Secondary Metabolites

By Prabhu Thirusangu,Molecular Biomedicine Laboratory,Sahyadri Science CollegeKuvempu University

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• Primary metabolites: Molecules that are essential for growth and development of an organism.

Examples: 1.Carbohydrates 2.Proteins 3.Lipids

4.Nucleic acids 5.Hormones

• Secondary metabolites: molecules that are not essential for growth and development of an or-ganism.

Metabolites

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Secondary metabolites are derived from primary metabolites

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Why secondary metabolites?

• are biosynthetically derived from primary metabolites. They

are more limited in distribution being found usually in spe-

cific families. • Chemical warfare to protect plants from

the attacks by predators, pathogens, or competitors

• Attract pollinators or seed dispersal agents• Important for abiotic stresses • Medicine • Industrial additives

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• Possibly over 250,000 secondary metabolites in plants

• Classified based on common biosynthetic pathways where a chemical is derived.

• Four major classes: Alkaloids, glycosides, phenolics, terpenoids

Secondary metabolites

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Alkaloids

• Most are derived from a few common amino acids (i.e., tyrosine, tryptophan, or-nithine or argenine, and lysine)

• Compounds have a ring structure and a ni-trogen residue.

• Indole alkaloids is the largest group in this family, derived from tryptophan

• Widely used as medicine

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Terpenoids

• Terpenes are generally polymers of 5-carbon unit called isoprene

• Give scent, flavors, colors, medicine...

• Three plant hormones are derived from the terpenoid pathway.

ALKALOIDS

WHAT ARE ALKALOIDS?

• These are commonly applied to basic nitrogenous com-

pounds of plant origin that are physiologically active.

• Organic nitrogenous compounds with a limited distribu-

tion in native nature.

Characteristics:

• They are bitter in taste.

• Derived from amino acids.The amino acids that are most often serve

as alkaloidal precursors are: phenylalanine, tyrosine, tryptophan,

histidine, anthranilic acid, lysine and ornithine.

• Alkaloids form double salts with compounds of mercury, gold, plat-

inum and other heavy metals. These salts are obtained as precipitate

which are microcrystals.

• Insoluble or sparingly soluble in water, but the

salts formed on reaction with acids are usually

freely soluble.

• Most are crystalline solids although a few are

amorphous.

• Free alkaloids are usually soluble in polar solvents

like ether, chloroform

• Some alkaloids are liquid because of lacking of

oxygen in their molecules. (e.g coniine, nicotine,

spartenine)

Sources and Occurrence of Alkaloids

• Alkaloids can occur in plant kingdoms; among the an-

giosperms,

• Leguminosae,

• Papaveraceae,

• Ranunculaceae,

• Rubiaceae,

• Solanaceae,

• Berberidaceae are outstanding alkaloid-yielding plants.

Uses of Alkaloids in Plants:

• Poisonous agents which protect plants against insects and

herbivores

• End products of detoxification reactions representing a meta-

bolic locking-up of compounds otherwise harmful to the plants.

• For regulatory growth factors

• Reserve substance capable of supplying nitrogen or other ele-

ments necessary to the plant’s economy

Naming for alkaloids

• From the generic name or the genus of the

plant yielding them (e.g vinblastine and vin-

cristine. atropine)

• The specific name or species of the plant

yielding alkaloids ( e.g belladonnine)

• From their physiologic activity (e.g emetine,

morphine)

• From the discoverer (e.g pelletierine)

~ All names of alkaloids should end in “-ine”.

~ A prefix or suffix is added to the name of a principal

alkaloid from the same source. (quinine, quinidine,

hydroquinine)

Pharmacologic action of Alkaloids:

• Analgesic (morphine, codeine)• Narcotics (strychnine, brucine which are central stimu-

lant)• Anti malarial ( quinine)• Anti pyretic • Anti cancer (vincristine) • Mydriatics (atropine)• Anti inflammatory • Miotics (physostigmine, pilocarpine) • Ephedrine (rises in blood pressure, bronchodilator) • Reserpine (produce fall in excessive hypertension)

