Structure-activity relationships of natural occurring plant growth-inhibiting substance caprolactam and its related compounds

The structure-activity relationships of naturally occurring plant growth-inhibiting substance caprolactam and its related lactams, and the corresponding open-chain amino carboxylic acids were studied for the inhibition of the growth of cress radicles. The lactams ranging from six- to nine-, and thirteen-membered rings showed significant growth inhibitory activity. Moreover, the activity was found to be enhanced by increasing the carbon number of lactams, except for 2-azacyclononanone. On the other hand, the open-chain amino carboxylic acids and the smallest ring lactam 2-pyrrolidinone did not inhibit the growth of cress radicles.