Trisubstituted purines are useful tools for developing potent plant mitogen-activated protein kinase inhibitors.

A number of compounds have been reported to be specific inhibitors of protein kinases mediated by structural-based selectivity, but the development of specific inhibitors has not yet been addressed in plant science. Here we tested C2, C6, and N9-trisubstituted purines to determine the basic relationship between their chemical structure and inhibitory activity versus a plant mitogen-activated protein kinase (MAPK). Modification of substitution at positions C2 and N9 caused increased inhibitory activity of 6-benzylaminopurine analogs. In the case of 6-isopentenyladenine derivatives, the addition of a methyl group at position N9 caused at least 2-fold increased inhibitory activity, as compared with the addition of an isopropyl group. The data indicate that the selectivity and potency of inhibitors can be improved by modification of the chemical structure, suggesting that trisubstituted purines are powerful tools for probing biological processes and understanding the physiological roles of MAPK signaling.