Influence of alterations in the purine ring on biological activity of cytokinins

The 1-deaza-, 3-deaza-, 8-aza-1-deaza- and 8-aza-3-deaza-analogs of kinetin and 6-(3-methyl-2-butenylamino)purine and some of their ribosides were synthesized and their growth-promoting activities in the tobacco bioassay were determined and compared with those of the parent compounds. The replacement of nitrogen by carbon in the 1 -position of the purine ring decreases cytokinin activity 15-fold for kinetin and 2-fold for 6-(3-methyl-2-butenylamino)purine (IPA); however, the replacement of nitrogen by carbon in the 3-position decreases the activity 2000 times for kinetin and 1000 times for 6-(3-methyl-2-butenylamino)-purine. The activity of 8-aza-1-deaza-analogs appears to be of the same order of somewhat lower than the corresponding 1-deaza-analogs. The corresponding 8-aza-3-deaza-analogs are less active than kinetin (400 times and 6-(3-methyl-2-butenylamino)purine (40 times). However, they are more active than the corresponding 3-deaza-analogs. The concentration range in which the ribosides show activity is nearly the same as for the corresponding free bases, but the maximum yield of tobacco-callus for the riboside of the 3-deaza-analog of 6-(3-methyl-2-butenylamino)purine is very low.