Biology and Chemistry Quiz

Quinoline, Isoquinoline, and Indole Alkaloids

• Quinoline alkaloids: Cinchona Alkaloids
  • Synonyms: Jesuit's Bark, Peruvian bark
  • Biological source: Cinchona bark, consists of various species, races, and hybrids of Cinchona (C. calisaya, C. ledgeriana, C. officinalis, C. succirubra) belonging to the Rubiaceae family.
  • It is a large tree, indigenous to Colombia, Ecuador, Peru, and Bolivia.
  • Thalleoquin test is a specific test for Cinchona alkaloids
• Chemical constituents:
  • Cinchona bark contains quinoline alkaloids.
  • The main alkaloids are stereoisomers, quinine, and quinidine and their 6-demethoxy derivatives, cinchonidine, and cinchonine.
  • Some of these (e.g., quinicine and cinchonicine) are amorphous.
• Uses:
  • Cinchona bark has long been used as a bitter tonic and stomachic.
  • Widely used for the treatment of malaria caused by Plasmodium falciparum (falciparum malaria).
  • Quinidine is used for the prophylaxis of cardiac arrhythmias and the treatment of atrial fibrillation.

Isoquinoline Derived Alkaloids: Opium and its Alkaloids

• Opium:
  • Raw Opium is the latex obtained by incision from the unripe capsules of Papaver somniferum (Papaveraceae).
  • It contains not less than 9.5% of morphine, calculated as anhydrous morphine.
• Chemical constituents:
  • Opium contains about 30 alkaloids which are largely combined with meconic acid; the drug also contains sugars, salts (e.g., sulfates), albuminous substances, coloring matters, and water.
  • Phenanthrene derivatives: Morphine (10% in opium), Codeine (0.5% in opium), Thebaine (0.2% in opium).
  • Benzoisoquinoline derivatives: Papaverine (1%), Noscapine (6%).

Tubocurarine (Chondrodendron, Curare)

• Tubocurarine is an isoquinoline alkaloid present in different species of Chondrodendron (viz. C. tomentosum, C. platyphyllum, C. microphyllum) belonging to the Menispermaceae family.
• Chondrodendron (Curare) appears as black or brown, resinous material with a bitter taste.
• Curare is soluble in cold water and dilute alcohol.
• The term 'curare' is a generic name applied to various South American arrow poisons.
• Tubocurarine chloride is an official drug in the BP, used to secure muscular relaxation in surgical operations and certain neurological conditions.
  • It is also used to aid in the diagnosis of myasthenia gravis.

Ipecacuanha or Ipecac

• Biological source: Ipecacuanha is the dried root or rhizome of Cephaelis ipecacuanha, known in commerce as Matto Grosso Ipecac or of Cephaelis acuminata (Rubiaceae) known in commerce as Costa Rica Ipecac.
  • It should contain a minimum of 2% of ether-soluble alkaloids.
• Chemical constituents:
  • Ipecacuanha contains the alkaloids emetine (Pelletier and Magendie, 1817), cephaeline (Paul and Cownley, 1891), psychotrine, psychotrine methylether, and emetamine.
  • Other constituents of the official drug are monoterpenoid isoquinoline glucosides, including ipecoside and langiside.
• Uses:
  • Ipecacuanha is used as an expectorant and emetic, and in the treatment of amoebic dysentery.
  • Emetine has a more expectorant and less emetic action than cephaeline.
  • In treating amoebic dysentery, emetine hydrochloride is frequently given by injection, and emetine and bismuth iodide by mouth.

Tryptophan Derived Alkaloids: Physostigma

• Biological source: Calabar beans (Ordeal beans) are the dried ripe seeds of Physostigma venenosum (Leguminosae).
  • It is a perennial woody climber found on the banks of streams in West Africa.
• Chemical Constituents:
  • The seeds contain the alkaloids: physostigmine or eserine, isophysostigmine, N-8-norphysostigmine, eseramine, eseroline, physovenine, geneserine, calabatine, and calabacine.
  • Physostigmine, the chief alkaloid, is present to about 0.15%.
  • It is derived from tryptophan. On exposure to air, it oxidizes into a red compound, rubreserine, and should therefore be protected from air and light.
  • The official salt, the salicylate, is more stable than the sulphate and is non-deliquescent.
• Uses:
  • Physostigmine salicylate is used for contracting the eye pupil, often to combat the effect of mydriatics.
  • It has also been investigated as an intravenous injection for reversing the effects of a number of sedatives.

Rauwolfia Alkaloids

• Biological source: Rauwolfia consists of the dried rhizome and roots of Rauwolfia serpentina and R. vomitoria (Apocynaceae).
  • It is a small shrub found in India, Pakistan, Burma, Thailand, Africa, and Java.
• Chemical constituents:
  • Rauwolfia contains at least 30 alkaloids (0.7-24%) mostly concentrated in the root barks.
  • In 1931 Siddiqui and Siddiqui isolated ajmaline, ajmalinine, ajmalicine, serpentine, and serpentinine.
  • The chief therapeutically important alkaloids are reserpine and rescinnamine.
  • Other alkaloids are yohimbine, rescinnamine, deserpine, and reserpinine.
• Uses:
  • Rauwolfia preparations and reserpine are used in the management of essential hypertension and certain neuropsychiatric disorders.
  • Ajmaline, with pharmacological properties similar to quinidine, is marketed in Japan for the treatment of cardiac arrhythmias.
  • Deserpidine is used as an antihypertensive and tranquilizer.
  • Rescinnamine is also used as an antihypertensive.

