Abscinazole-F1, a conformationally restricted analogue of the plant growth retardant uniconazole and an inhibitor of ABA 8′-hydroxylase CYP707A with no growth-retardant effect

To develop a specific inhibitor of abscisic acid (ABA) 8′-hydroxylase, a key enzyme in the catabolism of ABA, a plant hormone involved in stress tolerance, seed dormancy, and other various physiological events, we designed and synthesized conformationally restricted analogues of uniconazole (UNI), a well-known plant growth retardant, which inhibits a biosynthetic enzyme ( ent-kaurene oxidase) of gibberellin as well as ABA 8′-hydroxylase. Although most of these analogues were less effective than UNI in inhibition of ABA 8′-hydroxylase and rice seedling growth, we found that a lactol-bridged analogue with an imidazole is a potent inhibitor of ABA 8′-hydroxylase but not of plant growth. This compound, abscinazole-F1, induced drought tolerance in apple seedlings upon spray treatment with a 10 μM solution.