Chirality measures resolution based

In some of the preceding representations, a natural interrelationship between fuzziness and resolution is used, leading to resolution-based chirality, symmetry and similarity measures. ... 

The chirality quantification technique proposed by Harary and Mezey [54,55] is motivated by the Resolution Based Similarity Measure (RBSM) approach used in more general molecular similarity analysis [243]. This method does not rely on a single reference object. Instead, it characterizes shape on any desired finite level of resolution by considering various A(J,n) parts of square lattices, called lattice animals or P(G,n) parts of cubic lattices called polycubes which can be inscribed within the two- or three-dimensional objects J or G, respectively. In the above... 

Molecular Similarity Measures and Chirality Measures Based on Resolution and Fuzzy Set Theory... 

The resolution by the mentioned column chromatography for chiral complexes is based on the interaction between a chiral adsorbent and a chiral eluent. From such a point of view the association constants have been determined for the ion pairs. A- and A-[Co(en)3p with L(+)-tartrate dianion and with L(-i-)-tartratoanti-monate(III) dianion ((+)-tartan), on the basis of CD measurements at two wave-... 

One of the first fluorescence-based ee assays uses umbelliferone (14) as the built-in fluorophore and works for several different types of enzymatic reactions 70,86). In an initial investigation, the system was used to monitor the hydrolytic kinetic resolution of chiral acetates (e.g., rac-11) (Fig. 8). It is based on a sequence of two coupled enzymatic steps that converts a pair of enantiomeric alcohols formed by the asymmetric hydrolysis under study (e.g., R - and (5)-12) into a fluorescent product (e.g., 14). In the first step, (R)- and (5)-ll are subjected separately to hydrolysis in reactions catalyzed by a mutant enzyme (lipase or esterase). The goal of the assay is to measure the enantioselectivity of this kinetic resolution. The relative amount of R)- and ( S)-12 produced after a given reaction time is a measure of the enantioselectivity and can be ascertained rapidly, but not directly. 

In a different approach, fluorescence-based DNA microarrays are utilized (88). In a model study, chiral amino acids were used. Mixtures of a racemic amino acid are first subjected to acylation at the amino function with formation of A-Boc protected derivatives. The samples are then covalently attached to amine-functionalized glass slides in a spatially arrayed manner (Fig. 10). In a second step, the uncoupled surface amino functions are acylated exhaustively. The third step involves complete deprotection to afford the free amino function of the amino acid. Finally, in a fourth step, two pseudo-Qn nX. om.Qx c fluorescent probes are attached to the free amino groups on the surface of the array. An appreciable degree of kinetic resolution in the process of amide coupling is a requirement for the success of the ee assay (Horeau s principle). In the present case, the ee values are accessible by measuring the ratio of the relevant fluorescent intensities. About 8000 ee determinations are possible per day, precision amounting to +10% of the actual value ((S(S). Although it was not explicitly demonstrated that this ee assay can be used to evaluate enzymes (e.g., proteases), this should in fact be possible. So far this approach has not been extended to other types of substrates. 

The ultimate stereochemical identity test is, of course, the direct resolution of the enantiomers using chiral liquid or gas chromatography (9). When compared to a reference standard of the racemate, and under experimental conditions that will resolve the peaks of both enantiomers, the occurrence of two equal peaks will identify the racemate, and one peak will signify an enantiopure material. A proof of the stereochemical identity of the analyte can be provided, based on a match of retention times with a reference standard of known stereochemistry. Inequality between the peaks is a measure of enantiomeric enrichment. Therefore, it is conceivable that both stereochemical identity and purity can be established from a single experiment. 

A measure of the interest in the biological activity of these dibenzyl-butyrolactone lignans is evinced in the recent spate of publications dealing with the total synthesis of the natural optically active products. Again, the Stobbe condensation pathway (Scheme 9) has been usefully exploited for this purpose. In a series of papers, resolution of the intermediate hemisuccinate esters (433 by chiral bases has been described (54), as has asymmetric hydrogenation (55), and the optically active lignan products synthesized in the usual way (42 - 44 45). 

Preceeding this work, palladium/NHC complexes had been used in the aerobic oxidative kinetic resolution of secondary alcohols [93]. The reaction was explored as a measure of match-mismatch interaction between a supporting NHC ligand and an exogenous chiral base. The NHC ligands met two essential criteria compatibility under oxidation conditions and stability toward dis-... 

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