Nux-vomica

• Biological source: Nux-vomica consists of the dried, ripe seeds of Strychnos nux-vomica (Loganiaceae).
  • A tree 10-13 m high with distribution including Ceylon, India, East Bengal, Burma, Thailand, Laos, Cambodia, and S. Vietnam.
• Chemical constituents:
  • Nux-vomica usually contains about 1.8–5.3% of the indole alkaloids strychnine and brucine.
  • Strychnine is physiologically much more active than brucine.
  • They usually contain about 1.23% of strychnine and about 1.55% of brucine.
  • Minor related alkaloids include a-colubrine, β-colubrine, 3-methoxyicajine, protostrychnine, vomicine, N-oxystrychnine, pseudo-strychnine, and isostrychnine.
• Uses:
  • The action of the whole drug closely resembles that of strychnine.
  • It was formerly used as a circulatory stimulant in cases like surgical shock but its use is now more limited to respiratory stimulants in certain cases of poisoning.
  • Like other bitters, strychnine improves the appetite and digestion, but it has been misused as a 'general tonic.'

Catharanthus roseus (Vinca Alkaloids)

• Synonyms: Madagascar periwinkle, Vinca rosea.
• Biological source: Obtained from the fresh whole plant of Catharanthus roseus (Apocynaceae).
  • Indigenous to Madagascar but is now widely distributed throughout warm regions.
• Chemical constituents:
  • About 150 alkaloids have been isolated from C. roseus.
  • Of particular interest is a group of about 20 bisindole alkaloids which have antineoplastic activity, including leurocristine (vincristine) and vincaleukoblastine (vinblastine).
  • Vinblastine is produced by coupling of the indole alkaloids catharanthine and vindoline.
  • Vinblastine (0.0003–0.001%) and vincristine (0.0001–0.0002%) on dry weight basis.
• Uses:
  • Vinblastine is mainly used for the treatment of generalized Hodgkin's disease and non-Hodgkin's lymphomas.
  • Vincristine is principally used in the treatment of acute lymphocytic leukemia in children.
  • Vindesine and Vinorelbine are other semi-synthetic drugs used in the treatment of acute lymphoid leukemia in children. Vinorelbine is a newer, orally active, semi-synthetic anhydro-derivative of 8'-norvinblastine with a broader anticancer activity and lower neurotoxic side-effects than other Catharanthus alkaloids.

Ergot and Ergot Alkaloids

• Biological source: Ergot (Ergot of Rye) is the dried sclerotium of a fungus, Claviceps purpurea (Clavicipitaceae), arising in the ovary of the rye, Secale cereal.
  • The most important producers are Czechoslovakia, Hungary, Switzerland, and Yugoslavia.
• Chemical constituents:
  • Ergometrine group (water-soluble): Ergometrine, Ergometrinine
  • Ergotamine group (water-insoluble): Ergotamine, Ergotaminine
  • Ergotoxine group: Ergocristine, Ergocristinine, Ergocryptine, Ergocryptinine, Ergocornine, and Ergocorninine
• Uses:
  • Although whole ergot preparations were traditionally used in labor to assist delivery and to reduce post-partum hemorrhage, ergot alkaloids have largely replaced them in pharmacopoeias.
  • Ergometrine produces an oxytocic effect; ergotoxine and ergotamine have quite different actions.
  • Ergometrine is soluble in water or dilute alcohol; it is often known as ergonovine in the USA.
  • Ergotamine and semi-synthetic dihydroergotamine salts are employed as specific analgesics for the treatment of migraine.

Imidazole or Histidine-derived Alkaloids: Pilocarpus

• Pilocarpine is isolated from different species of Pilocarpus (Rutaceae).
  • The name 'jaborandi' now applies to the leaflets of various species of Pilocarpus.
  • Found in South America and the West Indies and Central America.
• Maracanhum Jaborandi: The major jaborandi imported now comes from the Brazilian plant Pilocarpus microphyllus.
  • Other jaborandi types are Pernambuco jaborandi (P. jaborandi Holmes), Paraguay Jaborandi (P. pennatifolius Lemaire), and Ceara jaborandi (P. trachylophus Holmes). Exported from Brazilian provinces of Ceara and Maranhão.
• Chemical constituents:
  • Pilocarpine, isopilocarpine, pilosine, and isopilosine, and about 0.5% of volatile oil.
• Uses:
  • Salts of pilocarpine (e.g., pilocarpine hydrochloride and nitrate) are used in ophthalmic practice, as they cause contraction of the pupil of the eye, having an antagonistic action to atropine.
  • Used in early glaucoma treatment to increase eye irrigation and relieve pressure.
  • A study in the USA found that oral pilocarpine relieved dry mouth in patients undergoing radiation treatments for cancer causing dry mouth.

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