Synthesis of All Stereoisomers of 3,3′-Dimethoxy-7,7′-epoxylignane-4,4′-diol and Their Plant Growth Inhibitory Activity

All stereoisomers of 3,3′-dimethoxy-7,7′-epoxylignane-4,4′-diol were synthesized to examine the effect of stereochemistry on their plant growth inhibitory activity using lettuce and Italian ryegrass. The effect of structural modifications such as dehydroxylation, methoxylation and hydroxylation at the 9- and 9′-positions of the lignans on the activity was also studied. Most of the epoxylignanes showed higher plant growth inhibitory potency against ryegrass than against lettuce, and the inhibitory activity varied depending on the configurations of each position of the tetrahydrofuran ring (7-, 7′-, 8-, and 8′-positions of the epoxylignanes). Among the 9,9′-position-modified derivatives, the dehydroxy derivatives showed the highest potency. These results suggested that the plant growth inhibitory activity should be influenced by the structure of the epoxylignanes.