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Simple Analogues (simple + analogue)

Distribution by Scientific Domains

Chemistry	77%

Selected Abstracts

Synthesis and in vitro Antimalarial Activity of Several Simple Analogues of Peroxyplakoric Acid

CHINESE JOURNAL OF CHEMISTRY, Issue 11 2005
He-Hua Liu
Abstract Several simple analogues of peroxyplakoric acid were synthesized by using Kobayashi's method to construct the key 1,2-dioxane core and tested in vitro for antimalarial activity. The scope and limitation of the method was also briefly examined. [source]

On the equivalence between Kalman smoothing and weak-constraint four-dimensional variational data assimilation

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 613 2005
M. Fisher
Abstract The fixed-interval Kalman smoother produces optimal estimates of the state of a system over a time interval, given observations over the interval, together with a prior estimate of the state and its error covariance at the beginning of the interval. At the end of the interval, the Kalman smoother estimate is identical to that produced by a Kalman filter, given the same observations and the same initial state and covariance matrix. For an imperfect model, the model error term in the covariance evolution equation acts to reduce the dependence of the estimate on observations and prior states that are well separated in time. In particular, if the assimilation interval is sufficiently long, the estimate at the end of the interval is effectively independent of the state and covariance matrix specified at the beginning of the interval. In this case, the Kalman smoother provides estimates at the end of the interval that are identical to those of a Kalman filter that has been running indefinitely. For a linear model, weak-constraint four-dimensional variational data assimilation (4D-Var) is equivalent to a fixed-interval Kalman smoother. It follows that, if the assimilation interval is made sufficiently long, the 4D-Var analysis at the end of the assimilation interval will be identical to that produced by a Kalman filter that has been running indefinitely. The equivalence between weak-constraint 4D-Var and a long-running Kalman filter is demonstrated for a simple analogue of the numerical weather-prediction (NWP) problem. For this nonlinear system, 4D-Var analysis with a 10-day assimilation window produces analyses of the same quality as those of an extended Kalman filter. It is demonstrated that the current ECMWF operational 4D-Var system retains a memory of earlier observations and prior states over a period of between four and ten days, suggesting that weak-constraint 4D-Var with an analysis interval in the range of four to ten days may provide a viable algorithm with which to implement an unapproximated Kalman filter. Whereas assimilation intervals of this length are unlikely to be computationally feasible for operational NWP in the near future, the ability to run an unapproximated Kalman filter should prove invaluable for assessing the performance of cheaper, but suboptimal, alternatives. Copyright © 2005 Royal Meteorological Society [source]

The gravitomagnetic clock effect and its possible observation

ANNALEN DER PHYSIK, Issue 12 2006
H. Lichtenegger
Abstract The general relativistic gravitomagnetic clock effect involves a coupling between the orbital motion of a test particle and the rotation of the central mass and results in a difference in the proper periods of two counter,revolving satellites. It is shown that at ,,(c -2) this effect has a simple analogue in the electromagnetic case. Moreover, in view of a possible measurement of the clock effect in the gravitational field of the Earth, we investigate the influence of some classical perturbing forces of the terrestrial space environment on the orbital motion of test bodies along opposite trajectories. [source]

4-Methoxy-1-naphthol: chains formed by O,H...O hydrogen bonds and ,,, stacking interactions

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2009
Bernard Marciniak
The structure of 4-methoxy-1-naphthol, C11H10O2, (I), contains an intermolecular O,H...O hydrogen bond which links the molecules into a simple C(2) chain running parallel to the shortest crystallographic b axis. This chain is reinforced by intermolecular ,,, stacking interactions. Comparisons are drawn between the crystal structure of (I) and those of several of its simple analogues, including 1-naphthol and some monosubstituted derivatives, and that of its isomer 7-methoxy-2-naphthol. This comparison shows a close similarity in the packing of the molecules of its simple analogues that form ,-stacks along the shortest crystallographic axes. A substantial spatial overlap is observed between adjacent molecules in such stacks. In this group of monosubstituted naphthols, the overlap depends mainly on the position of the substituents carried by the naphthalene moiety, and the extent of the overlap depends on the substituent type. By contrast with (I), in the crystal structure of the isomeric 7-methoxy-2-naphthol there are no O,H...O hydrogen bonds or ,,, stacking interactions, and sheets are formed by O,H..., and C,H..., interactions. [source]

5-Amino-1-naphthol: two-dimensional sheets built up from R44(18) rings formed by O,H...N, N,H...O and ,,, interactions

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2009
Ewa Rozycka-Sokolowska
The crystal structure of the title compound, C10H9NO, (I), contains intermolecular O,H...N and N,H...O hydrogen bonds which together form sheets parallel to the (001) plane containing rings with an unusual R44(18) motif. These rings are additionally stabilized by an intermolecular ,,, stacking interaction. The significance of this study lies in the comparison drawn between the molecular structure of (I) and those of related compounds (1,5-diaminonaphthalene, 8-amino-2-naphthol, 3-amino-2-naphthol and aniline), which shows a close similarity in the noncoplanar orientation of the amine group and the aromatic moiety. Comparison of the crystal structures of (I) and several of its simple analogues (1-naphthol, naphthalene-1,4-diol, naphthalene-1,5-diol and 4-chloro-1-naphthol) shows a close similarity in the packing of the molecules, which form ,-stacks along the shortest crystallographic axes with a substantial spatial overlap between adjacent molecules. [source]

4-Chloro-1-naphthol

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2009
Ewa Rozycka-Sokolowska
Molecules of the title compound, C10H7ClO, (I), are connected by a single strong O,H...O hydrogen bond into a simple C(2) chain, which runs parallel to the c axis and is additionally stabilized by intermolecular ,,, stacking interactions. The significance of this study lies in the comparison drawn between the crystal structure of (I) and those of several of its simple analogues. This comparison shows a close similarity in the packing of the molecules that form ,-stacks along the shortest crystallographic axes. A substantial spatial overlap is observed between adjacent molecules in such a ,-stack, depending mainly on the kind of substituent. [source]

Simplified Synthetic TMC-95A/B Analogues Retain the Potency of Proteasome Inhibitory Activity

CHEMBIOCHEM, Issue 6 2003
Zhi-Qiang Yang Dr.
Abstract The proteasome regulates diverse intracellular processes, including cell-cycle progression, antigen presentation, and inflammatory response. Selective inhibitors of the proteasome have great therapeutic potential for the treatment of cancer and inflammatory disorders. Natural cyclic peptides TMC-95A and B represent a new class of noncovalent, selective proteasome inhibitors. To explore the structure,activity relationship of this class of proteasome inhibitors, a series of TMC-95A/B analogues were prepared and analyzed. We found that the unique enamide functionality at the C8 position of TMC-95s can be replaced with a simple allylamide. The asymmetric center at C36 that distinguishes TMC-95A from TMC-95B but which necessitates a complicated separation of the two compounds can be eliminated. Therefore, these findings could lead to the development of more accessible simple analogues as potential therapeutic agents. [source]

Synthesis of 1,2-Dioxane Type Antimalarial Peroxides,

CHINESE JOURNAL OF CHEMISTRY, Issue 9 2006
He-Hua Liu
Abstract Synthesis of five simple analogues of peroxyplakoric acid by using Kobayashi,s method to construct the key 1,2-dioxane core is detailed. [source]