Secondary metabolites derived from Shikimic acid (Phenyl propanoids and Lignans)

SCH 308 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 308 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 308 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 308 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 308 Dr. Solomon Derese 5 DAHP

SCH 308 Dr. Solomon Derese 6 SCH 308 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 308 Dr. Solomon Derese 8 NAD+ - CO2

- CO2 - H O Chorismic acid 2

SCH 308 Dr. Solomon Derese 9 Phenylalanine Ammonia Lyase (PAL)

Tyrosine Ammonia Lyase (TAL)

SCH 308 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 308was 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 308 Dr. Solomon Derese 12 Biosynthesis of Coumarins

Lactone formation

Lactone formation

SCH 308 Dr. Solomon Derese 13 SCH 308 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 308 Dr. Solomon Derese 15 Biosynthesis of Lignans

SCH 308 Dr. Solomon Derese 16 Radical pairing A + D; B + D; D + D, etc yield different types of lignans.

SCH 308 Dr. Solomon Derese 17 D

D

SCH 308 Dr. Solomon Derese 18 SCH 308 Dr. Solomon Derese 19 SCH 308 Dr. Solomon Derese 20 SCH 308 Dr. Solomon Derese 21 Secondary metabolites derived from mixed biosynthetic origin (The flavonoids).

SCH 308 Dr. Solomon Derese 22 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.

SCH 308 Dr. Solomon Derese 23 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 C6-C3-C6 (two benzene rings joined by three carbons) carbon framework.

SCH 308 Dr. Solomon Derese 24 O

From shikimic From Polykeide O acid pathway pathway

SCH 308 Dr. Solomon Derese 25 Chalcones

Flavonoids 3' 3' 3' 2' 2' 2' B B B O O O 2 2 2 A C A C A C 3 3 3 5 4 5 5 Flavan O O Flavanone Flavone SCH 308 Dr. Solomon Derese 26 Isoflavonoids

SCH 308 Dr. Solomon Derese 27 Naming of flavonoids OH H HO O IUPAC NAME (S)-5,7-dihydroxy-2-(4- hydroxyphenyl)chroman-4-one OH O

5' 6' OH 4' 8 H B HO O 3' 1' 7 A C 2 2' SEMISYSTEMATIC NAME 6 4 3 5 4’,5,7-Trihydroxyflavanone OH O

SCHFLAVANONE 308 Dr. Solomon Derese 28 IUPAC Name 7-Hydroxy-3-(4-hydroxyphenyl)-6-methoxy-4H-chromen- 4-one

Semisystematic Name 4',7-Dihydroxy-6-methoxyisoflavone

SCH 308 Dr. Solomon Derese 29 4 5 O O 6 A B 7 6a 8 O 2 1 11a C D O OMe 10 IUPAC Name 9-Methoxy-8-(3-methylbut-2-enyl)-6a,11a-dihydro-6H- benzofuro[3,2-c][1,3]dioxolo[4,5-g]chromene

Semisystematic Name 9-Methoxy-2,3-methylenedioxy-8-prenylpterocarpan

SCH 308 Dr. Solomon Derese 30 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 CHalcone Synthase (CHS).

SCH 308 Dr. Solomon Derese 31 HO OH

O SCoA SCoA O

O O O O O O Tetraketide intermediate

SCH 308 Dr. Solomon Derese 32 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 (CHS).

SCH 308 Dr. Solomon Derese 33 OH

O SCoA

O

O O

NADPH, -H2O CHS CHS

Leguminosae + other Leguminosae plantSCH 308 families. Dr. Solomon Derese 34 CHalcone Isomerase (CHI) 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.

SCH 308 Dr. Solomon Derese 35 Flavanone SCH 308 Dr. Solomon Derese 36 These flavanones are the precursors for the construction of 5-deoxyflavonoid and 5- hydroxyflavonoid skeletons.

