Essential oils of plants

Eicosanoids and terpenoids are still other classes of lipids. Eicosanoids, of which prostaglandins are the most abundant kind, are derived biosynthetically from arachidonic acid, are found in all body tissues, and have a wide range of physiological activity. Terpenoids are often isolated from the essential oils of plants, have an immense diversity of structure, and are produced biosynthetically from the five-carbon precursor isopentenyl diphosphate (IPP). lsopentenyl diphosphate is itself biosynthesized from 3 equivalents of acetate in the mevalonate pathway. 

Cutting oils (the inhibitor or antiseptic they contain) Essential oils of plants and flowers Linseed oil Mustard oil" ... 

A class of hydrocarbons occurring in many essential oils of plants. They can be regarded as low-molecular weight polymers of isoprene (C5I I8)n. Dipentene is a terpene, while natural rubber, gutta percha and balata have been termed polyterpenes. 

Terpenoids and Steroids. The Information given in Tables IV-VII and the blogenetlc relationships shown in Figures 2 and 3 speak for themselves. This class of compounds accounts for more than one-third of the known cotton plant secondary metabolites. The monoterpenoids listed in Table V, many of which have the para-menthane skeleton, are generally common compounds widely spread in the essential oils of plants. 

Higher plants produce a great variety of terpenoids (78) but only a few of these have been implicated in allelopathy. The monoterpenoids are the major components of essential oils of plants and they are the predominant terpenoid inhibitors that have been identified from higher plants. Many fungi (82) and algae (83) produce terpenoid allelochemicals also. 

Many of the monoterpenes found in essential oils of plants also occur as pheromonal substances in insects (45,57-60) and are often involved in plant-insect interactions. Some compounds found both in plants and insects are the monoterpenes citronellal, cit-ronellol, geraniol, myrcene, citral, 6-phellandrene, limonene, 2-terpinolene, a-pinene, 6-pinene, 1,8-cineole, and verbenone. 

Terpenes are natural products usually obtained from the essential oils of plants. They contain multiples of five-carbon atoms (5, 10, 15, and so on). Each five-carbon arrangement is called an isoprene unit, a four-carbon chain with a one-carbon branch at C-2. Terpenes are frequently used in fragrances and perfumes. Steroids are lipids that contain a unique four-ring structure and are biosynthetically related to terpenes. Important examples of steroids include cholesterol, the bile acids, and the sex hormones. 

Terpenes are a diverse family of compounds with carbon skeletons composed of five-carbon isopentyl (isoprene) units. Terpenes are commonly isolated from the essential oils of plants the fragrant oils that are concentrated from plant material by steam distillation. The term essential oils literally means oils derived from the essence of plants. They often have pleasant tastes or aromas, and they are widely used as flavorings, deodorants, and medicines. Figure 25-12 shows the structures of four terpenes that are isolated from essential oils. 

The isoprenoids consist of terpenes and steroids. Terpenes are an enormous group of molecules that are found largely in the essential oils of plants. (Essential oils are plant extracts used for thousands of years in perfumes and medicines.) Steroids are derivatives of the hydrocarbon ring system of cholesterol. 

Monoterpenoids, nominally containing two isoprene units, are particularly abundant in higher plants and algae. Because of their volatility they are important as at-tractants (e.g. insect pheromones), but are probably best known as components of the essential oils of plants (e.g. menthol in peppermint oil). Esters of chrysanthemic acid, found in pyrethrum flower heads, are natural insecticides. Some examples are shown in Fig. 2.17a. 

Terpenes are functional compounds with an isoprenoid structure, found in the essential oils of plants such as lemon grass, cherry, mandarin, and citronella. To utilize functional terpenes, especially in the pharmaceutical field, geraniol, famesol, geranylgeraniol, phytol, perillyl alcohol, myrtenol, and nerol were phosphatidylated, and their antiproliferative effects on cancer cells were investigated in vitro [52,53]. Among these seven compounds, phosphatidyl-monoterpenes showed a markedly antiproliferative effect on human prostate PC-3 and human leukemia HL-60 cells. 

Calamus grows wild in India, China, Europe, and North America, and the phytochemical profile of the plant material varies according to origin. The essential oil of plants from India contains up to 75% p-asarone see Alkenylbenzenes in Appendix 1), while the oil of calamus from Japan and eastern Russia contains 10-40%, oil from European plants contains... 

Mustard oils. Name for organic isothiocyanates, R-N=C=S, occurring in the essential oils of plants, mainly Brassicaceae, as the components responsible for sharp odors and pungent tastes. They exist in the plant in glycosidically bound form (see glucosinolates) and are released from the latter by tbioglycosidases (myrosinases) and subsequent rearrangements. 

Many hydroxybenzoic-acid-derived (Ce-Ci) compounds (acids, esters, aldehydes, alcohols, etc.) are found in the essential oils of plants. Several essential oils have commercial importance, although many important components are readily synthesized. In many cases, the synthetic products have eclipsed the naturally occurring ones in importance. For example, vanilla extract contains vanillin (Fig. 8.18). As the user of synthetic vanilla will realize, however, synthetic substitutes often lack minor components that make natural vanilla preferable. 

Bayala, B., Bassole, 1. H., Gnoula, C., Nebie, R., Yonli, A., Morel, L. et al. (2014). Chemical composition, antioxidant, anti-in ammatory and anti proliferative activities of essential oils of plants from Burkina Faso. PLoS ONE9 3), E-ISSN 1932-6203. 

A wide variety of terpenes are isolated from the essential oils of plants. Terpenes generally have a strong fragrance and are often used as flavorants and odorants in a wide variety of applications, including food products and cosmetics. 

Fujita, S., and Y. Fujita Essential Oils of Plants from Various Territories. XXX. Components of the Essential Oils of Cymbopogon goeringii. Yakugaku Zasshi 92, 1285 (1972) Chem. Abstr. 78, 33 791 x (1973). 

Phenols are found in several of the essential oils of plants, which produce the odor or flavor of the plant. Eugenol is found in cloves, vanillin in vanilla bean, isoeugenol in nutmeg, and thymol in thyme... 

Monoterpenes, sesquiterpenes, and their oxygen-containing derivatives are an important class of volatile constituents in essential oils of plants that have been found in many types of environmental and geological samples and in other natural or synthetic sources. The identification of terpenes as flavor, fragrance, and curative compounds is important in medicine, veterinary science, and the cosmetics, flavor, and food industries. 

---