Ampelopsin, a Major Antifungal Constituent from Salix sachalinensis, and its Methyl Ethers

To measure the antifungal potency of plant secondary metabolites, we did an antifungal test using Cladosporium herbarum as a test fungus and minute extracts of some plants. This test showed that the methanol extract of Salix sachalinensis leaves had strong antifungal activity. An antifugal principle in the leaves has been identified as (2R, 3R)-(+)-5,7,3',4',5'-pentahydroxy-dihydroflavonol (ampelopsin). The antifungal potency of S.sachalinensis leaves was not due to an antifungal constituent with high specific activity, but due to the high content of ampelopsin. To improve the antifungal activity, ampelopsin was made into variously methylated derivatives,and these products were bioassayed. 7,3',4'-Tri-omicron-methylampelopsin,out of 8 derivatives, had the strongest antifungal activity, which was about 4 times that of ampelopsin. The structure-activity relationship is briefly discussed.