Cladobotryal: a fungal metabolite with a novel ring system.

In screening for antifungal metabolites a novel compound, cladobotryal, was isolated from the mycoparasitic fungus Cladobotryum varium. Its structure was established as (+)-(2R*,3R*)-2-[(Z)-2-buten-2-yl]-3, 7-dihydro-3-formyl-3-methyl-5-phenylfuro[2,3-b]pyridin-4(2H)-one on the basis of spectroscopic evidence and single crystal X-ray analysis of its methyl hemiacetal. The fused furo[2,3-b]pyridinone skeleton of cladobotryal seems unprecedented within the chemical literature.