Terpenoid
Introduction
Terpenoids, also known as isoprenoids, are a large and diverse class of naturally occurring organic chemicals derived from five-carbon isoprene units assembled and modified in thousands of ways. They are found in all classes of living things and are the largest group of natural products.
Classification
Terpenoids 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. Hemiterpenes consist of a single isoprene unit. Monoterpenes consist of two isoprene units and are derived from geranyl pyrophosphate. Sesquiterpenes consist of three isoprene units and are derived from farnesyl pyrophosphate. Diterpenes are composed of four isoprene units and are formed from geranylgeranyl pyrophosphate. Larger terpenes are known as triterpenes (six isoprene units), tetraterpenes (eight isoprene units), and polyterpenes (many isoprene units).
Biosynthesis
Terpenoids are derived biosynthetically from units of isopentenyl pyrophosphate, which is formed in the MVA pathway (mevalonate pathway) and the MEP/DOXP pathway (non-mevalonate pathway). Although both pathways, MVA and MEP, are mutually exclusive in most organisms, interactions between them have been reported in plants and few bacteria species.
Functions
Terpenoids contribute to the scent of eucalyptus, the flavors of cinnamon, cloves, and ginger, the yellow color in sunflowers, and the red color in tomatoes. They have roles in traditional herbal remedies and are under investigation for antibacterial, antineoplastic, and other pharmaceutical functions. Terpenoids are also major biosynthetic building blocks within nearly every living creature, making them essential to human well-being, particularly as nutrients and pharmaceuticals.