AbstractStructure‐activity correlations for the toxicity of nicotinanilides toBiomphalaria glabratahave been studied in terms of partitioning, charge transfer and steric properties. Partition coefficients or πNA values (substituent constants for nicotinanilides, reflecting the influence on the partition coefficient of a substituent on the parent molecule) have been shown to contain a significant electronic component and to be related to chromatographically determinedRMvalues (derived from a relationship between the partition coefficient andRFvalue for liquid‐liquid chromatographic systems). There was no overall correlation between LC50values and partitioning, electronic or steric effects. However, for ten 4′‐substituted nicotinanilides, the LC50values correlated significantly with partitioning, an increase in lipophilic character leading to an increase in biological activity. The greater activity of the unsubstituted parent compound could not be explained by purely advantageous steric effects but the 4′‐position may be an important metabolic site. Use of compounds labelled with deuterium failed to clarify this point because no isotope effects w
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