Shikimic Acid Pathway

O

H

O

OH

OH

OH

Shikimic AcidIllicium anisatum L. Illicinaceae {Shikimino-ki in Japanese} (1885)E. coli mutant strains pathway intermediate

Shikimic Acid Pathway

• Important for aromatic compounds • Precursor of aromatic amino acids (Phe, Tyr, Try)

biosynthesis in bacteria, fungi & higher plants. ANIMALS! HUMAN!

• Building block for other compounds: certain alkaloids, coumarins, phenyl propanes, vol. oils,..

• Starting point for tannins in all plants• Provide protection of plants against micro-

organisms

Biosynthesis of shikimic acid

Scheme of the conversion of shikimic acid to cinnamic acid

Shikimic acid → Chorismic acid → Prephenic acid → p-OH-phenylpyruvate

↓ ↓ ↓

Anthranilic acid Phenylpyruvate Tyrosine→alkaloids

↓ ↓ ↓

Tryptophan Phenylalanine p-coumaric acid

↙ ↓ ↓ ↘

↙ Cinnamic acid ↘p hytohormones (indol-3-

ace tic acid Alkaloids alkaloids

Possibilities of derivatives of cinnamic acid• 1-Substitution in aromatic ring• 2-State of the oxidation of the side chain• -CH=CH-COOH →Propenic acid, cinnamic acids• -CH=CH-CH2OH → Propenol, coniferylalcohols

• CH2-CH=CH2 →Allyl, Eugenol (volatile oil)

• -CH=CH-CH3 → Propenyl, Anethol (volatile oil)• -CH2-CH2-CH3 →n-propyl

• 3- Shortening of the side chainFormation of phenol carboxylic acids and simple phenols

Cinnamic acidsCinnamic acid p-coumaric acid

Caffeic acid Ferulic acid

Sinapic acid 5-OH-ferulic acid Tri-OH-cinnamic acid

Formation of Phenylpropane Derivatives with Shorter Side Chain: Shortening of side chain by β-oxidation and subsequent decarboxylation (simple phenols) which might be linked to oxidation→hydroquinone → quinone

OH

COOH O

H

O

OH

OH

OHp-Coumaric acid

p-Hydroxybenzoic acid Hydroquinone

O

OQuinone

Benzoic acids related to cinnamic acids

Cinnamic acid ………………...Benzoic acid

p-coumaric acid……………….p-OH-benzoic acidCaffeic acid………………........Protocatechuic acid

Ferulic acid………………………Vanillic acidSinapic acid……………………..Syringic acidTri-OH-cinnamic acid……….Gallic acid

Derivatives of dehydroshikimic acid

Vanilla planifolia (Orchidaceae) • Vanillin produced from eugenol (in plants) or lignin is a degradation by-product of

paper from wood (large scale preparation of vanillin)• Fermentation under blankets in the sun

Eugenol Coniferylalcohol (lignin)

Vanilloside (odourless ) is liberated during fermentation & oxidized to vanillin

• Fine aroma and taste is due to other compounds better than pure vanillin

H O

OCH3

OH

Vanillin

H O

OCH3

O-Glucose

Vanilloside

fermentation

CH2OH

OCH3

OH

CH2OH

OCH3

O-Glucose

H O

OCH3

OHVanillyl alchoholVanilloloside

fermentation fermentation

Vanillin

Coumarins

Name derived from Coumarouna (local Guyana name) for the seeds of Dipteryx odorata (Fabaceae) common name for Tonka beanSeeds as spirits spice (not used now, hepatotoxic & carcinogenic)Characteristic new mown hay smell Commonly used as sun UV protector Absorb short wave UV 230-315 nm & transmit long-wave UV 315 - 400 nm resulting in brown sun tan

O123

45

6

5,6-Benzopyran-1-oneisocoumarin

OO O1

23

45

6

5,6-Benzopyran-2-onecoumarin

Characters of Coumarins• Free coumarins are organic solvents-soluble• Derivatives of α-chromone, differ in benzene ring substitutions

(OH, OCH3, CH3)• Common in Apiaceae, Asteraceae, Fabaceae, Lamiaceae, Poaceae,

Moraceae, Rutaceaea & Solanaceae

• Characteristic UV (blue, yellow & purple) enhanced by ammonia• Umbelliferone R1=OH, R2=H

