Synthesis, characterization of novel citronellic acid-based amides and their activity against rice root-knot nematode

A novel, efficient and environmentally benign enzymatic method for the synthesis of citronellic acid based amides has been developed, avoiding the use of activating agents for the conversion of citronellic acid to amides, which is otherwise not possible by conventional method. A series of eleven novel amides were prepared by condensation of citronellic acid with different alkyl amines in the presence of Candida antartica lipase at 6090°C in 16-20 h. Reactions were performed without solvents or activating agents, yielding products in significant amounts (72.4-82.3%). The synthesized compounds were characterized using FT-IR and NMR (¹H and ¹³C) and LC-HRMS and tested against the rice root-knot nematode, Meloidogyne graminicola. While all the compounds exhibited promising activity, 3a demonstrated the highest potency with LC₅₀ value of 64.79 mg L^-1 and 30.50 mg L^-1 after 24 and 96 h of exposure, respectively. Though synthesised amides were found less effective than commercial nematicide, fluopyram (LC₅₀ = 3.46 and 0.05 mg L^-1 at 24 and 96 h, respectively) but development of suitable formulations of these compounds will increase the nematicidal activity.