Two New Stereoisomers of Neolignan and Lignan from the Flower Buds of Magnolia fargesii

A new stereoisomer of 8-0-4' system neolignan, (7R,8S)-1-(3,4-dimethoxyphenyl)-2-[4-(3-hydroxy-1-propenyl)-2-methoxyphenoxy]-propane-1,3-diol (1) and a new stereoisomer of tetrahydrofuranoid lignan, (7R,8S,7'S,8'R)-(3,4,5,3',4')-pentamethoxy-9,7'-dihydroxy-8.8',7.O.9'-lignan (2) along with seven known lignans and neolignans (3-9) were isolated from the methanol extracts of the flower buds of Magnolia fargesii. The structures of these compounds (1-9) were elucidated by spectroscopic methods including 1D- and 2D-NMR as well as by comparison with reported values. Absolute configurations of new stereoisomers 1 and 2 were determined by circular dichroism (CD) spectra. The absolute configuration of (7S,8S,10S)-[tetrahydro-4-hydroxy-2-(3,4,5-trimethoxyphenyl)furan-3-yl]methyl 3,4-dimethoxy benzoate (3) was determined by Mosher's esterification method for the first time in this study. Three lignans, tanegool (4), (+)-dehydrodiconiferyl alcohol (5), and epieudes-min (6), were isolated from this plant for the first time. Superoxide radical scavenging activities of the isolates (1-9) were measured by irradiated riboflavin/ethylenediaminetetraacetic acid (EDTA)/Nitroblue tetrazolium (NBT) system, and their in vitro rat lens aldose reductase (RLAR) inhibitory activities were also evaluated.