Kinetin-like Growth-promoting Activity of 1-substituted Adenines (1-benzyl-6-aminopurine and 1-(gamma, Gamma-dimethylallyl)-6-aminopurine.

Biological activity of the type exhibited by kinetin (I) in promoting growth (cell division, organ formation, etc.) in plant tissues has been found to be limited almost entirely to 6-substituted purine derivatives.", 2 Activity has been reported for a few other substances including a 3-substituted adenine derivative, the alkaloid triacanthine,3 isolated from honey locust leaves and identified by procedures including synthesis as 3-(Qy,-y-dimethylallyl)-adenine.4 This alkaloid may be widely distributed in plants as it also has been isolated under the names chidlovine and togholamine from two other species.5 In tests carried out in our laboratory, however, triacanthine was active only when it had been heated in the test procedures and, even so, only in relatively high concentrations (1-100 /.M/l compared with ca. 0.001-0.05 jAM/l of kinetin).6 It was established that the activity was due not to triacanthine but to a product formed by autoclaving it with the nutrient medium as in routine bioassay procedures or merely by heating it in weakly acid aqueous solutions. The active product has an Rf higher than that of triacanthine (Rf 0.73) and in the same region as that of 6-(Qyy-dimethylallylamino)-purine (II) (Rf 0.95) in a n-butanol:water:glacial acetic acid 75:20:5 v/v/v solvent system. This 6-isomer of triacanthine has ten times higher specific activity than kinetin in the range from barely detectable to maximum response in the tobacco callus bioassay; i.e., 0.0001-0.01 ,IAI/l of 6-(-y,y-dimethylallylamino)-purine compared with ca. 0.001-0.10 juAiI/l of kinetin.6 Thus it was estimated that a conversion of 0.01 per cent or less of the tested dosages of triacanthine to the 6-isomer would account for the observed biological activities. Certain kinetin analogues and other adenine derivatives substituted in position two, seven, or nine have been negative in tests for growth-promoting activity.8' 7 Recently, Leonard and Fujii8 have synthesized 1-(Qyy-dimethylallyl)-adenine (III) and 1-benzyladenine (IV). Evidence is presented here that these compounds are biologically active. Quantitative activities of these, the corresponding 6Nisomers, and of kinetin have been compared in tests of growth promotion in callus cultures and chlorophyll retention in leaf tissue. Materials and Methods.-The test chemicals 1-benzyladenine (IV), 6-benzylaminopurine (V), 1-(-y,'y-dimethylallyl)-adenine (III) and 6-(,y,'y-dimethylallylamino)purine (II) were prepared by Leonard et al., University of Illinois. Synthesis and biological activity of the 6N-substituted adenines are well established. 1-6 Synthesis of the l-substituted adnines is described in this issue.8 Kinetin was prepared locally.9 Growth-promoting activity was measured in terms of yields and observed morphogenetic effects in bioassays with tobacco tissue cultures. The procedures and media employed were essentially as reported by Murashige and Skoog.10 The organic supplements were 2.0 mg/1 3-indoleacetic acid (IAA), 0.5 mg/i niacin, 0.5 mg/i pyridoxine, 0.1 mg/1 thiamin*HC1, 100 mg/1 myo-