• Aseculetin R1=R2= OH

• Scopoletin R1=OCH2, R2= OH

• Aseculus hippocastanum (horse-chestnut) (Hippocastanaceae) rich in aesculin (6β-D-glucosyloxyl-7-OH-coumarin ); used in sun tan preparations (both glycoside & aglycone)

• Symptomatic Rx of cutaneous capillary fragility

O O

R1

R2

6

7

Biosynthesis of the coumarins

Dicoumarol

• Melilotus officinalis (Fabaceae) mould-infected sweet clover• Discovered by studying grazing cattle coagulation pattern

(sweet clover disease) • Dicoumarol replaces vitamin K in prothrombin result in anti-

coagulant effect• Prevention of thrombosis• Pharmaceutical industry: synthetic derivatives for p.o

preparations• Extract: p.o & topically to Rx minor vascular disorders & acute

attacks of piles

O O OO

OH OH

Furanocoumarins (Photosensitizers)

Furan ring is derived from isopentyl pyrophosphate (mevalonic acid pathway)

6,7 or 7,8 furanocoumarinsFuranocoumarins-rich plant families:Apiaceae, Fabaceae, Moraceae & Rutaceae Roots, fruits or seeds

O OO

6

7

Furnaocoumarin

Furanocoumarin Natural Derivatives

• Psoralea corylifolia (Fabaceae) fruits

• Ammi majus (Apiaceae) fruits الشيطاني الخّلة• Ammi visnaga !!!• Cause dermatitis after consumption or direct contact of skin

with such plants followed by exposure to sun (only 6,7-furanocoumarins; 7,8-furanocoumarin derivatives are inactive)

Medicinal value:1) Photo chemotherapy: Rx of vitiligo as part of PUVA for

repigmentation of skin2) UVA= 320nm + p.o+ topical psoralen or derivativesPsoriasis: abnormal epidermal production of scaly skin

O OO

R1

R2

12

3

456

7

8

4'

5'

Example of Medicinally-valuable Furanocoumarins

• Commonly known as Psoralens• Psoralen R1=R2= H

• Bergapten R1= OCH3, R2=H [5-MOP]

• *Xanthotoxin R1= H , R2= OCH3

* Xanthotoxin= Methoxsalen = 8-MOP nat. or semisynthetic derivative of psoralen p.o medication

• Imperatorin R1=H , R2 = CH2-CH=C(CH3)2

• Trioxalon = TMP 4,5,8-trimethylpsoralen (synthetic) topical or bath sol. Then exposure to UVA @ 320-380 nm

O OO

R1

R2

12

3

456

7

8

4'

5'

MOP of PUVA & Toxicity

1. Interfere with DNA by forming bridges between its base pairs (pyrimidine part)

2. Double bonds of furanocoumarin are activated by UV radiation

3. Inhibits replication & transcription of DNA & synthesis of RNA & cell division

4. Rx of psoriasis is based on the basis of DNA synthesis, inhibitory effect by furanocoumarins

Photosensitization Mechanism: Binding of activated 3,4- double bond in furanocoumarin with 5,6-double bond of pyrimidine base pair in DNABinding of 4’,5’-double bond of psoralen molc. with a second molecule of pyrimidine base of another base pair

O OO

6

7

Xanthotoxin

34N

N

O

O

CH3

Sugar

P

4`

5`

N

N

O

Sugar

P

NN

Sugar

P

N N

N

H

H

Thymine

OCH3

AdenineCytosine

20

Lignin & Lignans • 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]

Formation of the lignans

Dimers of cinnamic acid linked via their ß-carbons and further modifications; i.e. Podophyllotoxin

•

↓ ↓

22

Podophyllotoxin: 2 C6C3 [Coniferylalcohol]via several intermediates

• Dried root & rhizhome of Podophyllum peltatum [May apple, mandrake] (Berberidaceae) USA & Canada

• Structure elucidated in 1930’s; planar structure with 4 chiral centers

• C2H5OH extract = Podophyllin (20% podophyllotoxin, 10% β-peltatin, 5% α-peltatin)

