Indole-3-acetic acid is an indispensable hormone (auxin) in plants and an important metabolite in humans, animals, and microorganisms. Here we introduce its 5- and 6-(2-aminoethyl)-derivatives for use in the design of novel research tools, such as immobilized and carrier-linked forms of indole-3-acetic acid and its conjugates with biochemical tags or biocompatible molecular probes. The aliphatic nitrogens of 5- and 6-(2-aminoethyl)indole were acetylated and the products were converted to the corresponding 3-(N,N-dimethylamino)methyl derivatives (gramines). These were reacted with cyanide. Saponification of the resulting acetonitriles was accompanied by N-deprotection to yield 5- and 6-(2-aminoethyl)indole-3-acetic acids. The latter were chemically stable and could be linked, via their amino groups, and without prior protection of their carboxyl moieties, to bovine serum albumin and to biotin, including appropriate spacer modules. One of the protein conjugates was used to elicit the formation of monoclonal antibodies, which were evaluated using the biotin conjugates in an enzyme-linked immunosorbent assay employing streptavidin-coupled alkaline phosphatase, and thus shown to recognize predominantly the indole-3-acetic acid moiety.
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We are indebted to Göran Sandberg who made it possible to complete part of this work at the Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Science, Umeå, Sweden. We also thank Thomas B. Krick (Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota) for high resolution mass spectra and Damir Kralj (Ruđer Bošković Institute) for determining the dissociation constants of 5- and 6-(2-aminoethyl)indole-3-acetic acids. This work was supported, in part, by US-Croatian (Yugoslav) Research Agreements JF-813 and JF-202, by grants 0098080 and 0098036 from the Croatian Ministry of Science and Technology, by grants DBI 0077769 and IBN 0111530 from the United States National Science Foundation and by funds from the Minnesota Agricultural Experiment Station and the Gordon and Margaret Bailey Endowment for Environmental Horticulture.