erpenes are natural products made from isoprene (2-methyl-1,3-butadiene) subunits.
The word terpene comes from turpentine, the pleasant-smelling
liquid extracted from pine sap. As might be expected, terpenes are ubiquitous
in plants, and account for many of the odors and colors we associate with plants.
For example, humans can detect p-menth-1-en-8-thiol, which produces the
characteristic taste of grapefruit, at concentrations as low as
5×10-13M, giving this molecule the distinction
of being the one with the lowest taste threshold for humans of any compound.
But terpenes are not only made in plants; vital molecules such as cholesterol, which is synthesized in animal cells, are also made from terpenes. Terpenes have even been found in meteorites. With over 30,000 terpenes known in the literature, it would be unrealistic to expect a thorough coverage of the field in this terse 214-page book. Nature in its amazing ingenuity adds aldehydes, peroxides, alcohols, and polycyclic ring structures to combinations of simple hydrocarbon units of isoprene to build substances that act as insecticides, pheromones, plant and animal hormones, and toxins. Other important terpenes include rubber, vitamins A, E, and K, tumor promoters such as phorbol, anticancer drugs such as taxol, hallucinogens such as cannabinols, and food flavors such as limonene.
In the first eight chapters, Breitmaier classifies the bewildering variety of terpenes into recognizable groups. The emphasis is on recognizing the fundamental backbone structures, which determine the carbon numbering. Some properties and medicinal uses of some terpenes are mentioned, but their biochemical effects and mechanisms of action are omitted. For example, the important phosphodiesterase inhibitor forskolin gets only a single sentence. There are also a few errors, such as classifying Aplysia (sea hare) as a type of algae (p.80). In chapter 9, he describes organic syntheses of selected terpenes, including citronellal, chrysanthemic acid methyl ester, camphor, retinol, and taxol. The last chapter discusses some rudimentary methods of structure determination. Although this book cannot by any stretch of the imagination be considered a definitive reference work on terpenes, it is nevertheless an excellent introduction and an orientation to a vast and fascinating subject. The information here is essential basic knowledge for biologists, chemists, or anyone in the pharmaceutical industry.
