CYTOKININ-AGONISTIC AND ANTAGONISTIC ACTIVITIES OF 4-SUBSTITUTED-2-METHYLPYRROLO[2,3-D]PYRIMIDINES, 7-DEAZA ANALOGS OF CYTOKININ-ACTIVE ADENINE-DERIVATIVES

Sixteen 4-substituted-2-methylpyrrolo[2,3-d]pyrimidines were tested for their activities as cytokinin agonists and antagonists in three bioassay systems. With the systematic variation of the 4-substituent, the activity changed consecutively from agonistic to antagonistic in the tobacco callus test, and this agonist-antagonist relationship was analysed by a steric substituent parameter as a common quantitative measure. Two compounds were found to possess bud-forming activity in the absence of added cytokinins. Eight compounds promoted betacyanin synthesis'in Amaranthus and 4 promoted germination in lettuce seeds. The 4-hydroxyethyl derivative, which was inactive in the tobacco test, suppressed betacyanin synthesis at 100 μM against 100 μM 6-(3-methyl-2-butenylamino)- purine. The 4-phenyl derivative showed antagonist activity in the tobacco test, little activity in the Amaranthus bio- assay and significant agonist activity in the lettuce seed germination. The 4-cyclobutyl derivative exerted the strongest anticytokinin activity (I50 at 0.06 μM against 0.05 μM kinetin) in the tobacco callus assay, while little activity was observed in the other two assay systems. © 1979.