Letenketals A and B, two novel spirocyclic polyketides from a marine crab-derived Letendraea sp. fungus

Two novel spiroketals, named as letenketals A and B, had been isolated from the cultural broth of marine fungal Letendraea sp. Two compounds were stereoisomers and contained the new carbon skeleton including benzodihydropyran ring and one tetrahydrofuran ring, which connected as spiro-fused ring system through one ketal carbon. Their relative and absolute configurations were determined by the 2D-NMR analysis together with single-crystal X-ray diffraction. The antibacterial and cytotoxic activities of letenketals were tested.