Design, Synthesis, and Biological Activity of 16,17-Dihydro Gibberellin A ₅ Derivatives as Novel Plant Growth Regulators

Designing 16,17-dihydro gibberellin A5-13-acetate (DHGA₅) derivatives based on GA3β-hydroxylase (GA3ox) structural features represents an ideal strategy for developing novel plant growth retardants. Building upon our previous findings, we designed and synthesized a series of carboxyl-protected DHGA₅ derivatives bearing thiosemicarbazone and 1,3,4-thiadiazole moieties. Following photolytic deprotection, compounds <b>10e</b> and <b>11l</b> emerged as the most active compounds in their respective series. Notably, compound <b>10e</b> exhibited superior activity (IC₅₀ = 90 μM) compared to DHGA₅ (IC₅₀ = 97 μM) in <i>Arabidopsis</i> root growth inhibition and exhibited enhanced activity in suppressing the elongation of rice second leaf sheath. The computational simulation results indicated that deprotected compound <b>10e</b> enhanced binding to <i>Os</i>GA3ox2 through interactions with additional amino acid residues. Interestingly, derivatives showed unexpected potential in alleviating oxidative damage caused by salt stress. This study presents a promising strategy for the development of novel gibberellin biosynthesis inhibitors as potential plant growth retardants.