Highly methoxylated neolignans from the endangered plant Yulania cylindrica and their chemotaxonomic significance

Three previously undescribed highly methoxylated neolignans, cylindrienones A-C (1-3, resp.), together with five related known neolignans (4-8) were isolated from the twigs and leaves of the ornamental and medicinal plant Yulania cylindrica, a 'vulnerable' species endemic to China. The new structures were established by spec-troscopic methods including HRESIMS, 2D-NMR, and electronic circular dichroism (ECD). The known ones were identified by comparing their observed and reported physicochemical properties and spectroscopic data. Com-pounds 1 and 2 are (C8-C3')-neolignan derivatives possessing a unique cyclohexadienone unit, while compound 3 is a rearranged neolignan containing a rare tricycle [4.2.0.02,8]octane moiety. Compounds 1-8 were isolated from Y. cylindrica for the first time. Compounds 4 and 7 were even firstly found from the family Magnoliaceae. The chemotaxonomic significance of the isolated methoxylated neolignans was briefly discussed.