Intermonomer Linkages Research Articles

Combination of Machine Learning and Empirical Computation for the Structural Validation of Trirosaline, a Natural Trimeric Monoterpene Indole Alkaloid from Catharanthus roseus.

Chemical investigation of the emblematic Catharanthus roseus led to the discovery of trirosaline (1), the first example of a tris-ajmalicine-type monoterpene indole alkaloid and the first natural trimeric MIA ever reported from this deeply dug plant species. Its structure was primarily elucidated based on NMR and HRESIMS analyses, and the nature of its unique intermonomeric linkages was firmly confirmed based on a combination of empirical computation and ML-J-DP4 study. Its absolute configuration was mitigated by comparison of experimental and TDDFT-simulated electronic circular dichroism (ECD) spectra. A possible biosynthetic pathway for trirosaline (1) was postulated.

Fractionation and Characterization of Glycol Lignins by Stepwise-pH Precipitation of Japanese Cedar/Poly(ethylene glycol) Solvolysis Liquor

Recently, we have demonstrated the initial process design of acid-catalyzed poly(ethylene glycol) (PEG) solvolysis of softwood Japanese cedar (JC) in a large-scale batch reactor (50 kg wood meal per batch) to produce PEG-modified glycol lignins (GLs) as a potential feedstock for high-value-added applications. Typically, GLs were produced by acidification (pH 2) of the alkaline JC/PEG solvolysis liquor (pH 11) obtained after the solvolysis reaction using three kinds of JC wood meal sizes (average meal size, JC-L (1.6 mm) > JC-M (0.8 mm) > JC-S (0.4 mm)) and PEG solvent molecular masses (PEG200 < PEG400 < PEG600). In this study, stepwise-pH precipitation (pH 11–8–6.5–4.5–2) was conducted using a JC/PEG solvolysis liquor to further understand the characteristics of bulk GLs. Notably, the molecular weight-dependent fractionation of four GL fractions was obtained with different fractional yields. Consequently, the contents of intermonomeric linkages and functional groups slightly varied according to the fractionation pH while exhibiting a similar chemical structure and thermal behavior to the corresponding bulk GLs. The overall thermal analysis data suggested that bulk GLs prepared from PEG400 solvolysis processes are suitable for the fabrication of melt-processed materials, such as fiber-reinforced plastics (FRPs), automobile parts, and speaker cones.

Five- and six-member bowl-shaped structures from acylphloroglucinols: an ab initio and DFT study.

Molecular structures containing bowl-shaped cavities are interesting for purposes such as hosting molecules or metal ions. Acylphloroglucinols are derivatives of phloroglucinol (1,3,5-trihydroxybenzene) containing a CRO group. A previous study had considered bowl-shaped structures consisting of 3 or 4 identical acylphloroglucinol units linked by methylene bridges, selecting representative R chains and including also a structure with phloroglucinol units. The presence of three 'binding' levels between neighbouring units (consecutive hydrogen bonds in the lower rim, the methylene bridges at intermediate level, and another set of hydrogen bonds in the upper rim) makes these bowls 'deeper' than bowls from other hydroxybenzenes. The current study considers larger bowls, consisting of 5 and 6 identical units, to investigate how the molecular properties change with the increase in the size of the bowl. The monomeric units are the same as in the previous study, and the levels of theory are the same as in the previous study, to enable meaningful comparisons. Like in the previous study, two conformers are considered for each bowl, differing by the orientation of the OH groups in the lower rim. Calculations were performed at the HF/6-31G(d,p) and DFT/B3LYP/6-31+G(d,p) levels with fully relaxed geometry, complemented by single-point MP2/HF/6-31G(d,p) calculations. The results show that the Cnv symmetry (with n being the number of constituting monomers) is maintained for 5-member bowls, while 6-member bowls do not show C6v symmetry but only C2v symmetry. The molecular properties of the calculated bowls are analysed in detail and also compared with the properties of the previously calculated 4- and 5-member bowls. Graphical abstract Bowls built from acylphloroglucinol units have three levels of intermonomer linkages: hydrogen bonds in the bottom rim, methylene bridges at intermediate level, and other hydrogen bonds in the upper rim. They are the deepest bowls that can be built from hydroxybenzene units.

Catalytic Mechanism of Aryl-Ether Bond Cleavage in Lignin by LigF and LigG.