TYPES OF ALKALOIDS

True or hetero cyclic alkaloids

• Pyridine- Piperidine alkaloids• pyrrole & pyrrolidine alkaloids• Tropane alkaloids• Quinoline alkaloids• Isoquinoline alkaloids• Indole alkaloids• Imidazole alkaloids• Norlupinane alkaloids• Steroid alkaloids• Purine alkaloids

CHEMICAL CLASSIFICATION OF ALKALOIDS

TRUE ALKALOIDS

PYRROLE & PYRROLIDINE

DERIVATIVES e.g. Hygrine, Cocca

species

• Pyrrolizidine Derivatives

e.g. senecionine, seneciphylline

Piperidine & pyridine deriva-tivesAreca

ArecolineHydrobromide

Lobeline Nicotine

N

H

TROPANE DERIVATIVES

e.g. Atropine hyoscine

cocaineHyoscyamineScopolamine

Coca

QUINOLINE

DERIVATIVES

e.g. Quinine, quinidine,

cinchonine

CINCHONA BARK

Quinine

• Dia-stereo-isomer of quinidine

• It occurs as white, odourless, bulky crystals or as

a crystalline powder.

• It darkens when exposed to light and effloresces

in dry air.

• It is freely soluble in alcohol, ether and chloro-

form but slightly soluble in water.

Uses

• Antimalarial

• For treating of chloroquinine resistant falciparum

malaria combination with pyrimethamine and sulfa-

doxine or tetracycline or clindamycin.

• It has a skeletal muscle relaxant effect.

• It is widely used for the prevention and treatment of

nocturnal recumbency leg cramps.

ISOQUINOLINE DERIVATIVES

e.g. Morphine,

codeine,

berberine,

emetine

APORPHINE

(REDUCED

ISOQUINOLINE-NAPTHALENE)

DERIVATIVES

e.g. boldine

INDOLE DERIVATIVES

e.g. ergometrine,

ergotamine,

reserpine,

vincristine,

vinblastine

IMIDAZOLE DERIVATIVES

e.g. Pilocarpine,

isopilocarpine

NOR LUPINANE DERIVATIVES

e.g. Cytisine,

lupanine N

PURINE DERIVATIVES

e.g. Theophylline, caffeine,

theobromine

STEROIDAL DERIVATIVES

e.g. protoveratrine, solanidine

PSEUDO ALKALOIDS

DITERPENES e.g. Aconitine, aconine, hypoaconitine

PROTO OR NON HETERO CYCLIC ALKALOIDS

ALKYLAMINES

e.g. Ephedrine,pseudoephedrine, colchicine

• C17H19NO3

• a component of blackpepper (Piper ni-grum)

• has been used in various traditional medicine preparations

• an insecticide. has various effects on human drug metabolizing enzymes, and is mar-keted under the brand name, Bioper-ine,

PIPERINE

Quinine,1. molecular formula C20H24N2O2

2. is a white crystalline quinoline alkaloid.3. Quinine is extremely bitter, and also　 possesses

antipyretic, analgesic and anti-inflammatory properties.

4. has strong anti malarial properties,5. quinine in therapeutic doses can cause various

side-effects, e.g. nausea, vomiting and cinchon-ism, and in some patients pulmonary oedema.

6. It may also cause paralysis if accidentally in-jected into a nerve.

7. Non-medicinal uses of quinine include its uses as a flavouring agent in tonic water and bitter lemon.

VINCRISTINE

A CANCER KILLER

Vinca alkaloids The Vinca alkaloids are a subset of drugs that are de-

rived from the periwinkle plant, Catharanthus roseus.

N

N

OH

C2H5

H3COOC

N

N

R

OAc

OH COOCH3

H

H

MeO

Vinblastine R=-CH3

Vincristine R=-CHO

VINCRISTINE

Periwinkle Structure

Serpentine

• Molecular Formula: C21H22N2O3

• Isolated from Rauwolfia serpentina • To treat High blood pressure • to treat insect stings and the bites of venomous reptiles

Terpenoids

Isoprene: Farnesol: Chlorophyll: β-Carotene

TERPENESThe chemist Leopold Ruzicka ( born 1887) showed that many compounds found in nature were formed from multiples of five carbons arranged in the same pattern as an isoprene molecule (obtained by pyrolysis of natural rubber).

