Spirograterpene A, a Tetracyclic Spiro-Diterpene with a Fused 5/5/5/5 Ring System from the Deep-Sea-Derived Fungus Penicillium granulatum MCCC 3A00475

A novel spiro-tetracyclic diterpene, spirograterpene A (1), was isolated from the deep-sea-derived fungus Penicillium granulatum MCCC 3A00475, together with two biosynthetically related cyclopianes, conidiogenone I (2) and conidiogenone C (3). The relative configuration of 1 was elucidated by extensive spectroscopic analyses, and the absolute structure was established by the modified Mosher’s method. Compound 1 is the second example of a diterpene featuring a 5/5/5/5 spirocyclic carbon skeleton. It showed modest antiallergic activity.