2. Biological effects of stereoisomers

A biological system (antibody, enzyme, receptor) is stereoselective when it reacts differently with each component of a pair of enantiomers. Stereoselectivity is characterized by the eudismic index: the decimal logarithm of the ratio of the affinity or activity of the most active enantiomer (eutomer) to the activity of the other (distomer). The greater the ratio, the more targeted the system, if the chirality center is involved in recognition. The eudismic index can guide the choice between several candidate substances for development.

In a family of organophosphates with an asymmetrical phosphorus, such as fonophos, an increasing linear variation of the eudismic index was observed with the logarithm of the rate of inactivation of acetylcholinesterase by the more active enantiomer. When operating with organophosphates whose center of chirality is not the phosphorus...