[Chemistry Class Notes] on Alkaloid Pdf for Exam

You can find many natural compounds in nature. Alkaloids is a special class among many classes of naturally occurring organic compounds such as carbohydrates, proteins, lipids, amino acids, anthocyanins, flavonoids and steroids. The thing which makes them special is that they are derived from amino acids. These can be synthesised by plants and some of the animals as secondary metabolites. These compounds are very important for living organisms. Alkaloids have been extremely important for human beings for ages, besides they are secondary metabolites, which suggests that they are useless.   Alkaloid shows strong biological effects on humans and animals also in very small amounts. Alkaloids are present in human life also. They are also used as stimulant drugs.

Alkaloids meaning can be defined as any naturally occurring organic nitrogen-containing class bases. Alkaloids contain diverse and essential physiological effects on humans and on other animals. A few of the well-known alkaloids can be given as strychnine, morphine, ephedrine, quinine, and nicotine.

Alkaloids originated from the word alkali. They react with acids and form the salts like the inorganic alkalis. In an acid-base reaction, these nitrogen atoms behave as a base. In general, alkaloids are also treated as amines. Although, it has the suffix -ine. Alkaloids in pure form are usually colourless, odourless crystalline solids, but sometimes they can be yellowish liquids. Quite often, they also have a bitter taste. 3000 alkaloids are known in more than 4000 plant species.

Definition of Alkaloid

Pelletier defined an alkaloid as: “a cyclic organic compound containing nitrogen in a negative oxidation state which is of limited distribution among living organisms”.

Alkaloid: An alkaloid is a group of chemicals that is made from plants. It contains nitrogen in them. Many alkaloids also have potent pharmalogic effects. Some of the examples of alkaloids are cocaine, nicotine, strychnine, caffeine, morphine, pilocarpine, atropine, methamphetamine, mescaline, ephedrine, and tryptamine.

Nature of Alkaloids: Basic Aspects

Some alkaloids are also poisonous. The poisonous activities of many alkaloids are known for ages. One of its examples is strychnine. It is derived from Strychnos species. It is one of the well-known poison curare. It is obtained from the Chondrodendron tomentosum species. It is used in South Africa as a narrow poison. It contains alkaloid tubocurarine.

Coniine is also an alkaloid that is isolated from Conium maculatum. Coniine is an active ingredient of hemlock poison. 

Mescaline isolated from Anhalonium species has hallucinogenic activity. Psilocybin is also a naturally occurring drug. It is isolated from fungi species Psilocybe Mexicana and possesses psychedelic activity. Also in previous decades, many semisynthetic derivatives of naturally occurring alkaloids with various activities have been synthesised. The heroine is one of the synthetic derivatives of morphine. It is prepared naturally from Lysergic acid present in C. 

Availability of Alkaloids

Alkaloids can be found majorly in plants and are especially in certain families of flowering plants. These are called plant alkaloids. In fact, as several as one-quarter of higher plants are estimated to have alkaloids, of which many thousand various types of alkaloids have been identified. Generally, a given species have only a few kinds of alkaloids, though both the ergot fungus (Claviceps) and opium poppy (which is Papaver somniferum) each contain up to 30 various types.

Certain plant families are specifically rich in alkaloids, where, for example, all plants of the poppy family (which is Papaveraceae) are thought to contain them. The Solanaceae (otherwise called nightshades), Amaryllidaceae (otherwise called amaryllis), and Ranunculaceae (otherwise called buttercups) are other prominent alkaloid-containing families. Some alkaloids have been found in the species of animals, such as the poison-dart frogs (otherwise called Phyllobates) and New World beaver (otherwise called Castor canadensis). Ergot and some other fungi also produce them.

Alkaloids – Their Importance in Nature and for Human Life

Alkaloids function in plants is yet to be understood. It has also been suggested that they are simply waste products of the metabolic processes of plants, but the evidence suggests that they can serve particular biological functions. In a few of the plants, alkaloids’ concentration gets increased just before the seed formation and after that, it drops off when the seed gets ripened, suggesting the way that alkaloids can play a role in this process. Alkaloids can also protect a few plants from the destruction by certain insect species.

Characteristics of Alkaloids

Almost several alkaloids have oxygen in their molecular structure, where such compounds are said to be colourless crystals at ambient conditions, in general. Oxygen-free alkaloids, like coniine or nicotine, are typically colourless, volatile, and oily liquids. A few alkaloids are coloured, like sanguinarine (orange) and berberine (yellow).

When swallowed, most alkaloids have a sour flavour or are toxic. Plants’ production of alkaloids appeared to have evolved in response to herbivorous animal feeding. However, a few animals have evolved the ability to detoxify alkaloids. Some can result in the production of developmental defects in the offspring of the animals that result in consuming but cannot detoxify alkaloids. An example is given as alkaloid cyclopamine, which is produced in corn lily leaves. 

In the 1950s, around 25% of lambs, born by the sheep that contained grazed corn lilies, had several serious facial deformations. These ranged from the deformed jaws to cyclopia. The responsible compounds for these deformities were later known as alkaloid 11-deoxy jervine, which was later called cyclopamine, following decades of study in the 1980s.

Classification of Alkaloids