scholarly journals Resolution of P-Sterogenic 1-Phenylphosphin-2-en-4-one 1-Oxide into Two Enantiomers by (R,R)-TADDOL and Conformational Diversity of the Phosphinenone Ring and TADDOL in the Crystal State

Molecules ◽  
2021 ◽  
Vol 26 (22) ◽  
pp. 6873
Author(s):  
Elżbieta Łastawiecka ◽  
Adam Włodarczyk ◽  
Anna E. Kozioł ◽  
Hanna Małuszyńska ◽  
Kazimierz Michał Pietrusiewicz
Keyword(s):  
Structural Analysis ◽  
Conformational Changes ◽  
Flash Chromatography ◽  
Ligand Molecule ◽  
X Ray Crystallography ◽  
Conformational Diversity ◽  
Chemical Correlation ◽  
The Absolute ◽  
The Individual ◽  
Diastereomeric Complexes

The resolution of racemic 1-phenylphosphin-2-en-4-one 1-oxide (2), was achieved through the fractional crystallization of its diastereomeric complexes with (4R,5R)-(−)-2,2-dimethyl -α,α,α′,α′-tetraphenyl-dioxolan-4,5-dimethanol (R,R-TADDOL) followed by the liberation of the individual enantiomers of 2 by flash chromatography on silica gel columns. The resolution process furnished the two enantiomers of 2 of 99.1 and 99.9% e.e. at isolated yields of 62 and 59% (counted for the single enantiomer), respectively. The absolute configurations of the two enantiomers were established by means of X-ray crystallography of their diastereomerically pure complexes, i.e., (R)-2•R,R)-TADDOL and (S)-2•(R,R)-TADDOL. The structural analysis revealed that in the (R)-2•(R,R)-TADDOL complex, the P-phenyl substituent occupied a pseudoequatorial position, whereas in (S)-2•(R,R)-TADDOL, it appeared in both the pseudoequatorial and the pseudoaxial positions in four symmetrically independent molecules. Concurrent conformational changes of the TADDOL molecules were best described by the observed changes of a pseudo-torsional CO...OC angle that could be considered as a possible measure of TADDOL conformation in its receptor–ligand complexes. The structural analysis of the (R,R)-TADDOL molecule revealed that efficiency of this compound for use as an effective resolving factor comes from its ability to flexibly fit its structure to both enantiomers of a ligand molecule, producing a rare case of resolution for both pure enantiomers with one chiral separating agent. The resolved (R)-2 was used to assign the absolute configuration of a recently described (−)-1-phenylphosphin-2-en-4-one 1-sulfide by chemical correlation. In addition, an attempted stereoretentive reduction of (R)-2 by PhSiH3 at 60 °C revealed an unexpectedly low barrier for P-inversion in 1-phenylphosphin-2-en-4-one.

Some 6,6-disubstituted 2,4-cyclohexadien-1-ones and the facial selectivity in their Diels–Alder reactions with dimethyl acetylenedicarboxylate

1989 ◽  
Vol 67 (1) ◽  
pp. 37-47 ◽  
Author(s):  
Peter Yates ◽  
Anabela Gomes ◽  
D. Jean Burnell ◽  
Dong Dao Cong ◽  
Jeffery F. Sawyer
Keyword(s):  
Spectroscopic Method ◽  
Diels Alder ◽  
The Other ◽  
Dimethyl Acetylenedicarboxylate ◽  
X Ray ◽  
Product Ratio ◽  
X Ray Crystallography ◽  
Facial Selectivity ◽  
Chemical Correlation ◽  
The Individual

6,6-Disubstituted 2,4-cyclohexadien-1-ones can be prepared by dibromination–bisdehydrobromination of the corresponding 6,6-disubstituted 2,2-dibromocyclohexanones. Such dienes undergo Diels–Alder reactions with dimethyl acetylenedicarboxylate to give 3,3-disubstituted 5,6-di(methoxycarbonyl)bicyclo[2.2.2]octa-5,7-dien-2-ones; when the substituents at C-6 in the dienones are different, two diastereomers of the adducts are formed in a ratio dependent on the "facial selectivity" in the Diels–Alder reactions. For the cases where one of the 6-substituents is methyl and the other is methoxycarbonyl, acetoxymethyl, dibromomethyl, or dichloromethyl it has been established via X-ray crystallography and chemical correlation that the endo-3-methyl/exo-3-methyl product ratio is 3.0, 0.9, 8, and 6, respectively. The origin of these differences is discussed briefly and a spectroscopic method for the assignment of structures to the individual diastereomers is proposed. Keywords: Diels–Alderreactions, substituted 2,4-cyclohexadien-1-ones, facial selectivity, dimethyl acetylenedicarboxylate.

