Structural Classification of Lignans, Neolignans, and Oxyneolignans: Linkage Modes and Cyclization Levels of C₆–C₃ Units

Introduction

Lignan-related natural products share a common phenylpropanoid structural basis. However, their fundamental classification as “lignans,” “neolignans,” or “oxyneolignans” does not depend on the presence of specific structural features such as furan rings, lactone rings, or biphenyl scaffolds. The International Union of Pure and Applied Chemistry (IUPAC) distinguishes these classes according to the positions and modes of linkage between two C₆–C₃ units: compounds in which the two units are directly connected through a C8–C8′ carbon–carbon bond are classified as lignans; compounds lacking a C8–C8′ bond but containing a direct carbon–carbon bond between other carbon positions are classified as neolignans; and compounds in which the two units have no direct carbon–carbon bond and are instead connected through an ether linkage (C–O–C) are classified as oxyneolignans.[1]

The terms lignan, neolignan, and oxyneolignan denote the respective compound classes, whereas lignane, neolignane, and oxyneolignane are the corresponding parent names used in IUPAC semisystematic nomenclature.[1]

The simple lignans, monoepoxy lignans, diepoxy lignans, lignan lactones, cyclolignans, and dibenzocyclooctadiene lignans commonly recognized in traditional Chinese medicinal chemistry describe specific scaffold types formed from 8–8′ lignans through side-chain oxidation, C–O cyclization, lactonization, or further C–C ring formation.[2,3] The classification of “lignan–neolignan–oxyneolignan” identifies the fundamental linkage mode between two C₆–C₃ units, whereas classifications such as simple lignans, monoepoxy lignans, and lignan lactones describe the specific ring systems and oxidation states formed after the fundamental linkage has been established. These two classification schemes operate at different structural levels and cannot replace one another.

1 C₆–C₃ Units and Carbon Numbering in Lignans

1.1 Composition of the C₆–C₃ Unit

C₆–C₃ denotes a phenylpropanoid unit composed of a six-carbon aromatic ring and a three-carbon side chain. In IUPAC nomenclature, the aromatic-ring carbon attached to the three-carbon side chain is designated C1, followed sequentially by C2–C6. The side chain is numbered C7, C8, and C9, beginning at the end closest to the aromatic ring. The second C₆–C₃ unit is numbered C1′–C9′.[1]

Traditional literature also frequently uses α, β, and γ to denote side-chain positions, with α, β, and γ corresponding to C7, C8, and C9, respectively.[3] Accordingly, the “β–β′ coupling” described in classical literature refers to the same scaffold relationship as the “C8–C8′ linkage” in structural numbering.[1]

Figure 1. Carbon numbering in lignans and the structure of secoisolariciresinol. The left panel shows the numbering relationship between two C₆–C₃ units, with a direct carbon–carbon bond between C8 and C8′; the right panel shows a representative structure of secoisolariciresinol.

The numbering shown in Figure 1 provides the basis for determining lignan classification. Although secoisolariciresinol contains no additional furan ring or lactone structure, a direct C8–C8′ bond is present between its two C₆–C₃ units. It is therefore classified first as a lignan and, under commonly used scaffold classifications, more specifically as a dibenzylbutane-type lignan.[2]

1.2 A C₁₈ Scaffold Cannot Replace Assessment of Linkage Positions

Two complete C₆–C₃ units contain a total of 18 skeletal carbon atoms; therefore, many lignans and neolignans possess a basic C₁₈ framework. However, the total carbon count does not determine the fundamental class. Two C₆–C₃ units may also be connected through C8–C5′, C8–C1′, aromatic ring–aromatic ring, or C–O–C linkages, producing different types of neolignans or oxyneolignans.[1,2]

Substituents such as methoxy, hydroxy, methylenedioxy, glycosyl, and ester groups are likewise not primary criteria for distinguishing lignans from neolignans. They mainly alter the oxidation state, hydrogen-bonding capacity, electronic properties, and subsequent reactivity of individual molecules, whereas the fundamental class remains determined by the linkage mode between the two C₆–C₃ units.

2 C8–C8′ Linkages and Lignans

2.1 The 8–8′ Bond Determines Fundamental Classification as a Lignan

When two C₆–C₃ units are directly connected through a C8–C8′ carbon–carbon bond, IUPAC classifies the compounds as lignans; in semisystematic nomenclature, the corresponding saturated parent is used as the basis for naming.[1] Provided that the C8–C8′ bond is retained, whether the molecule remains open-chain or forms oxygen-containing rings, lactone structures, or additional carbocycles does not alter its fundamental classification as a lignan.

