Secondary metabolites derived from mixed biosynthetic origin (The flavonoids). SCH 511 Dr. Solomon Derese

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1 Secondary metabolites derived from mixed biosynthetic origin (The flavonoids). 22

2 The flavonoids comprise a large group of secondary metabolites which are derived from sub-units supplied by the acetate and shikimate pathways. They occur almost exclusively in higher plants and are responsible for much of the flavor of food and drink of plant origin and for the colors of flowers. 23

3 In plants, flavonoids are involved in such diverse processes such as UV protection, pigmentation, stimulation of nitrogen-fixing nodules and disease resistance. The term flavonoid is generally used to describe a broad collection of natural products that has a C 6 -C 3 -C 6 (two benzene rings joined by three carbons) carbon framework. 24

4 From Polykeide pathway From shikimic acid pathway 25

5 Chalcone Dihydrochalcone Retro-Chalcone A B 2' 3' 2 3 Chalcones A B 2' 3' 2 3 C Flavan 4 5 A B 2' 3' 2 3 C Flavanone 5 A B 2' 3' 2 3 C 5 Flavone Flavonoids SC Dr. Solomon Derese

6 Isoflavonoids 27

7 Naming of flavonoids IUPAC NAME (S)-5,7-dihydroxy-2-(4- hydroxyphenyl)chroman-4-one A C FLAVANNE 5' 6' B 1' 2' 4' 3' SEMISYSTEMATIC NAME 4,5,7-Trihydroxyflavanone 28

8 IUPAC Name 7-ydroxy-3-(4-hydroxyphenyl)-6-methoxy-4-chromen- 4-one Semisystematic Name 4',7-Dihydroxy-6-methoxyisoflavone 29

9 IUPAC Name A B 1 11a C 6 6a 9-Methoxy-8-(3-methylbut-2-enyl)-6a,11a-dihydro-6benzofuro[3,2-c][1,3]dioxolo[4,5-g]chromene Semisystematic Name 9-Methoxy-2,3-methylenedioxy-8-prenylpterocarpan 7 D 10 8 Me 30

10 Flavonoids are synthesized by extension of p-hydroxycoumaroyl CoA with three molecules of malonyl CoA in linear manner in order to form a tetraketide intermediate. This step is catalyzed by the enzyme Calcone Synthase (CS). 31

11 SCoA SCoA Tetraketide intermediate 32

12 The intermediate then folds and condenses further to give a chalcone. This reaction is the first committed step in flavonoid biosynthesis and is also catalyzed by chalcone synthase (CS). 33

13 SCoA CS NADP, - 2 CS Chalcone Narigeninchalcone Isoliquiritigenin Leguminosae + other plant families. Leguminosae 34

14 Calcone Isomerase (CI) is the second enzyme involved in the biosynthesis of flavonoids and it catalyzes the stereospecific intramolecular cyclization of the chalcones isoliquiritigenin and naringeninchalcone into the flavanones (2S)-liquiritigenin and (2S)-narigenin, respectively. 35

15 Narigeninchalcone Isoliquiritigenin CI CI (2S) -Naringenin Flavanone (2S) -Liquiritigenin 36

16 These flavanones are the precursors for the construction of 5-deoxyflavonoid and 5- hydroxyflavonoid skeletons. (2S ) -Naringenin NADP, 2-2 (2S ) -Liquiritigenin Flavone synthase (FNS) FLAVNE 37

17 2 Naringenin NADP 1,2-aryl migration 2-2 NADP Genistein Isoflavone 38

18 [] NADP, + + Pterocarpan 39

19 Biosynthesis of Rotenoids C 3 2, NADP C 2 Me Me Me Me Me Demethylmunduserone Me Me 40 : Me

20 Me Demethylmunduserone Me DMAPP PP Me Me Me Rotenone Me Me Rotenonic acid Deguelin Me 41

21 Anthocyanin Flower Pigments 42

22 Anthocyanin Leaf Pigments Autumn Leaves In Spring and Summer chlorophyll (green) masks the anthocyanin colors. 43

23 Anthocyanidins and Anthocyanins 2 R R R NADP NADP Naringenin (R=) [] + R R Anthocyanins are red, violet or blue Pigments, have sugar at C-3. Anthocyanidins pelargonidin (R=) cyanidin (R=) plant flower and leaf pigments cyanidin is blue pelargonidin is pink 44

24 Chrysin Sun flower (Compositae) Quercetin FLAVNES 45