monoterpenoid

Monoterpenoids are a class of terpenoids defined by a C10 carbon skeleton derived from two isoprene units. They are typically oxygenated derivatives of monoterpenes, formed by oxidation, rearrangement, or cyclization of the monoterpene framework. Common functional groups include alcohols, ketones, aldehydes, epoxides, and phenolic moieties. Some authors include all monoterpenes, while others reserve monoterpenoids for oxygenated or rearranged forms.

In plants, monoterpenoids are synthesized from isopentenyl pyrophosphate and dimethylallyl pyrophosphate via the mevalonate pathway or the MEP/DOXP pathway to produce geranyl pyrophosphate (GPP). Monoterpene synthases generate the hydrocarbon skeletons, which are subsequently modified by oxidases, dehydrogenases, and cytochrome P450 enzymes to yield monoterpenoids. The products can be acyclic, monocyclic, or bicyclic and are frequently chiral, with different enantiomers often carrying distinct fragrances or flavors.

Monoterpenoids are abundant in essential oils and plant resins, contributing to many characteristic aromas of mint, citrus, thyme, eucalyptus, and pine. They have wide uses in flavors, fragrances, and cosmetics, and several have pharmacological or antimicrobial properties. Notable examples include menthol, menthone, pulegone, carvone, thymol, carvacrol, and linalool. Their structural diversity and sensory profiles make them a central group within natural product chemistry.