Cavicularin

Cavicularin is a phenolic secondary metabolite isolated from the liverwort Cavicularia densa. This macrocycle is unusual because it was the first compound isolated from nature displaying optical activity due to the presence of planar chirality and axial chirality. The specific rotation for (+)-cavicularin is +168.2° [1]. It is also a very strained molecule. It incorporates a benzene ring that is bent 17° out of planarity. This type of angle strain in aromatic compounds is normally reserved for synthetic cyclophanes.



The liverwort was obtained from Mt. Ishizuchi in the district of Shikoku. The material is dried for one day, ground to a powder and 5 gram was refluxed in methanol for 4 months (!) to yield 2.5 mg (0.049%) of cavicularin after column chromatography and preparative TLC. Fortunately in 2005 the compound was prepared by total synthesis together with the unstrained compound riccardin C [2].