1. Classification, Biosynthesis and Functions of Alkaloids
Submitted From: SubmittedTo:
Aleena Stanley Dr. Elsam Joseph
1stMSc Botany Associate Professor
St.Teresa’s College Ekm St.Teresa’s College Ekm
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2. What is an alkaloid?
• The term Alkaloid (Alk=Alkali, Old=Like) was proposed by
W.Meissnerin in 1819 for basic nitrogen containing compounds of
plant origin.
• It may be defined as physiologically active basic compound of plant
origin in with atleast one nitrogen atoms form part of a cyclic system.
• Alkaloids are cyclic organic compounds containing nitrogen in a
negative state of oxidation with limited distribution among living
organisms.
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3. Forms of Alkaloids:
• Free Bases
• Salts with organic acids e.g. Oxalic, acetic acids
• Salts with inorganic acids e.g. HCl,H2SO4
• Salts with special acids e.g. Meconic acid in Opium
• Glycosidal form e.g. Solanine in Solanum
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4. Distribution and Occurrence:
• Rare in lower plants.
• Dicots are more rich in Alkaloids than Monocots
• Families rich in Alkaloids: Apocynaceae, Rubiaceae, Solanaceae and
Papaveraceae.
• Families free fromAlkaloids: Rosaceae, Labiatae
• Alkaloids occur in all plants parts, but are usually localized in one organ.
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5. Distribution in plants
• All Parts – Datura
• Barks- Cinchona
• Seeds- NuxVomica
• Roots- Aconite
• Fruits-Black pepper
• Leaves-Tobacco
• Latex- Opium
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6. Classification of Alkaloids
• Classification based on botanical origin of alkaloids are also used, e.g.
Papaver, Cinchona, Rauvolfia, Strychonos Alkaloids etc..
• CLASSIFICATION BASED ONTHEIR CHEMICAL NATURE
• Alkaloid that contain a ring system, which is called indole are referred as
Indole Alkaloids.
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7. • PHARMACOLOGICAL CLASSIFICATION
• Depending on the physiological response, the alkaloids are classified under various
pharmacological categories like
• E.g. Narcotic analgesics: Morphine
• Vasodilation: Ephedrine, Ergonovine
• Local anesthetic:Cocaine
• Hallucinating: Psilocybin
• TAXONOMIC CLASSIFICATION
• This method classifies the vast number of alkaloids based on their distribution in various
Plant families like Solanaceae or Papillionaceous alkaloids. Preferably, they are grouped as per
the name of the genus in which they occur.
E.g. Ephedra, Cinchona etc.
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8. • BIOSYNTHETIC CLASSIFICATION
• This method gives significance to the precursor from which the alkaloids are
biosynthesized in the plant.
• E.g. Ornithine-Tropane, Pyrrolidine, Pyrrolizidine.
• Tyrosine- Benzyl isoquinoline.
• Tryptophane-Indole alkaloids,Quinoline
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9. • CLASSIFICATION OF ALKALOIDS BASED ON PRIMARY GROUPS
• TRUE ALKALOIDS : The Alkaloids containing true heterocyclic rings are called True Alkaloids and they are
classified according to the ring system present in the molecule.
• PROTOALKALOIDS : The Alkaloids which do not contain heterocyclic ring are called Protoalkaloids.
• PSEUDOALKALOIDS : Those alkaloids which are not derived directly from amino acids are called Pseudo-
alkaloids.
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10. BIOSYNTHESISOF ALKALOIDS
Biosynthesis of Protoalkaloids
A typical protoalkaloid Hordenine is synthesized from amino acid tyrosine or
phenylalanine. The methyl groups present in Hordenine originate from methionine by the
process of methylation in presence of enzyme tyramine methylpherase.
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11. Biosynthesis ofTrue Alkaloids
The true alkaloids may be derivative of (i) Pyrrolidine, (ii) Pyrolizidine, (iii) Pyridine,
(iv) Piperidine, (v) Quinolizidine, (vi) Isoquinone, (vii) Indole, (viii)Quinoline and (ix) Imidazole
PYRROLIDINE DERIVATIVES:
The pyrrolidine ring is a part of skeleton of tropane alkaloids like
hyoscyamine. It is synthesized through amino acid ornithine via an intermediate pyrrolidine 5-
carboxylic acid.
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12. PYRROLIZIDINE DERIVATIVES:
It is synthesized from two ornithine molecules. The alkaloid contains pyrrolizidine nucleus
made up of two pyrrolidine nuclei. e.g. Retronecine alkaloid.
