Alkaloids Found in ~20% of vascular plants. Compounds usually basic (alkaline). ~40,000 compounds currently described. Structurally the most diverse class of secondary metabolites. N H H (+)-coniine (Conium maculatum) poison hemlock HO H HO O H O O NH N batrachotoxin (Phyllobates aurotaenia) Columbian arrow frog LD 50 (mice) = 2mcg/kg sc
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CM3101 Alkaloids I - UCC Alkaloids I.pdf · 1963 – Definition based on chemotaxonomy. Alkaloids should be divided into 3 subgroups • Proper alkaloids • Proto alkaloids • Pseudo
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Alkaloids Found in ~20% of vascular plants. Compounds usually basic (alkaline). ~40,000 compounds currently described. Structurally the most diverse class of secondary metabolites.
NH
H
(+)-coniine(Conium maculatum)
poison hemlock
HOH
HO
O
HO
O
NH
N
batrachotoxin(Phyllobates aurotaenia)
Columbian arrow frogLD50 (mice) = 2mcg/kg sc
Many natural product alkaloids are of biological interest • Morphine (painkiller) • Vincristine (anticancer agent) • Cocaine (anaesthetic, drug of abuse) • Nicotine (tobacco, poison) • Caffeine (stimulant)
Relatively straightforward to isolate. Of intense interest to organic chemists for the challenge of structural elucidation and total synthesis.
• Devise new synthetic methodologies
Alkaloids - Definitions First definition (1817)
• Basic compounds • Contain N (nitrogen) in molecule • Can form salts with acids • Occur in plants • Pharmacologically active
1963 – Definition based on chemotaxonomy. Alkaloids should be divided into 3 subgroups
• Proper alkaloids • Proto alkaloids • Pseudo alkaloids
Proper Alkaloids Also known as true alkaloids. Basic. Nitrogen part of a heterocyclic ring system. Chemically complex. Derived biosynthetically from amino acids, especially the cyclic amino acids:
• Phe, Tyr, Try, His Many physiologically active. Have limited distributions in the plant kingdom.
N
N
O
O
H H
HH
H
NH
COOH
NH2
L-tryptophan(−)-strychnine
(Strychnos nux vomica)
(–)-strychnine – from the dried seeds of Strychnos vux vomica. Small tree found from India to Northern Australia. Fruit is a large berry with a hard coat and pulpy interior containing 3-5 fleshy grey seeds – contain ~1.2% strychnine. 60mg can kill an adult.
Proto Alkaloids Physiologically active. Nitrogen atom is outside the ring system.
COOH
NH2
L-Phenylalanine
OH
NHCH3
(−)-ephedrinesympathomimetic amine
(Ephedra sp.)
O
OMe
H
NH
O
colchicine(Colchicum autumnale)used in the tx of gout
cycloheptatrienonering
Pseudoalkaloids Nitrogen containing (physiologically active) compounds not derived from amino acids. The purine ring is gradually elaborated by piecing together small components from primary metabolism.
HN
N N
N
O
O
OHHO
PO
inosine monophosphate(IMP)
N
N N
HN
O
O
theophylline
HN
N N
N
O
O
theobromine
N
N N
N
O
O
caffeine
N
N NH
Nformate
formate
L-GlnL-Gln
L-asp
CO2 Gly
purine alkaloids from Coffea species (C. arabica, C. canephora, C. liberica, etc)