Plants, terpenes from

It is often difficult to know whether terpene compounds formd in insects are made de novo by the insect or whether the insect has altered some terpenes it finds in its food or environment. The boll weevil is known to alter plant terpenes from cotton. Ips beetles which bore under the bark of pine trees produce an aggregation pheromone consisting of ipsdienol or ipsenol (Figure 6.8) which were thought to be conversion products of myrcene from the pine tree. However studies with radio-labelled acetate and mevalonate showed that at least two species, Ips paraconfusus and Ips pini were able to synthesize their pheromones from scratch . On the other hand, both males and females of Ips paraconfusus convert a-pinene from the tree to cw-verbenol, which adds to the attraction of the male-produced pheromone. 

Francesconi and Sernagiotto have isolated a terpene from the essential oil of Crithmum maritirmim distilled from plants grown in Sardinia. 

In plants, terpenes (see Chapter 6 Focus On) are biosynthesized by a pathway that involves loss of CO2 from 3-phosphomevalonate 5-diphosphate to yield isopentenyl diphosphate. Use curved arrows to show the mechanism of this reaction. 

Until rather recently, our choice among chemicals repellant to insects was very limited (9), and some of the available remedies seem to have been almost equally repellent to their human users. The most familiar of them undoubtedly is the classical oil of citronella, a mixture of plant terpenes which consists principally of geraniol, citronellol, and citronellal. It is a remarkable coincidence that at least one insect species, an ant discussed by Dr. Happ, also makes use of some of these same terpenes as repellents against other insects. It biosynthesizes them de novo rather than simply taking them from plant sources. Many other examples of insect repellency have been observed (9), and Roth and Eisner (28) list over 30 compounds which have been identified as defense substances of anthropods. 

FIGURE 12-13 Interaction of Gs with adenylyl cyclase. (PDB ID 1AZS) The soluble catalytic core of the adenylyl cyclase (AC, blue), severed from its membrane anchor, was cocrystallized with G,, (green) to give this crystal structure. The plant terpene forskolin (yellow) is a drug that strongly stimulates the enzyme, and GTP (red) bound to Gsa triggers interaction of Gsa with adenylyl cyclase. 

Plant terpenes may deter herbivores and attract pollinators. They may participate in competition among plants and may act as antibiotics, called phytoalexins, to protect plants from bacteria and fungi.84 In invertebrate animals terpenes serve as hormones, pheromones, and defensive repellants (Figs. 22-3,22-4). The terpene squalene is the precursor to sterols. Some terpenes are toxic. For example, thujone (Fig. 22-3), which is present in the liqueur absinthe, causes serious chronic poison-... 

The isolation of terpenes from plants entails several problems (e.g, very low concentrations). Therefore other sources of these flavour compounds are searched for microorganisms for example (especially bacteria and fungi) are used for the production of terpenoids [22]. Since terpenoids are very important flavour and fragrance compounds, the biotransformation of terpenes offers a very interesting source of novel... 

The odor of a freshly crushed mint leaf, like many plant odors, is due to the presence in the plant of volatile C10 and Ci5 compounds, which are called terpenes. Isolation of these substances from the various parts of plants, even from the wood in some cases, by steam distillation or ether extraction gives what are known as essential oils. These are widely used in perfumery, as food flavorings and medicines, and as solvents. Among the typical essential oils are those obtained from cloves, roses, lavender, citronella, eucalyptus, peppermint, camphor, sandalwood, cedar, and turpentine. Such substances are of interest to us here because, as was pointed out by Wallach in 1887 and reemphasized by Ruzicka in 1935, the components of the essential oils can be regarded as derived from isoprene ... 

What is clean air Unpolluted air is a concept of what the air would be if humans and their works were not on earth, and if the air were not polluted by natural point sources such as volcanoes and forest fires. The true composition of unpolluted air is unknown because humans have been polluting the air for thousands of years. In addition there are many natural pollutants such as terpenes from plants, smoke from forest fires, and fumes and smoke from volcanoes. Table 4.1 lists the components that, in the absence of such pollution, are thought to constitute clean air. 

The traditional nomenclature used in the terpene field is at best an exacting exercise in memory. Most of the terpene names are derived from the genus or family names of the plants or from the essential oils from which the products were first isolated or in which they occur most abundantly. Many terpene names currently used, both for fundamental structures and especially for derivatives, give no clue as to the nature of the specific compounds or to the structural relationships which exist among several terpenes or between terpenes and similar organic compounds. 

Renwick J. A. A. (1967) Identification of two oxygenated terpenes from the bark beetles Dendroctonus frontalis and Dendroctonus brevicomis. Contrib. Boyce Thompson Inst, of Plant Res. 23, 355-360. 

XOCHIPILLI UPDATED, TERPENES FROM MEXICAN PLANTS... 

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