Given the abundance of lignin in nature, multiple enzyme systems have been discovered to cleave the β-O-4 bonds, the most prevalent intermonomer linkage. In particular, stereospecific cleavage of lignin oligomers by glutathione S-transferases (GSTs) has been reported in several sphingomonads. Here, we apply quantum mechanics/molecular mechanics simulations to study the mechanism of two glutathione-dependent enzymes in the β-aryl ether catabolic pathway of Sphingomonas sp. SYK-6, namely, LigF, a β-etherase, and LigG, a lyase. For LigF, the free-energy landscape supports a SN2 reaction mechanism, with the monoaromatic leaving group being promptly neutralized upon release. Specific interactions with conserved residues are responsible for stereoselectivity and for activation of the cofactor as a nucleophile. A glutathione conjugate is also released by LigF and serves the substrate of LigG, undergoing a SN2-like reaction, in which Cys15 acts as the nucleophile, to yield the second monoaromatic product. The simulations suggest that the electron-donating substituent at the para-position found in lignin-derived aromatics and the interaction with Tyr217 are essential for reactivity in LigG. Overall, this work deepens the understanding of the stereospecific enzymatic mechanisms in the β-aryl ether cleavage pathway and reveals key structural features underpinning the ligninolytic activity detected in several sphingomonad GSTs.

A thermally remendable multiwalled carbon nanotube/epoxy composites via Diels-Alder bonding

Mechanically robust and self-healing epoxy composites are highly desired to satisfy the increasing demand of high-performance smart materials. Herein, a dual functionalized epoxy composite (EpF-MWCNT-PA-BM) with self-healing performance based on Diels-Alder chemistry has been investigated. The furfuryl grafted epoxy (EpF) and furfuryl modified MWCNTs (MWCNT-F) are reacted with bifunctional maleimide (BM) and normal anhydride curing agent (PA) to form a covalently bonded and reversibly crosslinked epoxy composite with two types of intermonomer linkage. That is, thermally reversible Diels-alder bonds between the furan groups of both epoxy and MWNCTs with malemide and thermally stable bonds of epoxide and anhydride groups. MWCNTs act as both reinforcer and a healant in the epoxy composite. In this way, the cured epoxy composite possessed not only enhanced mechanical properties but also thermal remendability that enabled elimination of cracks. The latter function took effect as a result of successive retro-DA and DA reactions, which led to crack healing upto 79.82% healing efficiency in a controlled manner through chain reconnection.

Theoretical Study on Hydrogenolytic Cleavage of Intermonomer Linkages in Lignin

Hydrogenolysis is an important approach for depolymerization of lignin, which provides attractive new sustainable platforms of fuels, chemicals, and materials. The theory of lignin hydrogenolysis is, however, still unsound, which limits the development of this approach and causes inconsistencies among experimental studies. In this paper, density functional theory is employed to investigate the initial hydrogenolytic cleavages of recognized five different types of interaromatic unit linkages of lignin, assuming the presence of hydrogen free radicals. The relative free energies of reactant complexes, reaction free energy changes, and rate constants for candidate reactions are calculated comprehensively at 298-538 K. On the basis of the results of calculation and a rapid equilibrium hypothesis, the major reaction channel is decided for each linkage, and its kinetics is assessed. It is concluded that the hydrogenolysis occurs at β-O-4 ether, diphenyl ether 4-O-5', and β-1' diphenylmethane linkages instantaneously if these are accessible to hydrogen free radicals, while β-5 phenylcoumaran and β-β' pinoresinol linkages are virtually inert to hydrogenolysis.

Structural and Biochemical Characterization of the Early and Late Enzymes in the Lignin β-Aryl Ether Cleavage Pathway from Sphingobium sp. SYK-6

There has been great progress in the development of technology for the conversion of lignocellulosic biomass to sugars and subsequent fermentation to fuels. However, plant lignin remains an untapped source of materials for production of fuels or high value chemicals. Biological cleavage of lignin has been well characterized in fungi, in which enzymes that create free radical intermediates are used to degrade this material. In contrast, a catabolic pathway for the stereospecific cleavage of β-aryl ether units that are found in lignin has been identified in Sphingobium sp. SYK-6 bacteria. β-Aryl ether units are typically abundant in lignin, corresponding to 50–70% of all of the intermonomer linkages. Consequently, a comprehensive understanding of enzymatic β-aryl ether (β-ether) cleavage is important for future efforts to biologically process lignin and its breakdown products. The crystal structures and biochemical characterization of the NAD-dependent dehydrogenases (LigD, LigO, and LigL) and the glutathione-dependent lyase LigG provide new insights into the early and late enzymes in the β-ether degradation pathway. We present detailed information on the cofactor and substrate binding sites and on the catalytic mechanisms of these enzymes, comparing them with other known members of their respective families. Information on the Lig enzymes provides new insight into their catalysis mechanisms and can inform future strategies for using aromatic oligomers derived from plant lignin as a source of valuable aromatic compounds for biofuels and other bioproducts.

