THIRD YEAR COURSE

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.•

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 AtropaSpecies name: e.g. Cocaine from cocaCommon name: e.g. Ergotamine from ergotPhysiological 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 nornicotineApo - : Designates dehydration e.g. apomorphineNeo - , 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:

TRUE ALKALOIDS

PROTOALKALOIDS

PSEUDOALKALOIDS

Derived from amino acids

Derived from simple amines

NOT derived from amino acids

Basic in Nature Basic in Nature Very weak basicity

N atom in heterocyclic ring

N atom not in heterocyclic ring

N atom in heterocyclic ring or not

e.g. Atropine, Morphine

e.g. Mescaline, Ephedrine

e.g. Caffeine

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: Norpseudoephedrineb.Secondary amines: Ephedrinec.Tertiary amines: Atropined.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 ppt2.Wagner’s Reagent Brown ppt3.Dargendorff (Kraut’s) Orange to reddish brown ppt4.Phosphomolybdic acid White ppt5.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. QUININE1. QUININE

NATURE : NATURE : Dry Cinchona Bark. Dry Cinchona Bark. C. succirubraC. succirubra, , C.LedgerianaC.Ledgeriana

Family : Rubiaceae.Family : Rubiaceae.

PHARMACOLOGICAL ACTIONS : PHARMACOLOGICAL ACTIONS : Anti-malarial.

OH

N

H

O

N QUININQUININEE

GENERAL PPTING AGENTS : GENERAL PPTING AGENTS : 1. Mayer’s reagent : creamy white ppt 2. Wagner’s reagent : reddish brown ppt3. Tannic acid : yellowish white ppt4. Hgcl2 reagent : white ppt

5. Phosphomolybidic acid: white ppt

GENERAL COLOURING AGENTS : GENERAL COLOURING AGENTS : 1. Mandalin’s reagent : -ve2. Froehd’s reagent : -ve3. Marqui’s reagent : -ve 4. Erdmann’s reagent: -ve5. Conc. HNO3 reagent : yellow colour

1 ml alkaloidal solution

Add dil H2SO4 till full test tube

Blue flourescence

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