Lignin Monomers Derived from the Flavonoid and Hydroxystilbene Biosynthetic Pathways

Rı́o, José C. del; Rencoret, Jorge; Gutiérrez, Ana; Lan, Wu; Kim, Hoon; Ralph, John

doi:10.1002/9781119545958.ch7

Cited by 12 publications

(9 citation statements)

References 116 publications

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“…Flavonoids are usually found in either free and glycosylated forms. However, and especially thanks to the great advances in two-dimensional nuclear magnetic resonance (2D-NMR) spectroscopy during the last two decades, the presence of flavonoids incorporated into the lignin polymer has been discovered, acting as natural lignin monomers together with other phenolic precursors biosynthesized outside the monolignol pathway (del Río et al, 2020(del Río et al, , 2021. In fact, all flavonoids with a free 4 -OH in the B-ring are potentially susceptible of being enzymatically oxidized, forming radicals compatible with lignification in cross-coupling reactions with monolignols.…”

Section: Introductionmentioning

confidence: 99%

“…The way tricin is incorporated into the lignin and its compatibility in cross-coupling reactions with monolignols have been studied extensively during the last years (Lan et al, 2015(Lan et al, , 2016a. Furthermore, studies with genetically modified plants have demonstrated that some flavonoid intermediates in the tricin biosynthetic pathway, such as apigenin and naringenin, can also be incorporated into the lignin polymers of mutant plants (Lam et al, 2017(Lam et al, , 2019, providing further evidence on the ability of flavonoids to act as true lignin monomers participating in cross-coupling reaction with traditional monolignols (del Río et al, 2020(del Río et al, , 2021. Whereas in primitive plants, both free and lignin-incorporated flavonoids could contribute to plant protection against UV radiation, flavonoids in the lignin of more evolved angiosperms, such as grasses, would have a structural function as initiation points of the lignin chains, and their removal results in transgenic plants with lower lignin content as shown by blocking the biosynthesis of tricin (Lam et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

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New Insights on Structures Forming the Lignin-Like Fractions of Ancestral Plants

et al. 2021

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In the present work, lignin-like fractions were isolated from several ancestral plants –including moss (Hypnum cupressiforme and Polytrichum commune), lycophyte (Selaginella kraussiana), horsetail (Equisetum palustre), fern (Nephrolepis cordifolia and Pteridium aquilinum), cycad (Cycas revoluta), and gnetophyte (Ephedra fragilis) species– and structurally characterized by pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) and two-dimensional nuclear magnetic resonance (2D-NMR) spectroscopy. Py-GC/MS yielded marker compounds characteristic of lignin units, except in the H. cupressiforme, P. commune and E. palustre “lignins,” where they were practically absent. Additional structural information on the other five samples was obtained from 2D-NMR experiments displaying intense correlations signals of guaiacyl (G) units in the fern and cycad lignins, along with smaller amounts of p-hydroxyphenyl (H) units. Interestingly, the lignins from the lycophyte S. kraussiana and the gnetophyte E. fragilis were not only composed of G- and H-lignin units but they also incorporated significant amounts of the syringyl (S) units characteristic of angiosperms, which appeared much later in plant evolution, most probably due to convergent evolution. The latter finding is also supported by the abundance of syringol derivatives after the Py-GC/MS analyses of these two samples. Regarding lignin structure, β−O−4′ alkyl-aryl ethers were the most abundant substructures, followed by condensed β−5′ phenylcoumarans and β−β′ resinols (and dibenzodioxocins in the fern and cycad lignins). The highest percentages of alkyl-aryl ether structures correlated with the higher S/G ratio in the S. Kraussiana and E. fragilis lignin-like fractions. More interestingly, apart from the typical monolignol-derived lignin units (H, G and S), other structures, assigned to flavonoid compounds never reported before in natural lignins (such as amentoflavone, apigenin, hypnogenol B, kaempferol, and naringenin), could also be identified in the HSQC spectra of all the lignin-like fractions analyzed. With this purpose, in vitro synthesized coniferyl-naringenin and coniferyl-apigenin dehydrogenation polymers were used as standards. These flavonoids were abundant in H. cupressiforme appearing as the only constituents of the moss lignin-like fraction (including 84% of dimeric hypnogenol B) and their abundance decreased in those of S. Kraussiana (with amentoflavone and naringenin representing 14% of the total aromatic units), and the two ancient gymnosperms (0.4–1.2%) and ferns (0–0.7%).

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

New Insights on Structures Forming the Lignin-Like Fractions of Ancestral Plants

et al. 2021

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“…2 and fig. S1) (10,39,40). The oxidative radical coupling is not necessarily limited to the same phenolic species.…”

Section: Biomimetic Preparation Of Cross-coupled Dimers and A Trimer ...mentioning

confidence: 99%

“…Stilbenolignins and stilbenolignan extractives can result from radical cross-coupling between hydroxystilbenes and monolignols. Yet, only a handful of stilbenolignans has been reported previously (10), mostly involving piceatannol P and isorhapontigenin IS. The most common products are benzodioxanes, phenylcoumarans, and the 3-oxabicyclo-[3.3.0]-octane ring structures.…”

Section: Cross-coupled Structures In Dhps From Hydroxystilbenes and M...mentioning

confidence: 99%

“…One of the main contributions to such structural variation is the plasticity of the lignification process that allows plants to increase the relative abundance of trace subunits or to add noncanonical components to lignin in many cases (7). To date, more than 35 different phenolic compounds have been found to participate in radical coupling reactions during lignification (8)(9)(10). These compounds are found in many plant species as the result of natural or induced mutations (11) or genetically engineered modifications (12).…”

Section: Introductionmentioning

confidence: 99%

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Biomimetic oxidative copolymerization of hydroxystilbenes and monolignols

et al. 2023

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Hydroxystilbenes are a class of polyphenolic compounds that behave as lignin monomers participating in radical coupling reactions during the lignification. Here, we report the synthesis and characterization of various artificial copolymers of monolignols and hydroxystilbenes, as well as low-molecular-mass compounds, to obtain the mechanistic insights into their incorporation into the lignin polymer. Integrating the hydroxystilbenes, resveratrol and piceatannol, into monolignol polymerization in vitro, using horseradish peroxidase to generate phenolic radicals, produced synthetic lignins [dehydrogenation polymers (DHPs)]. Copolymerization of hydroxystilbenes with monolignols, especially sinapyl alcohol, by in vitro peroxidases notably improved the reactivity of monolignols and resulted in substantial yields of synthetic lignin polymers. The resulting DHPs were analyzed using two-dimensional NMR and 19 synthesized model compounds to confirm the presence of hydroxystilbene structures in the lignin polymer. The cross-coupled DHPs confirmed both resveratrol and piceatannol as authentic monomers participating in the oxidative radical coupling reactions during polymerization.

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