The document discusses the shikimic acid pathway, a biochemical process crucial for the biosynthesis of aromatic amino acids such as phenylalanine and tyrosine in various organisms, excluding animals. It outlines the seven steps of the pathway, starting with phosphoenolpyruvate and erythrose-4-phosphate, leading to the formation of shikimic acid and subsequently chorismic acid, which is a precursor for phenolic compounds. Furthermore, the pathway facilitates the production of various metabolites, including flavonoids, lignin, and gallic acid.

1. PHARMACOGNOSY AND PHYTOCHEMISTRY
SHIKIMIC ACID PATHWAY
Dr.S.RADHA
Associate Professor of Chemistry
Saiva Bhanu Kshatriya College
Aruppukottai

2. SHIKIMIC ACID PATHWAY
Introduction of Shikimic Acid
Shikimic Acid is also know as Shikimate is its anionic form. Structurally it is
a cyclohexane, a cyclitol and a cyclohexane carboxylic acid.
It is an important biochemical metabolite in plants and micro-organisms.
Its name derived from a Japanese plant Shikimi (Illium anisatum). Shikimic
acid is first isolated from this plant in 1885 by Johan Fredric Eykman.
Some hydrolysable tannins produced Shikimic acid as a glycoside part.

3. Shikimic acid pathway is utilized by bacteria, fungi, algae,
parasites and plants for the biosynthesis of aromatic amino acid
like phenylalanine, tyrosin and tryptophan.
This pathway is not found in animals.
Animals can synthesize tyrosine from phenylalanine and
therefore it is not an essential amino acid except for individuals
who unable to hydroxylate phenylalanine to tyrosine .

4. SHIKIMIC ACID PATHWAY
The Shikimic acid pathway is related to the metabolism of
carbohydrate and aromatic amino acid.
The pathway consist of seven steps, starting with the condensation
of phosphoenolpyruvate and erythrose-4-phosphate.
The condensation and cyclization lead to formation of shikimic
acid and end with synthesis of chorismic acid.

5. Active form of these co-enzyme A ( CoA) can access the main classes of
phenolic compounds, quoting some transformation to acids of benzoic acid
series (gallic, protocatechuic, etc.) by - oxidation.
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Gallic acid itself, in combination with simple sugar, leads to the hydrolysable
tannins (gallic and ellagic tannins), or, after the addition of molecule of
phosphoenolpyruvate and additional series of intermediate stages, followed by
amination, give rise to aromatic amino acids tyrosine and phenylalanine, the
starting point of the phenylpropanoid pathway.

7. DHQ is dehydrated to 3- dehydroshikimic acid with the help of
enzyme 3-dehydroquinate dehydratase.
 Further, 3- dehydroshikimic acid is formed is then reduced to
Shikimic acid in the presence of enzymes Shikimate
dehydrogenase, Which utilizes Nicotinamide adenine dinucleotide
phosphate (NADPH) as a cofactor.

8. Shikimic acid also gets converted to Shikimic acid 3-phosphate in the
presence of enzyme Shikimate kinase, an enzyme which catalyzes the ATP
dependant phosphorylation.
Shikimic acid 3-phosphate is then combine with phosphoenol pyruvate to 5-
enolpyruvyl Shikimate-3-phosphate in the presence of enzyme 5-
enolpyruvylshikimate-3-phosphate (EPSP) Synthase.
 Finally, 5-enolpyruvyl Shikimate-3-phosphate is get converted to Chrosimate in the
presence of enzyme Chrosimate Synthase
Shikimic acid 3-phosphate Chrosimate

9.  Prephenic acid is then synthesized by Claisen
rearrangement of Chrosimate with the enzyme
chrosimate mutase.
 Prephenate is oxidatively decarboxylated with
retention of hydroxyl group with the help of
enzyme Prephenate dehydrogenase to produce
p-hydroxy phenylpyruvate.
 This p-hydroxy phenylpyruvate is then
transaminated using glutamate as a source of
nitrogen precursor and produces tyrosine and
α-ketoglutarate.

10. ROLE OF SHIKIMIC ACID PATHWAY
1. Shikimic acid is the starting point in the biosynthesis of many phenolic
compounds.
2. Through Shikimic Acid Pathway phenylalanine and tyrosine are obtained which
act as a precursor for the biosynthesis of phenypropanoids. The
phenylpropanoids are then used to produce flavonoids, coumarins, lignin and
tannins.
3. Shikimic acid pathway is also helpful in Gallic acid biosynthesis Gallic acid is
formed 3-dehyroshikimate in the presence of enzyme Shikimate dehydrogenase
and produce 3,5-didehydroshikimate which rearranges and give Gallic acid.
4. Shikimic acid pathway also involved in the biosynthesis of other compounds like
Indole, Indole derivatives and aromatic amino acid derivatives, many alkaloids
and other metabolic metabolites.