Plant growth retardant activity of 4-homoisotwistane derivatives

A variety of simple derivatives of 3-substituted 4-homoisotwistane derivatives were prepared, and their effect on the growth of cucumber seedlings in complete darkness was investigated. The 3-hydroxy derivative was found to show a strong inhibitory activity at 50 μg/ml, so a series of other hydroxy derivatives of 4-homoisotwistane, endo-2-, exo-2-, and 5-hydroxy- and exo-2,3-dihydroxy-4-homoisotwistane were prepared in order to obtain information on structure-activity relationships. The endo-2-hydroxy derivative inhibited the growth of cucumber and the germination of lettuce seed at 12.5 μg/ml. All the hydroxy derivatives tested increased the number of adventitious roots in hypocotyls of kidney bean at 100 μg/ml, but they inhibited root formation at the lowest part of the cuttings, and the effect was again exhibited most strongly by the endo-2-hydroxy compound. It is suggested that the 2- and 3-hydroxy derivatives possess a potent activity as plant growth retardants.