NADPH, O2 -H2O

SCH 308 FlavoneDr. Solomon Derese 37 1,2-aryl migration

NADPH

- H2O

Isoflavone

SCH 308 Dr. Solomon Derese 38 HO O HO O [O]

O O OH HO OH

NADPH, H+

HO O HO O

HO + HO OH H O HO OH

HO O H Pterocarpan H O OH SCH 308 Dr. Solomon Derese 39 Biosynthesis of Rotenoids H OH HO O CH3 O HO O CH2 O O2, NADPH O OMe O OMe OMe OMe

H HO O HO O O O

H O O OMe OMe H: OMe OMe Demethylmunduserone SCH 308 Dr. Solomon Derese 40 H HO O O

Demethylmunduserone H O OMe OMe DMAPP OPP

H H H O O HO O O O O O O

H H H O O O OMe OMe OMe OMe OMe OMe Rotenone Rotenonic acid Deguelin

SCH 308 Dr. Solomon Derese 41 Anthocyanin Flower Pigments

SCH 308 Dr. Solomon Derese 42 Anthocyanin Leaf Pigments

Autumn Leaves

In Spring and Summer chlorophyll (green) masks the anthocyanin colors.

SCH 308 Dr. Solomon Derese 43 Anthocyanidins and Anthocyanins

OH OH OH

HO O HO O HO O R R R O2 NADPH OH NADPH OH OH O OH O OH OH

Naringenin (R=H)

[O]

OH OH + OH HO O HO O R R

OH OH Anthocyanins are - 2 H2O red, violet or blue OH OH OH Pigments, have sugar at pelargonidin (R=H) C-3. cyanidin (R=OH) Anthocyanidins plant flower and cyanidin is blue leaf pigments pelargonidin is pink SCH 308 Dr. Solomon Derese 44 OH

HO O

O Chrysin OH OH

HO O

OH OH O Sun flower Quercetin (Compositae) FLAVONES SCH 308 Dr. Solomon Derese 45 Anthocyanin

SCH 308 Dr. Solomon Derese 46 ANTHRAQUINONES

Knifofia

SCH 308 Dr. Solomon Derese 47 What are Alkaloids? ‘any non-peptidic & non- nucleotide nitrogenous secondary metabolite’

SCH 308 Dr. Solomon Derese 48 OH N H O N H H HO N

O N H N NH Sparteine HO Quinine Lysergicacid N H H O N N

H O O HO H Morphine Strychnine

HO OH H

H N N N O OH Retronecine N H Coniine O CO H N Nicotine H 2 Clavulanic acid SCH 308 Dr. Solomon Derese 49 Alkaloids have one or more nitrogen, typically as primary, secondary, or tertiary amines, and this usually confers basicity to the alkaloid, facilitating their isolation and purification since water-soluble salts can be formed in the presence of mineral acids. There also alkaloids which are neutral.

The name alkaloid is in fact derived from alkali.

SCH 308 Dr. Solomon Derese 50 The nitrogen atoms in alkaloids originate from an amino acid, and, in general, the carbon skeleton of the particular amino acid precursor is largely retained intact in the alkaloid structure, though the carboxylic acid carbon is often lost through decarboxylation.

SCH 308 Dr. Solomon Derese 51 The most common amino acids from which alkaloids are derived from are: I) Ornithine II) Lysine O HO

HO NH2 O NH2 NH2 NH2 ornithine lysine

III) Tryptophan O OH

NH2 N H tryptophan SCH 308 Dr. Solomon Derese 52 IV) Tyrosine V) Phenylalanine

H2N O OH

HO O OH NH2 tyrosine phenylalanine VI) Nicotinic acid N O

OH nicotinic acid SCH 308 Dr. Solomon Derese 53 Decarboxylation

SCH 308 Dr. Solomon Derese 54 O d a HO NH2 NH2 Non-protein amino acid Ornithine

Ornithine contains both d - and a - amino groups, and it is the nitrogen from the former group which is incorporated into alkaloid structures along with the carbon chain, except for the carboxyl group. SCH 308 Dr. Solomon Derese 55 Alkylation O PLP H2N NH NH 2 RHN NH2 NH 2 HO 2 Putrescine CO2 Ornithine OXIDATIVE DEAMINATION

