The biological effects of a new chemical compound can often be predicted from its molecular structure using data about other similar compounds. This is because similar compounds may have similar physical and biological properties. There is a relationship between structure and activity, and this principle is referred to as Structure Activity Relationship (SAR).
The SAR tools, correlations, and models used to evaluate specific chemical structures and their biological effects are continuously being refined. They are applied both to discover and develop new compounds, as well as in the assessment of side effect health risks posed by existing compounds.
SAR depends on the recognition of which structural characteristics correlate with chemical and biological reactivity. Thus the ability to draw conclusions about an unknown compound depends upon both the structural features that can be characterized as well as the database against which they are compared. When combined with appropriate professional judgment, SAR can be a powerful tool to understanding functional implications when similarities are found. For example, in the case of risk assessment of uncharacterized compounds, data from the most sensitive toxicological endpoints should be included in the analysis, such as carcinogenicity or cardiotoxicity.
Structure Activity Relationship is typically evaluated in a table form, called an SAR table. SAR tables consist of the compounds, their physical properties, and activities. Experts review the table by sorting, graphing, and even scanning structural features in order to find possible relationships.
The United States and the European Union are currently promoting use of SAR for screening large numbers of chemicals that have already entered commerce, for example EPA's High Production Volume and EU's REACH programs, as well as for development and registration of novel compounds.
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