This document discusses lignans, which are non-flavonoid polyphenols found in many plant families. Lignans are dimers of phenylpropane units linked by carbon-carbon bonds and have antioxidant properties. They are classified into subgroups based on their carbon skeleton and cyclization patterns. Lignans are biosynthesized from phenylalanine and hydroxycinnamic acids via the shikimic acid pathway. Food sources of lignans include whole grains, seeds, nuts, fruits and vegetables. Lignans have therapeutic properties such as anticancer and antihypertensive effects. Some lignans are converted by gut bacteria into enterolignans, which may help lower cancer risks.

1. Pharmacognosy and Phytochemistry –II
(BP504T)
Institute of Pharmaceutical Research,
GLAUniversity, Mathura
Module I
Sonia Singh
Assistant professor
GLA University, Mathura

2. Objective of the
class
Lignan: Definition
Lignin Vs Lignan
Chemistry of Lignans
Biosynthesis
Examples of Lignans
Thereapeutic Uses
Commercial products
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3.  Lignans are a subgroup of non-
flavonoid polyphenols.
 Widely distributed in the plant kingdom, being present
in more than 55 plant families.
 Act as antioxidants and defense molecules against
pathogenic fungi and bacteria.
 In humans, epidemiological and physiological studies
have shown that they can exert positive effects in the
prevention of lifestyle-related diseases, such as type II
diabetes and cancer.
 The lignans are bioactive, non-nutrient,
non-caloric phenolic plant compounds
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4.  Their basic chemical structure consists of two
phenylpropane units linked by a C-C bond between
the central atoms of the respective side chains
(position 8 or β), also called β-β’ bond.
 Lignans and lignins are very
different and should not be confused
with each other. Lignans are
stereospecific dimers of these
cinnamic alcohols (monolignols)
bonded at carbon 8 (C8-C8)
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5. Sonia Singh, Assistant Professor, GLA University, Mathura
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6. Lignin is plant polymer acting as
strengthening material for plant cell wall &
matrix for cellulose micro-fibrils
• Represent a large no. of aromatic material
based on C6C3 building unit
• Lignins formed by oxidative coupling of
hyroxycinnamyl alcohol monomers by
peroxidase enzymes [p-coumaryl-, coniferyl-
and sinapyl-alcohol]
Lignans are dimeric phenylpropanes (C-18)
coupled at the central carbon of the side chain
[via their ß-carbon of the side chain]
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7. Sonia Singh, Assistant Professor, GLA University, Mathura
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8.  Based on their carbon skeleton, cyclization pattern,
and the way in which oxygen is incorporated in the
molecule skeleton, they can be divided into 8
subgroups;
 Main subclasses of Lignans-
1.Furofuran,
2.Furan,
3.Dibenzylbutane,
4.Dibenzylbutyrolactol,
5.Dibenzylbutyrolactones,
6.Aryltetralin,
7.Arylnaphtalene,
8.Dibenzocyclooctadienes.
Polyphenolic substances derived from phenylalanine via
dimerization of substituted cinnamic alcohols , known as
monolignols, to a dibenzylbutane skeleton 2. This reaction is
catalysed by oxidative enzymes.
Classification of Lignans Sonia Singh, Assistant Professor, GLA University, Mathura
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9. Chemical structures: Classification of
Lignans Sonia Singh, Assistant Professor, GLA University, Mathura
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10. Biosynthesis of
lignans
 The pathway starts from 3 of the 4 most common
dietary hydroxycinnamic acids: p-coumaric acid,
sinapic acid, and ferulic acid (caffeic acid is not a
precursor of this subgroup of polyphenols).
Therefore, they arise from the shikimic acid
pathway, via phenylalanine.
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11. Sonia Singh, Assistant Professor, GLA University, Mathura
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12. • Monolignol, derived from hydroxycinnamic acids (p-coumaric, ferulic, and sinapic acids), are either
dimerized to lignans in the cell or polymerized into larger lignin structures in the cell wall.
• These structurally diverse compounds are involved in plant defense (as antioxidants, biocides,
phytoalexins, etc.), providing protection against diseases and pests, and possibly participating in plant
growth control.
• In the plant, lignans (monolignol dimers) usually occur free or bound to sugars.
• Diglucosides of pinoresinol, secoisolariciresinol, and syringaresinol are common.
• Sesaminol triglucoside and sesaminol diglucoside occur in sesame seeds.
• In flax, secoisolariciresinol is present as a diglucoside and is part of an ester-linked complex or oligomer
containing 3-hydroxyl-3-methylglutaric acid, a number of cinnamic acid glycosides (usually ferulic or p-
coumaric acid) and the flavonoid herbacetin.
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13. Secondary
metabolites
 The plant lignans most commonly distributed in foods are
lariciresinol, matairesinol, pinoresinol, and
secoisolariciresinol.
 Several other lignans are present in some foods,
including medioresinol (in sesame seeds, rye, and
lemons), syringaresinol (in grains), sesamin and the
lignan precursor sesamolin (in sesame seeds).
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14. Sonia Singh, Assistant Professor, GLA University, Mathura
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15. Food sources of
lignans
 Lignans are found in whole grains (especially in
the bran layer) and seeds (in the seed coat).
 Barley, buckwheat, flax, millet, oats, rye,
sesame seeds and wheat contain fairly high
levels of lignans.
 Nuts and legumes are also reasonably good
sources.
 Although in lesser amounts than in grains, lignans
are also present in fruits and vegetables such as
asparagus, grapes, kiwi fruit, lemons,
oranges, pineapple, wine and even in coffee
and tea.
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16. Absorption of plant lignans and bioconversion of plant lignans to enterolignans and their
subsequent absorption varies greatly from person to person.
Lignans are present in plants both as aglycones (without sugars) and as glycosides (with
sugars).
At present, only in flaxseed has secoisolariciresinol been found as a lignan oligomer.
Lignan glycosides are absorbed in the gastrointestinal tract after metabolism by intestinal
bacteria to lignan aglycones and the enterolignans (enterolactone and enterodiol), which
are formed from them.
The extent of hydrolysis to release the lignans from the sugars (and in flax from the
oligomer), the formation of enterolignans, and the bioavailability of these compounds vary
quite significantly from person to person.
Lignan metabolism
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17. Distributionoflignansinherbalplants
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18. Distributionoflignansinherbalplants
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19. secoisolariciresinol (SECO),
matairesinol
(MAT),pinoresinol
(PINO), medioresinol (MED),
lariciresinol (LAR),
syringaresinol (SYR),
sesamin (SES, a lignan
precursor), 7′-
hydroxymatairesinol (HMR),
arctigenin (ARC) and
isolariciresinol (isoLAR)
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20. Sonia Singh, Assistant Professor, GLA University, Mathura
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21. Therapeutic
uses of Lignans
 Anticancer, antioxidant, antihypertensive, antiviral,
estrogenic, and insecticidal properties.
 Semisynthetic derivatives of podophyllotoxin include the
antineoplastic drugs etoposide and teniposide.
 Etoposide is employed in the treatment of testicular and
small cell lung cancers along with other tumors.
 Teniposide is approved for the treatment of acute
lymphoblastic leukemia.
 The dietary lignans matairesinol and secoisolariciresinol
are converted by intestinal flora to enterolactone and
enterodiol.
 Enterolactone and enterodiol possess estrogenic activity
and have been attributed with lowered incidences of
breast cancer mortality in patients with diets rich in
matairesinol and secoisolariciresinol
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22. Commercial products
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