ACHIRAL CYCLOHEXADIENONE ANALOGS OF ABSCISIC-ACID - SYNTHESIS AND BIOLOGICAL-ACTIVITY

Novel achiral cyclohexadienone (divinyl) analogues of abscisic acid (A BA) were synthesized and tested for biological activity. Oxidation of 2,6-dimethylphenol with iodobenzene acetate in ethylene glycol and hex ane afforded ,6-dimethyl-4,4-ethylenedioxycyclohexa-2,5-dienone as the key intermediate which was further transformed to a series of ABA ana logues with cyclohexa-2',5'-dien-4'-one ring and dienoic or enynoic si dechains at different oxidation levels. Their biological activity was compared to racemic ABA in assays for germination of cress seeds and f reezing tolerance in bromegrass cell suspension cultures and related t o the activity of the corresponding analogues with the ABA ring system . The divinyl dienoic methyl ester was as active as racemic ABA and me thyl ABA in inhibiting cress seed germination. The divinyl dienoic met hyl ester and divinyl acetylenic methyl ester had comparable activity to methyl ABA in inducing freezing tolerance. The results suggest that the vinyl methyl group is sufficient for recognition by ABA response systems in these assays and the axial methyl is not absolutely require d.