Chirality descriptors

Coordination to the central P atom of two different types of symmetrical bidentate ligands leads to structures of type P(aa)2(bb), which are this time C2-symmetric as detailed in Fig. 16. The same chiral descriptors A and A apply to these compounds. Derivatives like 3,4,14-17 and 19-22 fit this description and have only been reported in racemic form so far. If the ligand bb is itself chiral, then diastereomers are generated. This will be described in the next section. 

Golbraikh, A., Bonchev, D., Tropsha, A. Novel chirality descriptors derived from molecular topology. J. Chem. Inf. Comput. Sci. 2001, 41, 147-158. 

Unsymmetrically disubstituted (and hence chiral) metallocenes (with point group C,) such as the ferrocene 122) provide a rather special problem they were first defined as planar chiral 19) and the specification of molecular chirality (descriptors Rp and Sp) applied accordingly19). Several authors still classify these structures as planar chiral21 23-24). 

To indicate the different QUINAPHOS derivatives the following notation will be used (chiral descriptors)-number, R, D, diol for example, (R Sc)-4cel corresponds to (S)-2-butyl-8-chloro-l-(R)-3,5-dioxa-4-phosphacyclohepta [2,l-a 3,4-a ]dinaphthalen-4-yl)-l,2-dihydroquinoline and (R Rc)-4ael to (R)-2-butyl-8-diphenylphosphino-l-(R)-3,5-dioxa-4-phosphacyclohepta[2,l-a 3,4-a ]dinaphthalen-4-yl)-l,2-dihydroquinoline, i.e., to the classical QUINAPHOS ligand itself... 

Fig. 5 Definition of skew-line chirality descriptors with rotational right- (8/ A) and left-(X/A) handed orientations...

The chiral identity of a molecule is included in the nomenclature of inorganic compounds, and today s comprehensive system is based upon suggestions made in 1990 in IUPAC s Recommendations on Nomenclature of Inorganic Chemistry [84], and ACS s Inorganic Chemical Nomenclature [90]. The basis for the usage of stereochemical descriptors was laid by Brown [91,92], from which three types of chiral descriptor conventions were developed (i) Steering-wheel-convention [93], (ii) Skew-lines convention [94] and (iii) Oriented-skew-lines convention [95]. 

The basic problem of this suggestion was that the chirality descriptors obtained by the central procedure are the opposite of those derived from the planar approach. Schlogl consequently changed his stereochemical nomenclature [5,9] and. 

CHGD index charged partial surface area descriptors chiral factors -> weighted matrices chirality descriptors... 

Simple 10,11-didehydro QCD and 10,11-didehydro QCI are also accessible using this reliable two-step procedure. Thus, QCI, which solidifies at room temperature when pure, forms alkyne 28 with a change of chirality descriptor from R to S at carbon C5. QCI-derived alkyne 28 crystallizes readily and also sublimes on warming, forming beautiful colorless needles, reaching from wall to wall of the reaction vessel [17]. 

This protocol presents the application of modern computer-aided modeling tools dealing with chirality - stereo drawing, chiral centers aimotation, chiral ligand docking and analysis of complexes with the receptor, chiral descriptors in QSAR, simulation of protein-DNA or DNA-DNA complexes with respect to their chirality, chiral catalysis. 

Several series of novel chirality descriptors of chemical organic molecules were introduced by Golbraikh et al. [5, 6]. These descriptors have been implemented in a QSAR study with a high content of chiral and enantiomeric compounds. It was shown fhat for all data sets 2D-QSAR models that use a combination of chirahty descriptors wifh conventional topological descriptors afford better or similar predictive abihty when compared to models generated wifh 3D-QSAR approaches. 2D-QSAR mefhods enhanced by chirahty descriptors present a powerful alternative to popular 3D-QSAR approaches. 

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