o-Nitrobenzyl-Based Caged exo-16,17-Dihydro-gibberellin A5-13-acetate for Photocontrolled Release of Plant Growth Regulators

Caged plant growth regulators (caged PGRs) that release bioactive molecules under irradiation are critical in enhancing the efficacy and mitigating the negative environmental effects of PGRs. The synthetically derived plant growth inhibitor exo-16,17-dihydro-gibberellin A5-13-acetate (DHGA5) regulates the development and stress resilience of plants. We report here the conception of novel caged DHGA5 derivatives wherein the photoremovable protecting groups (PRPGs) serve not only to enable light-controlled release but also to protect the carboxyl group during chemical synthesis. Three o-nitrobenzyl-based caged DHGA5 derivatives with different substituents on the nitrobenzyl moiety were obtained and evaluated for their properties in vitro and in vivo. The photolysis half-life values of caged DHGA5 derivatives 7a, 7b, and 7c under a UV lamp were 15.6 h, 1.2 h, and 28.2 h, respectively. Experiments in vivo showed that 0.2 mM of the caged compounds significantly inhibited the growth of the model plant Arabidopsis thaliana and important crop rice in a precise photoactivated form.