Chemical structure and juvenile hormone activity: Comparative tests on Rhodnius prolixus

Abstract

Some forty-two compounds have been assayed for juvenile hormone activity in Rhodnius by topical application and by injection. The basis of comparison is the dose in μg that will give the median score of 10 (normal adult = 0; complete supernumerary larva = 19) in the assay described. The juvenile hormone of cecropia, dl- trans, trans, cis isomer (Dr. H. Röller), was the most active substance tested: 0·07 μg needed for a score of 10. The other seven isomers fall far below this activity. Of the farnesene derivatives, trans, trans, farnesyl methyl ether has about one-quarter the activity of the cecropia hormone: 0·32 μg needed for a score of 10. A rough estimate of the minimum dose in μg/g body weight required to produce a complete supernumerary larva in Rhodnius is as follows: farnesol > 2300; ethyl farnesenate dihydrochloride 38·4; dl-cecropia hormone, trans, trans, trans isomer 19·2; farnesyl methyl ether 6·9; dl-cecropia hormone trans, trans, cis isomer 2·3. A survey of the whole range of substances tested shows: (1) the importance of the trans, trans configuration at C-2 and C-6 in all these compounds; (2) the importance of a suitable balance between polar and apolar properties: the presence of -OH, -NH 2, or -COOH groups reduces or abolishes activity; (3) transfer of the epoxy ring from C-10,11 to C-6,7 reduces activity in all the isomers of the cecropia hormone. Introduction of a second epoxy ring in the farnesene derivatives likewise reduces activity. These results are discussed in the light of the earlier hypothesis ( Wigglesworth, 1957) that the juvenile hormone influences the gene-controlled enzyme system within the cells by regulating permeability relations in cellular membranes.