Cosmochlorins A (1), B (2), and C (3) were isolated from the endophytic fungus Cosmospora vilior IM2-155. The structures of 1, 2, and 3 were elucidated by a combination of extensive spectroscopic analyses, including extensive 2D NMR, HRESITOFMS, and chemical reactions. Compounds 1, 2, and 3 were evaluated for their biological activity. Compounds 1 and 2 partially restored the growth inhibition caused by hyperactivated Ca2+-signaling in mutant yeast and showed glycogen synthase kinase (GSK)-3b inhibition activity at IC50 values of 62.5 and 60.6 mu M, respectively. Further, compound 2 significantly increased osteoclast formation by more than 1.5-fold in RAW264.7 cells compared to receptor activator of nuclear factor-kB ligand (RANKL) alone. (C) 2016 Phytochemical Society of Europe. Published by Elsevier Ltd. All rights reserved.