Phenylpropanoids

Dr. Mohammed N. SabirDecember 2021

2Lecture outline

• Introduction to phenylpropanoids.

• Chemistry and biosynthetic origin.

• Classes.

• Medicinal significance.

• Herbal products.

Biomolecules formed from a

C6C3 unit [originally made-up

from the aromatic amino

acids, L-Phenyl alanine, and

L-Tyrosine].

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Source,https://www.sciencedirect.com/topics/food-science/phenylpropanoid

The L-phenyl alanine will undergo deamination

and a double bond formation at carbon number.

The formed cinnamic acid will be the trans isomer

(the most common isomer).

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L-Phenyl alanine

L-Tyrosine

Trans-cinnamic acid

P-Hydroxy coumaric acid

NH3

NH3

L-Ph. ala. ammonia lyase (PAL)

Tyr. ammonia lyase (TAL)

Various post-synthesis modifications may take

place according to the species involved. These

include, different oxygenation levels, cyclization,

condensation, and substitution leading to a vast

number of secondary metabolites termed as

phenylpropanoids.

These molecules serve important roles to the producing

species and show interesting medicinal values.

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6

Vargas-Tah A. and Gosset G., 2015, Front. Bioeng. Biotechnol.,Source: https://www.frontiersin.org/articles/10.3389/fbioe.2015.00116/full

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The classes of

Phenylpropanoids

Source,https://www.frontiersin.org/research-topics/14215/phenylpropanoid-systems-biology-and-biotechnology

8Flavonoids

Source,https://www.naturesbest.co.uk/images/blog/flavonoids_and_vision_2.jpg

• The largest group of naturally occurring phenolic compounds.

They occur in different plant parts including, fruits, stem, barks,

root, leaves, heartwood, flowers, rhizomes and seed.

• Flavonoids are plant pigments or co-pigments (the yellow-

orange color of many fruits) exist in different plant families

including, Rutaceae, Rosacea, Astraceae, Lamiaceae,

Moraceae, Rubiaceae, and Myrtaceae.

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Classes of

flavonoids

The flavonoids’ biosynthesis

Obtained from two pathways,

• Shikimate [Phenyl propanoids (4-hydroxy coumaric acid)].

• Acetate [Malonyl-CoA (3 Acetyl-CoA)].

https://en.wikipedia.org/wiki/Flavonoid_biosynthesis

The role of flavonoids in plants include,

1. Insect attractant (pollinating agents).

2. Plant pigments.

3. Growth regulators.

4. Antioxidants.

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The medicinal values of flavonoids include,

•Antioxidants (free radical scavengers).

•Antimicrobial.

•Anti-inflammatory

•Mitochondrial adhesion inhibitors.

•Antiulcer.

•Estrogen receptor binding.

•Cell cycle arrest.

•Topoisomerase inhibitors.

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Structure-activity relationship (SAR) 14

Source,https://static-01.hindawi.com/articles/bmri/volume-2017/8386065/figures/8386065.fig.005.svgz

15

Source,https://www.mdpi.com/antioxidants/antioxidants-10-01262/article_deploy/html/images/antioxidants-10-01262-g006.png

Antioxidant mechanism of flavonoids 16

Ivonne et al. “The pro-oxidant chemistry of the natural antioxidants vitamin C, vitamin E, carotenoids and flavonoids.” Environmental Toxicology and Pharmacology. 2002. Vol. 11(3–4). P:321-333

17Antimicrobial activity of flavonoids

Gomiac I. et al. “Comprehensive review of antimicrobial activities of plant flavonoids.” Phytochemistry Reviews. 2019. 18:241–272.

18

Yatoo et al. “Beneficial health applications and medicinal values of Pedicularis plants: A review.” Biomedicine & pharmacotherapy. 2017. 95:1301-1313

Anti-inflammatory action of flavonoids

• Quercetin.

• Naringin.

• Hesperidin.

• Rutin.

• Resveratrol.

