| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||
Book Review |
Dean, College of Agriculture; California State Polytechnic University, Pomona
The rapid growth of interest in herbal remedies and bioactive phytochemical components has stimulated renewed attention toward natural product chemistry. Identification of the bioactive components is essential to an identification of the mechanisms of action and an evaluation of the efficacy of these new agents. Although the previous volumes of this series were dedicated to the structure and synthesis of various classes of natural products, this volume begins a transition to specific bioactive natural products which will be carried forward in future volumes. Each of the seventeen chapters is well written by internationally recognized chemists. The majority of the chapters integrate synthetic and structural chemistry with relevant biological applications.
Several chapters discuss the role of terpenoids in higher plants. The evolution of the repellent nature of terpenoids made coexistence possible among different species of plants and animals. The shikimic acid pathway forms phenols and tannins, which prevent attack by microorganisms and animals. Evolution led to dominance of the acetate-mevalonate pathway in angiosperms, which opened an immense chemical source to specifically acting poisons and repellents, many of which are terpenes. Lignin is a major component of wood essential to the formation of the stroma, yet presents antifungal and insecticide properties for protection. Terpenes serve as repellents for animals, producing discomfort due to bad taste or smell via terpene alkaloids. Plants excrete germicides from their roots or from leaves; these are washed to the soil by rain, suppressing competitive plant growth nearby. Microorganisms and insects can develop resistance quickly. Some insects accumulate terpenes and excrete them in chemo-signals as means of communication. In addition, some terpenes act as hormones regulating plant growth.
Terpene toxicity may be the most important concern, affecting grazing food animals, home pets, small children and now adults selecting herbs and roots for natural therapy. Thirteen plant families and 20 species are presented, with specific phytochemical examples of toxicity. Additional chapters illustrate other terpenes, clearly identifying structure and synthetic pathways.
The Taxus species possess numerous biologic activities. Taxane alkaloids, diterpenoids with taxane skeleton, lignans, bioflavonoids, steroids, sugar derivatives and diterpenes possessing tropone skeletons are all commonly found in this genus. Although many of these plants are quite toxic, interest has been stimulated by identification of antitumor and antileukemic taxanes, molting hormones, alkaloids, antineoplasmic diterpenes—all triggered by the importance of taxol/paclitaxe. Indeed, taxol has been shown to be the major cytotoxic, antieoplastic and antileukemic constituent, acting as a strong antimitotic agent. Taxol promotes microtubule formation, decreasing the lag time for microtubule assembly. Thus, taxol blocks the processes essential for prostate tumor cell invasion and metastasis. Other taxonoids have been determined to be more or less active than taxol.
Withanolides, biologically active natural steroidal lactones, occur mainly in the Solanacea family, which contains more than 2000 species of plants. The withanolides are polyoxygenated steroids constructed from the ergostane skeleton. A large number of oxygenated species are produced, and their structures have been identified by NMR and mass spectral analysis.
Selection of toxic plant compounds that have potential anticancer activity requires establishing methodologies for extraction and fractionation based on bioassays for specific bioactivity. The use of the yeast bioassay for the detection and isolation of DNA-damaging agents in plant and marine extracts is described; the assay is easy to set up, economical to run and selective. Natural products with DNA-damaging activity include sesquiterpenes, diterpenoids, steroids and alkaloids. The yeast assay is a mechanism-based assay independent of chemical structure. Several of these natural products have been determined to be planar compounds that could intercalate into DNA. The bioassay also detected topoisomerase I and II inhibition, but only one compound was actually found to inhibit topoisomerase I. Another chapter reviews in vitro models of human disease states, including evaluation of cytotoxicity activity using cultured human cancer cells and testing for agents that might produce cancer prevention by the inhibition of initiation through antimutagenic effects or the induction of quinone reductase, by the inhibition of tumor promotion through induction of ornithine decarboxylase or arachidonic acid metabolism, or by the inhibition of progression by inhibiting terminal differentiation in HL-60 cells, induction of non-specific esterase and antihormone activity. The chapter also demonstrates antimalarial and antihepatitis B screening methods and bioactivities.
A detailed chapter on chemical synthesis of carotenoids is presented, indicating at least four compounds currently used in commercial production. A second chapter in this area describes the synthetic chemistry for some natural food colorants, including anthocyanins, the betalaines, the carotenoids, chlorophyll a, cochineal and curcumin. The authors discuss the importance of commercial synthesis of very pure nature-identical materials, such as those employed in structure and property studies requiring pure standards.
Inconsistencies of style exist among the different chapters, e.g. double spacing vs. single spacing, but these do not alter the value of the material presented. The index at the end of the volume is an all-inclusive general subject index of the first 20 volumes, including cumulative indexes on organic synthesis, pharmacological activity and biological sources. Because the index will make the entire series more useable, perhaps it should have been published as a separate volume.
This volume is designed for researchers working in phytochemistry and natural bioactivity and educators and students having a strong chemistry interest. The authors have provided exceptional consideration of the selected bioactive compounds, their identification and their synthesis. Their insight into synthesis will enable better analytical determination of unknown natural bioactive components. Organic chemists working in the area will greatly welcome this addition to the series, and biochemists will appreciate the insight into bioactivity and future applications.
Received January 1, 2000.
| ||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
