Phyto Chemistry

7/30/2019 Phyto Chemistry

http://slidepdf.com/reader/full/phyto-chemistry 1/6

PHYTOCHEMISTRY SECTIONS

THIRD YEAR COURSE

ALKALOIDS

Introduction

DEFINITION:

Alkaloids (mean alkali-like substances),

Basic nitrogenous compounds,

Nitrogen in a heterocyclic ring system and a few do

not contain nitrogen in a ring system,

Of plant or animal origin

Possessing a marked physiological action

Sources of alkaloids:

a) Plant sources:

The important alkaloid-bearing families are: Liliaceae,Amarylidaceae,Asteraceae,Ranunculaceae,

Papaveraceae, Leguminosae, Rutaceae, Loganiaceae, Apocyanaceae, Solanaceae and Rubiaceae.

•



b) Animal sources:

Recently alkaloids were found in animals and insects e.g,

Pyocyanine Pseudomonas aeruginosa.

Ergotamine and Ergometrine Ergot fungus.

Lycopodine Lycopodium spores,

Muscopyridine Musk deer.

c) Marine sources

Distribution of alkaloids:

In general, alkaloids occur in a salt form with organic or inorganic acids, or in combination

with specific acids

e.g. Opium alkaloids occur with meconic acid

Cinchona alkaloids with cinchotannic acid.

Some occur in combination with sugars as glycosides e.g. solanine

Function of alkaloids in plants:

1) Protective for the plant against insects

2) As end products of metabolism.

3) As waste products.

4) Source for energy and reserve of nitrogen.

Nomenclature:

Alkaloids terminate with the suffix-ine, their names may be derived from the:

Genus name: e.g. Atropine from Atropa

Species name: e.g. Cocaine from coca

Common name: e.g. Ergotamine from ergot

Physiological activity: e.g. Emetine (emetic)



Discoverer e.g. Pelletierine from pelletier

Sometimes prefixes and suffixes are usually added to describe related alkaloids:

A) PREFIXES:

Nor - : Designates N-demethylation e.g. norpseudoephedrine and nornicotine

Apo - : Designates dehydration e.g. apomorphine

Neo - , iso - , pseudo - , epi - : Indicates different types

of isomers.

Seco - : means Ring opening.

B) SUFFIXES:

dine: Refer to isomerism as in the case of the Cinchona alkaloids, quinidine and cinchonidine are the

optical isomers of quinine and cinchonine, respectively.

Classification of Alkaloids:

Physicochemical Properties:

Physical characters:

a) Alkaloids are crystalline solids.

b) Colorless.

c) Free bases are soluble in organic solvents and insoluble in water.

Chemical characters:

a) Basicity:

The basicity of alkaloids is due to the presence of a lone pair of electrons on the nitrogen atom.

Alkaloids are converted to their salts by aqueous mineral acids.



Alkaloids occur as free bases, salts or N-oxides (NO). When the salt of an alkaloid is treated

with hydroxyl ion, nitrogen gives up a hydrogen ion and the free amine is liberated.

Alkaloids contain N atom either in a heterocyclic ring or in the side chain.

a. Primary amines: Norpseudoephedrine

b. Secondary amines: Ephedrine

c. Tertiary amines: Atropine

d. Quaternary amines: Tubocurarine

Detection of alkaloids:

A. Precipitating agents:

Alkaloids are ppted from their neutral or acidic solution by reagents contain heavy metals as Hg,

Bi.

1ml alkaloidal sol. in a test tube + 1ml dil HCl

REAGENT PPT.

1. Mayer’s Reagent Creamy white ppt

2. Wagner’s Reagent Brown ppt

3. Dargendorff (Kraut’s) Orange to reddish brown ppt

4. Phosphomolybdic acid White ppt

5. Tannic acid White ppt

B. Coloring agents:

Give characteristic colour with alkaloids and most contain C.H2SO4 and C.HNO3

in a porcelin 1ml alkaloidal sol. E.t.d add the colouring reagent.

1. Erdmann’s reagent: Conc. nitric acid / conc. H2SO4

2. Froehd’s reagent: Ammonium molybdate / conc. H2SO4



3. Mandalin’s reagent: Ammonium vanadate / conc. H2SO4

4. Marquis‘ reagent: Formaldehyde / conc. H2SO4

The colors formed are characteristic. The tests are sensitive to micro amounts and can be used

for colorimetric assay.

1. QUININE

NATURE :

Dry Cinchona Bark. C. succirubra, C.Ledgeriana

Family : Rubiaceae.

PHARMACOLOGICAL ACTIONS :

Anti-malarial.

STRUCTURE :

GENERAL PPTING AGENTS :

1. Mayer’s reagent : creamy white ppt

2. Wagner’s reagent : reddish brown ppt

3. Tannic acid : yellowish white ppt

4. Hgcl2 reagent : white ppt

5. Phosphomolybidic acid: white ppt

GENERAL COLOURING AGENTS :

1. Mandalin’s reagent : -ve

2. Froehd’s reagent : -ve

3. Marqui’s reagent : -ve

4. Erdmann’s reagent: -ve

5. Conc. HNO3 reagent : yellow colour



1. FLOURESENCE TEST:

Documents

Phyto Chemistry