Quinoline Alkaloids In general, the alkaloids containing essentially the ‘quinoline’ nucleus include a series of alkaloids obtained exclusively from the cinchona bark, the major members of this particular group are, namely: quinine, quinidine, cinchonine and cinchonidine. More than twenty five alkaloids have been isolated and characterized either from the Yellow Cinchona, or from the Red Cinchona (Family: Rubiaceae). The aforesaid alkaloids are also found in their hybrids as well as in the Cuprea Bark obtained from Remijia pedunculata and Remijia purdieana belonging to the natural order Rubiaceae. However, it has been revealed that an average commercial yield of the cinchona alkaloids in the dry bark materials from the said plant materials are as follows: quinine (5.7%); quinidine (0.1-0.3%); cinchonine and cinchonidine (0.2-0.4%). Nevertheless, the other closely related minor alkaloids are present in relatively smaller quantities.

. Basic Structures of Cinchona Alkaloids The various quinoline alkaloids, which possess potent medicinal activities are, namely: quinine, quinidine, cinchonine, and cinchonidine. It is interesting to observe that these alkaloids not only have a closely related structure but also similar medicinal characteristics. These alkaloids possess the basic skeleton of 9’-rubanol that is derived from the parent compound known as ruban. Thus, ruban is obtained from the combination of two distinct heterocyclic nuclii, namely: (a) 4-methyl quinoline nucleus, and (b) quinuclidine nucleus. However, this particular nomenclature was suggested by Rabe so as to simplify the naming of such compounds and also to signify its origin from the natural order Rubiaceae

Properties Quinine is very slightly soluble in H2O, soluble in ethanol, chloroform, ether, benzene and other organic solvents. Quinine is a diacidic base. It forms 2 types of sulfates: Quinine sulfate (neutral and H2O insoluble). Quinine bisulfate (acidic and H2O soluble). Quinine (l-isomer) gives quinidine (d-isomer) among other products when warmed with KOH in amyl alcohol. Quinine is levorotatory, while quinidine is dextrorotatory. 4. Tartrates of Quinine and Cinchonidine are insoluble, whereas the tartrates of Cinchonine and Quinidine are soluble in water.

Tests for identification 1- Fluorescence test: Solution of the alkaloid in oxygenated acids (e.g H2SO4, HNO3 or phosphoric acid)  blue fluorescence (+ ve with quinine and quinidine). 2- Thalleoquine test: Aqueous solution of the alkaloidal salt + Br2 /H2O (few drops till the appearance of yellow color) + NH4OH  emerald green color (+ ve with quinine and quinidine). 3- Rosequin test (Erythroquinine test): Aqueous solution of the alkaloidal salt + dil HCl + Br2 /H2O (few drops till the appearance of yellow color) + CHCl3 + pot. Ferrocyanide + NH4OH  red color in the CHCl3 layer (+ ve with quinine and quinidine).

Cinchonine and cinchonidine are used as anti-inflammatory. Uses Quinine is used mainly as anti-malarial in a dose of 2g of quinine sulfate or other salt for 14 days. Quinidine is used as a cardiac depressant (anti-arrhythmic), particularly to inhibit auricular fibrillation in a dose of 0.6-1.6 g of quinidine sulfate daily. Cinchonine and cinchonidine are used as anti-inflammatory. Quinine is used as a flavor in carbonated beverages.