Phylogenetic and kinetic characterization of a suite of dehydrogenases from a newly isolated bacterium, strain SG61-1L, that catalyze the turnover of guaiacylglycerol-β-guaiacyl ether stereoisomers.

Lignin is a complex aromatic polymer found in plant cell walls that makes up 15 to 40% of plant biomass. The degradation of lignin substructures by bacteria is of emerging interest because it could provide renewable alternative feedstocks and intermediates for chemical manufacturing industries. We have isolated a bacterium, strain SG61-1L, that rapidly degrades all of the stereoisomers of one lignin substructure, guaiacylglycerol-β-guaiacyl ether (GGE), which contains a key β-O-4 linkage found in most intermonomer linkages in lignin. In an effort to understand the rapid degradation of GGE by this bacterium, we heterologously expressed and kinetically characterized a suite of dehydrogenase candidates for the first known step of GGE degradation. We identified a clade of active GGE dehydrogenases and also several other dehydrogenases outside this clade that were all able to oxidize GGE. Several candidates exhibited stereoselectivity toward the GGE stereoisomers, while others had higher levels of catalytic performance than previously described GGE dehydrogenases for all four stereoisomers, indicating a variety of potential applications for these enzymes in the manufacture of lignin-derived commodities.

Quantitative structural characterization of the lignins from the stem and pith of bamboo (Phyllostachys pubescens)

Abstract Milled wood lignins (MWL) were isolated from the stem (MWLS) and pith (MWLP) of bamboo (Phyllostachys pubescens). The nonacetylated and acetylated bamboo MWLs were investigated by Fourier transform infrared, quantitative 13C-nuclear magnetic resonance (NMR), 2D heteronuclear single quantum coherence (HSQC) NMR, and 31P-NMR spectroscopy. The MWL consists of p-hydroxyphenyl (1–2%), guaiacyl (21–31%), and syringyl (67–78%) units associated with p-coumarates and ferulates. A modified quantitative 13C-NMR and 2D-HSQC analysis has demonstrated that the predominant intermonomeric linkages are of the type β-O-4 (45–49 per 100 C9 units, i.e., per C900) along with small amounts of other structural units such as resinols (3.6–7.4 per C900), tetrahydrofuran (2.0–2.3 per C900), phenylcoumaran (2.8–4.5 per C900), spirodienones (1.3–2.3 per C900), and α,β-diaryl ethers (2.8–2.9 per C900). MWLP contained more p-coumarates than MWLS. The various degrees of γ-acylation (17–27%) were positively associated with S/G ratios in the lignins; however, γ-acylation was inversely correlated to the ratio between β-β and β-O-4 side chains in these lignin fractions. Moreover, a flavonoid compound (tricin) was also detected in the MWLS but not in MWLP. The two MWLs are very similar in terms of molecular weights and the contents of OHphen and OHaliph.

Identification of oenological tannins extracted from oak wood

Our study is dealing with the determination of the origin of oenological tannins using the modified OIV procedure. The method is based on HPLC analyses of proanthocyanidol content (catechin, epicatechin, epigallocatechin, epicatechin-3-O-gallate and epigallocatechin-3-O-gallate) after thioacidolysis - thiolytic cleavage of the flavonol intermonomer linkages in proanthocyanidols under heat in an acid medium. The purpose of the study was to differentiate oenological tannins gained from Quebracho cortex and tannins extracted from oak wood. As the results show, both groups of tannins do not produce any flavan-3-ols after thioacidolysis, but they show specific peaks, which enable determination of their origin.

