Pharmacognosy-I

A precise definition of the term 'alkaloid'((alk=alkali and oid=like i.e. alkali- like) is somewhat difficult because there is no clear cut boundary between alkaloids and naturally occurring complex amines Introduction Coniine

Distribution

Plant PartDrug ( Alkaloids)Plants Whole aerial plantLobeline, Tylophorine, EphedrineLobelia. Tylophora. Ephedra SeedsStrychnine, Physostigmine, Colchicine Nux vomica. Physostigma, Colchicum Rhizomes & RootsEmetine, Reserpine, AconitineIpecac, Rauwolfia, Aconite BarkConessine, CinchonineKurchi, Cinchona FruitPiperineBlack pepper LeavesScopolamine, Atropine, EcgonineDatura, Belladonna, Coca StemAnaferineWithania Flowering budsHyoscyamineHyoscyamus

Properties of alkaloid Alkaloids exhibit a variety of physical and chemical properties

Chemical Properties of alkaloid Alkaloids possess carbon, hydrogen and nitrogen and in most cases oxygen as elements. Alkaloids usually contain one nitrogen atom, although some, like ergotamine, may contain up to 5. The nitrogen may exist as a primary amine (RNH), as a secondary amine (R 2 NH), or as a tertiary amine (R 3 NH). Like basic compounds they form their crystalline salts with acids like hydrochloric acid, sulphuric acid, citric acid, and tartaric acid. On treatment with phosphotungstic acid, phosphomolybdic acid, picric acid, potassium mercuri-iodide and tannic acid, they yield insoluble precipitates (double salts)

Pharmacological Action of Alkaloid Activity Alkaloids Analgesic & Narcotic Morphine and Codeine CNS-stimulant Caffeine, Strychnine & Brucine Cardiac depressant Qinidine Mydriatic Atropine & Hematropine Miotic Physostigmine, Pilocarpine Hypertensive (  BP) Ephedrine Anti-Hypertensive Reserpine Anti cancer Vincristine, Vinblastine Antimalarial Quinine Diuretic Theobromine, Theophylline Antiamoebic & Emetic Emetine, Sanguinine Anticholinergic Atropine, hyoscyamine Antitussive Codeine, Noscapine

Why alkaloids occur in the plants? In plants alkaloids act as poisonous and stimulating agents. 1.They may act as protective against insects and herbivores due to their bitterness and toxicity. For e.g. Nicotine and anabasine act as powerful repellents for many insect groups and thus protects plants from insects and herbivorous. 2.They function as reserve substances for nitrogen and supply it as well as other elements necessary for the plant's economy. 3.They sometimes, act as growth regulators in certain metabolic systems. 4.They are end product of detoxification reactions representing a metabolic locking up of harmful substances for the plant. 5.They occur as pigments, such as pteridine and betalains, and attract animals for pollination.

Classification of Alkaloids There are various schemes for the classification of alkaloids. Widely accepted classification system is as:

Based on the ring structure or nucleus of the chief alkaloid group in the plant drug are classified as follows: (1), (2) Alkaloids Ring Examples Pyridine-piperidine The alkaloids in this group contain Pyridine or Piperidine in the molecule Pyridine-piperidine NicotineConiine Tropane Tropane is a dicyclic compound where both Pyrrolidine and Piperidine ring systems are present Pyrrolidine-piperidine- Tropane Atropine +e.g. +e.g. lobelia alkaloids, lupine alkaloids, +e.g. +e.g. hyoscyamine and scopolamine,

(3), (4) On the basis of nucleus/ Ring structure (3), (4) Alkaloids Ring Examples Quinoline The alkaloids in this group contain Quinoline ring as the principal nucleus Quinoline Quinine Isoquinoline The Isoquinoline ring occurs in a number of alkaloids in widely separated plant families Isoquinoline Papaverine +e.g. +e.g. Quinidine, Cinchonine, Cinchonidine, +e.g. +e.g. Morphine, Emetine,

(5), (6) On the basis of nucleus/ Ring structure (5), (6) Alkaloids Ring Examples Indole A number of important alkaloids possess an indole ring in their structure Indole Reserpine Imidazole The Imidazole ring occurs in the alkaloids. Imidazole Pilocarpine +e.g. +e.g. Strychnine, Brucine, Vinblastine, Vincristine +e.g. +e.g. Isopilocarpine, Reserpine

