C-H arylation enables synthesis of imidazole-4-carboxamide (ICA) based fairy chemicals with plant growth promoting activity

Imidazole-4-carboxamide (ICA), which is one of a group of “fairy chemicals” (FCs) that cause the fairy ring phenomena, has plant growth inhibitory activity. FCs have the potential as candidates for a new family of plant hormones as they have been found endogenously in all plant species tested, and show growth-regulating activity against the plants. While basic research on FCs is progressing, they are also expected to be applied not only to agrochemicals but also as pharmaceuticals. Derivatization of one of FCs, 2-azahypoxanthine (AHX) and the structure-activity relationship (SAR) studies have clarified its activity as a plant growth promoter. Yet, imidazole-4-carboxamide (ICA) has not been derivatized at all and SAR regarding its activity remains unknown. In this study, we synthesized the derivatives of ICA by direct C-H arylation of ICA precursors and evaluated its activity in rice. The 12 total compounds including the arylated ICAs and their precursors were evaluated for root and shoot elongation in rice, resulting in the discovery that a number of compounds unexpectedly have an elongation activity in the root and shoot.