Absolute configuration at C(20) of the derivatives of 21-nor-5α-cholane-20,24-diol

1980 ◽  
Vol 45 (9) ◽  
pp. 2443-2451
Author(s):  
Vladimír Pouzar ◽  
Miroslav Havel
Keyword(s):  
Absolute Configuration ◽  
Side Chain ◽  
Chemical Correlation ◽  
The Absolute ◽  
Derivatives Of

Derivatives of 21-nor-5α-cholane-20,24-diol XI and XIX were prepared by stepwise construction of the side-chain in the position 17β. Their absolute configuration at C(20) was determined on the basis of chemical correlation with the derivatives of 21-nor-5α-cholan-20-ol, XVI and XXIV. The absolute configuration of alcohols XVI and XXIV was determined from the ratio of the yields in which they are formed during the reduction of ketone X and using the benzoate rule. To compounds XI-XVIII the configuration 20R and to compounds XIX-XXVI the configuration 20S has been assigned.

scholarly journals A structural framework for unidirectional transport by a bacterial ABC exporter

2020 ◽  
Vol 117 (32) ◽  
pp. 19228-19236
Author(s):  
Chengcheng Fan ◽  
Jens T. Kaiser ◽  
Douglas C. Rees
Keyword(s):  
Conformational Changes ◽  
Iron Homeostasis ◽  
Atp Hydrolysis ◽  
Transmembrane Helix ◽  
Reverse Direction ◽  
Conformational States ◽  
X Ray Crystallography ◽  
Binding Domains ◽  
Structural Framework ◽  
Glutathione Derivatives

The ATP-binding cassette (ABC) transporter of mitochondria (Atm1) mediates iron homeostasis in eukaryotes, while the prokaryotic homolog fromNovosphingobium aromaticivorans(NaAtm1) can export glutathione derivatives and confer protection against heavy-metal toxicity. To establish the structural framework underlying theNaAtm1 transport mechanism, we determined eight structures by X-ray crystallography and single-particle cryo-electron microscopy in distinct conformational states, stabilized by individual disulfide crosslinks and nucleotides. AsNaAtm1 progresses through the transport cycle, conformational changes in transmembrane helix 6 (TM6) alter the glutathione-binding site and the associated substrate-binding cavity. Significantly, kinking of TM6 in the post-ATP hydrolysis state stabilized by MgADPVO4eliminates this cavity, precluding uptake of glutathione derivatives. The presence of this cavity during the transition from the inward-facing to outward-facing conformational states, and its absence in the reverse direction, thereby provide an elegant and conceptually simple mechanism for enforcing the export directionality of transport byNaAtm1. One of the disulfide crosslinkedNaAtm1 variants characterized in this work retains significant glutathione transport activity, suggesting that ATP hydrolysis and substrate transport by Atm1 may involve a limited set of conformational states with minimal separation of the nucleotide-binding domains in the inward-facing conformation.

scholarly journals Unusual Conformational Changes in 6-Hydroxymethyl-7,8-dihydropterin Pyrophosphokinase as Revealed by X-ray Crystallography and NMR

2001 ◽  
Vol 276 (43) ◽  
pp. 40274-40281 ◽  
Author(s):  
Bing Xiao ◽  
Genbin Shi ◽  
Jinhai Gao ◽  
Jaroslaw Blaszczyk ◽  
Qin Liu ◽  
...  
Keyword(s):  
Conformational Changes ◽  
X Ray ◽  
X Ray Crystallography

scholarly journals Failure to collectively assess security surveillance technologies will inevitably lead to an absolute surveillance society.

2013 ◽  
Vol 12 (1) ◽  
pp. 73-88 ◽  
Author(s):  
Timothy Mitchener-Nissen
Keyword(s):  
New Technology ◽  
Security Technology ◽  
Security Technologies ◽  
Small Rise ◽  
The Absolute ◽  
Waking Up ◽  
Surveillance Society ◽  
The Individual ◽  
Security Surveillance ◽  
The Impact

