Monoterpenoids and Sesquiterpenoids

Terpenoids are classified according to the number of five-carbon multiples they contain. Monoterpenoids contain 10 carbons and are derived from two isopentenyl diphosphates, sesquiterpenoids contain 15 carbons and are derived from three isopentenyl diphosphates, diterpenoids contain 20 carbons and are derived from four isopentenyl diphosphates, and so on, up to triterpenoids (C30) and tetraterpenoids (C40). Monoterpenoids and sesquiterpenoids are found primarily in plants, bacteria, and fungi, but the higher terpenoids occur in both plants and animals. The triterpenoid lanosterol, for example, is the precursor from which steroid hormones are made, and the tetraterpenoid /3-carotene is a dietary source of vitamin A (Figure 27.6). 

G.l.c. papers of interest include the classification of 22 acyclic monoterpenoid alcohols according to retention indexes, resolution of cyclic ketones [e.g. ( )-menthone, ( )-isomenthone] as diethyl (+)-tartrate acetals, and the use of lanthanide shift reagents to resolve non-terpenoid racemic epoxides.The occurrence and prevention of monoterpenoid hydrocarbon isomerization during silica gel chromatography has been examined and the separation of monoterpenoids and sesquiterpenoids by gel permeation chromatography is reported. Monoterpenoid hydrocarbons have been selectively extracted from essential oils using dimethylsilicone. ... 

That certain secondary metabolites from plants promote biodiversity has received experimental support. Thus, com, Zea mays, responds to the release of an amino acid ester, volicitin (Table 12.1), by a caterpillar, Spodoptera exigua, with the emission, at the foraging period of the day, of volatile mixtures of indole, monoterpenoids, and sesquiterpenoids. These attract a caterpillar predator, the female parasitic wasp, Cotesia marginiventris (Albom 1997). 

Halogenated Monoterpenoids.—A separate section is devoted this year to halogen-ated monoterpenoids twenty-four acyclic and four cyclic compounds in this class have been reported. A review of halogenated monoterpenoids and sesquiterpenoids has been published.151... 

A further example of the structural similarity between many monoterpenoids and sesquiterpenoids is provided in a recent paper describing the isolation and structural elucidation of zingiberenol (82), sesquisabinene (83), sesquisabinene hydrate (84), and sesquithujene (85). ... 

Monoterpenoids and sesquiterpenoids are the main components of plants essential oils known to be effective antimicrobials (Fig. 17). Bactericidal activity of essential oils and some of their constituents on foodbome bacteria have been reported a decade ago [164]. Among essential oil constituents, terpinen-4-ol has been shown to significantly affect T. hrucei bloodstream forms viability [165]. Sesquiterpenes were found less active against trypanosomes, allo-aromadendrene 10-fold more effective than its diastereoisomer aromadendrene. Another sesquiterpene artemisinin, isolated from A. annua, is the antiparasitic drug most widely used in the world [166]. However,... 

It is clear from the mechanism shown in Figure 5.14 that terpenoid structures will always contain a multiple of five carbon atoms when they are first formed. The first terpenoids to be studied contained 10 carbon atoms per molecule and were called monoterpenoids. This nomenclature has remained and so those with five carbon atoms are known as hemiterpenoids, those with 15, sesqui-terpenoids, and those with 20, diterpenoids, and so on. In general, only the hemiterpenoids, monoterpenoids, and sesquiterpenoids are sufficiently volatile to be components of essential oils. Degradation products of higher terpenoids do occur in essential oils, so they will be included in this chapter. 

The terpenoids can be defined as a group of natural products whose structure may be divided into isoprene units (13). Isoprene, or isopentenyl, is a C5 (five carbon atom) compound, which can be viewed as the terpenoid building block (Figure 2). Both the lower terpenoids (monoterpenoids and sesquiterpenoids) and the higher terpenoids (diterpenoids and triterpenoids) are built up from multiples of these isoprene units. When freshly exuded, resins tend to be liquid or semi-liquid, as they contain either one or the other of the two higher terpenoids in solution in a mixture of the more volatile lower terpenoids. 

Khan VA, Dubovenko ZV, Pentegova VA 1976 Monoterpenoids and sesquiterpenoids of the oleoresin of Larix sibirica. Khim Prir Soedin 11 100... 

Many other diterpenoids and also monoterpenoids and sesquiterpenoids have been used as starting materials for naphthofuran (375), but none of these syntheses are of... 

Chiral chemodiversity is particularly displayed among monoterpenoids and sesquiterpenoids [41]. Some monoterpene compounds have already been described. The parent compound for monoterpenoids — geranyl pyrophospate (GPP) — gives rise to over 1000 compounds which may be acyclic, monocyclic, or bicyclic. 

Smedman, L. A., E. Zavarin, and R. Teranishi Composition of Oxygenated Monoterpenoids and Sesquiterpenoid Hydrocarbons from the Cortical Oleoresin. of Abies Magnifica A. Murr. Phytochem. 8, 1457 (1969). 

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