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931.
A concise enantioselective total synthesis of 4'-ethynyl-2-fluoro-2'-deoxyadenosine (EFdA), an extremely potent anti-HIV agent, has been accomplished from (R)-glyceraldehyde acetonide in 18% overall yield by a 12-step sequence involving a highly diastereoselective ethynylation of an α-alkoxy ketone intermediate. 相似文献
932.
Miyagawa T Nagai K Yamada A Sugihara Y Fukuda T Fukuda T Uchida R Tomoda H Omura S Nagamitsu T 《Organic letters》2011,13(5):1158-1161
The first total synthesis of citridone A has been achieved through regioselective intramolecular iodocyclization and regio- and stereoselective Pd(0)-catalyzed coupling as key reactions. 相似文献
933.
In 3-ethoxycarbonyl-2,4-dienal compounds, a thermal [1,5]-H shift of aldehyde hydrogen easily proceeded to produce the corresponding vinyl ketenes due to the remarkable substituent effect caused by the C3 ester group. The produced ketenes were captured by an alcohol and olefins to afford the corresponding esters and four-membered ring compounds, respectively. 相似文献
934.
The direct arylation on the thienyl groups of a diarylethene with various aryl iodides efficiently provided arylated dithienylethenes under palladium catalysis. Unsymmetrically substituted dithienylethenes were also synthesized by this protocol. This procedure allows a rapid access to a variety of aryl-substituted dithienylethenes from a single substrate of a simple dithienylethene. 相似文献
935.
Ogawa T Hattori H Kaneko R Ito K Iwai M Mizutani Y Arinobu T Ishii A Seno H 《Analytical and bioanalytical chemistry》2011,400(7):1959-1965
In this report, a high-throughput and sensitive method for analysis of eight central-acting muscle relaxants in human plasma
by ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) in the positive and negative ionization modes
using tolbutamide as internal standard is presented. After pretreatment of a plasma sample by solid-phase extraction with
an Oasis HLB cartridge, muscle relaxants were analyzed by UPLC with Acquity UPLC BEH C18 column and Acquity TQD tandem quadrupole mass spectrometer equipped with an electrospray ionization interface. The calibration
curves for muscle relaxants spiked into human plasma equally showed good linearities in the nanogram per milliliter order
range. The detection limits (signal-to-noise ratio = 3) was as low as 0.1–2 ng/mL. The method gave satisfactory recovery rates,
accuracy, and precision for quality control samples spiked with muscle relaxants. To further validate the present method,
250 mg of chlorphenesin carbamate was orally administered to a healthy male volunteer, and the concentrations of chlorphenesin
carbamate in plasma were measured 0.5, 1, 2, 4, 6, and 8 h after dosing; their concentrations in human plasma were between
0.62 and 2.44 μg/mL. To our knowledge, this is the first report describing simultaneous analysis of over more than two central-acting
muscle relaxants by liquid chromatography–tandem mass spectrometry. This has been realized by the capability of our instrument
for simultaneous multiple reaction monitoring of the target compounds in both positive and negative ionization modes. Therefore,
the present method seems very useful in forensic and clinical toxicology and pharmacokinetic studies. 相似文献
936.
Let A be an n×n complex matrix and c=(c1,c2,…,cn) a real n-tuple. The c-numerical range of A is defined as the set
937.
For a pair of n×n Hermitian matrices H and K, a real ternary homogeneous polynomial defined by F(t,x,y)=det(tIn+xH+yK) is hyperbolic with respect to (1,0,0). The Fiedler conjecture (or Lax conjecture) is recently affirmed, namely, for any real ternary hyperbolic polynomial F(t,x,y), there exist real symmetric matrices S1 and S2 such that F(t,x,y)=det(tIn+xS1+yS2). In this paper, we give a constructive proof of the existence of symmetric matrices for the ternary forms associated with trigonometric polynomials. 相似文献
938.
The rank-k-numerical range of an n×n matrix A is defined as
939.
A homology cylinder over a surface consists of a homology cobordism between two copies of the surface and markings of its
boundary. The set of isomorphism classes of homology cylinders over a fixed surface has a natural monoid structure and it
is known that this monoid can be seen as an enlargement of the mapping class group of the surface. We now focus on abelian
quotients of this monoid. We show that both the monoid of all homology cylinders and that of irreducible homology cylinders
are not finitely generated and moreover they have big abelian quotients. These properties contrast with the fact that the
mapping class group is perfect in general. The proof is given by applying sutured Floer homology theory to homologically fibered
knots studied in a previous paper. 相似文献
940.
A set of n-principal points of a distribution is defined as a set of n points that optimally represent the distribution in terms of mean squared distance. It provides an optimal n-point-approximation of the distribution. However, it is in general difficult to find a set of principal points of a multivariate distribution. Tarpey et al. [T. Tarpey, L. Li, B. Flury, Principal points and self-consistent points of elliptical distributions, Ann. Statist. 23 (1995) 103-112] established a theorem which states that any set of n-principal points of an elliptically symmetric distribution is in the linear subspace spanned by some principal eigenvectors of the covariance matrix. This theorem, called a “principal subspace theorem”, is a strong tool for the calculation of principal points. In practice, we often come across distributions consisting of several subgroups. Hence it is of interest to know whether the principal subspace theorem remains valid even under such complex distributions. In this paper, we define a multivariate location mixture model. A theorem is established that clarifies a linear subspace in which n-principal points exist. 相似文献