Effect of the minor ABA metabolite 7′-hydroxy-ABA on Arabidopsis ABA 8′-hydroxylase CYP707A3

To examine the effect of the minor abscisic acid (ABA) metabolite 7′-hydroxy-ABA on Arabidopsis ABA 8′-hydroxylase (CYP707A3), we developed a novel and facile, four-step synthesis of 7′-hydroxy-ABA from α-ionone. Structural analogues of 7′-hydroxy-ABA, 1′-deoxy-7′-hydroxy-ABA, and 7′-oxo-ABA were also synthesized to evaluate the role of the 7′-hydroxyl group on binding to the enzyme. The result of enzyme inhibition assay suggests that the local polarity at C-7′, neither steric bulkiness nor overall molecular hydrophilicity, would be the major reason why (+)-7′-hydroxy-ABA is not a potent inhibitor of CYP707A3.