Elucidation of biosyntheric mechanisms and metabolisms for lignans

为了阐明木脂素的生物合成机制，我们对几种植物中木脂素的形成进行了研究。首先，我们对白玉兰中呋喃木脂素的形成进行了重点研究。从木脂素中分离得到的木脂素的对映体组成中，酚类呋喃木脂素如pinorersinol和syringaresinol光学不纯。另一方面，非酚类呋喃木脂素如udesmin， yangambin和kobusin是光学纯的。这些结果表明，对映选择酶参与了非酚类呋喃木脂素的形成。此外，我们还研究了酚类呋喃木脂素的o -甲基化反应，该反应与无细胞的北方野檀提取物孵育。结果表明，无细胞提取物可催化松脂醇和丁香紫杉醇的o -甲基化反应，分别将松脂醇和丁香紫杉醇转化为茴香素和丁香紫杉醇。体外转甲基化反应具有对映选择性，(+)-形式是首选底物。接下来，我们研究了刺五加中木脂素的形成。从木脂素的对映异构体组成来看，两分子sinapyl醇经非选择性偶联转化为丁香木脂醇二糖苷形成外消旋丁香木脂醇，(+)-丁香木脂醇为首选底物。在对亚麻木脂素（Linum usitatissimum）的研究中，发现在亚麻籽中不以游离形式存在，而是以络合酯的形式存在。初步实验表明，在亚麻植物中，有一个有序的生物合成顺序，首先是立体选择偶联得到呋喃木脂素(+)-松脂醇，然后转化为四氢呋喃和二苯丁烷骨架。

In order to clarify biosynthetic mechanism for lignans, we investigated the formation of lignans in several plant.First, we have focused our research efforts on the formation of furofuran lignans in magnolia kobus var. borealis. With respect to enantiomeric composition of isolated lignans from M. kobus var. borealis, phenolic furofuran lignans such as pinorersinol and syringaresinol were optically impure. On the other hand, non-phenolic furofuran lignans such as eudesmin, yangambin and kobusin were optically pure. these results suggested that enantioselective enzyme are in formation of the non-phenolic furofuran lignans. Also, we examined O-methlation reactions of phenolic furofuran lignans by incubation with cell-free extracts from M. kobus var. borealis. It was shown that the cell-free extracts catalyzed the O-methylation reactions of pinoresinol syringaresinol, suggesting the conversions of pinoresinol into eudesmin, and syringaresinol into yangambin, respectively, The in vitro transmethlation reactions observed were enantioselective with the (+)-forms being the preferred substrates.Next, we investigated lignan formation in Acanthopanax senticosus. Based on the enanyiomeric composition of their lignans, it was suggested that racemic syringaresinol formed from two molecules of sinapyl alcohol by a non-selective coupling followed by transformation into syringaresinol diglucoside with the (+)-syringaresinol being the preferred substrate.In study of lignans flax (Linum usitatissimum), it was shown that secoisolariciresinol diglucoside does not occur in flaxseed in a free form, but rather occurs in a complex ester. Preliminary experiments have indicated that in flax plant there is an orderly biosynthetic sequence initially involving stereoselective coupling to give the furofuran lignan(+)-pinoresinol, and its subsequent transformation into tetrahydrofuran and dibenzylbutane skeleta.