INHIBITORS OF CYTOKININ METABOLISM .4. SUBSTITUTED XANTHINES AND CYTOKININ ANALOGS AS INHIBITORS OF CYTOKININ N-GLUCOSYLATION

A series of 3-substituted xanthines, 2-(2-hydroxy-2-methylpropylamino)-9-methyl-6-benzylaminopurine and 7-benzylaminooxazolo[5,4-d]pyrimidine were synthesized as potential inhibitors of cytokinin N-glucosylation. In maize leaf segments the latter compound was found to be the most effective inhibitor tested, inhibiting the formation of the 9-glucoside of 6-benzylaminopurine (BAP) and raising the amount of free BAP. N-glucosylation of BAP in radish leaves was found to be suppressed most effectively by 1,7-dimethyl-3-(3-methylbutyl)xanthine, 1,7-dimethyl-3-(5-hexenyl)xanthine and 1,7-dimethyl-3-(3-methyl-2-butenyl)xanthine. The first two compounds were also effective inhibitors in radish cotyledons and elevated the concentrations of both free BAP and BAP nucleotide. These results indicate that the structural requiremens for effective inhibitors of N-glucosylation differ between the two species.