Presentation on theme: "PHG 322 PHARMACOGONSY II LECTURE 2 PRESENTED BY ASSISTANT PROF. DR. EBTESAM ALSHEDDI بسم الله الرحمن الرحيم."— Presentation transcript:
PHG 322 PHARMACOGONSY II LECTURE 2 PRESENTED BY ASSISTANT PROF. DR. EBTESAM ALSHEDDI بسم الله الرحمن الرحيم
Stability: Generally alkaloids are decomposed by heat except:caffeine sublimes without decomposition 2 Effect of Acids: hot dil. acids or conc. mineral acids may cause: Dehydration apoalkaloids morphine e.g. apomorphine O-demethylation codeine morphine e.g. conc HCl or HI + CH 3 Cl or CH 3 I Next page !
Hydrolysis of - ester alkaloids: e.g.atropine - glucoalkaloids: e.g.solanine 3 Stability: (cont.) Effect of Acids: (cont.) hot dil. acids or conc. mineral acids may cause:
Effect of Alkalies: Effect of weak alkalies Effect of hot dil. alkalies Effect of strong alkalies Stability: (cont.) liberate most alkaloids from their salts form salts with alkaloids containing carboxylic group e.g Narceine + NaHCO 3 Na salt
b) Effect of strong alkalies: salt salt(phenates) phenolic alkaloid + aq. NaOH or KOH cleavage of lactone ring c) Effect of hot dilute alkalies: e.g. pilocarpine hydrolysis of ester alkaloids e.g.atropine corresponding acid Pilocarpic acid
Tests for identification: Precipitation reactions Colour reactions include two types of reactions: include two types of reactions: 1) Precipitation reactions: precipitating reagent Coloured ppts (amorphous or crystalline) aqueous soln. of alkaloidal salts + (contains heavy metals e.g. Hg, Cd, Bi, …) N.B. certain alkaloids do not react e.g. caffeine 6 most reagents precipitate: proteins, tannins, … false positive results are possible false positive results are possible
Colour Reagents: 1- Froehd’s Reagent: Phosphomolybdic acid 2- Marqui’s Reagent: Formaldehyde/ Conc. H 2 SO 4 3- Mandalin’s Reagent: Sulphovanidic acid 4- Erdmann’s Reagent: Conc. HNO 3 /Conc. H 2 SO 4 5- Mecke's Reagent: Selenious acid / conc. H 2 SO 4 6- Shaer's Reagent: Hydrogen peroxide / conc. H 2 SO 4 7- Rosenthaler's Reagent: Potassium arsenate / conc. H 2 SO 4 8- Conc. HNO 3 These tests are sensitive to micro amounts used for colourimetric determination (quantitative) solid (free base) colour reagent + (contain conc H 2 SO 4 + an oxidizing agent) + an oxidizing agent)characteristiccolour
9 1) Vitalis test for solanaceous alkaloids: + conc HNO 3 & alc. KOH + conc HNO 3 & alc. KOH violet colour 2) Van-Urks test for ergot alkaloids: + PDAB in conc H 2 SO 4 blue colour - specific for - specific for one alkaloid or a group of related alkaloid:
N.B. + ve with: + ve with: - most alkaloids 10 Pharmacological activity: wide range of pharmacological activities Pharmacological activity Alkaloid Analgesic & narcotics Morphine CNS stimulant Caffeine & strychnine Anti-tussiveCodeine MydriaticAtropine Anticancer Vincristine, vinblastine, taxol
11 Chemical classification: Chemical classification: Non-heterocyclic Heterocyclic = typical alkaloids = Atypical alkaloids (Protoalkaloids) 14 major groups according to ring structure
I.Alkaloids of the Pyridine nucleus: classified according to building nucleus into: Pyridine nucleus only Pyridine nucleus + another nitrogenous ring Tetrahydro- pyridine nucleusPiperidinenucleusPyridone nucleus nucleus 12
Volatileliquids 1) Pyridine alkaloids containing another nitrogenous ring: nitrogenous ring: e.g. Tobacco alkaloids (-)-nicotine (major) nor-nicotine nicoteine non-volatileliquid 13
Properties: Nicotine Colourless or pale yellow oily liquid air or light brown 2 basic N atoms form salts with acids less basic 14 Tests: Colour tests aq. soln + aq. soln +PDAB rose red colour rose red colour violet colour gradually nicotine + nicotine + picric acid Crystals
Pharmacological actions & uses: Little use in medicine due to high toxicity In small doses respiratory stimulant In larger doses respiratory depressant Increases incidence of abortion Main use: Insecticide & anthelmintic in veterinary medicine 15
