Quinoline alkaloids N Quinoline nucleus (liquid, b.p. 238) -Quinoline is a colorless liquid with an odour similar to that of pyridine, miscible with most organic solvents and with water to the extent of 0.7%. A-Major example for quinoline alkaloids is Cinchona alkaloids (Rubiaceae) which represent pairs of diastereoisomeric alkaloids: quinine, cinchonine, quinidine and cinchonidine and their dihydroderivatives. Alkaloids 1-Source. 2-Biosynthesis. 3-Structures and chemical classes. 4-Preparation in brief. 5-Chemical testing and assay in brief. 6-Applications in therapy. 7-Related drugs. -Cinchona contains 6-7% total alkaloids, 1/2 - 2/3 of which should be quinine and cinchonidine. -Cinchona also contains minor alkaloids of quinoline and indole types such as cinchonamine and quinamine . B-Rutaceae quinoline alkaloids are derived from anthranilic acid e.g. skimianine and platydesmine. Structure of Cinchna alkaloids -The structure of Cinchona alkaloids can be dissected to two ring systems: quinoline and quinuclidine. CH 2 N N N Quinuclidine nucleus Ruban ring system (8,9`-quinuclidyl-methylquinoline) H HO N H R N Quinine, R=OCH3 Cinchonidine, R=H H HO N H R N Quinine, R = OCH3: 8S,9’R Quinidine, R = OCH3: 8R,9’S Cinchonidine, R = H Cinchonine, R = H *Cinchona alkaloidsH occur in salt form with organic acids e.g. quinic acid (tetrahydroxyhexahydrobenzoicHO N acid) and H cinchotannicR acid. N HO COOH HO OH OH Quinic acid Biosynthesis of Cinchona alkaloids 1-biosynthesized from amino acid tryptophan and secologanin to give strictosidine thus called terpenoid indole alkaloids (Mannich like reaction). 2-Rearrangement of indole skeleton of strictosidine into quinoline skeleton. 1-Quinine -represents 1/2 - 2/3 of the total alkaloids of Cinchona -colorless needles, m.p 177 oC. -Insoluble in water but soluble in alcohol, ether, CHCl3 and boiling benzene. -Quinine sulfate is the most frequently used salt. -Quinine forms double compounds with some solvents such as benzene, toluene and phenol. -Solutions of quinine in oxygenated acids e.g. H2SO4 & H3PO4, but not halogenated acids have blue fluorescence. -It also forms insoluble tartarates. -On heating with KOH/amyl alcohol, quinine isomerizes into quinidine (quinidine is semi synthesized from quinine). Tests for identity 1-Quinine + Oxygenated acids blue flourescence. 2-Thalleioquine test. 3-Herpathite test. 4-Rosquin test (Erythoquinine test). Physical and chemical characters of Cinchona alkaloids Alkaloid test Quinine Quinidine Cinchonine Cinchonidin 1-Solubility Soluble in Soluble in. Soluble in Soluble in alc., alc., ether & alc., benzene alc., benzene, CHCl3 CHCl3 & ether benzene, moderately sparingly sol. insol. in soluble in in H2O ether ether, insol. in H2O 2- Tartarates Insolube Soluble Soluble Insoluble 3- Optical rotation Levo Dextro Dextro Levo 4-Reactions A-Fluorescence + + - - B-Thalleioquin + + - - c-Rosequin + + - - d- Herpathite + - + - e- Mono-sulfate Insolube Soluble Soluble Soluble Tests for identity 1-Quinine + Oxygenated acids blue flourescence. 2-Thalleioquine test: Solution in water + 2-5 drops Br2 water + 1 ml NH4OH green color, extractable with CHCl3. 3-Herpathite test: Boiling mixture of quinine + glacial acetic acid + alcohol + drops of conc. H2SO4 is treated with 3.5 ml of 1% iodine solution. On cooling green crystals of iodosulfate of quinine are obtained. 4-Rosquin test (Erythoquinine test): Dil. soln. of quinine + bromine water gives faint yellow color. Addition of 2-3 drops 10% Potassium ferricyanide + 2 drops of dil. NH4OH produces red color. Therapeutic uses of Cinchona alkaloids 1-Quinine: -It is an anti-malarial drug (Malaria is caused by protozoon Plasmodium falciparum). -It acts by intercalation with DNA double helix and complexes with toxic hemoglobin breakdown products formed by the parasite. -Quinine is now replaced by other synthetic anti- malarial agents e.g. chloroquin, but still used in case of drug resistance. -Quinine has also a mild curare- like skeletal muscle relaxant effect and thus used to treat nocturnal recumbency leg cramps especially in the elderly. -Other Cinchona alkaloids have anti-malarial effect also, but less effective than quinine. 2-Quinidine sulfate: -is the major alkaloid used from Cinchona. -It is used in treatment of different cardiac arrhythmias by membrane stabilization as it combines with Na+ channels in the membrane. -It inhibits fibrillation (uncoordinated contraction of the heart muscle - Quinidine is rapidly absorbed by GIT and overdose may lead to diastolic arrest, which makes it unsuitable as anti-malarial agent. -Quinidine gluconate is used in treatment of severe malaria caused by P. falciparum, but it's use is limited due to its effect on the heart. 