Ovality descriptors, molecular shape

This study suggests that the ovality descriptors codify a quantity of molecular shape information which can be used in structure - activity studies. The more or less spherical or elongated shape of amine molecules quantified by these ovality descriptors can be an important structural requirement for a good interaction between the toxic molecule and its target. 

In this chapter we presented two structural measures of molecular shape that can be used as predictor variables in MLR (multiple linear regression) analysis of structure-activity studies - cylindrical (8,G) and ovality ( in, i = 1,2,3) molecular descriptors - and two inexpensive overlapping methods useful for quick receptor mapping - MTD (minimal topological difference) and MVD (minimal volume difference). A subsequent statistical analysis of QSAR models developed with these shape molecular descriptors explained well the variance in the observed reactivity data (8 descriptor of cylindrical shape) and biological activity of retinoids (MTD) and sulfonamides (MVD). 

The ovality index O is an anisometry descriptor, i.e. a measure of the departure of a molecule from the spherical shape, based on the property that, for a fixed volume, the spherical shape presents the minimum surface [Bodor et al, 1989 Bodor et al, 1998]. It is calculated from the ratio between the actual molecular surface area SA and the minimum surface area SAq corresponding to the actual molecule van der Waals volume... 

One may observe that the relations (15.27) and (15.29) are the same. Consequently, the two-dimensional (2D) ovality molecular vdW descriptor, 2d, is identical with the ovahty index, O. The relations (15.30) and (15.32) extend the index O so that one can also measure the deviation of a molecule from the spherical shape on one- (ID) and on three-dimensions (3D) of the vdW space. 

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