Two new stereoisomers of tetrahydrofuranoid lignans from the flower buds of Magnolia fargesii

Two new stereoisomers of tetrahydrofuranoid lignans, 7S,8R,7′S, 8′R- (1) and 7R,8S,7′S,8′R-3,4,3′,4′-tetramethoxy- 9,7′-dihydroxy-8.8′,7.O.9′-lignan (2) along with nine known lignans including tetrahydrofuranoids (3, 4) and tetrahydrofurofuranoids (5-11) were isolated from a CHCl₃-soluble fraction of the flower buds of Magnolia fargesii. Two tetrahydrofuranoids, magnostellin A (3) and lariciresinol dimethyl ether (4) were isolated from this species for the first time. The structures of these compounds (1-11) were identified by spectroscopic methods as well as by comparison with published values. Absolute configurations of new stereoisomers (1, 2) were determined by the Mosher's esterification method and Circular Dichroism (CD) studies. All the isolates (1-11) were evaluated for their antioxidant activities using modified superoxide radical-scavenging assay. Compounds 5-8 showed the potent superoxide radical-scavenging activities with the ED₅₀ values of 19.2, 19.2, 16.5, and 27.7 μM, respectively, as compared with standard antioxidants (BHA: 22.8 μM; Trolox: 940 μM).