Quantitative structure-activity relationships (QSAR) of cinnamic acid bird repellents

Plants have evolved an array of defense chemicals that inhibit the feeding of vertebrate herbivores and therefore have potential for agricultural and environmental applications to reduce feeding damage. we investigated the relationship between structure and repellency for 14 derivatives of the plant secondary compound, cinnamic acid, using the feral pigeon (Columba livia) as the test species. The mechanism behind the repellent activity of these derivatives is explained by a combination of four descriptors: heat of formation (Delta H-f), polarizability (XY and YY) and superdelocalizability (Sr). All these parameters are electronic, indicating that changes in electronic distribution within cinnamic acid structures are crucial for activity. This is the first published quantitative structure-activity model for avian repellents, and as a result we can now begin to predict which cinnamic acid derivatives should make effective repellents. The full power of this model to aid the selection and screening of new repellents awaits further experimentation on both related compounds and other avian species. However, this modeling approach promises to provide a more efficient and economic method for prospecting chemical databases for new effective bird repellents.