3-Totaquin (Mixture of Cinchona alkaloids) has been used as substitute for quinine in time of shortages. Quinine and related alkaloids, especially quinidine were also isolated from the bark of Remijia pedunculata (Rubiaceae). Gravimetric estimation of total alkaloids 1-Known amount of Powdered Cinchona is treated with lead subacetate. 2-The mixture is extracted with ammoniacal alcohol in a soxhlet till exhaustion. 3-The extract is concentrated by removing most of the alcohol and treated with dil. H2SO4 to form alkaloidal bisulfate. 4-Acid solution is washed with CHCl3 and chloroformic extract is washed with H2SO4. 5-Combined acid solution is alkalinized with NH3 and extracted several times with CHCl3 till exhaustion. 6-Chloroformic extract is washed with little water and distilled in a tared dry flask. Alcohol (5 ml) is added and residue dried to constant weight at 100oC. Assay of quinine and cinchonidine 1-The residue containing total alkaloids, from the last experiment is converted to neutral sulfates, then to tartarates by treatment with sodium potassium tartarate. 2-The precipitated tartarate is decomposed by NaOH to give free bases which are extracted with CHCl3. 3-The chloroform extract is evaporated and dried at 100 oC. The amount of quinine and cinchonidine is weighed. An HPLC assay and separation of cinchona alkaloids has been published, J. chromatography 295, 276-281 (1984). Isoquinoline alkaloids *Many alkaloids contain the aromatic or reduced isoquinoline ring system. *Isoquinoline was first isolated and characterized from coal tar first and crude petroleum and occurs as a colorless liquid with benzaldhyde- like odour. N Isoquinoline *Isoquinoline alkaloids are widely-distributed in nature e.g. in families Rubiaceae (Ipecacuanha), Papaveraceae (Opium) and Menispermaceae (Curare). More than 700 isoquinoline alkaloids of Pharmaceutical interest have been characterized. *Isoquinoline alkaloids are generally biosynthesized from aromatic amino acids: phenylalanine and tyrosine. 1-Ipecacuanha alkaloids (Terpenoid tetrahydroisoqunoline alkaloids) -Source: alkaloids are localized in the cortex of the roots and rhizomes of Cephalis ipecacuanha and C. accuminata (Rubiaceae), which contain 2-2.5% total alkaloids, 70% of which is emetine. -Major alkaloids are emetine and cephaline, while psychotrine and its O-methyl ether occur in smaller amounts. MeO MeO MeO N MeO N NH H N OMe OR OMe OR R=Me, emetine R=H, cephaline R=Me, O-methylpsychotrine R=H, psychotrine *Psychotrine and cephaline are phenolic, while emetine and O-methylpsychotrine are non phenolic. -These benzyltetrahydroisoquinoline alkaloids occur naturally mainly in Rubiaceae genera such as Cephalis and Pogonopus. They also exist in families Alangiaceae and Icacinaceae. Biosynthesis: Ipecac. alkaloids are biosynthesized from two dopamine and a secologanin molecule. Mannich reaction of one molecule of dopamine and one molecule of secologanin gives 3a- desacetylipecoside, which on reaction with a second molecule of dopamine produces emetine and related alkaloids. Isolation of Ipecac. Alkaloids Alcoholic extract of the rhizome or root 1-concentrate 2-add lead acetate to precipitate tannins and coloring matter Filtrate tannins + coloring matter evaporate to dryness Residue of crude alkaloid mixture + HCl Hydrochlorides, filter Mixture of alkaloid Filtrate of alkaloid reject insoluble material Hydrochlorides + NaOH + ether aqueous contains Ether Contains the non cephaline + psychotrine Phenolic emetine + HCl + NH4OH + ether ether aqueous cephaline psychotrine ext with CHCl3 Chromatographic isolation was reported in phytochemistry 52, 1169-1176 (1999). Pharmacological actions and uses of Ipecac. Alkaloids 1-Emetine and cephaline are emetic alkaloids in case of drug overdose. They act by irritation of the stomach. Emetine also causes emesis by stimulation of chemoreceptor trigger zone 2-Cephaline is more toxic than emetine and in small doses, these alkaloids have expectorant effect (in this case, crude extract is used not pure alkaloid). 3-Emetine has been used to treat amoebic dysentery with no effect on bacillary infection. However, it is toxic and cumulative and the treatment should not be continue for more than 10 days. 4-Both emetine and cephaline are potent protein synthesis inhibitors acting at the stage of translocation. They have anti- tumor and antiviral effects but too toxic to be used therapeutically. 5-O-methyl psychotrine possesses fairly low effect on protein synthesis but showed promising ability to curb viral replication by inhibition of HIV-reverse transcriptase (potential to be used in treatment of AIDS infection). 6-Emetine inhibits protein synthesis in the animal and protozoon. It inhibits DNA synthesis and kills viruses but is not anti-bacterial. Emetine is extremely toxic causing cardiac