Design, Synthesis and Gibberellin-Like Activity of Novel 1-Substituted 3-[3-(Trifluoromethyl)phenyl]thiourea Derivatives

It has previously been demonstrated that a thiourea derivative, namely 1-phenethyl-3-[3-(trifluoromethyl)phenyl]thiourea (Y21), exhibits high gibberellin-like activity. In this work, the influence of the alkyl chain length and various benzene ring substituents on the biological activity of Y21 was investigated. 1-Substituted 3-[3-(trifluoromethyl)phenyl]thiourea derivatives were designed, synthesized, and comprehensively evaluated. The biological activity analysis demonstrated that at a dose of 0.1 μM, compound S8, i.e., 1-(3-bromophenethyl)-3-[3-(trifluoromethyl)phenyl]thiourea), exhibited significantly higher promoting activity with respect to Arabidopsis thaliana hypocotyl elongation and rice germination than did gibberellin A3 (GA3) and Y21. Moreover, the physiological response of the A. thaliana mutant ga1-1 to treatment with S8 suggested that this compound possessed GA-like function. The molecular docking analysis indicated that S8 formed hydrogen bonding interactions with residues Phe238 and Ser191 of the gibberellin insensitive DWARF1 (GID1) receptor, which resulted in stronger binding with GID1 than Y21. The bioactivity of derivatives S1–S22 exhibited a clear negative monotonic association with the molecular docking-based score values. Overall, it was determined that S8 displayed excellent GA-like bioactivity and facilitated hypocotyl elongation and germination; therefore, it could be applied as a potential plant growth regulator.