Constituents of cultivated mulberry tree.

From the ethyl acetate extract of the cultivated mulberry tree (Morus alba L.), two new flavonoid derivatives with a fused dihydrochalcone partial moiety were isolated, and named kuwanons K and L. The structures of kuwanons K and L were shown to be 1 and 2 respectively, on the basis of chemical and spectral data. Kuwanons K ( 1) and L ( 2) are regarded biogenetically as Diels-Alder adducts of a chalcone derivative and a dehydroprenylflavonoid derivative, and are the first example of a flavonoid derivative possessing a cyclohexene ring at a B ring of a flavonoid derivative.