Structure-activity relationships of N-phenyl-N'-benzothiazol-6-ylurea synthetic derivatives: Cytokinin-like activity and adventitious rooting enhancement

Some years ago we demonstrated the cytokinin-like activity of the synthetic N-phenyl-N'-benzothiazol- 6-ylurea (PBU) and a relevant adventitious rooting adjuvant activity of symmetric urea derivatives devoid of any cytokinin- or auxin-like activity per se. Here we report the synthesis and the biological activity evaluation of nine symmetric or asymmetric ureas/thioureas, structurally related to PBU. None of them show cytokinin-like activity, while we demonstrate for the first time that PBU interacts with Arabidopsis cytokinin receptor CRE1/AHK4 in a heterologous bioassay system. Among the PBU derivatives, all the symmetric ureas/thioureas show an adventitious rooting adjuvant activity in various bioassays, confirm- ing that this activity is strictly dependent on their chemical structure.