Secondary metabolites, terpenoids

Mostly, terpenoids originate from plants, but they are also synthesized by other organisms, including yeast and bacteria, as primary or secondary metabolites. Terpenoids are S5mthesized from two 5-car-bon building blocks that consist of isoprenoid units [62]. Based on the number of building blocks, terpenoids have been classified into four classes monoterpenes (geraniol, carvone, d-limonene, and perillyl alcohol), diterpenes (retinol and trans-retinoic acid), triterpenes (lupeol, oleanic acid, betulinic acid, and ursolic acid), and tetraterpenes (lutein, a-carotene, yS-carotene, and lycopene) [66]. 

Figure 11.1 Representative secondary metabolites produced by Streptomyces ceolicolor and other microorganisms, including aromatic polyketides actinorhodin and tetrohydroxynaphthalene (a), side-rophore desferrioxamines (b), polyunsaturated fatty acid eicosapentaenoic acid (c) and terpenoids beta-...

A recent example demonstrates that corals rely on induced biosynthesis of terpenes as a dynamic defense strategy as well. The induction of terpenoid secondary metabolites was observed in the sea whip Pseudopterogorgia elisabethae [162]. Levels of pseudopterosins 89-92, a group of diterpene glycosides with anti-inflammatory and analgesic properties (Scheme 23) [163-165], are increased in response predation by the mollusk Cyphoma gibbosum. First bioassays indicate that these natural products are involved in the chemical defense. 

About 120 chemical constituents have been identified in chamomile as secondary metabolites, including 28 terpenoids, 36 flavonoids and 52 additional compounds [4]. A substantial part of drag effects are determined by the essential oil content. Oil is collected from flower heads, either by steam distillation or solvent extraction, for yields of 0.24-1.90% of fresh or dry plant tissue. Among the essential oil constituents the most active are /-/-a-bisabolol and chamazulene. /-/-a-bisabolol has demonstrated anti-inflammatory, antispasmodic, antimicrobial, antiulcer, sedative and CNS activity. Chamazulene is also anti-inflammatory. Topical applications of chamomile preparation have shown benefit in the treatment of eczema, dermatitis and ulceration [5]. 

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. 

The nutritional value of the diet influences the ability of herbivores to detoxify plant secondary metabolites (Schwass and Finley, 1985). For instance, voles in winter have to consume the bark of birch Betula sp.). This causes stress and leads to poor growth and high mortality among young animals. Birch bark contains phenolics and terpenoids. Both are metabolized by cytochrome P450 monooxidases in phase I and conjugated with glucuronic acid in phase II. 

It was only recently that the presence and significance of the sano, or structurally closely related, natural products on land and in the sea has received specific attention (Pietra 1995). Three main conclusions were arrived at (a) the highest fiequency of structural similarities for secondary metabolites occurs with terpenoids fi om anthozoans and land plants (b) biosynthetic routes became adapted to the fimction of the metabolite, such as a defensive one that must persist, or a hormonal one that needs to be rapidly switched off, so, the synthesis of the same compoimd in phylogeneticalfy close organisms should occur by the same pathway, while different biosynthetic routes should be used by phylogenetically distant organisms, and (c) the contribution of marine bacteria to the genes for secondary metabolites in eukaryotes was scarce (Pietra 1995). 

Volatile compounds formed by anabolic or catabolic pathways include fatty acid derivatives, terpenes and phenolics. In contrast, volatile compounds formed during tissue damage are typically formed through enzymatic degradation and/ or autoxidation reactions of primary and/or secondary metabolites and includes lipids, amino acids, glucosinolates, terpenoids and phenolics. 

The terpenoids are secondary metabolites that are found in essential oils, resins, tissues of higher plants and micro-organisms, whilst recently some have also been located in liverworts [5,6]. The terpenoids are formed from linear arrangements of isoprene units, Fig. (1), which are derived from acetate metabolism through mevalonic acid (MVA). This pathway was found to be common to the whole range of natural terpenoid derivatives... 

There is a huge variety of plant defensive secondary metabolites that has been the subject of major phytochemical [1-6] or pharmacological and toxicological [7-12] compilations. This structural complexity is very briefly reviewed below before considering those plant bioactives with signal transduction targets. The major groups are the phenolics, the terpenoids and the alkaloids as well as bioactives structurally related to... 

The nematicidal activities of extracts from different parts of a chicory root were examined. The relative survival ratios (R. S. R.) at the root skin, inner root tissue, wounded root tissue and hairy roots were measured (Figure 3). The extract from the root skin exhibited the highest nematicidal activity. Interestingly, the nematicidal activity of an acidic fraction from rhizoplane soil was much higher than that from bulk field soil. We found that some phenolics from the root also exhibited nematicidal activity. Thus, it seems that secondary metabolites such as terpenoids and phenolics can play an important role in chicory defense. 

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