SECONDARY METABOLITES BY CHEMICAL-SCREENING .29. AGISTATINES, NOVEL PYRANACETALS FROM THE FUNGUS FH-A-6239

Novel pyranacetals, named agistatines A, B, D, and E (1 to 4), were di scovered by a chemical screening in the culture broth of the fungus FH -A 6239. The structures were established by detailed spectroscopic inv estigations and confirmed by X-ray analysis of agistatine B (2), 4-O-( 2-bromobenzoyl)dihydroagistatine A (6), 4-O-(2-bromobenzoyl)agistatine B (7), and agistatine E (4) leading to the stereochemical information . The described secondary metabolites exhibit unusual bicyclic (1 and 3) and tricyclic (2 and 4) structures with a characteristic ketal moie ty at C-2 (except 3). The instability of the main fermentation product agistatine E (4) is caused by an additional hemiketal located at the adjacent C-8a.