Structures of Three New Natural Diels-Alder Type Adducts, Kuwanons P and X, and Mulberrofuran J, from the Cultivated Mulberry Tree (Morus lhou KOIDZ.)

Two new stilbene derivatives, named kuwanons P and X, as well as a new 2-arylbenzofuran derivative, named mulberrofuran J, were isolated from the acetone extract of the root bark of cultivated mulberry tree (Japanese name"Roso, "a variety of Morus lhou KOIDZ.) together with a known 2-arylbenzofuran derivative, albafuran C. The structures of the new compounds were elucidated on the basis of the spectral evidence, and the compounds can be regarded biogenetically as Diels-Alder type adducts of chalcone derivatives and dehydroprenylphenols. In view of the biogenetic route to 2-arylbenzofuran derivatives, involving oxidative cyclization of hydroxystilbenes, it is noteworthy that two stilbene derivatives, kuwanons P (1) and X (2), coexist with two 2-arylbenzofuran derivatives, albafuran C (4) and mulberrofuran J (3), in the mulberry root bark.