Synthesis and physiological activity of monodemethyl abscisic acids and methyl 5-(1′, 6′-epoxy-2′, 2′-dimethylcyclohexyl)-3 -methyl-(2z, 4e)-2, 4-pentadienoate

For the elucidation of the role of methyl substituents on cyclohexene ring of abscisic acid (ABA, I) on the physiological activity, 2′-demethyl-ABA (II), the two stereoisomers (III and IV) of 6′-demethyl-ABA and methyl 5-(1,′ 6′-epoxy-2′, 2′-dimethyIcyclohexyl)-3-methyl-(2Z, 4E)-2, 4-pentadienoate (VI) were synthesized. From the result of rice seedling assay, it was concluded that 2′-methyl group of ABA was indispensable for strong growth inhibitory activities and that at least one of the 6′-gem-dimethyl groups was unnecessary for growth inhibition.