Structures of Two Natural Hypotensive Diels-Alder Type Adducts, Mulberrofurans F and G, from the Cultivated Mulberry Tree (Morus lhou KOIDZ.)

Two novel 2-arylbenzofuran derivatives named mulberrofurans F and G (=albanol A), as well as albanol B (3), were isolated from the ethyl acetate extract of the root bark of cultivated mulberry tree (Japanese name "Roso, " a cultivated variety of Morus lhou KOIDZ.). The structures of mulberrofurans F and G were shown to be 1 and 2, respectively, on the basis of spectral and chemical evidence. Mulberrofurans F (1) and G (2) were derived from chalcomoracin (4) and mulberrofuran C (5), respectively, by photocyclization in acidic solution. The compounds (1, 2, and 3) are optically active and can be regarded biogenetically as variations of Diels-Alder type adducts of chalcone derivatives and a dehydroprenyl-2-arylbenzofuran derivative. Intravenous injection of mulberrofuran F (1), as well as G (2), caused a marked depressor effect in rabbit.