Accordingly, although secoisolariciresinol, lariciresinol, pinoresinol, matairesinol, podophyllotoxin, and dibenzocyclooctadiene-type Schisandra lignans differ markedly in their final scaffolds, they all share an 8–8′ bond as part of their common structural basis.[2]

2.2 “Simple Lignans” Constitute a Scaffold Type Within 8–8′ Lignans

In traditional Chinese medicinal chemistry, the term “simple lignans” mainly describes open-chain structures that retain an 8–8′ linkage and whose side chains have not formed additional oxygen-containing rings or complex carbocycles.[3] In modern natural-product reviews, these structures generally correspond to dibenzylbutane lignans.[2]

Secoisolariciresinol and nordihydroguaiaretic acid differ in their aromatic-ring substitution patterns, but the core carbon scaffold connecting their two phenylpropanoid units is based on an 8–8′ bond.

The term “simple” describes the complexity of the final scaffold; it does not imply that the chemical properties, stereochemistry, or biosynthetic processes of these molecules are necessarily simple.

3 Oxygen-Containing Cyclization and Monoepoxy Lignans

3.1 Formation of a Tetrahydrofuran Ring While Retaining the 8–8′ Bond

Monoepoxy lignans retain the direct C8–C8′ carbon–carbon bond between two C₆–C₃ units and contain an additional intramolecular oxygen bridge in the side chains, thereby forming a tetrahydrofuran ring. Traditional Chinese medicinal chemistry refers to these structures as “monoepoxy lignans,” whereas the international natural-product literature also commonly classifies them as tetrahydrofuran lignans.[3,4]

According to the attachment positions at the two ends of the oxygen bridge, these structures may be further divided into 7-O-7′, 9-O-9′, and 7-O-9′ cyclization modes, corresponding to C7–O–C7′, C9–O–C9′, and C7–O–C9′ linkages, respectively.[3]

Figure 2. Three representative cyclization modes of monoepoxy lignans. From left to right, the structures show 7-O-7′, 9-O-9′, and 7-O-9′ cyclization. All three structures retain the direct C8–C8′ carbon–carbon bond and differ only in the position of the additional C–O ring closure formed on this fundamental linkage.

Figure 2 illustrates a frequently confused classification relationship: the addition of a C–O bond does not make a compound an oxyneolignan. The C8–C8′ bond remains intact in all three structures; therefore, their fundamental classification remains that of lignans.

3.2 “Monoepoxy” Does Not Indicate the Presence of a Three-Membered Epoxide

“Monoepoxy lignan” is a traditional term in natural-product classification. Structurally, it refers to a five-membered tetrahydrofuran ring containing an oxygen atom, rather than the three-membered epoxide, or oxirane, composed of two carbon atoms and one oxygen atom in conventional organic chemistry.

When a precise scaffold description is required, the term “tetrahydrofuran lignan,” together with a specific linkage designation such as 7-O-7′, 9-O-9′, or 7-O-9′, can reduce terminological ambiguity.[4]

3.3 The Number and Mode of Ring Closures Provide a Second Level of Classification Within Lignans

Formation of one tetrahydrofuran ring in an 8–8′ lignan produces a tetrahydrofuran-type lignan, whereas formation of two related ether bridges produces a furofuran structure. Side-chain oxidation and lactonization can generate dibenzylbutyrolactone structures, while further carbon–carbon ring formation can produce aryltetralin, arylnaphthalene, or dibenzocyclooctadiene structures.[2]

Modern reviews commonly divide 8–8′ lignans into major scaffold types including dibenzylbutanes, dibenzylbutyrolactols, dibenzylbutyrolactones, tetrahydrofuran/furan, furofuran, aryltetralin, arylnaphthalene, and dibenzocyclooctadiene lignans.[2]

Traditional Common Name	Principal Structural Feature	Modern Scaffold Description
Simple lignans	8–8′ linkage; no additional oxygen-containing ring in the side chains	Dibenzylbutane type
Monoepoxy lignans	Retention of the 8–8′ bond with the addition of one oxygen-containing five-membered ring	Tetrahydrofuran type
Diepoxy lignans	Retention of the 8–8′ bond with the formation of two related ether bridges	Furofuran type
Lignan lactones	Further side-chain oxidation and lactone formation	Dibenzylbutyrolactone type
Cyclolignans/cyclolignan lactones	Formation of an additional C–C ring	Aryltetralin, arylnaphthalene, and related types
Dibenzocyclooctadiene lignans	Further formation of a biaryl bond and an eight-membered ring on the 8–8′ scaffold	Dibenzocyclooctadiene type

