Acaulins A and B, Trimeric Macrodiolides from Acaulium sp. H-JQSF

Acaulin A (1) and its macrolactone ring-opened congener acaulin B (2) were characterized from the culture of Acaulium sp. H-JQSF (an isopod-associated fungus) as architecturally undescribed trimeric macrodiolides, with the former being antiosteoporotic at 0.4 μM in the prednisolone-induced osteoporotic zebrafish. Identification of acaudiolic acid (3) as the monomeric macrodiolide precursor facilitated the proposal of the acaulin biosynthetic pathway.