Pyrolidine alkaloids N RHN H O R

OXIDATIVEDEAMINATION Monoamine H oxidase R R NH 2 O Diamine oxidase H H2N n NH2 H2N n O

SCH 308 Dr. Solomon Derese 56 SCoA O R SCoA O O O N N N R O O O Iminium salt R SCoA SCoA Malonyl CoA O O [O]

Enz B H N N HO N R R CoAS CoAS R O OH O SCoA O O O

N N + H2O N R R R CoAS - CO2 O O SCH 308O O Dr. Solomon Derese 57 Tropinone N O

NADPH CoAS N O O N OH O

CO2Me N O

O

SCH 308 Dr. Solomon Derese 58 O O PLP OXIDATIVE CO2H DEAMINATION SCoA NH2 NH NH2 NH NH2 O N 2 CO 2 Lysine 2 Cadaverine Piperideine H OH O O SAM + H2O SCoA N N - CO2 N SCoA N H H O O O H N-Methylpelletierine Pelletierine

N H H N

N O H Anaferine SCH 308 Dr. Solomon Derese 59 O OH

NH NH N 2 PLP 2 2 SAM

- CO N 2 N N H H H Tryptophan Tryptamine

OH N

N H Psilocin

SCH 308 Dr. Solomon Derese 60 O H

O Glucose NH O O

NH2 O N O Glucose Secoganin H N O O H Tryptamine O Strictosidine

SCH 308 Dr. Solomon Derese 61 O L-tyrosine OH NH HO 2

SCH 308 Dr. Solomon Derese 62 HO H HO N HO H O + H N 2 HO HO

HO

MeO MeO HO

NMe SAM NH NMe [O] HO HO HO H H H HO SAM

HO HO MeO Reticuline

SCH 308 Dr. Solomon Derese 63 MeO O

NMe NMe HO O H H

MeO MeO OH OH o,p Bulbocapnine MeO MeO

NMe NMe HO o,o HO H H HO HO

MeO MeO Boldine Reticuline

OXIDATIVE COUPLING SCH 308 Dr. Solomon Derese 64 O OH

NH2 phenylalanine

SCH 308 Dr. Solomon Derese 65 O O O O - NH3 SCoA b-Oxidation SCoA HSCoA NH3 phenylalanine O

O O KHAT =MIRAA Pyruvate

OH O O SAM Transamination NADPH NHMe NH2 O (–)-ephedrine (–)-cathinone NADPH

OH OH SAM

NH2 NHMe (+)-norpseudoephedrine (+)-pseudoephedrine

SCH 308 Dr. Solomon Derese 66 Khat (Catha edulis, family Celastraceae; Somali: Jaad; pronouncedقات; :Arabic [ˈkæt]; Ge'ez ጫት č̣āt; miraa in Kiswahili), is a flowering plant native to tropical East Africa and the Arabian Peninsula.

Khat contains the alkaloid called cathinone, an amphetamine-like stimulant which causes excitement, loss of appetite, and euphoria. In 1980 the World Health Organization classified khat as a drug of abuse that can produce mild to moderate psychological dependence. SCH 308 Dr. Solomon Derese 67 N O

OH nicotinic acid

SCH 308 Dr. Solomon Derese 68 O O Ornithine

NH2 O N H N N N Nicotinamide Nicotine Tigonelline

Lysine N H N H H N H N Nornicotine Anabasine

SCH 308 Dr. Solomon Derese 69 O O H H H - CO O OH 2 N

H N N Me H From L-orinthine NADPH N H Nicotinic acid Dihydronicotinic acid

H N H H Me N N H H Me N NADP Nicotine

SCH 308 Dr. Solomon Derese 70 N Nicotinic acid N H H From L-lysine

H N N H H H H H N H N Anabasine NADP

SCH 308 Dr. Solomon Derese 71 Enamine-Imine Nicotinic acid tautomerization N N H 1,4-Dihydropyridine 1,2-Dihydropyridine

N H N H N N H H Anatabine

SCH 308 Dr. Solomon Derese 72