4 Non-8–8′ Carbon–Carbon Linkages and Neolignans

4.1 Other Direct C–C Linkages Produce Neolignans

When no 8–8′ bond is present between two C₆–C₃ units but a direct carbon–carbon bond is formed at other positions, IUPAC classifies the compound as a neolignan.[1] The linkage may occur between a side chain and an aromatic ring or directly between two aromatic rings. Consequently, the fundamental scaffold diversity of neolignans is markedly greater than that of a single 8–8′ linkage system.[1,2]

Common neolignan scaffolds include 8–5′ dihydrobenzofuran types, 3–3′ biphenyl types, and other non-8–8′ carbon–carbon coupling patterns.[1,2] Although an 8–5′ dihydrobenzofuran structure also contains an intramolecular ether bridge, its direct interunit 8–5′ carbon–carbon bond determines its classification as a neolignan.

4.2 Biphenyl-Type Neolignans Are Established by a Direct C–C Bond Between Aromatic Rings

Magnolol and honokiol are typical biphenyl-type neolignans. Magnolol can be represented as 5,5′-diallyl-2,2′-dihydroxybiphenyl, whereas honokiol has different hydroxy and allyl substitution positions. Both compounds possess a direct non-8–8′ carbon–carbon linkage between their aromatic rings.[5]

Figure 3. Biphenyl-type neolignans and representative structures. The left panel illustrates two C₆–C₃-related units directly connected through aromatic-ring positions C3–C3′; the middle and right panels show magnolol and honokiol, respectively. Neither compound contains an 8–8′ bond; therefore, both are classified as neolignans according to the IUPAC fundamental-linkage rules.[1,5]

4.3 The Presence of a Biphenyl Unit Alone Cannot Replace Assessment of the Fundamental Linkage

Dibenzocyclooctadiene lignans also contain a biaryl structure, but their original 8–8′ linkage remains present; their fundamental parent therefore remains a lignan. In contrast, biphenyl-type neolignans such as magnolol and honokiol contain no 8–8′ bond.

Accordingly, determining whether a molecule is a lignan or a neolignan requires tracing the fundamental linkage between the two complete C₆–C₃ units rather than considering only whether the final structure contains a biphenyl, furan, or other ring system.

5 Differences in Linkage Modes Between Oxyneolignans and Oxygen-Containing Lignans

5.1 Oxyneolignans Are Fundamentally Linked by an Interunit Ether Oxygen

The IUPAC definition of an oxyneolignan includes two structural conditions: there is no direct carbon–carbon bond between the two C₆–C₃ units, and the two units are connected through an ether oxygen atom.[1]

For example, the fundamental linkage of an 8-O-4′ structure can be represented as:

C8—O—C4′

Here, the oxygen atom directly connects the two C₆–C₃ units. This structure differs fundamentally from the monoepoxy lignans shown in Figure 2.

A typical 1,4-benzodioxane structure may contain an additional 7-O-3′ oxygen bridge formed on the fundamental 8-O-4′ ether linkage. If no direct carbon–carbon bond exists between the two C₆–C₃ units, its fundamental parent remains an oxyneolignan.[1]

5.2 Differences Between Monoepoxy Lignans and Oxyneolignans

Comparison Item	Monoepoxy Lignans (Usually Tetrahydrofuran Lignans)	Oxyneolignans
Direct C8–C8′ C–C bond	Retained	Absent
Direct C–C linkage between the two C₆–C₃ units	Present; the fundamental linkage is C8–C8′	Absent
Structural role of the C–O bond	Forms an intramolecular ether bridge and an oxygen-containing ring on an existing 8–8′ lignan scaffold	The C–O–C ether linkage directly connects the two C₆–C₃ units
Fundamental classification	Lignan	Oxyneolignan
Representative linkage modes	7-O-7′, 9-O-9′, and 7-O-9′ cyclization, generally forming a tetrahydrofuran ring	Interunit aryl ether linkages such as 8-O-4′

6 Classification by Fundamental Linkage and Specific Scaffold

6.1 Two Levels of Classification Establish a Complete Structural Assessment Sequence

Lignan-related natural products can first be assigned to a fundamental parent according to the interunit linkage and then to a specific scaffold according to their cyclization and oxidation state:

