Chirality metric

Wildman, S. A., Crippen, G. M., Validation of DAPPER for 3D QSAR Conformational Search and Chirality Metric,... 

Therefore, the chiral nature of the drug substance must be known and controlled. This must be done throughout the synthesis of the drug substance, so that the exact chiral species is consistently generated. Also, once an enantiopure compound has been generated, it must be shown that the chirality does not change on stability. Clearly, a chiral metric is required. 

Application of a field up, however, leads to a dramatic switching of the extinction brushes counterclockwise, to give the configuration shown on the left in Figure 8.35. This dramatic, chiral EO response is mirrored by other domains in the sample of opposite handedness but similar metrics. If the field is then removed, domains of the type shown on the left in Figure 8.35 are... 

Due to re- and si-coordination of prochir-al substrates at a catalyst with C2-sym-metric chiral ligands two diastereomeric catalyst-substrate complexes emerge. In the case of C,-symmetric ligands already four stereoisomer intermediates result. 

N symmetric Strecker Synthesis via a Crystal I ization-Ind >< 7 metric Transformation using a Chiral Auxillap... 

Mezey, P. G. (1998) The proof of the metric properties of a fuzzy chirality measure of molecular electron density clouds. J. Molec. Struct. (Theochem.) 455, 183-190. 

Values of the skeletal complexity metric S for these alkaloids are small, in the range 36-49. In contrast, S/H values are relatively high, in particular for strychnos alkaloids (0.88, Chart 6.1.3.A) this reflects a high molecular complexity that stems from the many cycles and chirality centers, in spite of the low molecular weights. 

Electroenzymatic reactions are not only important in the development of ampero-metric biosensors. They can also be very valuable for organic synthesis. The enantio- and diasteroselectivity of the redox enzymes can be used effectively for the synthesis of enantiomerically pure compounds, as, for example, in the enantioselective reduction of prochiral carbonyl compounds, or in the enantio-selective, distereoselective, or enantiomer differentiating oxidation of chiral, achiral, or mes< -polyols. The introduction of hydroxy groups into aliphatic and aromatic compounds can be just as interesting. In addition, the regioselectivity of the oxidation of a certain hydroxy function in a polyol by an enzymatic oxidation can be extremely valuable, thus avoiding a sometimes complicated protection-deprotection strategy. 

Hexabromocyclododecanes are additive BFRs used in polystyrene. In 2001 the global market demand for HBCD was 16 700 metric tons [29]. Of this amount, 2800 tons (17%) were used in North America, and 9500 tones (57%) were used in Europe [29]. The commercial product contains three isomers, among which the y isomer is the most predominant at 75-90% of the total. The a isomer is 10-13% of the total, and the p isomer is < 0.5-12% of the total [56]. The structures of these compounds are given here, but because there has been some confusion about their exact three-dimensional structures, their Chemical Abstracts Registry numbers are also given. Incidentally, these compounds are chiral. 

The protonation constants and the binding constants with different chiral carboxylates have been determined by means of pH-metric titrations. The triprotonated form of (S,S,S,S)-6 showed moderate enantioselectivity with malate and tartrate anions (AAG=0.62 and 0.66 kcal/mol, respectively), the strongest binding being observed in both cases with the L-enantiomer. Good enantiomeric discrimination was obtained with tetraprotonated (R,R)-5 and... 

The Lythraceae alkaloids have four centers of chirality—three chiral carbon atoms at the quinolizidine ring C-l, C-3, and C-5, and the dissy-metric biphenyl or biphenyl ether link. The chirality of the biphenyl system in all alkaloids of the group is the same. The chirality of the biphenyl ether link is also the same for all alkaloids in this class (22, 23, 32). 

Iron-containing cytochrome P-450 constitutes the most famous example of a selective C-H bond oxidizer. Although the exact nature of the mechanism remains controversial, the reaction most likely proceeds through radical intermediates [2]. The hydroxylation of activated C-H bonds has also been carried out in the presence of synthetic porphyrin complexes. In these biomimetic processes, ruthenium plays a relatively minor role when compared with iron. Zhang et al. [50], however, recently reported the enantioselective hydroxylation of benzylic C-H bonds using ruthenium complexes supported by a D4-sym-metric porphyrin bearing a crafted chiral cavity. Thus, complex 23 reacts in a stoichiometric manner with ethylbenzene to give phenethyl alcohol with a... 

Some examples of asymmetric epoxidations of alkenes using chiral ruthenium porphyrins have been reported for example, the previously reported D4-sym-metrical chiral ruthenium porphyrin complex Run(D4-Por )(CO)(MeOH) [58], which produced (R)-styrene oxide in 57% ee with Cl2PyNO as a donor, was readily converted into the dichloro derivative A [59] (Fig. 11). This di-chlororuthenium porphyrin gave (R)-styrene oxide in 69% ee using Cl2PyNO and was highly active (875 TON in 1.5 h). The use of unsubstituted pyridine N-oxide or NMO as oxidants resulted in low substrate conversions as well as... 

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