Pharmacognosy & Phytochemistry - II Unit II Notes. GENERAL INTRODUCTION, COMPOSITION, CHEMISTRY AND CHEMICAL CLASS, BIOSOURCES, THERAPEUTIC USES AND COMMERCIAL APPLICATION OF VARIOUS SECONDARY METABOLITES

 Pharmacognosy & Phytochemistry - II

Unit II

GENERAL INTRODUCTION, COMPOSITION, CHEMISTRY AND CHEMICAL CLASS, BIOSOURCES, THERAPEUTIC USES AND COMMERCIAL APPLICATION OF VARIOUS SECONDARY METABOLITES

Points to be covered.

1. Alkaloid: Vinca, Rauwolfia, Belladonna, Opium

2. Phenylpropanoids and flavonoids : Lignans, Tea, Ruta

3. Steroidal, cardiac and triterpenoid glycoside : Liquorice,

    Dioscorea, Digitalis

4. Glycosides : Senna, Aloe, Bitter almond.

5. Volatile oil : Mentha, clove, Cinnamon, Fennel, Coriander

6. Iridoids, other terpernoids and Napthaquinoñes: Gentian,

Artemisia, Taxus, Carotenoids.

ALKALOIDS

Definition:

The term ‘alkaloid’, means alkali-like, is a group of naturally occurring chemical| compounds that contain one or more basic nitrogen atoms in heterocyclic ring. These compounds having marked physiological action on human and animal when taken at low dose, otherwise become toxic or poisonous at high concentration.

                                                                            Ephedrine                                                                 

Classification of Alkaloids:

1.      True or typical alkaloids are derived from amino acids and have nitrogen atom in heterocyclic ring. E.g. Atropine.

2.      Proto alkaloids are derived from amino acids and do not contain nitrogen atom in heterocyclic ring. E.g. Ephedrine.

3.      Pseudo alkaloids are not derived from amino acids, but contain nitrogen atom in heterocyclic ring. E.g. Caffeine.

4.      False alkaloids are non-alkaloids which give false positive reaction with alkaloidal reagents.

 

1. True alkaloids: These are subdivided into 12 groups:

1. Pyrrole and pyrrolidine: Hygrine, coca species.
2. Pyridine and piperidine: Arecoline, Anabasine, trigonelline.
3. Pyrrolizidine: Echimidine, symphitine. Cho
4. Tropane: Atropine, hyoscine.
5. Quinoline: Quinine, Quinidine, Chinchonine.
6. Isoquinoline: Morphine, codeine.
7. Aporphine: Boldine.
8. Indole (Benzpyrole): Vincristin, Ergometrine, Reserpine.
9.  Imidazole: Pilocarpine, Isopilocarpine.
10. Norlupinane: Cytisine, Sparteine.
11. Purine (pyrimidine/imidazole): Caffine, theobromine, theophylline.
12. Steroidal (cyclopentano perhydrophenathrene ring): Solanidine, Conessine.

 

 

2. Pseudo alkaloids: @ Diterpenes: Aconitine, Aconine.

3. Proto alkaloids: Alkyl amines or amino alkaloids: Ephedrine, Colchinine.

Physico-chemical Properties of Alkaloids:

• Alkaloids have molecular weight from 100 - 900.
• Although most of the bases that do not contain oxygen atom are liquids at ordinary temperature (nicotine, coniine), those that contain oxygen atom are normally crystallizable solids and in rare cases they are coloured (berberine).
• Almost all of the crystallized bases rotate the plane of polarized light and have melting points without decomposition especially below 200°C.
• As a general rule, alkaloids as bases are not soluble in water, but are soluble in a polar or only slightly polar organic solvents.
• The basicity of alkaloids varies greatly since this property depends entirely on the availability of the lone pair of electrons on the nitrogen atom.
• Electron withdrawing group in proximity to the nitrogen atom decreases the basicity whereas electron donating group enhances it.
• The basic character allows the formation of salts with mineral acids (hydrochloridg sulphates, nitrates) and organic acids (tartarate, sulphonate).
• Alkaloid salts are generally soluble in water and in dilute alcohols and they are except in rare case, not soluble in organic solvents.
• Pseudoalkaloids and protoalkaloids show higher solubility in water, while free base, of alkaloids are soluble in organic non-polar immiscible solvents.

 

Tests for Identification of Alkaloids:

The different reagents used for the identification are:

·         Mayer's reagent (Potassium mercuric iodide solution) 1 ml of test solution + a drop or two of the Mayer’s reagent white or a creamy precipitate.

·         Dragendorff's reagent (Potassium bismuth iodide solution) 2 ml of the filtrate+1 ml of Dragendorff’s reagent. Formation of orange or reddish brown precipitate.

·         Wagner's reagent (lodine potassium Iodide solution) 2 drops of Wagner’s reagent was added to 1ml of the test solution. The formation of yellow or brown precipitate confirmed the test as positive for alkaloids.

·         Hager's reagent (picric acid solution) 1 ml of test solution + a drop or two of Hager’s reagent formation of yellow precipitate.

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