Secondary metabolites derived from Shikimic acid (Phenyl propanoids and

Lignans)

Shikimic acid

OH

OH

HO

CO2H

SCH 511 1Dr. Solomon Derese

Learning Objectives

• Recognize the role of shikimic acid, chorismic acid

and prephenic acid in biosynthesis.

• Recognize that cinnamic acid derivatives are

precursors to other natural products like lignans

and coumarines.

2SCH 511 Dr. Solomon Derese

The Shikimic Acid PathwayThis pathway (unique to plants) leads to theformation of the aromatic amino acidsphenylalanine and tyrosine and to the formation ofmany other phenyl-C3 compounds(phenylpropanoids).

C C C

Phenylpropanoids

Phenyl-C3

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Cleavage of the C3 side chain leads to manyphenyl-C1 compounds.

Phenyl-C1

C C C C

b-Oxidation

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Biosynthesis of Shikimic Acid

The shikimate pathway begins with thecondensation of PhosphoEnolPyruvate(PEP) and D-erythrose 4-phosphategiving 3-Deoxy-D-Arabino-Heptulosonate-7-Phosphate (DAHP) in areaction catalysed by the enzymephospho-2-dehydro-3-deoxyheptonatealdolase (DAHP synthase).

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DAHP

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Chorismate is a key Intermediate in theSynthesis of Tryptophan, Phenylalanine, andTyrosine.

Aromatic rings are not readily available in theenvironment, even though the benzene ringis very stable. The branched pathway totryptophan, phenylalanine, and tyrosine,occurring in bacteria, fungi, and plants, is themain biological route of aromatic ringformation.

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Chorismic acid

NAD+

- H2O

CO2H

OHO

4-Hydroxyphenylpyruvicacid

- CO2

- CO2

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Phenylalanine Ammonia Lyase (PAL)

Tyrosine Ammonia Lyase (TAL)SCH 511 10Dr. Solomon Derese

CoumarinsSecondary metabolites with the general formula:

It has a sweet scent, readily recognized as the scentof newly-mown hay.

Coumarins have a C6-C3skeleton, with an oxygenheterocycle as part of theC3-unit.

Coumarins owe their class name to ‘Coumarou’, thevernacular name of the tonka bean (Dipteryxodorata Willd.,Fabaceae), from which coumarinitself was isolated in 1820.SCH 511 11Dr. Solomon Derese

O OHO

Umbeliferone

O OHO

HO

Aesculetin Herniarin

O OMeO

O OO

Psoralen

O OO

OImperatorin

Examples of Coumarins

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O OCoumarin

Lactone formation

Lactone formation

Biosynthesis of Coumarins

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Lignans

Lignans are a large group of natural productscharacterized by the coupling of two C6C3units.

Lignans are a class of naturally occurringplant phenols that are derivedbiosynthetically from dimerization ofcinnamic acid.

Definition

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Biosynthesis of Lignans

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Radical pairing A + D;B + D; D + D, etcyield different typesof lignans.

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D

D

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OH

OMe

OH

HO

O

MeO

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H+

OH

OMe

OH

HO

O

MeOOH

OH

OH

OMe

HO

MeO

IsolariciresinolSCH 511 20Dr. Solomon Derese

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