19Some examples of known bioflavonoids

20

https://www.researchgate.net/profile/Mohammed-Hossain-47/publication/301332394/figure/fig3/AS:351878010425347@1460905663391/Cla

ssification-and-example-of-flavonoids-and-their-chemical-structures-Flavonoids-are.png

21Quercetin

A plant bioflavonoid found in onions, apples, green tea, red wine,

and berries.

The compound shows antioxidant, anti-inflammatory,

antimicrobial, antitumor, antidiabetic, and cardiovascular

protectant.

Recent studies showed that quercetin inhibits SARS-CoV 19

cellular entrance through inhibition of Angiotensin receptor.

Used as a reference agent for antioxidant comparison in research

protocols.

Naringin

From Citrus paradisi

Fam: Rutaceae

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Naringin is an aldose reductase inhibitor which means that it

can help to fight diabetic retinopathy.

https://www.wisegeek.com/what-is-citrus-paradisi.htm

Naringin enhance our perception for taste by

stimulating the taste buds; that's why some

people consume a small amount of grapefruit

juice before a meal.

Citrus aurantium Peels

Fam: Rutaceae

Uses:-

Hesperidin and Naringin inhibits capillary

bleeding through epithelial protection

(membrane stabilizer)

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Source,https://www.alibaba.com/product-

detail/Bitter-Orange-Oil-Citrus-Aurantium_148711980.html

24Rutin

A bioflavonoids obtained from apples,

buckwheat, citrus, figs, and both black

and green.

Rutin demonstrate antioxidant

properties and enhance collagen

production when used with vitamin C.

The drug interactions of flavonoids,

1. Calcium channel blockers.

2. Sedatives.

3. Cholesterol lowering drugs.

4. Caffeine.

5. Estrogen.

6. Antacids.

7. Minerals and proteins.

Metabolic

interaction through

interfering

metabolism of these

drugs and increasing

their t1/2.

The side effects of flavonoids include,

1. Diarrhea.

2. Allergy.

3. Photosensitivity.

4. At large doses may cause iron deficiency.

27Flavonolignans

Phenylpropanoids formed from

condensation of a flavonoid and a

lignan.

Both, the flavonoid and the lignan

are obtained from shikimic acid.

These compounds are considered as

rare products and isolated from

Silymarin.

Silymarin (Silybum marianum L.)

Milk Thistle

Fam: Astraceae

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Source,https://www.ebay.com/itm/Silybum-

marianum-Culinary-and-Medi-50-Seeds-Milk-Thistle-Seeds-Organic-

/283341110690

Source,https://www.alamy.com/stock-photo-blessed-milk-thistle-our-ladys-

thistle-silybum-marianum-seeds-one-25262647.html

The plant seed contains the

heist concentrations of the

flavonoids. The most

abundant flavonolignans are

Silybin A and B.

Mechanisms of action of Silybins

1. As antioxidant (inhibit lipid-peroxidation) through free

radical scavenging (antioxidant) Key mechanism.

2. Regulators of intracellular content of glutathione.

3. Cell membrane stabilizer and permeability regulator that prevent entrance of toxins.

4. Promoters of ribosomal RNA synthesis and stimulating liver regeneration (Hepatocytes protein synthesis).

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Mechanisms of action of Silybins

5. Inhibits transformation of stellate hepatocytes into myofibroblasts.

6. Decrease the activity of tumor promoters.

7. Enhances apoptosis.

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Hepatotoxic agents

•Carbon tetrachloride (CCl4).

•Chloroform (CHCl3).

•Acetaminophen (Paracetamol©).

•Amanita phalloides.

•Xenobiotics.

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Fatty degeneration in Rat Liver after exposure to CCl4.

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Sabir M. “Pharmacognostic Study of Silybum marianum,” Lambert Academic Publishing, Germany, 1st Ed. 2014.

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▪ Water solubility problems of silybin and methods for

solubility enhancement.

▪ Water solubility affects bioavailability and its efficacy.

