Terpenes: what they are, where they are found and why they are useful

Terpenes: what they are, where they are found and why they are useful

Everything you need to know about natural terpenes

Terpenes are part of the largest class of natural products and have several roles mediating in antagonistic and beneficial interactions between organisms. In particular, they defend many species of plants, animals and microorganisms from predators and pathogens. Most of the interactions of terpenes are of the plant-insect type (Dudareva, 2006) but also act as pheromones (Francke, 2005; Hick, 1999).

One of the most important roles for these molecules is to act as messengers between plants and other organisms for their reproduction. Thanks to the use of gas chromatography, it was discovered that their task is to attract pollinating insects that, otherwise, would not have approached the plants (Raguso 1998).

Despite the variety of known terpenes, these organisms (phylogenetically distant from each other) use similar structures for common purposes. Although it is difficult to analyze them in their natural habitat, new genetic and molecular methods have developed experimental tools for their functions.

But what, specifically, are terpenes? We’ll tell you at Terpy.

Terpenes: what they are, where they are found and why they are useful

What are terpenes?

Terpenes are natural compounds that give particular scents and tastes to plants (and even to some animals, especially insects).

They are contained in almost all plants, but some of them have very high percentages and varieties of terpenes: an example is that of aromatic plants, with intense and persistent tastes and smells. Their presence in nature is very important; the flavours of the terpenes have in fact the purpose of warding off predators, for example plant parasites, and at the same time attracting pollinators.

Specifically, terpenes are biomolecules made up of isoprene units and are divided into classes according to the number of isoprene units that compose them.

For example, there are monoterpenes, diterpenes, triterpenes, sesquiterpenes and so on. Most terpenes follow the isoprene rule: they are composed of units of five carbon atoms with an isoprene structure and the isoprenes are linked together according to the head-tail system.

The isoprene rule is not always valid, as some terpenes have carbon chains with a number of atoms multiple of five in which the isoprene structure is identified … But the bond between the isoprene units is not based on the head-tail system .

Maybe you have heard of both terpenes and terpenoids, thinking they are synonyms. In reality this is not the case: let’s see the differences below.

Terpenoids or terpenes? Here are the differences

The terms terpene and terpenoid are often used interchangeably, although they have slightly different meanings. Terpene is a natural hydrocarbon based on combinations of the isoprene unit. On the other hand, terpenoids are compounds related to terpenes and have different properties depending on their biochemical structure.

It is important to understand the difference because their application in different fields also depends on it.

Terpenes belong to the largest class of secondary metabolites, the product of the enzymatic resections of primary metabolites such as amino acids, sugars and vitamins. They are basically composed of five carbon isoprene units which can occur in thousands of different combinations.

While terpenes are simple hydrocarbons, terpenoids are a modified class of terpenes with different functional groups.

Terpenoids come with an immense variety of types and structural compounds. Their composition is due to the number of isoprene units which integrate their molecules and which give rise to different linear arrangements. This can happen thanks to the biosynthetic modification consisting of various cyclizations and new combinations of the hydrocarbon skeleton.

The rapid growth of their structures has led scientists to wonder if their transformations could affect their functions and therefore focus on their biosynthesis (which we will discuss in the following paragraph). In most cases, terpenoids occur as complex mixtures and can be extracted by several methods, such as the following:

  • Steam distillation of plants, which allows to extract essential oils.
  • Extraction with solvent.
  • By liquid-liquid division starting from a first acetonic or alcoholic extract.

To prevent any manipulation, it is important to pay close attention during the extraction and the isolation process.

Let us now focus on the biosynthesis of terpenes, which is the subject of a great scientific attention.

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Biosynthesis of terpenes: how does it happen?

In the scientific field there have been uncertainties for some time about who was the precursor of terpenes. Then, an acid was discovered, namely mevalonic acid, which seems to be interested in the conversion of units to C5.

This acid was discovered during the beer fermentation process and allows the development of a strain of bacteria which needs to be acetate to grow even in the absence of acid. Scientists Lynen, Bloch, Cornforth and Popják were the pioneers of the studies about mevalonic acid and the subsequent discovery of the biosynthesis of cholesterol. Actually, their discoveries led them to the Nobel Prize in 1964.