Lignin characteristics of bast fiber and core in kenaf, bark and wood of paper mulberry and mulberry

The structural features of bast fiber and core lignins in kenaf (Hibiscus cannabinus), bark and wood lignin of paper mulberry (Broussonetia papyrifera (L.) Vent × Broussonetia kazinoki Sieb.) and mulberry (Morus bombycis) were characterized by alkaline nitrobenzene oxidation, ozonation and methoxyl group determination. Björkman lignins were isolated from bast fiber and core, and bark and wood fractions of the plant samples, and structural characteristics were investigated by 1H NMR and 13C NMR spectroscopies. Kenaf bast fiber gave very high molar ratio of syringaldehyde to vanillin (S/V) of alkaline nitrobenzene oxidation products, while methoxyl content was about the same as that of the core fraction. Results of 1H NMR and 13C NMR of Björkman lignin suggested the presence of aliphatic fragments in lignins isolated from paper mulberry and mulberry bark, but not in kenaf bast fiber. The lower yield of alkaline nitrobenzene oxidation products from bast fiber and bark might be due to the higher content of condensed structure of lignin compared to core fraction. Total yield of erythronic (E) and threonic (T) acids of ozonation products and the molar ratio of erythronic acid to threonic acid (E/T) of the bast fibers and bark were lower than the corresponding core and wood fractions, suggesting that the contents of arylglycerol-β-aryl ether intermonomer linkages in the bast fiber and bark lignin were lower than those of the core and wood fractions. Methoxyl content of bark lignin was lower than the corresponding wood lignin. The methoxyl content of the extract-free kenaf bast fiber was similar to that of the core fraction, while the values of paper mulberry and mulberry bark were about one-half of the corresponding wood fractions, respectively. In bark lignins, the methoxyl contents of Klason lignin and Björkman lignin from bark were lower than those of the extract-free barks. This result suggests that the purity of Klason lignin and Björkman lignins of bark may be rather low.

Thermoresponsive Dynamers: Thermally Induced, Reversible Chain Elongation of Amphiphilic Poly(acylhydrazones)

A nanostructured poly(acylhydrazone), which is reversibly formed in acidic aqueous solution from di(aldehyde) and di(acylhydrazine) monomers with appended hexaglyme groups, was found to display lower critical solution (LCS) behavior. Remarkably, under acidic conditions in which polymerization is reversible, large and reversible molecular weight (M(w)) increases were observed in response to elevated temperatures, both below and above the LCS temperature. No variation in M(w) was evident under neutral and alkaline conditions, in which the acylhydrazone condensation is essentially irreversible. Results of turbidometry studies, size-exclusion chromatography-multiangle laser light scattering (SEC-MALLS), and transmission electron microscopy (TEM) suggest that heating the polymer below the LCS temperature leads to polymer growth with preservation of the characteristic nanostructured morphology, whereas the onset of the microphase separated state causes a fundamental change in morphology, in which the polymer chains aggregate into larger bundles and fibers. van't Hoff analysis of a small molecule model system indicates that the acylhydrazone condensation is enthalpy driven (ΔH(eq) = -8.2 ± 0.2 kcal·mol(-1) and ΔS(eq) = -11.1 ± 0.4 = cal·mol(-1)·K(-1)), which suggests that the observed polymer growth with temperature is not a consequence of the intrinsic thermodynamics of the intermonomer linkage but is likely the result of the thermoresponsive characteristics conferred by the multiple hexaglyme groups. The system described displays double control of the dynamer state by two orthogonal agents, heat and protons (pH). It also represents a prototype for dynamic materials displaying multiple control adaptive behavior.

Rationalization and In Vitro Modeling of the Chemical Mechanisms of the Enzymatic Oxidation of Phenolic Compounds in Planta: From Flavonols and Stilbenoids to Lignins

Enzymatic oxidation of phenolic compounds is a widespread phenomenon in plants. It is responsible for the formation of many oligomers and polymers, which are generally described as the result of a combinatorial coupling of the different radicals formed through oxidation of the phenol group and delocalization of the radical. We focused our interest on several phenolic compounds that are present in plants and known to form, under enzymatic oxidation, oligomers with different type of linkages between monomers. To explain this diversity of inter-monomer linkages and their variation according to the experimental procedure used for the enzymatic oxidation, we report an alternative mechanistic pathway involving dismutation of the radicals, leading to the formation of carbocations which, thereafter, react with nucleophilic species present in the medium. This alternative pathway allows the understanding of peculiar linkages between monomeric units in the oligomer and offers new insights for understanding the formation of phenolic biopolymers in plants.