(7), (8) On the basis of nucleus/ Ring structure (7), (8) Alkaloids Ring Examples Steroidal The steroidal alkaloids are characterized by the cyclopentanoperhydro phenanthrene (CPP) nucleus. CPP Conessine Lupinane The alkaloids in the group contain a dicyclic Lupinane structure/ring. Lupinane Lupinine +e.g. +e.g. solanine, Protoveratrine A & B, Aconitine +e.g. +e.g. Sparteine Conessine

(9), (10) On the basis of nucleus/ Ring structure (9), (10) Alkaloids Ring Examples Alkaloidal amino group The alkaloids in this group do not contain heterocyclic nitrogen atoms. Some are derivatives of Phenylethylamine. Phenylethylamine Ephedrine Purine The alkaloids in this group contain the Purine nucleus which consists of the six membered Pyridine ring fused to the five membered Imidazole ring.. Purine Caffeine +e.g. +e.g. Mescaline,Colchicine +e.g. +e.g. Theobromine

Basic ring structures

Chemical Tests for Alkaloids Most alkaloids are precipitated from neutral or slightly acid solutions by various re-agents. The precipitate may be amorphous or crystalline and are of various colours such as:- Reagents ( Chemical composition) Clours of PPT Mayer’s Reagents (Potassium mercuric iodide solution) Creamy ( Pale yellow) precipitate with True alkaloid Exception: Alkaloids of the purine group and few others. Wagner’s Reagent (solution of iodine in KI) Reddish brown ( or brown) precipitate with alkaloids Hager's Reagents (a saturated solution of picric acid) Yellow (characteristic crystalline) precipitate (with many alkaloids) Dragendorff’s Reagents (Solution of potassium bismuth iodide) Reddish brown (Orange coloured) precipitate with alkaloids Tannic Acid Test (A freshly prepared aqueous solution of tannic acid (5%, w/v)) Gives recipitate with most of the alkaloids which is soluble in dilute acid or ammonia solution. Ammonia Reineckate Test (A saturated aqueous solution of ammonia retneckate slightly acidified with HCl) Pink flocculent precipitate with most of the alkaloids.

Extraction of Alkaloid Moisture with aqueous alkali ( e.g. NaCO 3, NaHCO 3 or Lime- Ca(OH) 2 Extract with organic solvent such as Benzene, Chloroform etc Organic layer (alkaloid & other plant constituents) Aqueous layer (water soluble components) Extract (shaken) with dilute ( aqueous) Acid Aqueous layer (Containing alkaloidal salts) Organic layer (Other organic components e.g. impurities ) Precipitate of free alkaloid (crude alkaloidal mixture) Finally purification is accompanied by crystallization method Add aqueous alkali

Description: The powdered material is moistened with aqueous alkali [water and mixed with lime which combines with acids, tannins and other phenolic substances and sets free the alkaloids (if they exist in the plant as salts)]. The alkaloids are set free with other plant constituents. Extraction is then carried out with organic solvents such as Benzene or chloroform (ether or petroleum spirit). The concentrated organic liquid which contains alkaloids and other plant constituents is then shaken with dilute acid (aqueous acid) and allowed to separate. Alkaloid salts are now in the aqueous liquid, while many impurities remain behind in the organic liquid. Aqueous alkali is added to the aqueous layer giving precipitation of free alkaloids.

Pharmacological Action of Alkaloid ActivityAlkaloid Analgesic & NarcoticMorphine and Codeine CNS-stimulantCaffeine, Strychnine & Brucine Cardiac depressantQinidine MydriaticAtropine & Hematropine MioticPhysostigmine, Pilocarpine Hypertensive (  BP) Ephedrine Anti-HypertensiveReserpine Anti cancerVincristine, Vinblastine MyoticPilocarpine Antiamoebic & EmeticEmetine, Sanguinine AnticholinergicAtropine, hyoscyamine AntimalarialQuinine DiureticTheobromine, Theophylline AntitussiveCodeine, Noscapine The alkaloids have a wide range of pharmacological actions: