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211.
212.
A method for preparative production of 3β,20S-dihydroxydammar-24-en-12-one 3,20-di-O-β-D-glucopyranoside (1), a glycoside from Panax japonicus, chikusetsusaponin-LT8 was developed. Chemical transformation of betulafolientriol, a component of Betula leaves extract, produced the 12-keto-20S-protopanaxadiol (3β,20S-dihydroxydammar-24-en-12-one) (2), exhaustive glycosylation of which by 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosylbromide (3) under Koenigs—Knorr reaction conditions with subsequent removal of protecting groups formed 3β,20S-dihydroxydammar-24-en-12-one
3,20-di-O-β-D-glucopyranoside (1). The principal glycosylation product was 3β,20S-dihydroxydammar-24-en-12-one 3-O-β-D-glucopyranoside if equimolar amounts of (2) and (3) were used.
__________
Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 44–48, January–February, 2006. 相似文献
213.
In this work, some results related to superatomic Boolean interval algebras are presented, and proved in a topological way. Let x be an uncountable cardinal. To each I
x, we can associate a superatomic interval Boolean algebra B
I of cardinality x in such a way that the following properties are equivalent: (i) I
I
x, (ii) B
I is a quotient algebra of B
J, and (iii) there is an homomorphism f from B
J into B
I such that for every atom b of B
I, there is an atom a of B
J satisfying f(a)=b. As a corollary, there are 2
x
isomorphism types of superatomic interval Boolean algebras of cardinality x. This case is quite different from the countable one. 相似文献
214.
A. M. Vinogradov 《Acta Appl Math》1986,5(2):169-180
First we propose a model of visual perception essentially based on the Keldysh-Chernavsky-Sossinsky three-channel theorem, from which three-dimensionality of space follows. Second, we associate with a system of subgroups H
1, ..., Hs of a given group G a geometric object, called a group crystal, in order to visualize G. How this notion works is illustrated via the Burnside problem. 相似文献
215.
Summary Under suitable conditions, we prove the convergence of the Bateman method for integral equations defined over bounded domains inR
d
,d1. The proof makes use of Hilbert space methods, and requires the integral operator to be non-negative definite. For one-dimensional integral equations over finite intervals, estimated rates of convergence are obtained which depend on the smoothness of the kernel, but are independent of the inhomogeneous term. In particular, for aC
kernel andn reasonably spaced Bateman points, the convergence is shown to be faster than any power of 1/n. Numerical calculations support this result. 相似文献
216.
HIV infection leads to progressive alterations of humoral immune functions, including B-cell hyperplasia, hypergammaglobulinemia,
elevated autoantibody titers, a poor response to neoantigens and mitogens, polyclonal B-cell activation, monoclonal gammopathies,
and a significant deterioration of the antigen-specific humoral response. There is also an important isotypic imbalance of
the antibody (Ab) response in the systemic compartment and a profound modification of mucosal immune functions. These abnormalities
may contribute to disease progression and development of opportunistic infections, despite the presence of serum-neutralizing
anti-HIV Abs. Equally important are the abnormal selection mechanisms of the Ab repertoire that seem to be responsible for
B-cell clonal deletions. The VH3 gene family, which encodes for approx 50% of immunoglobulins expressed by peripheral B-cells from normal adults, is underrepresented
in human monoclonal antibodies to HIV-1 and in the peripheral B-cells of AIDS patients. These abnormalities, together with
features of germinal center alteration, could be responsible for the clonal elimination of a subset of B-cells, and could
contribute to HIV pathogenesis. 相似文献
217.
两个具有特殊骨架的C_(20)-二萜生物碱北乌灵(kusnezoline)和峨翠灵( omeieline)分别分自中国特产毛茛科植物北草乌(Aconitum hkusnezoffii Paritz)、彭州岩乌头(A. racemulosum var. pengzhouense)和峨眉翠雀花( Delphinium omeiense W. T. Wang)。应用2D NMR技术(~1H-~1H COSY, HMQC, HMBC, NOESY)全面归属了这两个生物碱的~1H和~(13)C信号的化学位移。 相似文献
218.
219.
Odinokov V. N. Galyautdinov I. V. Nedopekin D. V. Khalilov L. M. 《Russian Chemical Bulletin》2003,52(1):232-236
Orifluoroacetylation of the 25(OH)-group with subsequent dehydration of the 14(OH)-group takes place in the reaction of 20-hydroxyecdysone 20,22-acetonide and 2,3:20,22-diacetonide with trifluoroacetic anhydride in the presence of pyridine. Dehydration of the 14(OH)-group gives rise to stachisterone B derivatives, which are hydrolyzed to give the phytoecdysteroid stachisterone B. 相似文献
220.
Pentacoordinate complex cations of the general formula [(C6F5)2SbL3]3+ stabilized as solid salts in combination with tetraphenylborate (BPh4), tetrafluorobroate (BF4) anions, where L=DMSO, Ph3AsO, PyO, DMF, α-, β- and γ-picoline have been isolated. The newly formed complexes were characterized by elemental analysis, molar conductance measurements, solid-state IR and and NMR. From these results, a five-fold coordination around antimony was required. 相似文献