8',8'-DIFLUOROABSCISIC ACID AND 8',8',8'-TRIFLUOROABSCISIC ACID AS HIGHLY POTENT, LONG-LASTING ANALOGS OF ABSCISIC-ACID

Racemic 8',8'-difluoroabscisic acid (difluoro-ABA) and 8',8',8'-trifluoroabscisic acid (trifluoro-ABA) were synthesized as highly potent, long-lasting analogues of abscisic acid (ABA). The individual optical isomers were obtained by optical resolution of the racemic mixture by HPLC with a chiral column. (+)-8',8'-Difluoro-ABA and (+)-8',8',8'-trifluoro-ABA inhibited the elongation of rice seedlings six and 30 times more strongly, respectively, than (+)-ABA. These analogues also showed double the (+)-ABA-induced inhibition of lettuce seed germination. In causing stomatal closure and inhibiting the induction of alpha-amylase by gibberellin A(3), these analogues were equally as effective as ( +)-ABA. The high activity in the assays over a long period suggested that the metabolism of difluoro- and trifluoro-ABAs was delayed. (-)-Enantiomers were equal to, or weaker than(-)-ABA in the assays.