SYNTHESIS, BIOLOGICAL-ACTIVITY AND METABOLISM OF (S)-(+)-3'-FLUOROABSCISIC ACID

(S)-(+)-3'-Fluoroabscisic acid (5a) was synthesized as an analogue of abscisic acid that can resist the metabolic cyclization of 8'-hydroxyabscisic acid to phaseic acid due to increased electron density at C-2'. The inhibitory activity of 5a was slightly higher than that of abscisic acid in lettuce seed germination, and war almost equal to that of abscisic acid in rice seedling elongation. When 5a was applied to bean shoots, 3'-fluoro-8'-hydroxyabscisic acid (8a), 3'alpha- and 3'beta-fluorophaseic acids (9a and 10a) and 3'alpha- and 3'beta-fluorodihydrophaseic acids (11n and 12n) were identified as the free metabolites. The methyl esters 8b, 9b and 10b coexisted at equilibrium in the ratio of 7:6:1. This result indicates that 8a is stable as back-isomerization of 9a and 10a occurs.