Lytic activity of l-menthol derivatives against the snow blight disease fungus,Micronectriella nivalis

Lytic activity of l-menthol (1) derivatives [(-)-(1S,3R,4S,6S)-6-hydroxymenthol (2), (-)-(1S,3R,4S)-1-hydroxymenthol (3), and (+)-(1S,3R,4R,6S)-6,8-dihydroxymenthol (4)] against the snow blight disease fungus, Micronectriella nivalis was investigated. Compounds 2, 3, and 4 had 85.0, 63.9, and 81.9% lytic activity, respectively, at a concentration of 0.2 mg/mL. The activity of each of the three compounds increased in a dose-response manner. To study the structure-activity relationship, acetyl esters of 1-4 [(-)-menthyl acetate (1Ac), (-)-6-hydroxymenthyl diacetate (2Ac), (-)-1-hydroxymenthyl 3-monoacetate (3Ac), and (-)-6,8-dihydroxymenthyl 3,6-diacetate (4Ac)] were synthesized with yields of 80.2-99.8% and were also assayed. The acetyl esters of 1Ac, 2Ac, 3Ac, and 4Ac had 51.2, 91.5, 66.0, and 95.2% lytic activity, respectively, at a concentration of 0.2 mg/mL, and these compounds showed further high lytic activity compared with the alcohols of 1-4. These acetyl esters also showed higher lytic activity as their concentration was increased. Of particular interest is the fact that 2Ac and 4Ac both had higher lytic activity at 0.05-0.2 mg/mL compared with copper 8-hydroxyquinolate, a standard chemical widely used to control snow blight. This is the first report on lytic activity of l-menthol derivatives.