Lignin, a major component of lignocellulose, is the largest source of aromatic building blocks on the planet and harbors great potential to serve as starting material for the production of biobased products. Despite the initial challenges associated with the robust and irregular structure of lignin, the valorization of this intriguing aromatic biopolymer has come a long way: recently, many creative strategies emerged that deliver defined products via catalytic or biocatalytic depolymerization in good yields. The purpose of this review is to provide insight into these novel approaches and the potential application of such emerging new structures for the synthesis of biobased polymers or pharmacologically active molecules. Existing strategies for functionalization or defunctionalization of lignin-based compounds are also summarized. Following the whole value chain from raw lignocellulose through depolymerization to application whenever possible, specific lignin-based compounds emerge that could be in the fu...

Bright Side of Lignin Depolymerization: Toward New Platform Chemicals

Chem. Pharm. Bull.(オピニオン)

https://bioone.org/journals/harvard-papers-in-botany/volume-13/issue-2/1043-4534-13.2.299/Flora-of-China/10.3100/1043-4534-13.2.299.pdf

Flora of China

Lignin, a phenolic polymer in the secondary wall, is the major cause of lignocellulosic biomass recalcitrance to efficient industrial processing. From an applications perspective, it is desirable that second-generation bioenergy crops have lignin that is readily degraded by chemical pretreatments but still fulfill its biological role in plants. Because plants can tolerate large variations in lignin composition, often without apparent adverse effects, substitution of some fraction of the traditional monolignols by alternative monomers through genetic engineering is a promising strategy to tailor lignin in bioenergy crops. However, successful engineering of lignin incorporating alternative monomers requires knowledge about phenolic metabolism in plants and about the coupling properties of these alternative monomers. Here, we review the current knowledge about lignin biosynthesis and the pathways towards the main phenolic classes. In addition, the minimal requirements are defined for molecules that, upon incorporation into the lignin polymer, make the latter more susceptible to biomass pretreatment. Numerous metabolites made by plants meet these requirements, and several have already been tested as monolignol substitutes in biomimetic systems. Finally, the status of detection and identification of compounds by phenolic profiling is discussed, as phenolic profiling serves in pathway elucidation and for the detection of incorporation of alternative lignin monomers.

/pdf/metabolic-engineering-of-novel-lignin-in-biomass-crops-4emnnx1bxv.pdf

Metabolic engineering of novel lignin in biomass crops

https://pubs.rsc.org/en/Content/ArticlePDF/2016/NP/C6NP00021E

Recent advances in research on lignans and neolignans

Nine new lignans, chushizisins A-I (1-9), and three known lignans, threo-1-(4-hydroxy-3-methoxyphenyl)-2-{4-[(E)-3-hydroxy-1-propenyl]-2-methoxyphenoxy}-1,3-propanediol (10), erythro-1-(4-hydroxy-3-methoxyphenyl)-2-{4-[(E)-3-hydroxy-1-propenyl]-2-methoxyphenoxy}-1,3-propanediol (11), and 3-[2-(4- hydroxyphenyl)-3-hydroxymethyl-2,3-dihydro-1-benzofuran-5-yl]propan-1-ol (12), were isolated from the fruits of Broussonetia papyrifera. Their structures were elucidated using spectroscopic methods. Compounds 1, 5, 6, 8, 9, and 11 exhibited antioxidant activities against H(2)O(2)-induced impairment in PC12 cells, while compounds 1, 2, 4, 7, and 11 showed DPPH radical-scavenging activities with IC(50) values of 236.8, 156.3, 273.9, 281.1, and 60.9 mu M, respectively.

Antioxidant Lignans from the Fruits of Broussonetia papyrifera.

Investigation of the n-BuOH extract of the roots of Rumex nepalensis afforded two new seco-anthraquinone glucosides, nepalensides A (1) and B (2), along with nine known compounds, torachrysone (3), rumexoside (4), orientaloside (5), orcinol glucoside (6), aloesin (7), lyoniresinol 3 alpha-O-beta-D-glucopyranoside (8), (-)-epicatechin-3-O-gallate (9), (3,5-dimethoxy-4-hydroxyphenol)-1-O-beta-D-(6-O-galloyl) glucose (10), and (-)-epicatechin (11). Their structures were elucidated on the basis of spectroscopic methods. The possible formation of nepalensides A and B is briefly discussed.

New Seco-anthraquinone Glucosides from Rumex nepalensis

Three new linear C-14 polyyne (= polyacetylene) glucosides, cordifolioidynes A-C (1-3), together with two known polyynes, lobetyol (4) and lobetyolin (5), and five known phenylpropanoids, i.e., sinapinaldehyde (6), coniferaldehyde (7), coniferoside (8), sachaliside (9), and isoconiferin (10), were isolated from the roots of Codonopsis cordifolioidea. The structures of 1-3 were established from spectral evidences and by characterization of their hydrolysis products. Acid hydrolysis of I afforded the aglycone la, while hydrolysis of 2 and 3 gave the cyclization products 2a and 3a, respectively. Compounds 4-10 were isolated from this plant for the first time. The antibacterial activity of compounds 1-5 were assessed against eight microbial strains by the agar dilution method, none of them exhibited antibacterial effects at concentrations up to 100 mu g/ml.

Three New Polyyne (= Polyacetylene) Glucosides from the Edible Roots of Codonopsis cordifolioidea

Two new neolignans selaginellol (1) and selaginellol 4'-O-β-D-glucopyranoside (2), together with seven known compounds (3-9), were isolated from the whole plant of Selaginella moellendorffii. The structures of the new isolates were determined through spectroscopic data analysis. Compounds 1-9, as well as compounds 10-18 previously isolated from the species, were measured for the activity against platelet aggregation induced by ADP or collagen. Three neoligans (8, 11, and 12), one flavanone (14), and one alkaloid (16) showed inhibitory activity against ADP- or collagen-induced platelet aggregation as compared with tirofiban. The dihydrobenzofuran neolignans (8, 11, and 12) are more potent than the benzofuran neolignan (13) and other types of neolignans (1-7). Glucosidation of the dihydrobenzofuran neolignans (11 and 12) is helpful for the activity. Two new neolignans selaginellol (1) and selaginellol 4'-O-β-D-glucopyranoside (2) were isolated from the whole plant of Selaginella moellendorffii. Several compounds from this plant showed the activity against platelet aggregation induced by ADP or collagen.

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Neolignans from Selaginella moellendorffii.

Two new compounds hastatusides A and B (1 and 2, resp.), together with five known compounds, resveratrol, rumeroside, torachrysone-8-yl beta-D-glucopyranoside, rutin, nepodin, and orientaloside were isolated form the roots of Rumex hastatus. Their structures were determined by spectroscopic methods including 1D- and 2D-NMR spectroscopy.

Ren-Qiang Mei

Papers

Antioxidant Lignans from the Fruits of Broussonetia papyrifera.

New Seco-anthraquinone Glucosides from Rumex nepalensis

Three New Polyyne (= Polyacetylene) Glucosides from the Edible Roots of Codonopsis cordifolioidea

Neolignans from Selaginella moellendorffii.

Hastatusides A and B: Two New Phenolic Glucosides from Rumex hastatus