He called these compounds “terpenes”.

C C

C

C C

.

isoprene

natural rubber

D

isoprene unit

head

tail

C C

C C

C

The Biological Isoprene Unit

• The isoprene units in terpenes do not come from isoprene.

• They come from isopentenyl pyrophosphate.• Isopentenyl pyrophosphate (5 carbons) comes

from acetate (2 carbons) via mevalonate

(6 carbons).

Terpenes

• Terpenes are natural products that are structurally related to isoprene.

H2C C

CH3

CH CH2or

Isoprene(2-methyl-1,3-butadiene)

The Biological Isoprene Unit

CH3COH

O

3 HOCCH2CCH2CH2OH

CH3

OH

O

Mevalonic acid

H2C CCH2CH2OPOPOH

CH3 O O

Isopentenyl pyrophosphate

Isopentenyl Pyrophosphate

H2C CCH2CH2OPOPOH

CH3 O O

Isopentenyl pyrophosphate

or

OPP

Isopentenyl and Dimethylallyl Pyrophosphate

Isopentenyl pyrophosphate is interconvertible with2-methylallyl pyrophosphate.

OPP

OPP

• Dimethylallyl pyrophosphate has a leaving group (pyrophosphate) at an allylic carbon; it is reactive toward nucleophilic substitution at this position.

Isopentenyl pyrophosphate Dimethylallyl pyrophosphate

Carbon-Carbon Bond Formation

• The key process involves the double bond of isopentenyl pyrophosphate acting as a nucleophile toward the allylic carbon of dimethylallyl py-rophosphate.

+OPP

OPP

After C—C Bond Formation...

+

OPP

• The carbocation can lose a proton to give a double bond.

After C—C Bond Formation...

+

OPP

OPP

• The carbocation can lose a pro-ton to give a double bond.

H–+

After C—C Bond Formation... OPP

• This compound is called geranyl pyrophosphate. It can undergo hydrolysis of its pyrophosphate to give geraniol (rose oil).

OPP OH

Geraniol

H2O

After C—C Bond Formation...

From 10 Carbons to 15 +

OPP

OPP

Geranyl pyrophosphate

+OPP

From 10 Carbons to 15

+OPP

H–+

OPP

From 10 Carbons to 15 OPP

• This compound is called farnesyl pyrophosphate.• Hydrolysis of the pyrophosphate ester gives the

alcohol farnesol.

Cyclization

• Rings form by intramolecular carbon-carbon bond formation.

OPP

OPP

+

E double bond

Z double bond

CLASSIFICATION OF TERPENES

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TYPE OF NUMBER OF ISOPRENE TERPENE CARBON ATOMS UNITS

hemiterpeneterpenesesquiterpenediterpene

triterpene

tetraterpene

C5

C10

C15

C20

C30

C40

one two three four

six

eight

hemi = half di = two Sesqui = one and a half tri = three

tetra = four

NOTE:

• Hemiterpenes consist of a single isoprene unit. Isoprene itself is considered the only hemiterpene, but oxygen-containing derivatives such as prenol and isovaleric acid are hemiterpenoids.

• Monoterpenes consist of two isoprene units and have the molecular formula C10H16. Examples of monoterpenes are: geraniol,limonene and terpineol.

• Sesquiterpenes consist of three isoprene units and have the molecular formula C15H24. Examples of sesquiterpenes are: humulene,farnesenes, farnesol.

• Diterpenes are composed of four isoprene units and have the molecular for-mula C20H32. They derive from geranylgeranyl pyrophosphate. Examples of diterpenes are cafestol, kahweol, cembrene and taxadiene (precursor of taxol).

CLASSIFICATION OF TERPENES

• Sesterterpenes, terpenes having 25 carbons and five isoprene units, are rare relative to the other sizes, example:  geranylfarnesol.

• Triterpenes consist of six isoprene units and have the molecular for-mula C30H48. The linear triterpene squalene, the major constituent of shark liver oil, is derived from the reductive coupling of two mole-cules of  farnesyl pyrophosphate. Squalene is then processed biosynthetically to generate either lanosterol or cycloartenol , the structural precursors to all the steroids.

