Since the occurrence of cytokinin' activity has been limited mainly to 6-substituted purine derivatives,2 -4 it was of special interest to determine the origin of the kinetin-like growth-promoting activity of the 1-substituted adenines, 1(-y, y-dimethylallyl)adenine (I, tautomeric forms shown), and 1-benzyladenine, which were made5 and tested6 in these laboratories. While consideration has been given to the possibility that the 1-substituted adenines might be active as such, our interpretation of the results previously reported has been that the development of activity was the consequence of chemical change to the N6-isomeric or other active N6-substituted compounds."t 6 Accordingly, our experiments have been directed toward determining the conditions under which 1to N6-isomer conversion will occur. First, it was necessary to ascertain that we could obtain pure 1-(Q,yy-dimethylallyl)adenine (I), free from any of the isomeric 6-(y,-y-dimethylallylamino)purine ("N6-2-isopentenyladenine") (II), the highly active cytokinin4 7-9 which was originally obtained synthetically5"0 and has been found more recently to be naturally occurring."1-'4 The 1-(y,y-dimethylallyl)adenine was prepared by the procedure previously reported:' alkylation of adenosine with -y,Y-dimethylallyl bromide in dimethylformamide at room temperature followed sequentially by hydrochloric acid hydrolysis in ethanol, cautious neutralization in ethanol with potassium carbonate to pH 6.8, and isolation of the initial product by an evaporative procedure during which the solution was kept below 35?. The product was recrystallized 10-12 times from ethanol. Cellulose column chromatography of both the crystals and the mother liquor from the last recrystallizations did not show the presence of any impurity. Thus, we could conclude that the level of impurity was less than 0.1 per cent since the chromatography of an artificially prepared mixture of 500 mg of 1-(y,y-dimethylallyl)adenine and 0.5 mg of 6-(y,y-dimethylallylamino)purine permitted easy detection of the latter by ultraviolet spectra of the eluted fractions. The pure compound I was characterized by the following properties: XEtOH9 mp 237-238?,5 Rf 0.55 (butanol, water, acetic acid -'75:20:5); X Hax 273 m,u (e 12,300), Xmin 246 (3900); Xmax (acidic) 260 (13,400), Xmin 233 (3,900); Xmax (basic) 274 (15,200), 268 (15,000, dual peak), 300 (sh) (4,100), Xmin 242 (4,500). Next, it was necessary to minimize chemical change of the 1-(y,'y-dimethylallyl)adenine in the test for cytokinin activity. The procedures and media employed were essentially those of Murashige and Skoog'5 using tobacco callus tissue (Nicotiniana tabacum var. Wis. #38) as described earlier.6 Solutions of pure 1(-,yy-dimethylallyl)adenine were sterilized by filtration and added to the medium