Product Milk Thistle HerbSilybum marianum

Size - Mg. Silymarin Silybin Silymarin / Silybin

- Fruit referred to as seed one cap/tab Percent of product % in mg.

Maximum Milk Thistle (Siliphos) (Natural Wellness)

Dried extract(Siliphos)

240 mg. 33% 80 mg.

Thisilyn(Nature's Way)

Dried extract 175 mg. 80% 140 mg.

Legalon(Madaus, Germany)

Dried extract (40:1) 90 mg. 80% 70 mg.

Silymarin 80(Planetary Formula)

Seed Extractplus Milk Thistle seed

210 mg.(plus 50 mg.)

80% 168 mg.

Milk Thistle(Kroeger)

Seed Extractplus Milk Thistle seed

175 mg. (plus 275 mg.)

80% 140 mg.

Silymarin(MediHerb, Australia)

Extract (70:1) 210 mg. 80% 168 mg.

Milk Thistle Seed (Gaia Herbs)

Liquid extract (1:1) 35 mg. 50% 17.5 mg.

Milk Thistle (generic)limited information

Extract 200 mg. 80% 160 mg.

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Tannins 37

Source,https://www.fs.fed.us/wildflowers/ethnobotany/images/tannins/persimmon.jpg

A large group of phenolic non-nitrogenous biomolecules

exhibiting astringent properties (precipitate proteins).

Because of their multiple polar functional groups, these

compounds are water-soluble.

Most are water-soluble, the multiple phenolic hydroxyls and carboxylic groups

are responsible for astringency and bitterness.

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Tannins are sub-classified into two groups,

1- Hydrolysable tannins

2- Non-hydrolysable tannins

1-The hydrolysable tannins, which are formed by the

esterification of sugars (e.g., glucose) with gallic acid.

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Tannic acid is an example of hydrolysable tannin. The gallic acid

molecules are attached to the D-glucose moiety through an ester

linkage.

2-The non-hydrolysable tannins (condensed tannins) expressed

through a polymerization (condensation) reactions between

flavonoids.

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n

One flavonoid molecule act as a core for which other

flavonoids will condense.

Flavonoids are formed from condensation of one p-

hydroxy-cis cinnamic acid with three acetate molecules.

42Isolation

Both hydrolysable and condensed tannins are highly water and

alcohol soluble but insoluble in organic solvents such as ether,

chloroform and benzene. Accordingly, these compounds are

extracted with water using maceration or percolation.

The general method for the extraction of tannic acid from various

Galls is either with water-saturated ether, or with mixture of water,

alcohol and ether.

43Acetone is added to the extraction procedure to inhibit

interaction between tannins and proteins or interfere with the

hydrogen bonding between them, thus increasing the yield.

After extraction, the aqueous and ethereal layers are separately

concentrated, dried, and subjected to further isolation by

sequential chromatographic purification.

The hydrolysable tannins are hydrolyzed in basic medium to their

simple acids and sugars.

44Tannins are isolated by open or flash column

chromatography and HPLC. The mobile phases varies

according to the chemical nature of the tannin, however

ethyl acetate, water, acetic acid, n-butanol are

commonly used.

A key feature of tannins is their ability to bind to

proteins, and they have been used to tan leather, clarify

beer and as astringent preparations in pharmacy.

They have a wide distribution in plants and produced as

a feeding deterrent, as their binding to proteins may

reduce the dietary value of the plant as a food.

Some of these tannins are also plant pigments like

anthocyanidins.

45

Source: https://www.mdpi.com/2076-3921/8/6/182/htm

Chemical tests for tannin identification,

• Reaction with FeCl3.

• Goldbeater's skin test.

• Stiasny's method using Folin-Ciocalteu reagent.

