Among 98 3-acyltetramic acid analogues, compounds 1c, 2c, 2f and 2g, showed >90% nematicidal activity against the pine wood nematode Bursaphelenchus xylophilus at a 10 μg/mL concentration. The nematicidal activities of compounds 1d, 1h, and 2k were a little lower at 88.0%, 85.8%, and 57.2% at a 10 μg/mL concentration, respectively. The nematicidal activity of emamection benzoate, widely used in Korea for the prevention of pine wilt disease, was 32.3% at a 10 μg/mL concentration. Other 3-acyltetramic acid analogues showed less than 30% nematicidal activity. A structure-activity relationship study indicated that the chain length of the C-acyl substituent was very important for high nematicidal activity. All active compounds had C13H27 or C11H23 acyl substituents, in two closely related groups with the common physicochemical properties of a polar surface area 57.6A², PSA (polar surface area) 7.8-8.6% and ClogP (calculated partition coefficient) 5.1-5.9 and a polar surface area 75-84A², PSA 11.1-11.6% and ClogP 4.7-5.1, respectively. Our study indicates that active 3-acyltetramic acid analogues could have potential as lead compounds for developing novel pine wood nematode control agents.
Keywords: 3-acyltetramic acid analogues; lead compounds; pine wilt disease; pine wood nematode; toxicity.