QSAR Theory

Quantitative Structure-Activity Relationship (QSAR) is an approach which can help to find relationships between structure properties of studied compounds and target property or biological activity.

For example, biological activity can be expressed quantitatively as in the concentration of a substance required to give a certain biological response. Additionally, when physiochemical properties or structures are expressed by numbers, one can form a mathematical relationship, or quantitative structure-activity relationship, between the two. The mathematical expression can then be used to predict the biological response of other chemical structures.

QSAR's most general mathematical form is:

Activity = f(physiochemical properties and/or structural properties)

Quantitative structure–activity relationships (QSAR) offer the possibility for screening a large number of chemicals in a short time and with low cost. The QSAR establish a statistical relationship between biological activity or environmental behavior of the chemicals of interest and their structural properties. Using QSAR, we can obtain an estimate of the activity of a chemical from its molecular structure only.

QSAR development requires three basic elements:
(1) an activity or property data set, measured experimentally,

(2) molecular descriptors, which are the quantitative descriptions of structural properties, and

(3) statistical techniques to establish the relationship between molecular descriptors and activities.

QSAR analysis consists of statistical modeling and, consequently, QSAR results are associated with some uncertainty and the predictive power of a QSAR model is related not only to the quality of the input data but also the power of the statistics.

To be continued....