Molecular Pharmacology, Vol 12, 598-604, Copyright © 1976 by the American Society for Pharmacology and Experimental Therapeutics

Quantitative Structure-Activity Correlation of Optical Isomers: a Molecular Basis for Pfeiffer’s Rule

¹ Pharmacological Institute, Medical Faculty, and Faculty of Science, Unviersity of Nijmegen, Nijmegen, The Netherlands

The quantitative approach of Hansch and his co-workers to structure-activity relationships has been extended to optical isomers of a series of phenoxyproprionic acids acting as plant growth regulators. We have treated the physicochemical constants of the two chiral substituents as independent variables. Pfeiffer’s rule, which states that the isomeric activity ratio of a more active compound is higher than that of a less active one, is explained in terms of different structural requirements for the substituents as measured by and van den Waals volume. A positive dependence on the aromatic ring substituent constant suggests a drug-receptor interaction of electronic nature in addition to hydrophobic interactions.