Lachnumon

The structures of four new biologically active halogenated dihydroiso coumarins isolated from submerged cultures of the ascomycete Lachnum papyraceum have been elucidated by spectroscopic methods. The compounds are structurally related to lachnumon and mycorrhizin A, which are also produced by the fungus.

During investigations on the influence of CaBr2 on the secondary metabolism of Lachnum papyraceum, the production of mycorrhizins and lachnumon type antibiotics was strongly inhibited in bromide-containing culture media. Instead, six isocoumarin derivatives, 6-hydroymellein (6), 4-chloro-6-hydroxymellein (7), 4-bromo-6-hydroxymellein (9), 6-methoxymellein (10). 4-chloro-6-methoxymellein (11), and 4-chloro-6,7-dihydroxymellein (12) were isolated. Compounds 7, 9, 11, and 12 have never been isolated from natural sources. 6-Hydroxymellein has been isolated previously from many sources including Gilmaniella humicola and proposed to be a precursor of mycorrhizin A (see reference 6). In comparison to the mycorrhizins, the isocoumarin derivatives exhibited only weak antimicrobial, cytotoxic, phytotoxic, and nematicidal activities.

The structure determination of lachnumon B1 (16) and lachnumon B2 (17), brominated derivatives of lachnumon (1), as well as mycorrhizin B1 (18) and mycorrhizin B2 (19), brominated derivatives of mycorrhizin A (3), is described. The compounds, which exhibit similar antimicrobial and nematicidal activity as their chlorinated analogues, were isolated from extracts of cultures of the ascomycete Lachnum papyraceum to which CaBr2 had been added. The structures were elucidated by spectroscopic methods.