• Sesquarterpenes are composed of seven isoprene units and have the molecular formula C35H56. Sesquarterpenes are typically microbial in their origin. Examples of sesquarterpenes are ferrugicadiol and tetraprenylcurcumene.

CLASSIFICATION OF TERPENES

• Tetraterpenes contain eight isoprene units and have the molecular formula C40H64. Biologically important tetraterpenes include the acyclic  lycopene, the monocyclic gamma-carotene, and the bicyclic  alpha- and beta-carotenes.

• Polyterpenes consist of long chains of many isoprene units,eg, Natu-ral

 rubber .

• Norisoprenoids,eg: C13-norisoprenoids 3-oxo-α-ionol present in

 Muscat of Alexandria leaves and 7,8-dihydroiononederivatives, such as megastigmane-3,9-diol and 3-oxo-7,8-dihydro-α-ionol found in 

Shiraz leaves (both grapes in the species Vitis vinifera)

CLASSIFICATION OF TERPENES

TERPENES

1. The number of C atoms is a multiple of 5, C5

C10 C15 C20 C25 C30 C35 C40

2. Each group of 5 C is an isoprene subunit

3. They can be saturated or unsaturated

4. Many contain O atoms as well.

5. What they all have in common is 1 & 2 above.

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JOINING ISOPRENE UNITS

The terms head-to-tail andtail-to-tail are often used todescribe how the isoprene

units are joined.

C C

C

C C

.

an extrabond

Head-to-Tail

Head-to-Tail

Tail-to-Tail

a-Phellandrene

(eucalyptus)Menthol

(peppermint)Citral

(lemon grass)

O

H

OH

Representative Monoterpenes

Representative Monoterpenes a-Phellandrene

(eucalyptus)Menthol

(peppermint)Citral

(lemon grass)

O

H

OH

a-Phellandrene

(eucalyptus)Menthol

(peppermint)Citral

(lemon grass)

Representative Monoterpenes

Representative Sesquiterpenes

a-Selinene(celery)

H

a-Selinene(celery)

H

Representative Sesquiterpenes

Vitamin A

OH

Representative Diterpenes

Vitamin A

OH

Representative Diterpenes

Vitamin A

Representative Diterpenes

Squalene(shark liver oil)

tail-to-tail linkage of isoprene units

Representative Triterpenes

Farnesol

Used as

1. Perfumes2. Pesticides3. Pheromones4. Anti- tumour agent5. Antibacterial drug

Structure of chlorophyll

Chlorophyll a & b• Chl a has a methyl

group

• Chl b has a car-bonyl group

Porphyrin ring delocalized e-

Phytol tail

Structure of chlorophyll a and b

β-carotene-TETRATERPENE

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β-carotenecarrots

tail-to-tailhead-to-tail

head-to-tail

β-carotene – a linear terpene

8 isoprene units

40 carbon atoms

CH2

CH2

CH2C

CC

CH3CH3

CHCH

CCH

CHCH

CCH

CHCH

CHC

CHCH

CHC

CHCH

CC

CH2

CH2CH2

CCH3

CH3 CH3CH3 CH3

CH3CH3

CH3

-carotene

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• Taxol is a terpenoid • "the best anti-cancer agent” by National

Cancer Institute • Has remarkable activity against advanced

ovarian and breast cancer, and has been approved for clinical use.

Taxol

Taxus brevifolia Nutt.

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• Camptothecin is an indole alkaloid, derived from tryptophan.

• Has anticancer and antiviral activity • Two CPT analogues have been used in can-

cer chemotherapy, topotecan and irinote-can.

Phenolics

• Derived from aromatic amino acids, such as phenylalanine, tyrosin, and trytophan.

• All contain structures derived from phenol• Some examples:

Coumarins: antimicrobial agents, feeding deterrents, and germination inhibitors.

Lignin: abundant in secondary cell wall, rigid and resistant to extraction or many

degradation reagents Anthocyanins

FlavonesFlavnols

Phenols are present in every plant they attract pollinators to the plant and even

impact how these plants act with one an-other.

.

