Seskwiterpenes

Seskwiterpenes, more commonly spelled sesquiterpenes, are a class of terpenes defined by their construction from three isoprene units, giving a nominal molecular formula of C15H24. They are produced by a wide range of organisms, including many plants, fungi, and some insects, and are major constituents of essential oils, resins, and other plant secretions. Seskwiterpenes can be hydrocarbon compounds or oxygenated derivatives such as sesquiterpene alcohols, ethers, and particularly sesquiterpene lactones, which are a prominent subclass.

Biosynthetically, sesquiterpenes arise from the five-carbon unit isopentenyl pyrophosphate (IPP) and its isomer dimethylallyl pyrophosphate (DMAPP) via two alternating biosynthetic pathways, converging to farnesyl pyrophosphate (FPP). Cyclization and rearrangement of FPP by specialized sesquiterpene synthases yield a wide variety of skeletons, including linear (open-chain) forms and multi-ring structures. Common skeletons include germacrene, humulene, and caryophyllene, along with numerous other cyclic frameworks. The diversity is further expanded by post-synthetic modifications such as oxidation and lactonization.

Ecologically and economically, sesquiterpenes play roles in plant defense against herbivores and pathogens and contribute characteristic aromas to many essential oils (for example, those of patchouli, cloves, and cannabis). They also find uses in perfumery and flavor industries, and some have pharmaceutical relevance, notably sesquiterpene lactones in traditional medicines and the antimalarial artemisinin, a highly oxygenated sesquiterpene lactone.

Note: the standard term is sesquiterpenes; "Seskwiterpenes" appears to be a misspelling or variant spelling.