Step 1: Fundamental Linkage Between the Two C₆–C₃ Units	Fundamental Classification	Step 2: Further Structural Changes
Direct C8–C8′ C–C bond	Lignan	Open-chain structures, oxygen-containing cyclization, lactonization, carbocycle formation, biaryl bond formation, and related changes
Direct non-8–8′ C–C bond	Neolignan	Benzofuran, biphenyl, bicyclic, and related systems
No direct C–C bond; linkage through an ether oxygen	Oxyneolignan	Further development into aryl ethers, oxygen-containing rings, and related structures

6.2 Summary of Common Classification Confusions

Commonly Confused Judgment	Correct Basis for Assessment
The two C₆–C₃ units form a C₁₈ scaffold, so the compound must be a lignan	C₁₈ is only the common carbon-skeleton composition of these compounds. The linkage positions and linkage mode between the two C₆–C₃ units must still be determined.
The molecule contains a C–O ring, so it is an oxyneolignan	The presence of a C–O ring alone does not determine the class. An oxygen-containing ring structure that retains the direct C8–C8′ carbon–carbon bond remains a lignan.
A “monoepoxy lignan” contains an ordinary three-membered epoxide	In “monoepoxy lignan,” “epoxy” does not refer to an ordinary three-membered epoxide. It denotes an oxygen-containing five-membered ring formed by an oxygen bridge and principally corresponds to a tetrahydrofuran lignan.
A biphenyl structure necessarily indicates a neolignan	It remains necessary to determine whether a C8–C8′ bond is also present between the two C₆–C₃ units. Although dibenzocyclooctadiene lignans contain a biphenyl scaffold, they retain a direct C8–C8′ carbon–carbon bond and are therefore lignans.
“Neolignan” means a newly discovered lignan	A neolignan is a structural class defined by the linkage mode between two C₆–C₃ units and is unrelated to the time of discovery.
A lactone or furan ring determines the fundamental classification as a lignan, neolignan, or oxyneolignan	Fundamental classification is determined by the positions and mode of linkage between the two C₆–C₃ units. Lactones, furan rings, and other additional ring systems are used to distinguish specific scaffold types further.

7 Role of Linkage-Based Classification in Lignan Research

The first structural question in lignan research is how the two C₆–C₃ units are connected. After the planar structure of a new natural product has been established, linkage positions such as 8–8′, 8–5′, 3–3′, or 8-O-4′ directly determine its fundamental class and the parent system used for subsequent searches, nomenclature, and structural comparisons with related compounds.[1,2]

This classification also has practical significance for synthetic research. The central challenge for 8–8′ lignans is constructing the bond between the β positions of the two side chains and controlling subsequent cyclization. Biphenyl-type neolignans require regioselective construction of a C–C bond between aromatic rings, whereas oxyneolignans involve interunit C–O linkages. Different linkage modes therefore correspond to different retrosynthetic disconnections and biomimetic-coupling problems.

In biosynthetic research, products containing 8–8′, 8–5′, and 8-O-4′ linkages reflect differences in the regioselectivity of phenylpropanoid coupling. The specific control exerted by radical coupling, dirigent proteins, and subsequent enzymatic catalysis constitutes a deeper biosynthetic question. Structural classification first provides a unified numbering system and scaffold language for describing these selective reactions.