PYRIDINE DERIVATIVES:
Alkaloid nicotine in higher plants, anaerobic yeast and bacteria is synthesized from nicotinic
acid which in turn is formed from L-aspartic acid and glycerol. But in animals and aerobic fungi
the nicotine is synthesized from tryptophan.
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13. • INDOLE DERIVATIVES:
The indole ring of reserpine and agroclavine alkaloids arises from
amino acid tryptophan. The tryptophan first yields ajmaline. The remaining part of the
molecule arises from a monoterpine vie mevalonic acid(MVA). This part is indicated by bold
lines in the fig:
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14. • The ergot alkaloids also arise from tryptophan but here a hemiterpene residue probably
dimethyallyl pyrophosphate is involved which are condensed forming 4- dimethylallyl
tryptophan is converted into agroclavine. Agroclavine provides the basic skeleton for the
synthesis of other ergot alkaloids.
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15. • QUINOLINE AND IMIDAZOLE DERIVATIVES
• Quinoline derivative alkaloids like Cinchonine and Quinine are synthesized from tryptophan
via an indole alkaloid like corynantheine. The imidazole alkaloids like pilocarpine are
probably synthesized from histidine. Nothing more is known about the biosynthesis of
imidazole alkaloids.
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16. • Biosynthesis of Pseudoalkloids
• Pseudo alkaloids include terpenoid derivatives which are usually derived from triterpenes. Two
types of sterol alkaloids are found in nature:
• (i) those which are C-27 compounds derived from cholesterol
• (ii) alkaloids containing C-21 pregnane skeleton .( Steroid derivatives with carbon present at
position 1 through 21)
• Pseudo alkaloids are synthesized in leaves rather than in the roots.
• E.g C-21 alkaloids are holarrhimine and conarrhimine. (which exists as esters)
Holarrhimine Conarrhimine 16
17. FUNCTIONS OF ALKALOIDS
• They may act as protective against insects and herbivores due to their bitterness and
toxicity.
• They are, in certain cases, the final products of detoxification in metabolic reactions,
therefore considered as waste products of metabolism.
• They may provide nitrogen to the plant organ in case of nitrogen deficiency(source of
nitrogen)
• They, sometimes acts as growth regulators in certain metabolic systems.
• They are utilized as a source of energy incase of deficiency in carbon dioxide assimilation,
especially those alkaloids containing a sugar moiety.
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18. • Some Alkaloids are extremely poisonous (e.g. Ergot)
• Ergot Alkaloids caused epidemic poisoning on the Middle Ages in Europe as a result of
feeding on rye bread contaminated with the fungus
• The extracts of this plants containing such alkaloids have long been used as arrow poisons
in hunting and warfare. E.g. Curare extract that contains tubocurarine alkaloid.(muscle
relaxant)
• Belladonna has been mixed with food for the purpose of murdering.
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19. Applications Of Alkaloids
• MEDICINE
Medical use of alkaloid-containing plants has a long history, and thus when the
first alkaloids were isolated in the 19th cent. Many alkaloids are still used in medicines, usually
in the form of salts .
e.g. Ajamaline (Alkaloid) (anti-arrhythmic)
Reserpine( anti-hypertensive)
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20. • Many synthetic and semisynthetic drugs are structural modifications of the alkaloids, which
were designed to enhance or change the primary effect of the drug and reduce unwanted
side-effects.
E.g. Naloxone
• Human Foods and Drinks
• The plants in the human diet in which alkaloids are present are not only coffee
seeds (caffeine), tea leaves (caffeine, theophylline) but also tomatoes (tomatine)
and potatoes (solanine).
• The common alkaloid caffeine improves the taste and are mainly used by the
sports men.
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21. • AGRICULTURE
Prior to the development of a wide range of relatively low-toxic synthetic
pesticides, some alkaloids, such as salts of nicotine and anabasine, were used as insecticides.
• USES OF PSYCHOACTIVE DRUGS
Cocaine, caffeine and cathinone-Stimulants of CNS
Mescaline and many Indole alkaloids (psilocybin, ibogaine)-Hallucinogen
Morphine and Codeine – Narcotic pain killers.
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22. Caffeine:
Which occurs in coffee, tea and cocoa is a central nervous system stimulant.
It is also used as antidote to barbiturate and morphine poisoning.
Emetine:
Key alkaloid used in the treatment of amebic dysentery and other protozoal
infections.
Ephedrine:
It causes peripheral contraction of arterioles and it is used to correct low blood
pressure conditions and also to dilate the pupil of the eye.
As a bronchodilator it is used in allergic conditions like asthma.
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