Synthesis, Absolute Configuration and Biological Activity of Both Enantiomers of 2-(5,6-Dichloro-3-indolyl) propionic Acid : New Dichloroindole Auxins

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Racemic 2-(5,6-dichloro-3-indolyl) propionic acid (5,6-Cl_2-2-IPA) was synthesized from 5,6-dichloroindole-3-acetic acid (5,6-Cl_2-IAA) by successive esterification, methoxycarbonylation, methylation, and double hydrolysis. The racemate was converted to the diastereomeric esters with those of the diastereomeric (S)-(-)-1-phenylethyl esters of (S)-(-)-1-phenylethyl alcohol. These were separated by HPLC into two optically active diastereomers and then hydrolyzed with p-TsOH to the optically active enantiomers of 5,6-Cl_-2-IPA. The absolute configurations of both the 5,6-Cl_-2-IPA enantiomers were determined by comparing the ^1H-NMR spectra of their diastereomeric (s)-(-)-1-phenylethyl esters with those of the diastereomeric (S)-(-)-1-phenylethyl esters of 2-(3-indolyl) propionic acid (2-IPA) whose absolute configurations are already known. There was no essential difference between (S)-(+)-and (R)-(-)-5,6-Cl_2-2-IPA in hypocotyl growth-inhibiting activity toward Chinese cabbage, but their inhibitory activities were stronger than that of the potent mother auxin, 5,6-Cl_2-IAA. No essential difference in the coleoptile elongating activity of Avena sativa was apparent for the enantiomers, this activity being about one-third that of 5,6-Cl_2-IAA.
社団法人日本農芸化学会の論文
2001-02-23