Extractives of kitakobusi Magnolia kobus DC. var. borealis Sarg., 2: Distribution in tree and seasonal variation in leaves of lignans
1996
Kim, Y.G. (Hokkaido Univ., Sapporo (Japan). Faculty of Agriculture) | Ozawa, S. | Sano, Y. | Sasaya, T.
The present work has been undertaken to clarify the distribution of lignans in each section, such as xylem, bark, leaves and flower buds from kitakobushi Magnolia kobus DC. var. borealis Sarg. The lignans obtained from each section consisted of furofuranoids and tetrahydrofuranoids. Lignans of the leaves were characterized as furofuranoids such as magnolin(IV), epimagnolin(IX), eudesmin(III) and yangambin(V), which were highly replaced with substituents such as methoxyl and methylenedioxy groups. The bark contained fourteen lignans of which main compounds were magnolin(IV) and yangambin(V), though the flower buds contained magnolin(IV) and yangambin(V) as main lignans. These four lignans did not have free hydroxyl group, but methoxyl groups replaced. Syringaresinol(XIII) was found in only xylem and bark but they were small portions. To investigated the seasonal accumulation of lignans, the leaves were collected at Hokkaido University campus from May to November in 1994. MeOH extracts obtained from the leaves were subjected to hydrolysis by beta-glucosidase to avoid the complexity of extractive resulting from glucosides. The enzymatic hydrolyzates were extracted with CH2Cl2, and the determination of lignans in the CH2Cl2 solubles was performed on HPLC. The amount of lignans increased during May to June, except aschantin(II). The contents of many lignans decreased to minimum in August, but the amount of pinoresinol(XIV) enhanced twice compared with those of the other months. This accumulation of compound XIV seemed that biosynthesis surrounding pinoresinol(XIV) in the leaves changed from normal state to abnormal. If this assumption was reasonable, it suggested that pinoresinol(XIV) may be correlated intensely to formation of the other lignans in the leaves
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