Neonectrolide A, a new oxaphenalenone spiroketal from the fungus Neonectria sp.

Neonectrolide A (1), an oxaphenalenone spiroketal with the previously undescribed (5,8'-dimethyl-5'-oxo-3a',4,5,5'-tetrahydro-3H,3'H-spiro[furan-2,2'-isochromeno[3,4,5-def]chromene]-3'-yl)but-3-enoic acid skeleton, was isolated from cultures of the fungus Neonectria sp. Its absolute configuration was assigned by electronic circular dichroism (ECD) calculations. The skeleton of an oxaphenalenone fused with a 1,6-dioxaspiro[4.5]decane moiety in 1 could be derived from the coisolated putative precursors, corymbiferan lactone E (2) and 3-dehydroxy-4-O-acetylcephalosporolide C (3).