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 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:TRUE ALKALOIDS PROTOALKALOIDS PSEUDOALKALOIDSDerived from amino acids Basic in Nature Derived from simple amines Basic in Nature NOT derived from amino acids 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
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.Mayers Reagent 2.Wagners Reagent 3.Dargendorff (Krauts)
brown ppt 4.Phosphomolybdic acid 5.Tannic acid White ppt
Creamy white ppt Brown ppt Orange to reddish White ppt
B. Coloring agents: Give characteristic colour with alkaloids and most 1. 2. 3.
contain C.H2SO4 and C.HNO3 in a porcelin 1ml alkaloidal sol. E.t.d add the colouring reagent. Erdmanns reagent: Conc. nitric acid / conc. H2SO4 Froehds reagent: Ammonium molybdate / conc. H2SO4 Mandalins 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. QUININENATURE :Dry Cinchona Bark. C. succirubra, C.Ledgeriana Family : Rubiaceae.
PHARMACOLOGICAL ACTIONS :Anti-malarial.
GENERAL PPTING AGENTS :1. Mayers reagent : 2. Wagners reagent : 3. Tannic acid : 4. Hgcl2 reagent :
creamy white ppt reddish brown ppt yellowish white ppt white ppt
5. Phosphomolybidic acid: white ppt
GENERAL COLOURING AGENTS :1. Mandalins reagent : -ve 2. Froehds reagent : -ve 3. Marquis reagent : -ve 4. Erdmanns reagent: -ve 5. Conc. HNO3 reagent : yellow colour
Add dil H2SO4 till full test tube
ml alkaloidal 1 solution