- Analysis of isomerization process of 8'-hydroxyabscisic acid and its 3'- fluorinated analog in aqueous solutions
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8'-Hydroxyabscisic acid (8'-HOABA), the first metabolite of abscisic acid (ABA) in plants, is spontaneously isomerized to low bioactive phaseic acid (PA). We investigated thermodynamic and kinetic properties of the isomerization process in aqueous solution buffered at the various pHs, along with the effects of 3'-fluorine. The 8'-HOABA/PA ratio at equilibrium was 2:98 at 25°C, while the 3'-fluoro-8'-HOABA/3'α-fluoro-PA ratio was 16:84, indicating that introduction of a fluorine at C-3' thermodynamically reduced isomerization of 8'-HOABA to PA. The isomerization became more rapid as pH increased; the rate constant at pH 10 was higher than that at pH 3 by a factor of 2000. Introduction of a fluorine at C-3' reduced the reaction rate by raising the activation enthalpy. This indicated that 8'-HOABA was also kinetically stabilized by the 3'-fluorine. These findings suggested that the control of pH and modification of the enone moiety of the ring would be useful to manipulate the catabolic inactivation rate of ABA. (C) 2000 Elsevier Science Ltd.
- Todoroki, Yasushi,Hirai, Nobuhiro,Ohigashi, Hajime
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p. 1649 - 1653
(2007/10/03)
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- Synthesis, Biological Activity, and Metabolism of 8′,8′,8′-Trideuteroabscisic Acid
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An 8′,8′,8′-trideuterated analog of abscisic acid (ABA) was diastereoselectively synthesized as a new analog of ABA that is resistant to 8′-hydroxylation, the first metabolic reaction of ABA, owing to the primary kinetic isotope effect. (+)-8′,8′,8′-Trideutero-ABA showed long-term activity in the rice elongation assay. The rate of metabolism of this analog in rice cell suspension culture was about two fold slower than that of (+)-ABA. The concentration of 8′,8′-dideuterophaseic acid produced was about 1/3 that of phaseic acid converted from (+)-ABA. This result indicated that the long-lasting activity of the (+)-trideutero-ABA in the rice assay was the result of the delayed 8′-hydroxylation as expected.
- Todoroki, Yasushi,Nakano, Sei-Ichi,Hirai, Nobuhiro,Mitsui, Toshiaki,Ohigashi, Hajime
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p. 1872 - 1876
(2007/10/03)
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- CHIRALITY OF THE ACYL GROUP OF β-HYDROXY-β-METHYLGLUTARYLHYDROXYABSCISIC ACID
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The β-carbon of the acyl group of β-hydroxy-β-methylglutarylhydroxyabscisic acid was shown to possess R-configuration by HPLC analysis of the reduced product. - Keywords: Robina pseudacacia; Leguminosae; β-hydroxy-β-methylglutarylhydroxyabscisic acid; chirality; optical resolution; mevalonolactone.
- Hirai, Nobuhiro,Koshimizu, Koichi
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p. 1867 - 1870
(2007/10/02)
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