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Tannic acid is a mixture of gallic acid esters of glucose

obtained from nutgall, which is an abnormal tissue

growth of the Oak tree, Quercus robur (Fagaceae)

.as a response of larvae inoculation by insects (داربەڕوو)

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Quercus infectoriaمازووAlepo Oak

Ferdinand Vietz Icones Plantarum 1800-1822Source: https://www.panteek.com/Vietz/pages/vi403-7a1.htm

Source: https://pansari.pk/aleppo-oak/

The galls are harvested and extracted with solvents

(ether and water); the aqueous layer is collected and

evaporated to yield tannic acid, which is further purified

and used as a topical preparation for cold sores.

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https://scienceline.org/2006/09/ask-leibach-herpes/comment-page-4/

Epigallocatechin gallate (EGCG), epigallocatechin-3-

gallate, is the ester of epigallocatechin and gallic acid and

is a type of catechin.

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EGCG is the most abundant catechin in tea and is a potent

antioxidant that have therapeutic applications in (e.g., cancer). It

is found in green tea but not black tea.

In black tea production, the catechins are converted to

theaflavins and thearubigins under high temperature, an

epimerization change is more likely to occur.

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51

https://www.sciencedirect.com/science/article/abs/pii/S0304416505000619

Theaflavin derivatives in black tea and catechin derivatives in green tea inhibit

HIV-1 entry by targeting gp41,

Liu et al., 2005, BBA, Vol. 1723(1–3); 270-281.

52In addition to the antioxidant and antiviral actions, tannins

also exhibit antimicrobial activity.

Tannin toxicity for fungi, bacteria and yeasts is attributed to

the bellow proposed mechanisms,

▪ Inhibition of extracellular microbial enzymes,

deprivation of the substrates required for microbial

growth.

▪ Direct action on microbial metabolism through

inhibition of oxidative phosphorylation.

▪ Iron chelation.

53Many microorganisms can overcome plant defenses

based on tannins through,

➢ Synthesis of tannin complexing polymers.

➢ Oxidation, tannin biodegradation.

➢ Synthesis of siderophores.

See the reference…

https://www.researchgate.net/publication/223084771_Antimicrobial_properties_of_tannin [accessed Apr 1, 2017].

Important herbs that are rich with tannins and used in

the treatment of diarrhoea include,

- Sangisorba officinalis L.

- Acacia catechu Willd.

- Oak bark

- Quercus robur L.

- Potentilla erecta (L.) Rausch.

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Tannin-containing medications are generally

safe, but care should be taken with concurrent

administration of other drugs since tannins are

not compatible with alkalis or alkaloids and form

complexes with proteins and amino acids and

some metals.

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In general, tannins are used for,

-Precipitate proteins in their solutions (astringent property).

-Hypolipidemia.

-Hypertension.

-Identification of Alkaloids.

-Tanning leather.

-Burns treatment.

-Diarrhea treatment.

-Antioxidant property.

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Tannins in Herbal Medicine,

Punica garnatum (Lythraceae)

In the ancient Ayurveda medicine, the pomegranate

has extensively been used as a source of traditional

remedies for thousands of years.

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Source,http://recipes.beewild.buzz/fermented-pomegranate-

honey/

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Hamamelis Leaf (Witch hazel leaves)

Dried leaf of Hamamelis virginiana (Hamamelidaceae)

Hama = sametime

Melis = leaf

Distilled witch hazel extract: prepared by steam hydroalcoholic distillation of

the dried leaves and twigs of H. virginiana. Contains the volatile oil of the

plant.

https://en.wikipedia.org/wiki/Hamamelis_virginiana

59Toxicities of tannins

High intake tannins in diet may cause,

hypoproteinemia, constipation, bowel obstruction

(surgical interpretation may be required), decrease

minerals’ absorption (Fe+2, Fe+3, Ca+2, Al+3, Mg+2, etc.),

and drug interaction with cytochrome P-450

metabolized drugs.

60Presence of tannins in fresh water

https://commons.wikimedia.org/wiki/File:Tannin_rich_fresh_water_draining_into_Cox_Bight_from_Freney_Lagoon.jpg

Lecture overview… 61

Thanks for listening…

Any questions?

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