The filamentous fungus, Lambertella sp. 1346 (L. sp. 1346) and Lambertella corni-maris are mycoparasites on Monilinia fructigena. We have isolated lambertellols A (1) and B (2) from L. sp. 1346 as a candidate of the substances related to the mycoparasitism. The other fungus L. corni-maris produces only trace amount of 1 and 2, however this fungus was found to produce them in a substantial amounts under acidic conditions. Our investigations revealed that the host M. fructigena changed its surroundings into acidic conditions, which suggests that the acidic conditions acted as kairomones that stimulated the production of 1 and 2. Since lambertellols A (1) and B (2) are labile to isomerize each other and to gradually decompose into lambertellin (3) even in methanol, the active species have not been figured out. In order to dissolve this question, we synthesized enantiomeric pairs of 1 and 2 as well as some other stable analogues.