8 Representative Chemicals and Research Applications Related to the Structural Classification of Lignans and Neolignans

Table 1. 8–8′ Lignans: Open-Chain, C–O-Cyclized, Lactone, and Aryltetralin Types

Category	CAS Number	Aladdin Product No.	Name	Specification or Purity	Product Features and Applications
8–8′ Lignan—Dibenzylbutane Type	500-38-9	N133726	Nordihydroguaiaretic acid	Moligand™, ≥95%	A classic polyphenolic dibenzylbutane lignan applicable to studies of lipoxygenase inhibition, lipid peroxidation and free-radical oxidation models, as well as catechol-structure modification and structure–activity relationships.
8–8′ Lignan—Dibenzylbutane Type	29388-59-8	S340456	Secoisolariciresinol	≥95%	An important product of the pinoresinol reduction pathway and a typical substrate of secoisolariciresinol dehydrogenase; applicable to studies of enzymatic lignan oxidation, matairesinol formation, and gut microbiota-mediated conversion to enterolignans.
8–8′ Lignan—Tetrahydrofuran Type	27003-73-2	L464031	(+)-Lariciresinol	≥95%(HPLC)	A key intermediate in the pathway catalyzed by pinoresinol–lariciresinol reductase; applicable to studies of enzyme–substrate selectivity, sequential reduction reactions, and stereoselective lignan biosynthesis.
8–8′ Lignan—Furofuran Type	487-36-5	P170562	Pinoresinol	≥95%(HPLC)	A classic lignan formed through 8–8′ oxidative coupling of monolignol radicals such as coniferyl alcohol; applicable to studies of dirigent protein-assisted stereoselective coupling, pinoresinol–lariciresinol reductase reactions, and plant lignan biosynthesis.
8–8′ Lignan—Furofuran Type	21453-69-0	S650099	(+)-Syringaresinol	≥99%	A symmetrical methoxylated furofuran lignan applicable to studies of plant lignan glycosylation, biotransformation, structure–activity relationships of methoxy-substituted lignans, and natural-product activity screening.
8–8′ Lignan—Furofuran Type	40957-99-1	M664446	5′-Methoxypinoresinol [(+)-medioresinol]	≥93%	A methoxylated member of the pinoresinol family applicable to homolog comparison, glycosylation, biotransformation, and structure–property relationship studies of methoxylated furofuran lignans.
8–8′ Lignan—Furofuran Type	607-80-7	S107347	Sesamin	Analytical standard, Moligand™	A key intermediate in sesame lignan biosynthesis and a direct substrate of CYP92B14; applicable to studies of CYP92B14-catalyzed oxidative rearrangement and the formation of sesamolin and sesaminol.[6]
8–8′ Lignan—Furofuran Type	526-07-8	S196398	Sesamolin	≥98%(HPLC)	One of the major sesame lignans generated through CYP92B14-catalyzed oxidative rearrangement of sesamin; applicable to studies of CYP92B14 catalysis, stable-isotope tracing, and sesame lignan biosynthesis.[6]
8–8′ Lignan—Furofuran Type	487-39-8	P414357	Phillygenin	≥98%	The lignan aglycone corresponding to phillyrin; applicable to studies of glycoside deglycosylation, aglycone pharmacokinetics, aromatic-ring substitution, and structure–activity relationships between lignan glycosides and aglycones.
8–8′ Lignan—Furofuran-Type Glycoside	487-41-2	F104482	Phillyrin	Analytical standard, ≥97%	A representative lignan glycoside applicable to studies of enzymatic and gut microbiota-mediated deglycosylation, oxidation and sulfation, aglycone formation, and pharmacokinetics.
8–8′ Lignan—Dibenzylbutyrolactone Type	26543-89-5	H648559	Hinokinin	≥99%	A dibenzylbutyrolactone lignan applicable to studies of oxidative transformation of the lactone scaffold, preparation of semisynthetic derivatives, modification of methylenedioxy-substituted structures, and antiparasitic and anti-inflammatory structure–activity relationships.
8–8′ Lignan—Dibenzylbutyrolactone Type	7770-78-7	A109807	Arctigenin	≥98%(HPLC)	The principal deglycosylation product of arctiin; applicable to studies of gut microbiota metabolism, glycoside–aglycone conversion, phase II conjugation, and structure–activity relationships of lignan aglycones.
8–8′ Lignan—Dibenzylbutyrolactone Type	580-72-3	M332694	Matairesinol	≥98%	A representative product formed through successive oxidation of secoisolariciresinol; applicable to studies of secoisolariciresinol dehydrogenase activity, intramolecular hemiacetal–lactone formation, and plant lignan biosynthesis.
8–8′ Lignan—Dibenzylbutyrolactone-Type Glycoside	20362-31-6	A463918	Arctiin	≥95%(LC/MS-ELSD)	Applicable to studies of β-glucosidase- and gut microbiota-mediated deglycosylation, arctigenin formation, pharmacokinetic differences between glycosides and aglycones, and metabolic transformation.
8–8′ Lignan—Aryltetralin Lactone Type	518-28-5	P105536	Podophyllotoxin	≥98%	A classic research molecule representing aryltetralin lactone lignans; applicable to studies of biosynthetic enzymes, selective C–C ring formation and construction of contiguous stereocenters, mechanisms of interaction with tubulin, and semisynthesis of derivatives such as etoposide.

