terpenes

Terpenes are a large and diverse class of natural products built from isoprene units (C5H8). They are produced by many plants, fungi, and some bacteria and are characterized by their often strong aromas and flavors. The simplest terpenes, monoterpenes, contain two isoprene units (C10); sesquiterpenes have three (C15); diterpenes four (C20); triterpenes six (C30); tetraterpenes eight (C40). Common examples include limonene and pinene (monoterpenes), myrcene and farnesene (sesquiterpenes), and the carotenoids (C40) which are tetraterpenes.

Terpenes arise from the assembly of isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP) into larger units. Two metabolic routes supply IPP and DMAPP: the mevalonate pathway in most eukaryotes and some bacteria, and the non-mevalonate (MEP) pathway in many bacteria and plant plastids. Sequential head-to-tail condensations produce GPP (C10), FPP (C15), GGPP (C20), and longer backbones, which are then modified by terpene synthases and other enzymes to yield the diverse structures and functional groups found among terpenes and terpenoids.

Ecological roles include defense against herbivores, attraction of pollinators, and signaling between plants. Many terpenes are volatile and comprise essential oils used in perfumery, flavorings, and aromatherapy. Some terpenoids—oxygenated derivatives or those with additional functional groups—have pharmaceutical or industrial applications. The term terpenes is sometimes used broadly to include these terpenoid compounds; when oxygenated or otherwise modified, they are often called terpenoids.