Terpene
Introduction
Terpenes are a large and diverse class of organic compounds, produced primarily by a variety of plants, particularly conifers, and by some insects. They often have a strong odor and may protect the plants that produce them by deterring herbivores and by attracting predators and parasites of herbivores. Terpenoids, also known as isoprenoids, are a large and diverse class of naturally occurring organic chemicals similar to terpenes, derived from five-carbon isoprene units assembled and modified in thousands of ways. Most are multicyclic structures with oxygen-containing functional groups.
Chemical Structure and Biosynthesis
Terpenes are derived biosynthetically from units of isoprene, which has the molecular formula C5H8. The basic molecular formulas of terpenes are multiples of that, (C5H8)n where n is the number of linked isoprene units. This is called the isoprene rule or the C5 rule. The isoprene units may be linked together "head to tail" to form linear chains or they may be arranged to form rings. One can consider the isoprene unit as one of nature's common building blocks.
Terpenes are classified by the number of isoprene units in the molecule. A prefix in the name indicates the number of terpene units needed to assemble the molecule. "Mono", "sesqui", "di", "tri", "tetra" and other prefixes refer to the number of terpene units. For instance, monoterpenes have two isoprene units and are derived from the dehydration of geranyl pyrophosphate, while sesquiterpenes, derived from farnesyl pyrophosphate, have three isoprene units, and so on.
Types of Terpenes
Terpenes can be classified into several types based on the number of isoprene units they contain. These include monoterpenes, sesquiterpenes, diterpenes, sesterterpenes, triterpenes, tetraterpenes, and polyterpenes. Each of these types has unique properties and can be found in different plants and organisms.
Monoterpenes
Monoterpenes are composed of two isoprene units and have the molecular formula C10H16. They may be linear (acyclic) or contain rings. Examples of monoterpenes and monoterpenoids include geraniol, terpineol (present in lilacs), limonene (present in citrus fruits), myrcene (present in hops), and pinene (present in pine trees).
Sesquiterpenes
Sesquiterpenes consist of three isoprene units and have the molecular formula C15H24. Like monoterpenes, they may be acyclic or contain rings. Examples of sesquiterpenes and sesquiterpenoids include humulene, farnesenes, farnesol. (present in many essential oils such as citronella, neroli, cyclamen, and ginger oil).
Diterpenes
Diterpenes are composed of four isoprene units and have the molecular formula C20H32. They derive from geranylgeranyl pyrophosphate. Examples of diterpenes and diterpenoids are cafestol, kahweol, cembrene and taxadiene (precursor of taxol). Diterpenes also form the basis for biologically important compounds such as retinol, retinal, and phytol.
Role in Plants and Ecosystems
Terpenes play crucial roles in plant growth and development, acting as hormones, messengers, and cellular regulators. They are involved in various plant processes, including photosynthesis, respiration, and the synthesis of vitamins, pigments, and other metabolites. Terpenes also contribute to the plant's immune system, protecting it against pests, diseases, and environmental stresses.
In ecosystems, terpenes have important roles in promoting biodiversity. They contribute to the characteristic scent of many plants and flowers, attracting pollinators and helping to ensure the plant's reproduction. Terpenes also deter herbivores, protecting the plant from being eaten. Some terpenes even attract the natural enemies of herbivores, such as predators and parasites, providing an additional layer of defense.
Applications and Uses
Terpenes have a wide range of uses in both natural and industrial contexts. They are a primary constituent of the essential oils of many types of plants and flowers, and are often used in perfumery and aromatherapy. Terpenes are also used as flavorings and spices in food and beverages, and as fragrances in cleaning and cosmetic products.
In the pharmaceutical industry, terpenes are used in the production of medicines and therapeutic agents. Some terpenes have been found to have medicinal properties, such as anti-inflammatory, antibacterial, antifungal, antiviral, and anticancer activities. For example, the monoterpene limonene is being studied for its potential to prevent and treat cancer.
In the industrial sector, terpenes are used in the manufacture of plastics, resins, and other materials. They are also used as solvents in a variety of applications.