Zoosporicidal activities of anacardic acids against Aphanomyces cochlioides

The EtOAc soluble constituents of the unripe fruits of Ginkgo biloba showed motility inhibition followed by lysis of zoospores of the phytopathogenic Aphanomyces cochlioides. We purified 22:1-omega7-anacardic acid (1), 24:1-omega9-anacardic acid (2) and 22:0-anacardic acid (3), together with other related compounds, 21:1-omega7-cardol (4) and 21:1-omega7-cardanol (5) from the crude extracts of Ginkgo fruits. Amongst them, compound 1 was a major active agent in quality and quantity, and showed potent motility inhibition (98% in 30 min) followed by lysis (55% in 3 h) of the zoospores at 1 x 10(-7) M. The 2-O-methyl derivative (1-c) of 1 displayed antibacterial activity against Bacillus subtilis, but practically inactive to Escherichia coli. A brief study on structure-activity relationships revealed that a carboxyl group on the aromatic ring and an unsaturated side chain in the anacardic acid derivative are important for strong motility inhibitory and lytic activities against the zoospore.