8′,8′-Difluoro- and 8′,8′,8′-trifluoroabscisic acids as highly potent, long-lasting analogues of abscisic acid

Abstract

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 α-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.