MOLECULAR RECOGNITION OF THE PHYTOHORMONE AUXIN AND RELATED COMPOUNDS. B. Kojic-Prodic, S. Antolic, S. Tomic and V. Magnus, Rudjer Boskovic Institute, P.O.B. 1016, 10001 Zagreb, Croatia

A molecular recognition approach was applied to the auxin family (indol-3-ylacetic acid, IAA), the most intensively studied plant hormone. The final goal of the research is to offer a mechanism of hormone binding to receptor(s) and to provide data for QSAR of indole and non-indole auxins. The study includes natural and synthetic alkylated and halogenated analogues of IAA. Both, active and inactive analogues have been included in the analyses. The problem has been tackled in three directions: analysis of the molecular geometry, study of electron redestribution by substitution effects, and correlation of the physico-chemical parameters with substitution effects and bioactivity. The analysis has been based on the results of X-ray structure analysis, computational chemistry, FT-IR, UV & NMR spectroscopies, physico-chemical parameters such as lipophilicity and acid-base properties of the pyrrole NH, and bioactivity (including bioaffinity for some of them, Klaembt, 1996). The 3D structure of the receptor has not been characterized yet. However, systematic analysis of a large number of substrates and inhibitors can provide information about the protein active site.