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Glycosides

• Compounds that contain a carbonhydrate and a noncarbohydrate

• Glycosides are present in vacuoles in inactive form

• Glucosinolates: found primarily in the mustard family to give the pungent taste

There are four type of linkages present between glycone and aglycone:

C-linkage/glycosidic bond, O-linkage/glycosidic bondN-linkage/glycosidic bondS-linkage/glycosidic bond

• .

Cyanogenic glycosidesAll of these plants have these glycosides stored in the vacuole, but, if the plant is attacked, they are released and become activated by enzymes in the cytoplasm. These remove the sugar part of the molecule and release toxic hydrogen cyanide.An example of these is amygdalin from bitter almondsCyanogenic glycosides can also be found in the fruit seeds (and wilting leaves) of many members of the rose family (including cherries, apples, plums, bitter almonds, peaches, apricots,raspberries, and crabapples

SourcesPlant resins[

A liquid compounds found inside plants or exuded by plants, But not saps, latex, or mucilage,The resin produced by most plants is a viscous liquid, composed mainly of volatile fluid terpenes resins do not serve a nutritive function. The toxic resinous compounds may confound a wide range of herbivores, insects, and pathogens; while the volatile phenolic compounds may attract benefactors such as parasitoids or predators of the herbivores that attack the plants

Latex latex as found in nature is a milky fluid found in 10% of all flowering plants (angiosperms). It is a complex emulsion consisting of proteins,  alkaloids, starches,  sugars, oils, tannins, resins, and gums that coagulate on exposure to air. It is usually exuded after tissue injury. In most plants, latex is white, but some have yellow, orange, or scarlet latex. It serves mainly as defense against herbivorous insects.

Natural rubber is the most important product obtained from latexThis latex is used to make many other products as well, including mattresses, gloves, swim caps, catheters and balloonsIn chewing gum, and glues

SourcesPlant sterol;The richest naturally occurring sources of phytosterols are vegetable oils and products made from them. They can be present in the free form and as esters of fatty acid/cinnamic acid or as glycosides, Phytosterols, which encompass plant sterols and stanols, are steroid compounds similar to cholesterol which occur in plants and vary only in carbon side chains and/or presence or absence of a double bond. Stanols are saturated sterols, having no double bonds in the sterol ring structure.

SourcesSapogeninssapogenins are the aglycones, or non-saccharide, portions of the family of nat-ural products known as saponins. Sa-pogenins containsteroid or other triterpene frameworks as their key organic feature. For example, steroidal sapogenins like tiggenin, neogitogenin, and tokorogenin have been isolated from the tubers of Chlorophytum arundi-nacelum. Some steroidal sapogenins can serve as a practical starting point for the semisynthesis of particular steroid hormones.

Essential OilAn essential oil is a con-centrated hydrophobic liquid containing volatile aroma compounds from plants. Essential oils are also known as volatile oils, ethereal oils, aetherolea, They are used in perfumes, cosmetics, soaps and other products, for flavoring food and drink, and for adding scents to incense and household cleaning products

Oil Tonnes

Sweet orange 12,000

Mentha arvensis 4,800

Peppermint 3,200

Cedarwood 2,600

Lemon 2,300

Eucalyptus globulus 2,070

Litsea cubeba 2,000

Clove 2,000

Spearmint 1,300

PhenylpropanoidsThe phenylpropanoids are a diverse family of organic compounds that are synthesized by plants from the amino acid phenylalanine

Phenylpropanoids are found throughout the plant kingdom, where they serve as essential components of a number of structural polymers, provide protection from ultraviolet light, defend against herbivores and pathogens, and mediate plant-pollinator interactions as floral pigments and scent compounds.

Plant-derived Insecticides

Outline: Plant-Derived Insecticides

Important insecticides from plants -rotenoids - New World and Asia -pyrethrins - Near Eastern cen-ter

-tobacco - New World Ryania speciosa, Flacourtiaceae

Antifeedants -neem, Azadirichta indica, Meli-aceae

Introduction

• Many insecticidal compounds are known from plants. Most plants make defensive compounds called allomones. Only a few are important commercially.

• Plant-derived insecticides have largely been replaced by synthetic materials, but there are some advantages to the naturally occurring materials. For ex-ample, these substances are biodegradable.

• Selectivity is needed. Compounds that are toxic to insects, but not toxic to mammals, are preferable, of course.

