ChemInform Abstract: Synthesis and Biological Activity of 3′-Chloro, -Bromo, and -Iodoabscisic Acids, and Biological Activity of 3′-Fluoro-8′-hydroxyabscisic Acid.

Abstract

Abstract (+)-3′-Chloro, -bromo and -iodoabscisic acids were synthesized, and their biological activities and metabolism were examined, as well as that of (+)-3′-fluoroabscisic acid. This was in order to estimate the effects of altered electron density at the C-2′ position of abscisic acid on both biological activity and metabolic stability. The biological activities of (+)-3′-chloro and -bromoabscisic acids were similar to, or higher than, those of (+)-abscisic acid in four bioassays, while (+)-3′-iodoabscisic acid was more potent in two bioassays and less potent than (+)-abscisic acid in the other two bioassays. The biological activities of 3′-haloabscisic acids seem to be dependent on the 3′-halogens, but not on the electron density at C-2′. The metabolism of (+)-3′-haloabscisic acids to ca. 50% of their original levels in the media of rice cell suspension culture was similar to that of (+)-abscisic acid. Metabolites from (+)-3′-chloro, -bromo and -iodoabscisic acids were not found in the culture media and cells, while (+)-3′-fluoroabscisic acid gave (+)-3′-fluoro-8′-hydroxyabscisic acid as a stable metabolite. (+)-3′-fluoro-8′-hydroxyabscisic acid showed biological activities lower than (+)-3′-fluoroabscisic acid, but higher than (−)-3′α-Fluorophaseic acid. These findings suggested that the biological activity of (+)-8′-hydroxyabscisic acid is intermediate between those of (+)-abscisic acid and (−)-phaseic acid. Abscisic acid may be inactivated in a stepwise manner by metabolism in plants.