Plant-derived terpenoids

In relation with resistance of weeds to herbicides, Duke et al. (2000) mentioned that new mechanisms of action for herbicides are highly desirable to fight evolution of resistance in weeds, to create or exploit unique market niches, and to cope with new regulatory legislation. Comparison of the known molecular target sites of synthetic herbicides and natural phytotoxins reveals that there is little redundancy. Comparatively little effort has been expended on determination of the sites of action of phytotoxins from natural sources, suggesting that intensive study of these molecules will reveal many more novel mechanisms of action. These authors gave some examples of natural products that inhibit unexploited steps in the amino acid, nucleic acid, and other biosynthetic pathways AAL-toxin, hydantocidin, and various plant-derived terpenoids. 

Sun IC, Kashiwada Y, Morris-Natschke SL, Lee KH. Plant-derived terpenoids and analogues as anti-HIV agents. Curr. Top. Med. Chem. 2002 3 155-169. 

Repellencv. A number of other plant-derived terpenoids have been demonstrated to be repellent to various insects. Many compounds in this class have been proven to be attractants to certain insects (1). Limonene at 1 or 10 mg/box repelled the cockroaches, to the untreated box, in significantly (p<0.05) greater numbers than the 0.001 mg rate or the controls (4). Pulegone and linalool at the 10 mg/box rate repelled significantly more individuals than the 0.0001 mg rate or the controls. Myrcene and a-terpineol did not demonstrate any repellency. Natural pyrethrins were significantly different from the controls at the 0.1 mg/box rate. 

This chapter focuses on the terpenoid production from plant species, hairy root cultures, and Ri-plants the terpenoid increase by hairy root elicitation and recent strategies as T-DNA activation tagging/transcriptome analyses for isolating novel genes and hairy root engineering in order to improve terpene metabolism pathways. Lastly, therapeutic properties of some plant-derived terpenoids are reported. 

The bulk of plant-derived medicines can be categorized into a number of chemical families, including alkaloids, flavonoids, terpenes and terpenoids, steroids (e.g. cardiac glycosides), as well as coumarins, quinines, salicylates and xanthines. A list of some better-known plant-derived drugs is presented in Table 1.16. 

When plants undergo various stresses, certain secondary metabolites, including defense compounds, accumulate. Several secondary metabolites such as terpenoid indole alkaloids, indole glucosinolate, nicotine alkaloids, and polyamines are known to accumulate through the induction of biosynthetic genes by jasmonates.898-900 MeJA also induces genes involved in the formation of tryptophan derivatives, terpenoid indole alkaloids.901 These compounds are known to be involved in defense response to pathogen attack as phytoalexins. 

Besides the naturally occurring saccharides and polyols, there are a number of plant-derived highly sweet compounds, which are mostly terpenoids, flavonoids, and proteins [16-18]. Several of these sweet substances are used commercially as sucrose substitutes, as will be described in the next section. In addition, a number of plant substituents are known to mediate the sweet-taste response, either by inducing or inhibiting the perception of sweemess [19]. Thus far, all of the known natural product sweet-tasting substances and sweetness modifiers have been obtained from green plants [16-19]. In the remaining sections of this chapter, plant-derived sweet compounds with commercial use will be described, followed by a section on recent theories on the sweet taste phenomenon, and then individual descriptions of potent sweeteners, sweetness inducers, and sweetness inhibitors from plants will be presented in turn. The literature has been surveyed for this chapter until the end of 1999. 

Terpenoids are main constituents of plant-derived essential oils. Because of their pleasant odor or flavor they are widely used in the food, fragrance, and pharmaceutical industry. Furthermore, in traditional medicine, terpenoids are also well known for their analeptic, antibacterial, antifungal,... 

Terpenoids are classified according to the number of five-carbon multiples they contain. Monoterpenoids contain 10 carbons and are derived from two isopentenyl diphosphates, sesquiterpenoids contain 15 carbons and are derived from three isopentenyl diphosphates, diterpenoids contain 20 carbons and are derived from four isopentenyl diphosphates, and so on, up to triterpenoids (C30) and tetraterpenoids (C40). Monoterpenoids and sesquiterpenoids are found primarily in plants, bacteria, and fungi, but the higher terpenoids occur in both plants and animals. The triterpenoid lanosterol, for example, is the precursor from which steroid hormones are made, and the tetraterpenoid /3-carotene is a dietary source of vitamin A (Figure 27.6). 

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. 

Many phytotoxic compounds produced by higher plants are phenolic compounds. Several of these have been implicated in allelopathy. Based on the biosynthetic pathway from which they are derived, phenolic compounds produced by higher plants fall into two general categories 1) terpenoid phenolic compounds derived from five... 

Classical cannabinoids (CCs) are tricyclic terpenoid derivatives bearing a benzopyran moiety. This class includes the natural product (-)-delta-nine-tetrahydrocannabinol (Fig. 8, 1) and the other pharmacologically active constituents of the plant Cannabis sativa. 

From the hair-pencils of butterflies in Danainae and Ithomiinae (Papilion-oidea Nymphalidae), a wider variety of pyrrolizines (la-d, and 6a-d) have been identified than from Arctiidae moths. These compounds are biosynthesized from pyrrolizidine alkaloids, which are included in host plants fed by the larvae and protect them from the attacks of other herbivores [122]. In addition to novel lactones (7, 8a, and 8b) derived from an acid part of the alkaloids, many volatiles of more than 100 compounds (aromatics, terpenoids, hydrocarbons, and others) constitute scent bouquets of the male butterflies [123]. For example, the hair-pencil of Idea leuconoe (Danainae) which is distributed in South-East Asia contained 16 compounds (6b, 8a, 8b, 9, and others), and a mixture of the major volatiles applied to a butterfly dummy elicited an abdomen-curling acceptance posture in the females as a crude extract of the male hair-pencils did [ 124]. A chiral GC analysis revealed the absolute config-... 

---