Nematocidal Activity of Picrodendrins against a Species of Diplogastridae

To develop parasiticides, the nematocidal activity of 22 picrotoxane terpenoids, picrodendrins isolated from the Euphorbiaceae plant Picrodendron baccatum (L.) KLUG et URBAN, was measured using a species of Diplogastridae (Nematoda). Picrodendrin P displayed the most potent nematocidal activity with a minimum lethal concentration (MLC) value of 4.4×10-3 M. The nematocidal activity of picrodendrin P was 9-fold more potent than that of kainic acid (4.0×10-2 M) and santonin (4.0×10-2 M) and 6-fold more potent than that of diethylcarbamazine citrate (3.0×10-2 M). Thus, picrodendrin P may eventually be used as a leading parasiticide. In light of the relationship between the structure of picrodendrins and their nematocidal activities, potent nematocidal activity was found to require the following elements within the picrotoxane skeleton : the γ-lactone that bridges C-3 and C-5, the epoxide group that bridges between C-6 and C-8, a cis-OCH3 group and a trans-CH2OH group related to carbonyl at α-methylene-γ-lactone ring (C-18), and the absence of 4- and 8-hydroxyl groups. These results are the first demonstration of nematocidal activity for these terpenes and thus are important in furthering our understanding.