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Title: STRUCTURAL STUDIES ON MONOFLUORINATED DERIVATIVES OF THE PHYTOHORMONE INDOLE-3-ACETIC ACID (AUXIN)

Author
item ANTOLIC, SNJEZANA - RUDER BOSKOVIC INSTITUTE
item KOJIC-PRODIC, BISERKA - RUDER BOSKOVIC INSTITUTE
item TOMIC, SANJA - RUDER BOSKOVIC INSTITUTE
item NIGOVIC, BILJANA - RUDER BOSKOVIC INSTITUTE
item MAGNUS, VOLKER - RUDER BOSKOVIC INSTITUTE
item Cohen, Jerry

Submitted to: Acta Crystallographica Section B: Structural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/21/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Indole-3-acetic acid (IAA) is an important plant hormone that is found in all plants and in all plant tissues. In some plants, such as fresh and canned peas and in faba beans, a halogen containing form of IAA has also been found. Synthesis of substituted compounds in which a specific hydrogen is changed to the halogen, fluorine, has been used in medicinal chemistry to alter the metabolic stability of target compounds without major effect on the chemical properties. In order to understand the metabolism and activity of IAA and related compounds better, we studied the molecular structure of a series of fluorinated IAAs and compared them to that of IAA. We show, for the first time, that substitution of IAA by fluorine results in dramatic increases in biological activity. These data will be useful to plant biochemists, physiologists and molecular biologists interested in hormone activity and may find application in the biorational design of growth regulating compounds. These data may also prove important to food chemists and nutritionists interested in studies on the fate of halogenated IAA in human and animal diets.

Technical Abstract: As part of molecular recognition studies on the phytohormone indole-3- acetic acid (IAA), a series of fluorinated IAAs was examined. Phenyl- ring substitution at positions 4-, 5-, 6-, and 7- yielded the four compounds that were subjected to analysis. Structure/activity correlation included the analysis of their molecular conformations, based on the X-ray diffraction and computational chemistry results, and bioactivity determinations in the Avena coleoptile and the Pisum sativum stem straight-growth tests, lipophilicity and UV-absorbance. The conformations of monofluorinated IAAs and the parent hormone, were defined by rotations about two bonds: one describes the relative orientation of a side chain towards the indole plane and the second one the orientation of the carboxylic group. The results of X-ray structure analysis revealed the folded shape of the molecules in all compounds studied. Molecular mechanics and dynamics located the folded conformation as the local minimum but failed to detect the planar conformation as one of the local minima which, according to ab initio results on IAA and 4-C1-IAA, could be possible as well.