A new diketopiperazine-like inhibitor of bone morphogenetic protein-induced osteoblastic differentiation produced by marine-derived Aspergillus sp. BFM-0085.

A new diketopiperazine-like compound, designated protuboxepin K (1), was isolated together with the known structurally related protuboxepin A (2) from culture broth of the marine-derived fungal strain Aspergillus sp. BFM-0085 isolated from a sediment sample of Tokyo Bay. The structure of protuboxepin K was elucidated by spectroscopic data, including 1D and 2D NMR. Compounds 1 and 2 inhibited bone morphogenetic protein (BMP)-induced alkaline phosphatase activity with IC50 values of 4.7 and 25.2 µM, respectively, in mutant BMP receptor-carrying C2C12(R206H) cells.