Sesquiterpenes are a structurally diverse class of C15 terpenoids synthesized by plants, fungi, and marine organisms. These compounds exhibit a wide range of pharmacological activities, including anticancer, anti-inflammatory, and antimicrobial effects, making them highly relevant in biomedical and pharmaceutical research.
Chemical Diversity and Structures
Sesquiterpenes consist of 15 carbon atoms derived from three isoprene units. They occur in multiple structural forms, including acyclic, monocyclic, bicyclic, and tricyclic configurations, as well as functionalized derivatives such as alcohols, lactones, and oxides. Representative skeletons include cadinene (fused six-membered rings), caryophyllene (a nine-membered ring with a cyclobutane moiety), and germacrene (a ten-membered ring structure).
More than 7,000 sesquiterpene variants have been identified, primarily originating from cyclization reactions of farnesyl pyrophosphate (FPP). Subsequent oxidation processes contribute to the formation of biologically active derivatives, including sesquiterpene lactones.
Biosynthesis Pathways
The biosynthesis of sesquiterpenes begins with the head-to-tail condensation of dimethylallyl pyrophosphate (DMAPP) and two isopentenyl pyrophosphate (IPP) units, forming farnesyl pyrophosphate (FPP) via the action of farnesyl pyrophosphate synthase. Sesquiterpene synthases (STSs) subsequently catalyze complex reactions involving ionization, cyclization, and deprotonation, generating structurally diverse and often highly strained polycyclic compounds such as presilphiperfolanol.
In plants and basidiomycetes, alternative biosynthetic routes involving Z,Z-FPP intermediates can lead to the production of unique olefinic structures. These enzymatic processes are frequently dependent on Mg²⁺ ions, which stabilize carbocation intermediates during the catalytic cycle.
