Synthesis and Biological Activity of 7'-, 8'-, and 9'-Alkyl Analogues of Abscisic Acid

抄録

In order to examine the hypothesis of pseudo-symmetry in the abscisic acid (ABA) molecule, (±)-7'-, 8'-, and 9'-methyl, and (±)-7'-, 8'-, and 9'-ethyl analogues of abscisic acid, whose pseudo-symmetry is decreased, were synthesized and, after optical resolution, tested for their inhibitory activity in four bioassays. The correlation of the decrease in the activity of (-)-7'- and 9'-alkyl-ABAs with that of (+)-9'- and 7'-alkyl-ABAs, respectively, seemed to agree with the hypothesis. The decrease in activity by alkylating C-8' of (+)-ABA was smaller than that by alkylating C-7' and C-9' of (+)-ABA, indicating that the activity was relatively unaffected by the bulky group at C-8' of (+)-ABA. Alkylation of C-8' and C-9', especially that of C-8', of (-)-ABA markedly reduced the activity. If the high activity of unnatural (-)-ABA is attributable to the pseudo-symmetry of the molecule, C-8' of (-)-ABA would occupy the space facing the re-face of C-2' in natural (+)-ABA. The low activity of (-)-8'-alkyl-ABA suggests the presence of a strict steric requirement of the binding sites to occupy the re-face of C-2' in (+)-ABA.