Biological evaluation of 5-substituted pyrimidine derivatives as inhibitors of brassinosteroid biosynthesis.

A series of 5-substituted pyrimidine derivatives was synthesized, and their ability to inhibit brassinosteroid biosynthesis was tested. The biological activity of these compounds was evaluated by the cress stem elongation method. Among the synthesized compounds, alpha-(4-chlorophenyl)-alpha-phenyl-5-pyrimidinemethanol (DPPM 4) exhibited potent inhibitory activity for retarding cress stem elongation in the light. This inhibition was reversed by the application of 10 nM brassinolide, but not by 1 microM GA3. DPPM 4 also affected Arabidopsis growth in the dark. DPPM 4-treated Arabidopsis had phenotypes like those of brassinosteroid-deficient mutants, with short hypocotyls and open cotyledons, in the dark. These biological changes were restored by the co-application of 10 nM brassinolide, but not by 1 microM GA3, suggesting that the primary site of action of DPPM 4 was the brassinosteroid biosynthetic pathway.