Lignin Monomers from beyond the Canonical Monolignol Biosynthetic Pathway: Another Brick in the Wall
Lignin Monomers from beyond the Canonical Monolignol Biosynthetic Pathway: Another Brick in the Wall
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DOI：
10.1021/acssuschemeng.0c01109
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发表时间：
2020-04-06
影响因子：
8.4
通讯作者：
Ralph, John
中科院分区：
文献类型：
--
作者：
del Rio, Jose C.;Rencoret, Jorge;Ralph, John
木质素通常被定义为通过三种主要的单木质素醇（对香豆醇、松柏醇和芥子醇）的氧化聚合形成，所述三种主要的单木质素醇衍生自一般的类苯丙素生物合成途径。还已知也衍生自类苯丙素途径的许多其它酚类化合物在许多植物中作为真正的木质素单体发挥作用，如单木质素酯缀合物、由截短的单木质素生物合成产生的酚类化合物或阿魏酸酯的情况。然而，最近的研究表明，酚类化合物产生于经典的苯丙素途径之外，即黄酮类化合物，羟基芪类化合物和羟基肉桂酰胺，也可能表现为真正的木质素单体，并在一些植物中被掺入木质素中，进一步挑战了木质素的传统定义。这就是黄酮麦黄酮的情况，它被掺入到草和其他单子叶植物的木质素中，羟基二苯乙烯白藜芦醇（与白藜芦醇和异甘草素一起，在较低水平），已发现在棕榈果壳的木质素，其各自的O-葡糖苷（收敛苷、白藜芦醇苷和异根皮苷），或阿魏酰胺阿魏酰酪胺，掺入到烟草和马铃薯块茎的木质素中的二阿魏酰腐胺，以及似乎掺入到玉米粒木质素中的二阿魏酰腐胺。这些有价值的化合物可能以高量和低成本获得，并且可以从来自农业或森林生物质加工的废物中获得。
Lignin is conventionally defined as being formed by the oxidative polymerization of three main monolignols, p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol, that are derived from the general phenylpropanoid biosynthetic pathway. Many other phenolic compounds that are also derived from the phenylpropanoid pathway are also known to perform as genuine lignin monomers in many plants, as is the case of the monolignol ester conjugates, phenolic compounds arising from the truncated biosynthesis of monolignols, or ferulate esters. Recent investigations, however, have indicated that phenolic compounds arising from beyond the canonical phenylpropanoid pathway, namely flavonoids, hydroxystilbenes, and hydroxycinnamic amides, may also behave as authentic lignin monomers and are incorporated into the lignin in some plants, further challenging the traditional definition of lignin. This is the case of the flavone tricin that is incorporated into the lignin of grasses and other monocots, the hydroxystilbene piceatannol (together with resveratrol and isorhapontigenin, at lower levels) that has been found in the lignins of palm fruit shells, their respective O-glucosides (astringin, piceid, and isorhapontin) that are present in the lignin of Norway spruce bark, or the ferulic amides feruloyltyramine, incorporated into the lignin of tobacco and potato tubers, and diferuloylputrescine, which appears to be incorporated into maize kernel lignin. These valuable compounds are potentially available in high amounts and at low cost and may be obtained from the waste products from the processing of agricultural or forest biomass.