Terpenes molecular structure

The terpenes are simple lipids whose base unit is isoprene. Oxygen-containing ter-penes are called terpenoids, and terpenes with hydroxyl groups are called terpenols. Terpenes are further classified based on the number of isoprene imits in the molecule as shown in Table 22.6. Examples of terpene molecular structures are presented in Figure 22.18. 

Secoiridoids are complex phenols produced from the secondary metabolism of terpenes as precursors of several indole alkaloids (Soler-Rivas and others 2000). They are characterized by the presence of elenolic acid, in its glucosidic or aglyconic form, in their molecular structure. Oleuropein, the best-known secoiridoid, is a heterosidic ester of elenolic acid and 3,4- dihydroxyphenylethanol containing a molecule of glucose, the hydrolysis of which yields elenolic acid and hydroxytyrosol (Soler-Rivas and others 2000). 

Alkaloids, nitrogen-containing compounds generally found as secondary metabolites in plants, are also classical examples of renewables. In contrast to terpenes, they show a great variety in molecular structure, and the different classes of alkaloids are usually based on their basic ring systems. Many pharmaceutically active... 

C5H8, and may be either acyclic or cyclic with one or more benzenoid groups. They are classified as mono-cyclic (dipentene), dicyclic (pinene), or acyclic (myr-cene), according to the molecular structure. Many terpenes exhibit optical activity. Terpene derivatives (camphor, menthol, terpineol, bomeol, geraniol, etc.) are called terpenoids many are alcohols. 

Provided that suitable crystals can be cultivated from a solid terpene, these can be used to determine the three-dimensional molecular structure within the crystal by means of X-ray diffraction... 

Terpenes, terpenoids, and rosin have been widely used as renewable chemicals, however, for a long time they have ignored as biomass for the S5mthesis of green polymers. This arose largely due to the difficulty to precisely control the molecular structures (1). 

Important benefits of GC/FTIR are also found in the food industry. Compounds from natural origin, such as terpenes, isomeric sugars, and conjugated unsaturated oils, are difficult to identify by GC/MS alone, and additional GC/FTIR data appear to be very helpful in these cases. The unraveling of the molecular structures of flavors and fragrances present in, for instance, cherimoya fruit and strawberries, are largely based on the results obtained by light-pipe GC/FTIR. 

Some steroids, such as cholic acid, progesterone and testosterone were already mentioned in the chapters discussing aldehydes, ketones and carboxylic acids. The most common steroid in humans is cholesterol. Although the compound has been discovered in the eighteenth century its complete molecular structure was determined only in the middle of the last century. Cholesterol appears in most of tissues and it has a special role in the regulation of blood circulation. An imbalance of cholesterol in the organism can cause serious health problems similar to arthero-sclerosis. The cholesterol molecule, like other steroids, is formed by a particular biosynthetic pathway from the terpene precursors, squalene and lanosterol. Since cholesterol has 27 carbon atoms, 3 atoms less than the triterpene squalene (which has 30 C-atoms), 3 C-atoms are eliminated during the biosynthetic process. 

Of the two pinene monomers (Fig. Ij, k), which can be isomerized into each other (cf. Scheme 3), the a-isomer exhibits an endocychc double bond and is thus the less reactive (and also less frequently used) in polymerization reactions. However, the polymerization of a-pinene was reported as early as 1937, using AICI3 as catalyst in hydrocarbon (i.e., benzene, toluene, xylene, or hexane) solution at <15°C, yielding 75%. Polymerization in the presence of aromatics, with AICI3 as Friedel-Crafts catalyst, takes place without the interaction of aromatic and terpene. However, structures and MWs of the polymers formed were not given [80]. A later comparative study shows that the polymerization of a-pinene produces 35% or less solid polymer with MWs of 0.6-0.7 kg/mol, depending on the catalyst used (p-pinene yield up to 96%, MW = 0.8-3.1 kg/mol). The molecular structure of the oligo(a-pinene) was, however, not provided [66]. 

Sesquiterpenes are a major class of terpenes consisting of three isoprene units, providing the formula of to then-molecular structures (Fig. 7.1) [1]. Like all terpenes, their carbon skeletons are derived from the sequential addition of the active isoprene unit isopentenyl diphosphate (IDP or IPP) to other active diphosphates. In the case of sesquiterpenes, addition of a further IDP unit to geranyl diphosphate (GDP or GPP) (the essential precursor of all monoterpenes, please see Chapter 6) provides the fundamental sesquiterpene precursor famesyl diphosphate (FDP or FPP). 

Terpenes often present a choice between a double bond and a ring structure. This question can readily be resolved on a microgram scale by catalytically hydrogenating the compound and rerunning the mass spectrum. If no other easily reducible groups are present, the increase in the mass of the molecular ion peak is a measure of the number of double bonds and other unsaturated sites must be rings. 

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