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What’s a phenolic compound?
A secondary product that contains a phenol group
- a hydroxyl functional group on an aromatic ring.
Phenolics are a chemically diverse group: many
different properties and functions.
Biosynthesis of phenolics
Shikimic acid pathway is most common in plants. Converts simple
carbohydrates into aromatic amino acids. Not present in animals.
Most plant phenolics are derived from cinnamic acid
formed from phenylalanine by phenylalanine ammonia lyase
(PAL) enzyme.
PAL activity is inducible: fungal infection, low nutrient levels, high light
Major types of phenolics
1. Simple phenolics - e.g. coumarins
2. Lignin - 2nd most abundant compound in plants
3. Flavonoids - two aromatic rings, 2 pathways
anthocyanins, flavones/flavonols
4. Condensed tannins
polymerized flavonoids
5. Hydrolyzable tannins
made of phenolic acids and sugars
smaller molecules than condensed tannins
1. simple phenolics
Fig. 13.10
Involved in
defense against
insect herbivores
and fungi, some may
have allelopathic
Simple phenolics
Caffeic acid
& ferulic acid
implicated in
Fig. 13.11
Psoralen is one
of several
(UV activated)
Furoanocoumarins can certain light wavelengths.
(common in Umbelliferae family – celery,
Leaf rolling insects
•Insects usually roll
leaves for protection
from predation and
to create a habitat
•Sometimes insects
roll leaves to prevent
from being activated
Furanocoumarins can bind to DNA or
react with lipids and proteins
Simple phenolics
Fig. 13.11
2. Lignin
Second most abundant compound in plants.
Highly branched polymer of phenylpropanoid groups
- often found in vessel
elements, tracheids, and
stems; confers structural
support. Primary structural
- Secondary role as a
herbivore deterrent by
reducing digestibility of
plant matter
- also difficult for microbes
to degrade; its presence
slows litter decomposition.
3. Flavonoids - basic structure is two aromatic
rings joined by a 3C bridge.
Fig. 13.10
a) anthocyanins
b) flavones
c) flavonols
d) isoflavonoids
Fig. 13.13
a) Anthocyanidins and
anthocyanins are pigments
that give plant tissues
red, blue, and purple
Pollinator attraction
Disperser attraction
Flavonoids continued
b & c) flavones and flavonols
UV absorbing
protection against UV (280 - 320 nm)
insect pollinator attraction
How we see the golden
How honeybees see golden eyes…
UV absorbing flavonols are present
in the inner part of petals
d) Isoflavonoids
common in legumes
antimicrobial properties
also involved in signalling
e.g. attracting rhizobia
Rhizobium is attracted to
legumes through signaling
by isoflavanoids released
from roots.
-formed by polymerization of flavonoid units
-common in woody plants
- contain phenolic acids: gallic acid, & simple sugars
- smaller molecules than condensed tannins
- more easily hydrolyzed and degraded
Tannins reduce growth and survival of many different
kinds of herbivores
Also act as antioxidants - eat your isoflavonoids Johnny!
Many foods contains tannins (e.g. tea, red wine)
and have some healthy side effects for humans
(e.g. disallowing constriction of blood vessels)
Tannins also make protein less digestible.
Animals can sense high levels of tannins in their
food and opt for another food resource (e.g.
mule deer, beavers).
High levels of tannins in diet can actually kill some
Condensed tannins
are polymerized
Hydrolyzable tannins are made of phenolics and sugars.
Fig. 13.15
The term “tannin” is derived from the tanning process
in which raw animal hides are preserved by rubbing
tannins on them. The tannins help to complex the
proteins and keep them from degrading.
This protein-binding property of tannins lends them
their toxicity to herbivores.
• tannins can bind digestion enzymes in the gut of
• tannins also form complex polymers when bound
to proteins which are difficult to digest, thus
decreasing the nutritional value of the plant
Tannins can reduce nutritional value of tissues
by binding to proteins, making them less digestible.
Fig. 13.16
Care for a spot of milk in your tea?
Creosote bush, Larrea tridentata
Leaves are 10-25% phenolic resin.
40% of resin is NDGA (nordihydroguaiaretic acid),
remainder is o-methylated flavones and flavonols.
Deters insect herbivory. Mammalian herbivores
select older leaves (less resin).
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Active compounds in creosote leaves.
· NDGA and similar compounds.
· Amino acids.
· Flavonoids.
· Volatile oils.
· Triterpenes.
· Saponins.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
USDA formerly used NDGA as an antioxidant to prevent rancidity in food.
Now known to cause liver and kidney disease in lab animals.
Creosote has long been used in traditional Native American and Mexican
herbal medicine
Creosote applications in herbal therapy
· To dissolve urinary kidney stones.
· Anti inflammatory for respiratory ailments (asthma) and
· To eliminate gallstones
· Against urinary infections
· For the treatment of venereal disease
· As an abortifacient
· Against diabetes
· Bronchitis and colds
· Rheumatism
· Against some types of cancer
· As a mouthwash against tooth decay and halitosis
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
After life effects of phenolic compounds.
Plant litter decomposition, and release of nutrients
from decomposing litter, are strongly influenced by
the chemical composition of the litter.
Litter higher in tannins and lignin decomposes more
Lignin/Nitrogen ratio
Bill Shakespeare, secondary chemist