Acaulide, an Osteogenic Macrodiolide from Acaulium sp. H-JQSF, an Isopod-Associated Fungus.

Acaulide (1), a macrodiolide with an unprecedented framework, was characterized along with its shunt products-acaulones A (2) and B (3)-from the culture of Acaulium sp. H-JQSF associated with the isopod Armadillidium vulgare. The spiro-linked 14-, 14-, and 6-membered cycles of 1 arise likely from iterative intermolecular Michael addition reactions. Biological evaluation in the prednisolone-induced osteoporotic zebrafish demonstrated that 1 is antiosteoporotic at 0.4 and 2.0 μM.