Comparative Effects of Heterocyclic Compounds on Inhibition of Lettuce Fruit Germination

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Abstract
The molecules of many biologically active plant constituents contain heterocyclic ring systems. Inhibitory effects of a number of heterocyclic compounds and their alicyclic and open-chain analogues on lettuce (Lactuca sativa L. cv. Great Lakes) germination were therefore determined under specified conditions. The most obvious property which correlates chemical structure with biological activity is lipophilicity, as was found in previous studies. However, other less obvious factors play a part. The inhibitory activity of coumarin, for instance, is much greater than would be expected in comparison with compounds of related structures. In general, substitution of a carbon atom in a ring structure by oxygen or nitrogen has either little effect or a lowering effect on activity, unless the increased solubility in water allows an inhibitory concentration to be reached which did not occur with the carbocyclic compound. However, introduction of unsaturation increases activity markedly, especially with some of the indole compounds.