Quinoline Alkaloids

Quinoline alkaloids are important N-based heterocyclic aromatic compounds with a broad range of bioactivities. They are found in extracts of several species of the Rutaceae, Rubiaceae, and Asteraceae, and also in fungal (Penicillium species), bacterial (Pseudomonas species) extracts and animals. They have attracted extensive attention from researchers for a long time in the past.

Figure 1. Basic structure of the quinoline nucleus.

Sources of quinoline alkaloids

There are three main sources of quinoline alkaloids, namely plants, microorganisms and animals.

• Plants

There are about 140 genera in the Rutaceae family, consisting of herbs, shrubs and small trees that grow all over the world and are widely used in traditional medicine. This plant family is an important plant source of quinoline alkaloids. Quinine and quinidine are two of the most important quinoline alkaloids in this group and they are found in Cinchona ledgeriana and C. officinalis respectively.

• Microorganisms

Over the last three decades, many structurally unique and biologically active quinoline alkaloids have been isolated from microorganisms. For example, a relatively simple quinoline alkaloid has been produced from a biologically inactive lipophilic extract of the Caribbean marine cyanobacterium Lyngbya majuscula (Figure 2), which has been shown to have a wide range of biological activities.

Figure 2. A quinoline alkaloid from microorganisms.

• Animals

Quinoline alkaloids are also found in the animal kingdom. They can act as active defence components for insects. For example, the strikingly coloured phasmid insect Oreophoetes peruana (the Peruvian fire stick insect) exudes a white fluid from a pair of thoracic glands when disturbed. This secretion has been shown to contain quinoline alkaloid components^[1].

Bioactivities of quinoline alkaloids

Many studies have documented that quinoline alkaloids possess a wide range of biological activities, mainly including antitumor activity, antimalarial activity and antiparasitic and insecticidal activity.

• Antitumor activity

A series of new natural products with antitumor activity have been isolated and potentially used for cancer treatment. Among these potential anticancer compounds or drugs, quinoline alkaloids fused with various heterocycles show strong anticancer activity. Camptothecin (CPT) is one of the most important and well known. It has been shown to be useful in a range of refractory tumors, particularly in some colon and ovarian cancers.

Figure 3. Structure of camptothecin.

• Antimalarial activity

Malaria is the most lethal human parasitic infection. The quinoline alkaloid quinine (Figure 4a) is obtained from the bark of Cinchona officinalis belonging to the family Rubiaceae. It was the first anti-malarial drug used in early 1600s. It has rapid schizonticidal action against intra-erythrocytic malaria parasites. It is also gametocytocidal for Plasmodium vivax and Plasmodium malariae, but not for Plasmodium falciparum. Quinidine (Figure 4b) is the dextro isomer of the anti-malarial alkaloid quinine. Quinidine is effective antimalarial drug against Plasmodium falciparum. Dihydroquinine (Figure 4c) is a natural impure compound found in commercial pharmaceutical formulations of quinine. Therefore, biological source of dihydroquinine is same to quinine. It is a cinchona alkaloid closely related to quinine. This alkaloid also has antimalarial activity.

Figure 4. Structures of quinine (a), quinidine (b) and dihydroquinine (c).

• Antiparasitic and insecticidal activities

Leishmaniasis (kala-azar), caused by Leishmania protozoa, is a major public health problem in Africa, Asia, and Latin America, causing significant morbidity and mortality. To date, more than 70 isolated natural alkaloids have been used to treat this disease. Some of these alkaloids are of the quinoline type. For example, the quinoline alkaloids, 2-n-propylquinoline (Figure 5a), chimanine-D (Figure 5b) and chimanine-B (Figure 5c) were isolated from Galipea longiflora Krause (Rutaceae), displayed significant antileishmanial activity against promastigotes of L. braziliensis.

Figure 5. Structures of 2-n-propylquinoline (a), chimanine-D (b) and chimanine-B (c).

What we offer

As a supplier of alkaloids, Alfa Chemistry has always shown great interest in the latest developments in quinoline alkaloids. Alfa Chemistry is committed to providing a wide range of quinoline alkaloids. If you do not find what you need, please contact us. We also offer product customization according to customer's detailed requirements.

Reference

1. Eisner, T.; et al. Defensive production of quinoline by a phasmid insect (Oreophoetes peruana). Journal of Experimental Biology. 1997, 200: 2493.