Table 2. 8–8′ Lignans: Dibenzocyclooctadiene Type

Category	CAS Number	Aladdin Product No.	Name	Specification or Purity	Product Features and Applications
8–8′ Lignan—Dibenzocyclooctadiene Type	61301-33-5	S117972	Schisandrin C	Analytical standard, ≥98%	A representative dibenzocyclooctadiene constituent of Schisandra; applicable to studies of in vitro and in vivo metabolism, tissue distribution, interactions with drug-metabolizing enzymes and transporters, and structure–activity relationships among homologous lignans.
8–8′ Lignan—Dibenzocyclooctadiene Type	61281-37-6	S117968	Schisandrin B	Analytical standard, ≥98%	Applicable to studies of hepatic microsomal oxidative metabolism, metabolite identification, interactions with drug-metabolizing enzymes and transporters, and the pharmacokinetics of Schisandra lignans.
8–8′ Lignan—Dibenzocyclooctadiene Type	69176-52-9	G664356	Gomisin N	Moligand™, ≥98%	Applicable to studies of the stereochemistry of dibenzocyclooctadiene lignans, structure–activity relationships among homologues, in vivo metabolic transformation, and antioxidant and hepatocyte-injury models.
8–8′ Lignan—Dibenzocyclooctadiene Type	58546-54-6	S683892	Schisandrol B	≥98%	A hydroxylated dibenzocyclooctadiene lignan applicable to studies of hydroxyl-group acylation and oxidative modification, metabolite identification, pharmacokinetics, and structure–activity relationships associated with differences in oxygen-containing substituents within the same scaffold.
8–8′ Lignan—Dibenzocyclooctadiene Type	7432-28-2	S1522825	Schisandrol A	≥98%	A representative lignan commonly studied in Schisandra; applicable to studies of pharmacokinetics, tissue distribution, oxidative metabolism, hydroxy and methoxy structural modifications, and structure–activity relationships among related lignans.

Table 3. Neolignans: Biphenyl and 8–5′ Dihydrobenzofuran Types

Category	CAS Number	Aladdin Product No.	Name	Specification or Purity	Product Features and Applications
Neolignan—Biphenyl Type	35354-74-6	H111271	Honokiol	Analytical standard, Moligand™	A representative biphenyl-type neolignan that can be paired with magnolol as a regioisomeric research system; applicable to phenolic-hydroxyl and allyl derivatization, metabolite identification, and structure–activity relationship studies.
Neolignan—Biphenyl Type	528-43-8	M111378	Magnolol	Moligand™, ≥98%(HPLC)	A diallylbiphenyl-type neolignan applicable to semisynthesis of biaryl scaffolds, conjugative metabolism of phenolic hydroxy groups, pharmacokinetics, and comparative structure–activity studies with honokiol as a regioisomer.
Neolignan—8–5′ Dihydrobenzofuran Type	4263-87-0	D1058544	Dehydrodiconiferyl alcohol	——	A representative product of 8–5′ oxidative coupling of phenylpropanoids; applicable to studies of radical coupling, intramolecular cyclization of quinone methide intermediates, dihydrobenzofuran formation, and subsequent reductive, demethylative, and acylative biotransformations.

Note: The products listed above are representative Aladdin products relevant to research. Specific uses should be determined according to the product specifications, lot-specific COA, and target reaction or evaluation system. Further information on product specifications, grades, and COAs can be found by searching the product name, CAS number, or product number on the official Aladdin website.

References

[1] Moss GP. Nomenclature of Lignans and Neolignans (IUPAC Recommendations 2000). Pure and Applied Chemistry. 2000, 72(8): 1493–1523. doi:10.1351/pac200072081493.

[2] Teponno RB, Kusari S, Spiteller M. Recent advances in research on lignans and neolignans. Natural Product Reports. 2016, 33: 1044–1092. doi:10.1039/C6NP00021E.

[3] Fan Kaifang, ed. Illustrated New Thinking: Chemistry of Traditional Chinese Medicine. Beijing: Chemical Industry Press, 2023. ISBN 978-7-122-41829-6.

[4] Ramos CS, Linnert HV, de Moraes MM, do Amaral JH, Yamaguchi LF, Kato MJ. Configuration and stability of naturally occurring all-cis-tetrahydrofuran lignans from Piper solmsianum. RSC Advances. 2017, 7: 46932–46937. doi:10.1039/C7RA09262H.

[5] Lin Y, Li Y, Zeng Y, Tian B, et al. Pharmacology, Toxicity, Bioavailability, and Formulation of Magnolol: An Update. Frontiers in Pharmacology. 2021, 12: 632767. doi:10.3389/fphar.2021.632767.

[6] Murata J, Ono E, Yoroizuka S, et al. Oxidative rearrangement of (+)-sesamin by CYP92B14 co-generates twin dietary lignans in sesame. Nature Communications. 2017, 8: 2155. doi:10.1038/s41467-017-02053-7.

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