Linear and Branched Poly(ω-hydroxyacid) Esters in Plant Cutins

Poly(omega-hydroxyacid) ester oligomers were obtained from the cutin of four plant cuticles by partial depolymerization methanolysis. The structure of these oligomers was determined by electrospray ionization coupled to tandem mass spectrometry (ESI-MS/MS) analysis of their lithium-adducts, showing which monomers were present and their relative position. Dimers up to heptamers were identified, in a total yield of oligomers of up to 50% of the total cutin content. Two main structural types of poly(omega-hydroxyacid) ester oligomers were found. Poly(10,16-dihydroxyhexadecanoic acid) esters were the main oligomers in the cutin of Lycopersicum esculentum fruit, with a predominantly branched structure. The 1D and 2D NMR analysis of these oligomers showed that inter-monomer linkages were mostly in secondary midchain hydroxyls, in a ratio of 4.5 to 1, compared with esterification in the primary omega-hydroxyls. In Hedera helix leaves cutin, poly(9-epoxy-18-hydroxyoctadecanoic acid) esters were the dominant oligomers, composed of monomers linearly linked head-to-tail. It is proposed that the cutin polyesters have different poly(omega-hydroxyacid)ester domains, either built of linear chains, where the C18-epoxy omega-hydroxyacids are dominant, or forming a highly branched network, where the C16-dihydroxy omega-hydroxyacids predominate. It is hypothesized that the C18 linear polyester can account for the ordered lamellae seen at ultrastructural level in H. helix cuticle, and that the C16 mostly branched polyester will be the basis of the reticulate structure seen in L. esculentum cuticle.

Synthesis and characterization of epoxy with improved thermal remendability based on Diels‐Alder reaction

AbstractTo produce an epoxy resin with high intrinsic self‐healing efficiency, furfurylglycidyl ether (FGE) was synthesized following a two‐step route. It carried one furan and one epoxide on each of its molecules. Having been cured using N,N′‐(4,4′‐diphenylmethane)bismaleimide and methylhexahydrophthalic anhydride, FGE was then polymerized with two types of intermonomer linkages. That is, thermally reversible Diels–Alder (DA) bonds from the reaction between furan and maleimide groups, and thermally irreversible bonds from the reaction between epoxide and anhydride groups. These two types of bonds provide the polymer with thermal remendability and load‐bearing capacity, respectively. Compared with N,N‐diglycidylfurfurylamine, which was previously developed by the authors and has a similar structure to FGE but with fewer furan rings, FGE can react with maleimide with lower activation energy and the DA bonds formed exhibit higher reversibility. Consequently, improved crack healability of the cured FGE characterized by nearly full recovery of fracture toughness was revealed using double cleavage drilled compression tests. Copyright © 2010 Society of Chemical Industry

Thermo characteristics of steam-exploded bamboo (Phyllostachys pubescens) lignin

Bamboo (Phyllostachys pubescens) internode was subjected to steam explosion treatment to produce an excellent fiber for binderless boards. Lignin was isolated from extract-free bamboo meal with Bjorkman’s procedure and steam-exploded pulp. The self binding-mechanism was discussed by scanning electron microscopy (SEM), thermo-gravimetry (TG), differential scanning calorimetry (DSC) and analytical ozonation. It is well-known that steam explosion treatment liberates lignin from the cell wall to the fiber surface, which is the most important component relevant to binderless board production. Results of TG and DSC analyses showed that steam-exploded bamboo pulp started mass loss at lower temperature compared to bamboo internode meal. The thermal softening temperature of lignin prepared from steam-exploded pulp was much lower than that of lignin prepared from extract-free bamboo meal. This suggests that intermonomer linkages of lignin, especially β-aryl-ether linkage which is the major intermonomer linkage of lignin, were cleaved during steam explosion treatment resulting in low molecular weight phenolic compounds. The cleavage of β-aryl-ether intermonomer linkage of lignin was also confirmed by ozonation analysis.

A thermally remendable epoxy resin

To provide epoxy resin with crack healing capability, an epoxy containing both furan and epoxide groups, N,N-diglycidyl-furfurylamine (DGFA), was synthesized through a two-step approach. When it reacted with N,N′-(4,4′-diphenylmethane) bismaleimide (DPMBMI) and methylhexahydrophthalic anhydride (MHHPA), respectively, a crosslinked polymer with two types of intermonomer linkage was yielded. That is, thermally reversible Diels–Alder (DA) bonds from the reaction between furan and maleimide groups, and thermally stable bonds from the reaction between epoxide and anhydride groups. In this way, cured DGFA possessed not only similar mechanical properties as commercial epoxy, but also thermal remendability that enabled elimination of cracks. The latter function took effect as a result of successive retro-DA and DA reactions, which led to crack healing in a controlled manner through chain reconnection.