• Traditionally as cathartic, purgative, antiviral, warts remedy• Trans lactone ring is essential for anti-tumor action; aromatization

of ring C↓activity. Too toxic to be used clinically!• [OH-] converts into inactive isomer (e.g.epi-podophyllatoxin)• Classified as microtubule inhibitor [inhibits polymerization of

tubulin and stop cell division at the beginning of metaphase]

Etoposide and teniposide• As semisynthetic anticancer agents developed from 4’-

demethylepipodophyllotoxin • They act as Topo II inhibitors (prevention of DNA synthesis

and replication)• Etoposide : small cell lung cancer, breast cancer, leukemia &

Hodgkin’s disease,… Teniposide : brain and bladder cancer,…• Glycosides < active than genins < side effects

24

Podophyllotoxin & Peltatins

• Lignans formed by oxidative coupling of 2 cinnamic acid residues (dimeric phenylpropane derivatives) known as LIGNANS

O

OO

OR1

H3CO OCH3

H O

H R2R3

Podophyllotoxin R1=CH3 R2= OH R3= HAlpha-Pelatin R1= R2= H R3= OHBeta- Pelatin R1= CH3 R2= H R3= OH

H

Tannins & Gallic acid • Gallic acid is the building block of many tannins

Properties of Tannins:• H2O solubility !! (colloidal aq. Solution in A` PH)• Binds proteins to form indigestible complex (leather tanning)• Amorphous• Astringent taste (unripe fruits, in all organs or organ-specific)• Fe+2 salts binding producing dark blue or greenish black sol. Complexes (ink)• Ppt with metals e.g. Cu, Pb (acetate salts to separate tannins from extracts);

ppt gelatin and alkaloids; • Large MW (1000-5000)• Pseudotannins (MW~500)

HO

OH

COOH

OHO

OH

COOH

OH HO

OH

COOH

OH

Shikimic acid 3-Dehydroshikimic Acid Gallic acid

Tannins

Hydrolysable tannins

• Possibilities of condensation of the gallic acid

HO

HO

HO

COO

HO

HO

COOH

COOH

HO

OH

COOH

HO

OHOH

OH

3-galloyl-gallic acid

Hexahydroxydiphenic acid

O

OO

O

OH

OH

HO

OH

Ellagic Acid

Classification of Tannins Hydrolysable

H+ or enzymes Rx produce simple molecules

A) Ellagitannins

B) Gallotannins

Condensed• H+ or Enzymes Rx

produce complex insoluble compounds

• Complex polymers• Biosynthesis from

acetate or shikimate pathway

• Building units are catechins + flavonoids estrefied with gallic acid

O

O

O

O

OH

OH

OH

HO

H+

Ellagic Acid

+ SugarEnzymes

Ellagitanins

CO2H

OHOH

HO

Gallic Acid

+ SugarH+

EnzymesGallotannins

O

OH

OH

HO

OH

OH

Catechin

Medicinal Value of Tannins

Limited Application:Based on ability to bind proteins to form indigestible

complex1. Diarrhea2. Bleeding gums3. Skin injuries preparations

Plant Material H2O/Alc

Ether Tannins (sugar + gallates) + Free Gallic A`

Hamamelis • Dried leaves of Hamamelis virginiana L.

(Hamamelidaceae)• North America & Canada • Gallotanins Uses:1. Infussions & extracts in haemorrhoids (topical

pharmaceuticals)2. Topically skin inflammation3. Face lotions as astringent

O

R'O

OHOR

H

OR

HH

OH

HR= GALLIC ACID

R' = TRIGALLIC ACID

HO

OH

COOH

OH

Gallic acid

Galls • Vegetable growths as a result of insect infections of the

leaves & twigs of Quercus infetoria (Fagaceae) • 70-80% tannins from Turkey, Syria, Greece & Iran

Uses:1. Rx of catarrh & infection2. Stop bleeding locally 3. Alkaloid poisoning remedy (insoluble comlex)4. Ink preparation5. Textiles dyeing esp. leather

HO

COOH

OH

O

O

TRIGALLIC ACID

HO

HO

OH

O

O

HO OH

O

R'O

OHOR

H

OR

HH

OH

HR= GALLIC ACID

R' = TRIGALLIC ACID