2) Piperidine alkaloids: e.g. alkaloids of: a) Black pepper b) Conium d) Pomogranate a) Pepper alkaloids: Occurrence: fruits Piper. P. nigrum Occurrence: fruits of Piper species e.g. P. nigrum piperine Major alkaloid: piperine 16 weak basic It is very weak basic No salt + acid Colour tests + H 2 SO 4 Red colour c) Lobelia
Uses: Mainly as condiment Used in rubefacient preparations Chronic toxicity: Prologed use at high doses loss of taste buds in tongue 18 Little use in medicine
C- LOBELIA ALKALOIDS Occurrence: the dried aerial parts of Lobelia inflata.(indian tobacoo) Major alkaloid: Lobeline crystalline)
Uses: -Asthma -Chronic bronchitis -Anti-smoking preparations -Injection of lobeline hydrochloride is used in the resuscitation of newborn infants. Caution: Toxic doses the herb has a paralytic effect
D- POMEGRANATE ALKALOID Occurrence: the fruit rind, root bark and stem bark of Punica granata Major alkaloid: pelltierine (liquid) pelletierine tannate (mixture, solid) Alkali decompose it to give free alkaloids Pomegranates have astringent properties because of the alkaloids (pelletierine tannate) present in the bark of the stems and roots and have been used for many years as an anthelmintic: removing tapeworms
II. Alkaloids of the Quinoline group Most important → Cinchona alkaloids Cinchona alkaloids Present in the barkCinchona species Present in the bark Cinchona species - C. succirubra (red Cinchona) F. Rubiaceae - Cinchona ledgeriana & C. calisaya (yellow Cinchona) e.g. of alkaloids: two groups of stereoisomers: Quinine (l) & Quinidine (d) Cinchonidine (l) & Cinchonine (d) 50% > 50% 22
RAlkaloidH Cinchonine & cinchonidine OCH 3 Quinine & quinidine Structure: 23 Quinine: Intensely bitter solid (few drops till yellow colour appears) Quinine (Cinchonidine epimer at C-9) Quinidine (Cinchonine epimer at C-9)
24 Cinchonine & Cinchonidine are less soluble in H 2 O than quinine & quinidine Test: 1) + dil H 2 SO 4 1) Fluorescence test: + dil H 2 SO 4 Fluorescence + ve for quinine & quinidine 2) Thalleoquine test: aq. soln of alkaloidal salt + Br 2 /H 2 O + NH 4 OH Emerald green colour Quinine (l) gives Quinidine (d) among other products when warmed with KOH in amyl alcohol
Uses: anti-malarial used as Quinidine used as used as cardiac depressant (anti-arrythmic) Quinine as Quinine sulphate or other salts has febrifuge effect (contra indicated in pregnancy as it causes abortion) Cinchonine and Cinchonidine are used as anti-rheumatic 25
Structure activity relationship: For antimalarial activity (Quinine): - Removal of vinyl group loss of activity - Replacement of CHOH by: - CHCl, CH 2, CO decreases activity Vinyl group 26
III. Alkaloids of the Isoquinoline group IpecacuanhaOpium (Papaverine type) 27
ISOQUINOLINE ALKALOIDS 1- IPECACUANHA ALKALOIDS Occurrence: Ipecac is the dried roots and rhizomes of Cephalis ipecacuanha (Brazilian ipecacuanha) or Cephalis acuminata (Cartagena or Panama ipecacuanha) Fam. Rubiaceae. It contains several alkaloids (2 –2.5 %), mainly emetine ( % of total alkaloids), with cephaline and psychotrine.
Emetine: It is non phenolic and levorotatory. It contains 2 basic nitrogens. Cephaline: It is phenolic and levorotatory. It gives emetine on methylation with (CH 3 ) 2 SO 4. Psychotrine: Occurs as yellow prisms. It is phenolic and gives cephaline on reduction. It gives emetine on reduction followed by methylation.
TESTS FOR IDENTIFICATION OF IPECA ALKALOIDS: Alkaloidal solution in HCl + Ca hypochlorite orange color. Emetine and cephaline + Froehd's reagent: dirty green color (the color with emetine fades by addition of HCl). Psychotrine + Froehd's reagent: pale green color. Cephaline and psychotrine + p-nitrodiazobenzene dye soluble in NaOH purple color. Psychotrine + conc. H 2 SO 4 + HNO 3 cherry red color. Emetine + Liebermann's reagent black color.
USES: Emetine and cephaeline have antitumour and antiviral activity, but are too toxic for therapeutic use. Emetine and psychotrine are mainly used as emetic drugs. The crude drug is used as expectorant (due to its saponin content). Emetine HCl has an antiamoebic effect, and are used for the treatment of amoebic dysentry and Fasciola. Ipeca alkaloids are diaphoretic, alone or in combination with opium (e.g. Dover's powder).