Returning to us, the biosynthesis of mevalonate, or mevalonic acid, is very important in the biosynthesis of terpenes. In fact it represents the starting point that leads to the synthesis of two units of C5, which leads to the production of terpenes.

The biosynthesis of mevalonate begins with the condensation of two units of acetyl cycenzene; this occurs in a manner very similar to the Claisen condensation.

Subsequently, the aldol condensation takes place from which hydroxymethylglutaryl coenzyme A (HMG-SCoA) derives. The reduction of HMG-SCoA with NADPH makes it possible to create mevalonic acid (MVA) in the phosphorylated form.

Following decarboxylation, the acid gives isopentenyl pyrophosphate, which loses hydrogen pro R (Hr) isomerized into dimethyl pyrophosphate.Now there is the biosynthesis of monoterpenes. The monoterpenes consist of two isoprene units, isopentenyl pyrophosphate and dimethyl pyrophosphate (which, as you could read in the previous paragraph, both derive from the biosynthesis of mevalonic acid).

After many hypotheses, it is now certain that dimethyl pyrophosphate (DMAPP) is initially ionized to a pair of very strong electrolytes. Subsequently, these electrolytes are attacked by isopentenyl pyrophosphate isopentenyl (IPP), causing the birth of geranyl diphosphate (GGPP), an intermediate in the metabolic pathway of mevalonic acid and used by living organisms in the biosynthesis of terpenes.

Do you know that the discovery of terpenes (and consequently the first research and hypotheses on their biosynthesis) took place in the nineteenth century, during the study of the chemical compounds of essential oils? Let’s see, below, what is the deep link between these products.

The role of terpenes in essential oils

In simple terms, terpenes are natural organic compounds found in plants and animals that have certain smells, tastes and effects. Even if we don’t notice it, we come to deal with natural terpenes every day of our life.

When we use rosemary in cooking, when we cut a lemon into slices, when we smell the lavender we feel the fragrances emanating from the terpenes.

Therefore, the role of terpenes is to give a certain aroma to certain plants and animals. If the aroma is strong and persistent, as in the case of aromatic plants, it means that the terpenes are very varied and / or present in large quantities in the plant or animal in question.

We also know that essential oils are natural oils obtained from plants and trees, but also from their derivatives such as roots, seeds, flowers and leaves.

From the chemical analysis of essential oils, it was found that terpenes are some of the hundreds of substances present in the oils. Terpenes are usually the reason for the smell and taste of essential oils (especially 100% natural ones) and which give beneficial effects to the oils.

It is not rare, for example, that essential oils have the reputation of being relaxing, releasing stress and instilling feelings of well-being in those who use them: these effects are mainly given by the terpenes contained in the oils.

The presence of terpenes in essential oils serves to give them the beneficial effects of the aroma of the plant / root / flower / fruit from which they derive. Without the terpenes it would be necessary to use synthetic flavours, which certainly do not have the exact same scent and taste or the same effects of the natural terpenes.

This does not mean that we should confuse terpenes with essential oils: they are completely different products, and, most of all, all terpenes have their own names! Once known, it is impossible to confuse them with, for example, the essential oil of lavender, lemon, rosemary etc.

Indeed: it is very likely that after reading the following paragraph, in which we will tell you the names of the main terpenes, you will learn to recognize their presence both in plants and in the essential oils of which you will smell.

Terpenes: what they are, where they are found and why they are useful

The most common terpenes in nature

You must know that the terpenes of plants and animals are hundreds and hundreds, and give them aromatic nuances (or, especially in the case of animals, bad smells) in order to ward off predators and attract other animals, such as pollinating insects and animals of the other sex to encourage mating.

