sesquiterpenen

Sesquiterpenen (sesquiterpenes) are a class of terpenoid organic compounds composed of three isoprene units, giving a molecular formula typically based on C15H24 before functionalization. They occur widely in plants, fungi and some insects and are common constituents of essential oils and resins.

Biosynthesis of sesquiterpenes proceeds from farnesyl pyrophosphate (FPP), itself formed by head-to-tail condensation of isopentenyl pyrophosphate and dimethylallyl pyrophosphate via the mevalonate or methylerythritol phosphate pathways. Cyclization and rearrangement reactions catalyzed by diverse terpene synthases produce a large variety of carbon skeletons; subsequent oxidation, reduction and conjugation create additional structural diversity, including alcohols, ketones, epoxides and lactones.

Structurally, sesquiterpenes are classified as acyclic, monocyclic, bicyclic or tricyclic, and include notable subclasses such as sesquiterpene lactones. Representative compounds include humulene, caryophyllene, farnesene, patchoulol and the pharmacologically important artemisinin.

Ecologically, sesquiterpenes function in plant defense, signaling and attraction of pollinators or predators of herbivores. Industrially they are used in fragrances, flavors, pharmaceuticals and as precursors for chemical synthesis. Analysis and identification commonly employ gas chromatography–mass spectrometry and nuclear magnetic resonance spectroscopy.

Many sesquiterpenes are biologically active and can cause sensitization or toxicity at high doses, so handling and application are regulated in food, cosmetic and pharmaceutical contexts.