) is a linear mapping satisfying T(AA* A) = T(A)A* A − AT(A*)A + AA*T(A) for all A ∈ (H). Then T is of the form T(A) = AB + BA for all A ∈ (H), where B is a fixed operator from (H). A result concerning functional equations related to bicircular projections is proved
相似文献
999.
The [ReOX2(hbt)(EPh3)] (X = Cl, Br; E = As, P) chelates have been prepared in the reactions of [ReOX3(EPh3)2] complexes (X = Cl, Br; E = P, As) with 2-(2′-hydroxyphenyl)-2-benzothiazole (hbtH) in acetone. From the reactions of [ReOX3(PPh3)2] with hbtH two kind of crystals [ReOX2(hbt)(PPh3)] · MeCN and [ReOX2(hbt)(PPh3)] with different arrangement of halide ions (cis and trans) were isolated, whereas the [ReOX3(AsPh3)2] oxocompounds react with hbtH to give only cis-halide isomers. The complexes were structurally and spectroscopically characterised. The electronic structures of both [ReOBr2(hbt)(PPh3)] isomers have been calculated with the density functional theory (DFT) method. The TDDFT/PCM calculations have been employed to produce a hundred of singlet excited-states starting from the ground-state geometry optimized in the gas phase of cis- and trans-halide isomers of [ReOBr2(hbt)(PPh3)] and the UV–Vis spectra of these complexes have been discussed on this basis. 相似文献
1000.