Synthesis of β-aminobutyric acid-Rhein conjugates and their bioactivity and phloem translocation

Amino-pesticide conjugates enable to improve the systemic conductivity of parent ingredients, increase utilization efficiency, and decrease the waste that was caused by the unreached target and thus pollution to the environment. In this study, four target compounds were designed and synthesized using the natural product Rhein as the leading compound and β-aminobutyric acid (BABA) as the directing group, and their antifungal activities against the six plant pathogens, effects on enzymatic activities of the phenylalanine ammonialyase (PAL) and peroxidase (POD) of wheat leaves, which were treated by the compounds, and their phloem translocation in Ricinus seedling were measured. The results showed that compound 4b (concentration at 0.5 mmol/L) had not only an inhibition effect on the Rhizoctonia solani Kühn (the inhibition rate of mycelial growth was 53.5%), but also an inducible resistance (duration was nearly 7 d), and phloem translocation (sap concentration was 15.1 µmol/L). This study provides a new idea for developing systemic and inducible fungicides.