Relationship between Structure and Phytogrowth-Inhibitory Activity of 2,5-Dihydroxy-1,4-dithiane-Related Compounds

Ten derivatives (II-VI and VIII-XII) from 2,5-dihydroxy-1,4-dithiane (I) and 2,5-dihydroxy-2,5-dimethyl-1,4-dithiane (VII) showed inhibitory activity against the growth of root of Brassica rapa L. The inhibitory activity of all ten derivatives was higher than that of the original compounds I and VII. In particular, VIII-XII inhibited the germination of this plant at the concentration of 1.0×10^<-3>M. Among the derivatives VIII-XII, IX exhibited the strongest inhibition. Compound III had the most potent inhibitory activity among the derivatives II-VI. The results indicate that acylation of hydroxyl group with propionic acid enhances the activity. The inhibitory effect of VIII-XII was much stronger than that of II-VI. The findings suggest that methyl groups at 2,5 dipositions play an important role in the inhibitory activity of 2,5-dihydrosy-1,4-dithiane-related compounds. In both derivatives II-VI and VIII-XII, the inhibitory effect of the substituent was in the order of propionyl > acetyl > butyryl > valeryl > isobutyryl. All radicles of this plant treated with the compounds I-XII showed negative geotropism.