Sesquiterpene

Sesquiterpenes are a class of terpenes composed of three isoprene units, giving a molecular formula of C15H24 in their hydrocarbon form. They are often found in essential oils and resins, and many exist as oxygenated derivatives called sesquiterpenoids. The name derives from sesqui-, meaning one and a half, reflecting the combination of three isoprene units.

Biosynthesis proceeds from the five-carbon building blocks isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). Through head-to-tail condensations, farnesyl pyrophosphate (FPP) is formed, the C15 precursor for sesquiterpenes. Sesquiterpene synthases mediate cyclization and rearrangements to yield diverse skeletons such as germacrene, humulene, caryophyllene, and farnesene, with subsequent oxidation or modification generating a wide array of sesquiterpenoids.

Occurrence and roles are widespread in plants and fungi, where they contribute to essential oils and resins. Notable examples include beta-caryophyllene, germacrene D, valencene, and nerolidol. Ecological roles encompass defense against herbivores and pathogens, attraction or signaling within plant communities, and participation in aroma and flavor profiles that interact with pollinators and herbivores.

Applications span fragrance and flavor industries, and many sesquiterpenoids exhibit biological activity. Beta-caryophyllene, for example, can interact with CB2 cannabinoid receptors, while others display anti-inflammatory or antimicrobial properties. Sesquiterpenes are valued both as pleasant scents and flavors and as leads for pharmaceutical research, with diversity arising from multiple biosynthetic pathways and post-synthetic modifications.