When assessing any security technology which impacts upon privacy, whether this constitutes a new technology or the novel application of existing technologies, we should do so by examining the combined effect of all security interventions currently employed within a society. This contrasts with the prevailing system whereby the impact of a new security technology is predominantly assessed on an individual basis by a subjective balancing of the security benefits of that technology against any reductions in concomitant rights, such as privacy and liberty. I contend that by continuing to focus on the individual effect, as opposed to the combined effects, of security technologies within a society the likelihood of sleep-walking into (or indeed waking-up in) an absolute surveillance society moves from a possible future to the logically inevitable future. This conclusion is based on two underlying assertions. Firstly that assessing a technology often entails a judgement of whether any loss in privacy is legitimised by a justifiable increase in security; however one fundamental difference between these two rights is that privacy is a finite resource with identifiable end-states (i.e. absolute privacy through to the absolute absence of privacy) whereas security does not have two finite end-states (while there exists the absolute absence of security, absolute security is an unobtainable yet desired goal). The second assertion, which relies upon the validity of the first, holds that one consequence of absolute security being unobtainable yet desirable is that new security interventions will continuously be developed, each potentially trading a small measure of privacy for a small rise in security. Examined individually each intervention may constitute a justifiable trade-off. However this approach of combining interventions in the search for ever greater security will ultimately reduce privacy to zero.

scholarly journals Hegelian Phenomenology of Spirit and Boxing Fight

2018 ◽  
Vol 77 (1) ◽  
pp. 48-54
Author(s):  
Jerzy Kosiewicz
Keyword(s):  
The Body ◽  
Special Role ◽  
Collective Consciousness ◽  
Phenomenology Of Spirit ◽  
Human Individual ◽  
The Subject ◽  
The Absolute ◽  
Low Culture ◽  
The Individual ◽  
Absolute Synthesis

Abstract In the presented text the author points out to anthropological as well as axiological foundations of the boxing fight from the viewpoint of Hegel’s philosophy. In the genial idealist’s views it is possible to perceive the appreciation of the body, which constitutes a necessary basis for the man’s physical activity, for his work oriented towards the self-transformation and the transformation of the external world, as well as for rivalry and the hand-to-hand fight. While focusing our attention on the issue of rivalry and on the situation of the fight - and regarding it from the viewpoint of the master - slave theory (included in the phenomenology of spirit), it is possible to proclaim that even a conventionalised boxing fight - that is, restricted by cultural and sports rules of the game - has features of the fight to the death between two Hegelian forms of selfknowledge striving for self-affirmation and self-realisation. In the boxing fight, similarly as in the above mentioned Hegelian theory, a problem of work and of the development of the human individual (that is, of the subject, self-knowledge, the participant of the fight) appears. There appears also a prospect of death as a possible end of merciless rivalry. The fight revalues the human way in an important way, whereas the prospect for death, the awareness of its proximity, the feeling that its close and possible, saturates the life with additional values. It places the boxer, just like every subject fighting in a similar or a different way, on the path towards absolute abstraction - that is, it brings him closer to his self-fulfilment in the Absolute, to the absolute synthesis. The Hegelian viewpoint enables also to appreciate the boxing fight as a manifestation of low culture (being in contrast with high culture), to turn attention to the relations which - according to Hegel - take place between the Absolute and the man, as well as to show which place is occupied by the subject both in the process of the Absolute’s self-realisation and in the German thinker’s philosophical system. Independently of the dialectical, simultaneously pessimistic and optimistic overtone of considerations connected with the very boxing fight (regarding destruction and spiritualisation on a higher level), it is possible to perceive farreaching appreciation of the human individual in Hegel’s philosophy since the Absolute cannot make its own self-affirmation without the individual, without the human body, without the fight aimed at the destruction of the enemy and without the subjective consciousness and the collective consciousness which appear thanks to this fight. Thus, it is justified to suppose that the foundation of the whole Hegel’s philosophy is constituted by anthropology and that in the framework of this anthropology a special role is played by the fight and by work, which changes the subject and his(her) environment. Admittedly Hegel does not emphasise it explicitly, nevertheless his views (with their centre, which, according to Hegel himself and his interpreters, is constituted by the Absolute) have, as a matter of fact, an anthropocentric character and the main source of the subject’s development is the struggle which, irrespectively of its result, always primarily leads to the destruction or even to the death of one of the sides, just like in the boxing fight. However, it is also a germ of the positive re-orientation of the subject, the beginning and a continuation of that what the phenomenology of the spirit describes as a movement towards absolute abstraction.

Finding the best-fit background function for whole-powder-pattern fitting using LASSO combined with tree search

2021 ◽  
Vol 54 (2) ◽  
Author(s):  
Hideo Toraya
Keyword(s):  
Linear Regression Analysis ◽  
Powder Pattern ◽  
Tree Search ◽  
Data Set ◽  
Tree Structures ◽  
Root Node ◽  
X Ray Crystallography ◽  
Pattern Decomposition ◽  
The Individual ◽  
Best Fit

