Phlegmadine A: A Alkaloid with a Unique Cyclobutane Ring from .

Phlegmadine A (), a alkaloid with a unique cyclobutane ring and featuring a complex tetracyclo[4.2.2.0.0]decane-bridged system, together with three biogenetically related known compounds, was isolated from the . The structures and absolute configurations of and were determined by NMR and single-crystal X-ray analysis. Among them, compound exhibited noticeable protective effects for long-term potentiation impairment by corticosterone induced in mice. Moreover, we succeeded in the efficient synthesis of from by a biomimetic synthesis method.