Lignin characteristics of Abies beshanzuensis, a critically endangered tree species

As one of the major components of plant cell walls, lignin structural features are closely related with taxonomical and genetic classification of plants. In this study, the structural features of lignin of Abies beshanzuensis were investigated. Abies firma, which is genetically the closest species to A. beshanzuensis, Cryptomeria japonica, a typical gymnosperm tree species, and Phyllostachys pubescens (bamboo), which includes p-hydroxyphenyl nuclei in arylglycerol-β-aryl intermonomer linkages, were also analyzed to compare lignin features with those of A. beshanzuensis. The lignin content of A. beshanzuensis (39.2%) was significantly higher than that of A. firma (33.7%). The high value may be due to the adaptation of A. beshanzuensis to environmental stresses in surviving the Riss glacial period. Alkaline nitrobenzene oxidation, ozonation, acidolysis, and 1H nuclear magnetic resonance spectra showed that the structural features of lignin of A. beshanzuensis were similar to those of A. firma, which is genetically the closest species of A. beshanzuensis. The results of this study suggest that A. firma would be a suitable mother tree species for grafting A. beshanzuensis on the basis of their lignin characteristics.

Lignin characteristics of peculiar vascular plants

Trochodendron aralioides Sieb. et Zucc. and Chloranthus glaber (Thunb.) Makino [Sarcandra globra (Thunb.) Nakai] belong to primitive angiosperms, and are characterized by the absence of vessels. Ephedra sinica Stapf, which is classified in the gymnosperms, contains vessel elements and fiber together with tracheids. Podocarpus macrophyllus (Thunb. Ex Murray) D. Don var. macrophyllus is reported to give a weak positive Maule test, although it is classified as a gymnosperm. Podocarpus macrophyllus gave only vanillin on alkaline nitrobenzene oxidation, while E. sinica, T. aralioides, and C. glaber gave both vanillin and syringaldehyde. The molar ratio of syringyl to guaiacyl nuclei (S/V ratio) of C. glaber was significantly low (S/V = 0.08) in comparison with the value for T. aralioides (S/V = 1.56). The erythro form is the predominant diasteromeric form of β-O-4 intermonomer linkages of T. aralioides and E. sinica [molar ratio of erythro to threo forms (E/T ratio): 1.93 and 1.67, respectively]; however, P. macrophyllus and C. glaber lignins, of which S/V ratios were 0 and 0.08, gave approximately equal amounts of erythro and threo forms (E/T ratio: 1.01 and 1.14). Results from 1H NMR spectroscopy agree well with S/V ratios of alkaline nitrobenzene oxidation and E/T ratios of ozonation products. In conclusion differences in guaiacyl lignin and guaiacyl-syringyl lignin do not exactly reflect taxonomical differences, as reported in previous articles. It was found that guaiacyl-syringyl lignin is not necessarily linked to the presence of vessels.

Structural characteristics of lignin in primitive pteridophytes: Selaginella species

The lignin chemical structures of eight species of the Selaginella family, which are primitive vascular plants, were characterized by alkaline nitrobenzene oxidation, acidolysis, and ozonation. Selaginella involvens, Selaginella tamariscina, and Selaginella remotifolia were collected from the University Forest in Chiba, the University of Tokyo, Japan, and Selaginella biformis, Selaginella pennata, S. involvens, Selaginella chrysorrhizos, and unidentified Selaginella species (Selaginella sp.) were collected from northern Thailand. Lignin of all Selaginella species examined in this study was rich in syringyl nuclei. It was confirmed that a considerable portion of syringyl nuclei of Selaginella lignin formed syringylglycerol-β-aryl ether intermonomer linkages. The major diastereomer of arylglycerol-β-aryl ether intermonomer linkages of Selaginella lignins was the erythro-form exhibiting angiosperm lignin characteristics. In addition, lignins of S. involvens, S. tamariscina, and S. remotifolia collected from the University Forest in Chiba, the University of Tokyo, Japan, were isolated according to Björkman’s procedure, and structural features of the lignins were spectrometrically analyzed. It was confirmed that lignin of Selaginella species, which are primitive pteridophytes, was typical guaiacyl-syringyl type as well as being similar to angiosperm lignin.