Secondary metabolites derived from Shikimic acid (Phenyl propanoids and Lignans) CO2H HO OH OH Shikimic acid SCH 511 Dr. Solomon Derese 1 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. SCH 511 Dr. Solomon Derese 2 The Shikimic Acid Pathway This pathway (unique to plants) leads to the formation of the aromatic amino acids phenylalanine and tyrosine and to the formation of many other phenyl-C3 compounds (phenylpropanoids). C C C Phenyl-C3 Phenylpropanoids SCH 511 Dr. Solomon Derese 3 Cleavage of the C3 side chain leads to many phenyl-C1 compounds. C C C C b -Oxidation Phenyl-C1 SCH 511 Dr. Solomon Derese 4 Biosynthesis of Shikimic Acid The shikimate pathway begins with the condensation of PhosphoEnolPyruvate (PEP) and D-erythrose 4-phosphate giving 3-Deoxy-D-Arabino- Heptulosonate-7-Phosphate (DAHP) in a reaction catalysed by the enzyme phospho-2-dehydro-3-deoxyheptonate aldolase (DAHP synthase). SCH 511 Dr. Solomon Derese 5 DAHP SCH 511 Dr. Solomon Derese 6 SCH 511 Dr. Solomon Derese 7 Chorismate is a key Intermediate in the Synthesis of Tryptophan, Phenylalanine, and Tyrosine. Aromatic rings are not readily available in the environment, even though the benzene ring is very stable. The branched pathway to tryptophan, phenylalanine, and tyrosine, occurring in bacteria, fungi, and plants, is the main biological route of aromatic ring formation. SCH 511 Dr. Solomon Derese 8 CO2H O HO 4-Hydroxyphenylpyruvic acid NAD+ - CO2 - CO2 - H O Chorismic acid 2 SCH 511 Dr. Solomon Derese 9 Phenylalanine Ammonia Lyase (PAL) Tyrosine Ammonia Lyase (TAL) SCH 511 Dr. Solomon Derese 10 Coumarins Secondary metabolites with the general formula: Coumarins have a C6-C3 skeleton, with an oxygen heterocycle as part of the C3-unit. It has a sweet scent, readily recognized as the scent of newly-mown hay. Coumarins owe their class name to ‘Coumarou’, the vernacular name of the tonka bean (Dipteryx odorata Willd.,Fabaceae), from which coumarin itselfSCH 511was isolated in 1820Dr. Solomon. Derese 11 Examples of Coumarins HO HO O O HO O O MeO O O Umbeliferone Aesculetin Herniarin O O O O O O Psoralen O Imperatorin SCH 511 Dr. Solomon Derese 12 Biosynthesis of Coumarins Lactone formation O O Coumarin Lactone formation SCH 511 Dr. Solomon Derese 13 SCH 511 Dr. Solomon Derese 14 Lignans Definition Lignans are a large group of natural products characterized by the coupling of two C6C3 units. Lignans are a class of naturally occurring plant phenols that are derived biosynthetically from dimerization of cinnamic acid. SCH 511 Dr. Solomon Derese 15 Biosynthesis of Lignans SCH 511 Dr. Solomon Derese 16 Radical pairing A + D; B + D; D + D, etc yield different types of lignans. SCH 511 Dr. Solomon Derese 17 D D SCH 511 Dr. Solomon Derese 18 OH OMe OH HO MeO O SCH 511 Dr. Solomon Derese 19 OH OMe OH HO H+ MeO MeO O OH OH HO OMe OH SCH 511 Dr. Solomon Derese Isolariciresinol 20 SCH 511 Dr. Solomon Derese 21.
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