Isolation and Synthesis of Two New 3-Arylcoumarin Derivatives from the Root of Glycyrrhiza Glabra (Licorice), and Structure Revision of an Antioxidant Isoflavonoid Glabrene

Two new 3-arylcoumarin derivatives were isolated from the root of Glycyrrhiza glabra (licorice; Fabaceae), and their structures were elucidated as 2′,4′-dihydroxy-[6″,6″-dimethylpyrano(2″,3″:7,8)]-3-arylcoumarin and [6′,6″-dimethylpyrano(2″,3″:7,8)]-2′-hydroxy-4′-methoxy-3-arylcoumarin on the basis of spectroscopic evidence. Chemical syntheses of these two pyrano-3-arylcoumarins are described. Two other known isoflavonoids glabrene and glabrone were also obtained, and the structure of the former is revised based on 13C-NMR analysis and NOE experiments.