What is Alkaloid?

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.

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.

Function of Alkaloids

Alkaloids function in plants is yet to be understood. It has also been suggested that they are simply waste products of metabolic processes of plants, but the evidence suggests that they can serve particular biological functions. In a few of the plants, alkaloid's 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.

Properties

Almost several alkaloids have oxygen in their molecular structure, where such compounds are said to be colorless crystals at ambient conditions, in general. Oxygen-free alkaloids, like coniine or nicotine, are typically colorless, volatile, and oily liquids. A few alkaloids are colored, 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 on corn lily, 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-deoxyjervine, which was later called cyclopamine, following decades of study in the 1980s.

Classification

Often, alkaloids are classified based on their chemical structure. For suppose, alkaloids that contain a ring system, which is called indole, are referred to as indole alkaloids. Based on the principal classes of alkaloids are the tropanes, pyrrolidines, indoles, isoquinolines, and steroids and terpenoids. In other ways, alkaloids are classified based on the biological system where they take place. For example, the opium alkaloids take place in the opium poppy (which is Papaver somniferum). Actually, this dual classification system produces a little confusion because there's a rough correlation between the biological distribution of alkaloids and their chemical types.

Often, the alkaloids are divided into the following primary groups:

  • The alkaloids which are called "True alkaloids" contain the nitrogen content in the heterocycle and it originates from the amino acids. The characteristic examples of alkaloids are nicotine, morphine, and atropine. Also, this group includes a few alkaloids that, besides nitrogen heterocycle, contain peptide fragments (for example, ergotamine) or terpene (for example, evonine). The piperidine alkaloids coniceine and coniine can be regarded as the true alkaloids, although they do not originate from the amino acids.

  • Polyamine alkaloids – the derivatives of spermidine, spermine, and putrescine.

  • Cyclopeptide and peptide alkaloids.

  • Pseudoalkaloids – The alkaloid-like compounds that don't originate from the amino acids. These groups are steroid-like and terpene-like alkaloids and purine-like alkaloids as well such as theobromine, theophylline, and caffeine. A few of the authors have classified the pseudo alkaloids compounds such as cathinone and ephedrine. Those particular alkaloids originate from the phenylalanine amino acid. But, they acquire their nitrogen atom not from the amino acid but via transamination.

A few alkaloids don't contain the carbon skeleton characteristic of their group. Therefore, homoaporphines and galanthamine do not contain isoquinoline fragments, but, in general, they are attributed to the isoquinoline alkaloids.

Extraction

Since alkaloids have such a wide structural diversity, there is no way to remove them from natural raw materials. And, most of the methods which are available exploit most of the alkaloid's property to be soluble in the organic solvents, but not in the water, and the opposite tendency of their salts.

Most plants have many alkaloids. First, their mixture can be extracted, and then, the individual alkaloids are separated. Plants are thoroughly ground prior to extraction. Most of the alkaloids, which are present in the raw plants in the salt form of the organic acids. The extracted alkaloids can also remain salts or changes into bases.

FAQs (Frequently Asked Questions)

1. Explain the Biosynthesis of Alkaloids?

Answer: Biological precursors of several alkaloids are amino acids, like lysine, phenylalanine, anthranilic acid, and aspartic acid. Nicotinic acid is synthesized from aspartic or tryptophan acid. Alkaloid biosynthesis ways are more numerous and cannot be classified easily. However, there are some typical reactions involved in various classes of alkaloid biosynthesis, including the synthesis of Mannich reaction and Schiff bases.

2. Give the Medicinal Applications of Alkaloids?

Answer: The use of alkaloid-containing plants in medicine has a long tradition, but when the first alkaloids were discovered in the 19th century, they were quickly put to use in clinical practise. Still, several alkaloids are used in medicine, generally in the salt form.

3. Give the Agricultural uses of Alkaloids?

Answer: Before the development of extensive, relatively low-toxic synthetic pesticides, a few alkaloids, like salts of anabasine and nicotine, were used as insecticides. Their uses were limited by the human's high toxicity.

4. Explain the use of Alkaloids as Psychoactive Drugs.

Answer: Plant preparations containing later pure alkaloids and alkaloids, as well as their extracts, have been used as psychoactive agents for a long time. Caffeine, cathinone, and cocaine are stimulants of the central nervous system. Mescaline and several indole alkaloids have hallucinogenic effects. Codeine and morphine are strong narcotic pain killers.