Rotenoids

• A series of compounds found in mem-bers of the genera Derris, Lonchocar-pus, Tephrosia are known as rotenones.

• Commercially, rotenoids are isolated mostly from the roots of Derris elliptica in Indonesia and from Lonchocarpus

• These compounds are isolated by grind-ing the plant and extracting with sol-vents such as hexane or petroleum ether or chloroform.

• The compounds are oil soluble or lipids. They make up 1-20% of the dry weight of the roots.

Derris elliptica, Fabaceae

Pacific Island Ecosystems at Risk (PIER)Photo by Agnes Rinehart

Rabo molle, Lon-chocarpus muehlen-bergianus, Fabaceae

Libro del Arbol, Celulosa Argentina, Vol. 2, 1975

False indigo bush, Amorpha fruticosa, Fabaceae

Pyrethrins

• Another major series of compounds, the pyrethrins, come from species of the genus Chrysanthemum (some people put these species in Pyrethrum) (Aster-aceae or Compositae).

• These were used as far back as the 1st century B.C. by the Chinese. Insecticidal plants mostly are grown in countries with inexpensive labor and high eleva-tions such as Kenya and New Guinea.

Pyrethrum, Chrysanthemum cinerariifolium, Asteraceae

Courtesy Dr. Saifu Dossaji

Harvesting pyrethrum flowers in Kenya

Courtesy Dr. Saifu Dossaji

• Ryania speciosa (Flacourtiaceae) is also used occasionally and an insec-ticide.

• A mixture of diterpene, alkaloids is isolated and used for specialty in-secticide uses.

• Because the extract is expensive, it is not commonly used.

Other plant-derived insecti-cides

Ryania speciosa, flower and fruit, Flacour-tiaceae

Tobacco, Nicotiana tabacum, Solanaceae

• Tobacco (which contains nicotine) is another major source of insec-ticides. Tobacco wastes are often extracted and used as a source of nicotine. Nicotine especially effective against aphids.

Tobacco, Nicotiana tabacum, Solanaceae,

Calabar bean

• Calabar bean (Physostigma venenosa, Fabaceae) is (or has been) a trial-by-ordeal drug in the Calabar coast of Nigeria. The ac-tive component is physostigmine, an acetyl choline esterase inhibitor.

• The structure of several commercial carbamate insecticides is patterned after the structure of the plant alkaloid.

Calabar bean, Physostigma venenosum, Fabaceae

R. Bentley and H. Trimen, Medicinal Plants, London, Churchill, 1880

Antifeedants

• Antifeedants are compounds that prevent insect feeding. Although many are toxic, the insects usually don’t consume enough to be poisoned.

• Only one of these, neem, Azadirachta indica, Meliaceae, is commercially available. The active compound, azadirachtin, is a structurally modified triterpene.

Neem, Azadirachta in-dica, Meliaceae

Courtesy Dr. Ramesh PandeyWilliam M. Ciesla, Forest Health Management International, United

States

108

Natural ColorsAnd

Flavors

Better & Safer Alter-natives

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Natural Colors saffron Anthrocyanin Carotenoids Carotene Chlorophyll Curcumin Iron oxides Riboflavin Titanium dioxides

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Carotenoids Yellow & Red colors.

Sources- Sweet potatoes, spinach and tomatoes. Antioxidant - Cancer research.

111

Carotene

Yellow to Orange colors.

Sources: Carrots, yellow or orange fruits.

Rich in Vitamin A.

Lycopenesaffron

112

Chlorophyll

Green coloring agent.

Occurs naturally in all plants

113

Curcumin• Extracted from turmeric.• Coloring and medicinal uses• Wound healing• Antiulcer• Anti inflammatory• Antimicrobial & antiviral • Hepatoprotective• Antioxidant• No toxicity.

114

Riboflavin (Vitamin B2)

Yellow to Orange colors.

Sources- Leafy vegetables, Eggs, Milk & Wheat.

Safe & Beneficial for health.

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Sweet Orange Oil

• Sweet orange fruit peel

Stress reducing agent

Aroma therapy: Peace of mind

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Flavor

Cocoa seedsVennilaStrawberryCinnamonCardamomClovesPepperareca