Acta Crystallographica Section B

Structural Science

Volume 56, Part 1 (February 2000)

research papers

Acta Cryst. (2000). B56, 94-111 [ doi:10.1107/S0108768199006199 ]

Correlation of structural and physico-chemical parameters with the bioactivity of alkylated derivatives of indole-3-acetic acid, a phytohormone (auxin)

B. Nigovic, S. Antolic, B. Kojic-Prodic, R. Kiralj, V. Magnus and B. Salopek-Sondi

Abstract: As part of molecular recognition studies on the phytohormone indole-3-acetic acid (IAA) a series of alkylated IAAs has been examined. Phenyl-ring substitution (alkyl = methyl and ethyl) at positions 4-, 6- or 7- as well as pyrrole substitution at the 2- site resulted in the six compounds which are analyzed: 2-Me-IAA, 4-Me-IAA, 6-Me-IAA, 7-Me-IAA, 4-Et-IAA and 6-Et-IAA. The structure-activity relationships investigated include those between the geometrical parameters of the molecular structures determined by X-ray analysis, the growth-promoting activities in the Avena coleoptile straight-growth bioassay and relative lipophilicities calculated from retention times on a reversed-phase HPLC column and from R_F values in reversed-phase TLC. Lipophilicities are correlated with the moments of inertia, average polarizability, molecular mass, and the van der Waals radii of the ring substituents. The influence of substitution on the electronic properties of the indole ring and its geometry is discussed on the basis of the UV and ¹H NMR spectra.

Keywords: Indole-3-acetic acid; Phytohormone; Bioactivity; Molecular recognition studies.