Abstract
Valsa ceratosperma, which is the pathogenic fungus of apple canker, was grown in a synthetic medium. The neutral extract from the culture filtrate was chromatographed on a silica gel column to give five isocoumarins. Their structures were determined by MS, UV, IR, 1H and 13C NMR, and CD spectra. Three of them were known compounds; (-)-5-methylmellein (1), (-)-5-carboxylmellein (2) and (-)-5-hydroxylmethylmellein (3). Since the absolute configurations at C-3 in 2 and 3 were not known until now, both were determined to be R by chemical correlations. The two were new compounds; (+)-(3R, 4S)-trans-4-hydroxy-5-methylmellein (4) and (-)-(3R, 4R)-cis-4-hydroxy-5-methylmellein (5). All the five compounds showed phytotoxicity in a bioassay using detached apple shoots and lettuce seedlings.