A new linear function for modelling the background in whole-powder-pattern fitting has been derived by applying LASSO (least absolute shrinkage and selection operator) and the technique of tree search. The background function (BGF) consists of terms b n L(2θ/180)−n/2 and b n H(1 − 2θ/180)−n/2 for the low- and high-angle sides, respectively. Some variable parameters of the BGF should be fixed at zero while others should be varied in order to find the best fit for a given data set without inducing overfitting. The LASSO algorithm can automatically select the variables in linear regression analysis. However, it finds the best-fit BGF with a set of adjustable parameters for a given data set while it derives a different set of parameters for a different data set. Thus, LASSO derives multiple solutions depending on the data set used. By regarding the individual solutions from LASSO as nodes of trees, tree structures were constructed from these solutions. The root node has the maximum number of adjustable parameters, P. P decreases with descending levels of the tree one by one, and leaf nodes have just one parameter. By evaluating individual solutions (nodes) by their χ2 index, the best-fit single path from a root node to a leaf node was found. The present BGF can be used simply by varying P in the range 1–10. The BGF thus derived as a final single solution was incorporated into computer programs for Pawley-based whole-powder-pattern decomposition and Rietveld refinement, and the performance of the BGF was tested in comparison with the polynomials currently widely used as the BGF. The present BGF has been demonstrated to be stable and to give an excellent fit, comparable to polynomials but with a smaller number of adjustable parameters and without introducing undulation into the calculated background curve. Basic algorithms used in statistics and machine learning have been demonstrated to be useful in developing an analytical model in X-ray crystallography.

scholarly journals Analysis of the FK5 System in the Equatorial Zone

1995 ◽  
Vol 166 ◽  
pp. 382-382
Author(s):  
Yu.B. Kolesnik
Keyword(s):  
Equatorial Zone ◽  
Motion System ◽  
Area Distribution ◽  
The Sixties ◽  
Hipparcos Catalogue ◽  
The Mean ◽  
The Absolute ◽  
The Individual ◽  
Right Ascension ◽  
Selection Of

15 catalogues produced in the eighties and 12 catalogues of the sixties-seventies have been used to assess the consistency of the FK5 system with observations in the declination zone from −30° to 30°. Positions of the FK4-based catalogues have been transformed at the equinox and equator J2000.0. Classical δ-dependent and α-dependent systematic differences (Cat-FK5) have been formed for individual instrumental systems of the catalogues by a method close to the classical Numerical Method. The weighted mean instrumental systems for the two subsets of catalogues centered at the epochs 1970 (MIS 60–70) and 1987 (MIS 80) and for all types of systematic differences have been constructed. The mean errors of the total systematic differences in α and δ have been estimated as 14 mas and 21 mas, respectively, for the catalogues of the 60-70ies, and 10 mas in both α and δ for the catalogues of the 80ies.It has been found that the mutual consistency of individual instrumental systems of catalogues of the 80ies with respect to δ-dependent systematic differences is superior by the factor 1.5 comparing with the catalogues of 60-70ies, while the consistency of both catalogue selections with respect to α-dependent systematic differences is comparable. Random accuracy of the FK5 positions and proper motions at the epochs under analysis has been assessed as close to expected from the formal considerations. Actual systematic discrepancies of the FK5 with observations at the respective epochs have been detected. For systematic differences δαδ cosδ and δδδ, the absolute deviations of the MIS 80 are, in general, within 40 mas, those of the MIS 60-70 are within 30 mas. For systematic differences δαα cosδ and δδα, the absolute deviations reach 30-40 mas for both MIS. For total systematic differences, local deformations of the FK5 system in the equatorial zone in both right ascension and declination has been found exceeding expected ones from the formal errors of the FK5 system by a factor about 1.5 for the MIS 60-70, and by a factor about 2 for the MIS 80. Consistency in area distribution between both MIS for the total systematic differences δαcosδ has been detected. Quick degradation of the FK5 system with time due to optimistic estimation of the errors of its proper motion system is supposed to be one of the main causes of its discrepancies with observations. The results in declination are recognized to be less reliable due to larger inconsistency of the individual instrumental systems.Before the next space astrometric mission will be realized, ground-based observations will continue to be the only available check of an external systematic accuracy of the HIPPARCOS catalogue. Evidently, random and, possibly, systematic accuracy of each individual catalogue observed from the Earth surface would be inferior to that of the HIPPARCOS catalogue. Taken as an ensemble, however, a certain selection of catalogues might give a rather definite idea about the actual distortions of the HIPPARCOS system. This study shows to which level of accuracy such ensembles of different selections of catalogues might check the HIPPARCOS system in the equatorial zone. The analysis of the FK5 gives also an idea about levels of random and systematic discrepancies which may be expected in the equatorial zone when the HIPPARCOS catalogue will be compared with the FK5 at different epochs.

Sign in / Sign up

Export Citation Format

Share Document