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1 MEDICINAL CHEMISTRY-II (NATURAL PRODUTS) Seminar on STRUCTURE ELUCIDATION OF EMETINE Presented by: Mr. ABDUL RAZZAQ M. Pharm. Department -: Pharmaceutical Chemistry Luqman College of Pharmacy Gulbarga.

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Points going to discuss are, 1. Introduction 2. Isolation 3. Properties 4. Constitution 5. Synthesis FOR EMETINE

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INTRODUCTION Emetine being an alkaloid was first isolated by Pelletier and Magendie in the year 1817 from roots of Cephalis ipecacuanha belonging to the family Rubiaceae.

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ISOLATION- Roots of iecacuanha & granadensis powder Agited with Ethyl Alco. Or Amyl alco. or Mix. Of Ben. & Lpetro. Decantation Residue Organic solvent + dil.HCl + NH3 Addition of ETHER Aqueous Liquid Ether Layer (Psychotrine alkaloids) (Remaining alkaloids containing EMETINE) Concentrated & convert into HCl salt Fractional Extraction EMETINE salts Remaining get converted gets crystallized out into oxalates

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PROPERTIES- White amorphous powder melting point 70°C. sparingly soluble in Water completely miscible in organic solvents like Alcohol, Chloroform and Ether. Uses- Emetic, Expectorant & Amoebic dysentery


CONSTITUTION Molecular formula- By analytical data it is found to be Emetine does not contain N-methyl groups but has a secondary and a tertiary nitrogen atoms. Presence of 4 methoxyl group- it is given by Zeisel Method where in on treating with hydroiodic acid this yields 4 molecules of methyl iodide showing presence of methoxyl groups. Presence of one unit of 6,7-dimethoxy isoquinoline- (a)oxidation with potassium permanganate in presence of acetone to give m-hemipinic acid(1) with small amounts of 6,7-dimethoxy,isoquinoline-1-carboxylic acid(2).

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(b) Oxidation with chromic acid- it yields 4,5-dimethoxy phthalonimide(3) Derivative of tetrahydro isoquinoline- this is shown by the UV-spectra of cephaline and emetine which resembles that of 1,2,3,4-tetrahydro isoquinoline Presence of o-dimethoxy benzene units- This is shown by the UV-spectra of emetine which closely resembles that of tetra hydro papaverine Further proof for 6,7-dimethoxy isoquinoline- (a)Gentle oxidation with alkaline potassium permanganate-this yields firstly Corydaldine(4) then when the remaining mother liquor is oxidized further with the permanganate it gives m-hemipinic acid(1)

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(b)Cephaeline another ipecac alkaloid on ethylation gives ethyl ether of cephaeline which yielded a mixture of corydaldine(4) and ethoxy methoxy isoquinoline (c) oxidation of emetine gives 96% yield of m-hemipinic acid which is higher when compared to papaverine this shows the presence of 2 isoquinoline units Partial structure of Emetine.

The nature of fragment this is given by Hoffmann Degradation of Emetine which removes the nitrogen atoms completely. It is given in the following steps.

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The formation of ketone is also shown as; The structure of (6) can also be given as;

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From the structure (6) structures (7),(8),(9)and (10) were proposed .Based on (7) the structure of emetine was given.

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Emetine is found to contain only one C-alkyl group hence structures (9) and (10) are ruled out as they contain 2 alkyl groups. For biogenetic reasons structure (8) is said to be the structure of emetine.

SYNTHESIS Openshaw and Whittaker’s Synthesis : 

SYNTHESIS Openshaw and Whittaker’s Synthesis

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REFERENCES Organic chemistry of natural products, by,Gurdeep Chatwal , Himalaya Publishing House, page no :- 398 – 407.

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Thank you