terpene

Terpenes are a large and diverse class of naturally occurring organic compounds built from isoprene units (C5H8). They are hydrocarbons or contain functional groups such as alcohols, aldehydes, ketones, or epoxides. In common usage, the term terpenes refers to the hydrocarbons, while oxygenated derivatives are often called terpenoids (isoprenoids). Terpenes are the primary constituents of many essential oils and contribute to the aromas of plants, fruits, and some insects.

Classification of terpenes is based on the number of isoprene units in the molecule. The main groups are monoterpenes (C10), sesquiterpenes (C15), diterpenes (C20), triterpenes (C30), and tetraterpenes (C40). These compounds form a vast array of structures, including linear, cyclic, and polycyclic skeletons, often generated by specialized enzymes known as terpene synthases that convert prenyl diphosphate substrates into diverse products.

Biosynthesis occurs from isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), produced via the mevalonate pathway in animals and many fungi, or the MEP/DOXP pathway in plants and bacteria. Condensation of IPP and DMAPP forms geranyl diphosphate (C10) for monoterpenes, farnesyl diphosphate (C15) for sesquiterpenes, and longer-chain precursors for higher terpenes.

Ecologically, terpenes serve defense, signaling, and attraction roles in plants, and contribute to the flavors and fragrances of many foods and cosmetic products. They have applications in flavors, fragrances, pharmaceuticals, and potential bio-based solvents and materials. Safety considerations include potential irritation or allergenicity for sensitive individuals, and regulation varies by country.