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

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.

Biofilm-associated indole acetic acid producing bacteria and their impact in the proliferation of biofilm mats in solar salterns

“…As established earlier, IAA production was dependent on the availability of tryptophan. In bacterial systems, the major pathway for IAA synthesis is a tryptophan-dependent pathway (Antolic et al 1996;Nigovic et al 2000;Woodward & Bartel 2005) which conforms with our four isolates. At tryptophan concentrations of 0 mg/mL, the IAA production for A. aquariorum (N2), P. alcaliphila (N3), V. diazotrophicus (N6) and P. pachastrellae (C3) varied from 0.58, 1.28, 0.68 and 0.05 µg/mL, respectively, whereas at higher tryptophan concentration (4 mg/mL), IAA production increased to 14.27, 14.08, 8.93 and 9.67 µg/mL, respectively, thus showing a positive effect of tryptophan on the IAA production by the bacterial isolates.…”

Combined computational and chemometric study of 1H‐indole‐3‐acetic acid

“…This schematic representation of formal single and double bonds that are not in the benzene ring is in accord with common structural formula for indole, indene, and indole‐3‐acetic acid 6, chemical behavior of IAA 5 and bond lengths from the crystal structure of IAA 2 compared with standard single and double CC, CN, and CO bond lengths from gas–phase determination of small molecules 7 or crystal structures of organic compounds 8. The benzene ring in indole, although traditionally drawn as delocalized, in Scheme appears as the Kekulé structure closer to bond lengths from crystal structure of IAA at 103 K 2. In fact, crystal structure determination of many IAA derivatives and some ab initio calculations on IAA 2 revealed systematically shortening of the bonds C4C5 and C6C7.…”

“…The benzene ring in indole, although traditionally drawn as delocalized, in Scheme appears as the Kekulé structure closer to bond lengths from crystal structure of IAA at 103 K 2. In fact, crystal structure determination of many IAA derivatives and some ab initio calculations on IAA 2 revealed systematically shortening of the bonds C4C5 and C6C7. Several papers 4, 5, 9–13 on aromaticity of indole and its isomers clearly showed that indole is a highly aromatic system, with the nitrogen free electron pair participating in electron delocalization as a requirement for indole's aromaticity 4 (the lone pair is formally equivalent to a double bond 11).…”

“…1 H ‐Indole‐3‐acetic acid (IAA) is the first isolated and the most important plant hormone from auxin class 1. Its quantitative structure–activity relationship/quantitative structure–property relationships (QSAR/QSPR) 2 are not simple, and the structure of an IAA receptor have just appeared recently 3. Consisting of an indole ring 4, 5 and acetic acid chain at position 3, IAA has a simple molecular structure (shown in Scheme ).…”

A study of the conformational profile and the vibrational spectra of the plant hormone indole-3-acetic acid

“…For those calculations the gg conformer was used, which is the second lowest-energy structure, but the closest one to the one present in the solid state. 5,6 The dihedral angles de¯ning the gg conformer in the experimental geometry (C 13 C 11 C 8 C 2 ¼ À84:4 and O 14 C 13 C 11 C 8 ¼ À11:5 Þ are clearly ones belonging to a gg conformer and not to t ð180 Þ or c ð0 Þ, although the calculated values for gg are quite di®erent (C 13 C 11 C 8 C 2 ¼ À66:4 and O 14 C 13 C 11 C 8 ¼ 96:8 Þ. Note, that the atom numbering of the three stable conformers is shown in Fig.…”