Studies on the nematocidal constituents of natural medicines

A new assay method was established for evaluation of nematocidal activity using second-stage larvae of dog roundworm, Toxocara canis, a main pathogenic parasite of 'larva migrans.' By using this method, the nematocidal activities of hot water and methanol extracts of spices (42 samples) and traditional medicines used in Southeast Asian countries (615 samples) and commercially available essential oils (82 samples) were determined. Some of the compounds showing a strong nematocidal activity were identified in these samples; Among them were piperamides and alkyl-amides from pepper, and a diarylnonanoid from mace. These compounds and their analogs were synthesized and the structure- activity relationships were investigated. A combination of a tannin and a nematocidal compound caused 'burst' of the larvae (tannin burst). Tannins with more galloyl or catechin groups showed a stronger bursting activity. A similar burst of slightly different features was induced by some essential oils (ES-burst) in which the responsible compounds were elucidated to be terpenoids such as citral and perilla aldehyde. Synergistic actions of constituents were observed in nematocidal and bursting activities by some samples. Such synergistic actions of constituents seemed to play a very important role in the effectiveness of natural medicines.