In nature there are extremely widespread terpenes especially in plants, which are the best known among all the other hydrocarbons. Here are:

  • Limonene
  • Myrcene
  • Pinene
  • Beta-Caryophyllene

Of course, there is no single terpene per plant: these natural compounds combine with each other and recreate different aromatic profiles for each plant. For example, although limonene is present in all citrus fruits, our sense of smell distinguishes the aroma of lemon from that of orange, grapefruit etc.

Having said that, let’s see the characteristics of the main terpenes of plants.

Characteristics of the best known terpenes: from limonene to beta-caryophyllene

Limonene terpene

As you will surely have guessed from the name, limonene is a terpene that gives the typical citrus aroma, such as lemon, orange and grapefruit, to the plants in which it is present.

At the moment little is known about the ways in which limonene interacts with our body and what doses are useful to obtain benefits from its intake.

However, what emerged from the studies in this regard is that this terpene has interesting potential in the following areas:

  • Mood improvement
  • Decreased stress
  • Relief of gastroesophageal reflux and heartburn in the digestive system
  • Antifungal and antibacterial properties

Furthermore, there seems to be good expectations regarding the use of limonene in order to fight and prevent skin, breast, lung and brain cancer. At the moment the experiments have only been conducted on laboratory animals, but highly positive results have emerged.

Scientific researches such as Safety and Feasibility of Topical Application of Limonene as a Massage Oil to the Breast and Human breast tissue disposition and bioactivity of limonene in women with early-stage breast cancer talk about how the application of limonene to topical and oral use has inhibited the growth of breast tumors.

Other studies have shown that limonene can cause the death of cancer cells related to brain and lung cancer, but the quantities used should be significant.

Myrcene

Myrcene is one of the most common terpenes in nature. Its smell is described as musky, earthy, herbaceous, and is often matched with the aroma of cloves and has relaxing effects given by its inhalation. Perfect for relieving stress and difficulty falling asleep.

Pinene

Pinene, as its name suggests, is a terpene that gives plants the characteristic aroma of pine and fir. This particular molecule reacts easily with other chemicals, causing the formation of other terpenes – such as the aforementioned limonene -.

Pinene tends to have balsamic, relaxing effects and promotes a good mood.

Beta-Caryophyllene

Beta-caryophyllene is a terpene that gives cannabis and other plants a spicy, woody and peppery aroma and appears to be the only terpene capable of interacting with the endocannabinoid system of our body.

It seems that the beta-caryophyllene used in aroma therapy (usually thanks to its presence in essential oils) gives feelings of joy and euphoria, improving mood and relieving stress.

Are you wondering why there is so much talk about terpenes? In the following paragraph we explain the reason for all this attention!

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The importance of terpenes and their application in various industrial sectors

As you have been able to read, terpenes are indispensable for plants and animals as they function at the same time as a defense tool towards predators and as a tool of attraction towards pollinators and for the reproduction of animals.

Once extracted, terpenes can be used in different areas, especially for aromatic purposes but not only. Specifically, the applicability of these natural compounds is extended to the following main sectors:

Their study focused on synthesis, biosynthesis and their biological activities in the different fields of application.

If you think about the use of pyrethroids (a class of the terpenes family) in the agricultural sector. Their reduced toxicity on the environment and on mammals, making them extremely effective as insecticides. Pyrethroids, in fact, act on the nervous system of insects, interrupting the transmission of the sodium channel protein.

This causes an over-excitation of the nervous system which results in paralysis, uncoordinated movements and death (Soderlund, 1995).

In the study by Villalba et al. (2006) it is also suggested to use a diet composed of sage in ruminants because it facilitates antimicrobial activities. The widespread use of terpenes in feed would decrease the consumption of conventional antibiotics and reduce the resistance rate of bacteria to the drug.

That’s not all: many terpenes, including limonene, boswellic acid and betulinic acid, are the subject of numerous clinical studies regarding their application in the pharmaceutical field. Till now, most of the research has been conducted, only on laboratory animals, but it is possible that the continuous studies on the biosynthesis of terpenes and on the benefits of these compounds give us good news for humans as well.

The advances in molecular research make it possible to use new tools of genetic know-how to understand the synthesis of terpene metabolism and apply them to the benefit of the human body.