Terpenes toxicity

Ergosterol, the predominant sterol in yeast cells, plays an important role in membrane fluidity, permeability and the activity of many membrane-bound enzymes. In terpene-treated cells, ergosterol synthesis was strongly inhibited, and a global upregulation of genes associated with the ergosterol biosynthesis pathway was described in response to terpene toxicity [80, 121]. 

Phytoalexins are low molecular weight compounds produced in plants as a defense mechanism against microorganisms. They do, however, exhibit toxicity to humans and other animals in addition to microbes (30). Coumarins, glycoalkaloids, isocoumarins, isoflavonoids, linear furanocoumarins, stilbenes, and terpenes aU. fall into the category of phytoalexins (31). Because phytoalexins are natural components of plants, and because their concentration may increase as a response to production and management stimuli, it is useful to recogni2e the possible effects of phytoalexins in the human diet. 

Molybdenum hexacarbonyl [Mo(CO)6] has been vised in combination with TBHP for the epoxidation of terminal olefins [44]. Good yields and selectivity for the epoxide products were obtained when reactions were performed under anhydrous conditions in hydrocarbon solvents such as benzene. The inexpensive and considerably less toxic Mo02(acac)2 is a robust alternative to Mo(CO)6 [2]. A number of different substrates ranging from simple ot-olefms to more complex terpenes have been oxidized with very low catalytic loadings of this particular molybdenum complex (Scheme 6.2). The epoxidations were carried out with use of dry TBHP (-70%) in toluene. 

Essential oils are known to have detrimental effects on plants. The inhibitory components have not been identified, but both alde-hydic (benzol-, citrol-, cinnamal-aldehyde) and phenolic (thymol, carvacol, apiol, safrol) constituents are suspected. Muller et al. (104) demonstrated that volatile toxic materials localized in the leaves of Salvia leucophylla, Salvia apiana, and Arthemisia californica inhibited the root growth of cucumber and oat seedlings. They speculated that in the field, toxic substances from the leaves of these plants might be deposited in dew droplets on adjacent annual plants. In a subsequent paper, Muller and Muller (105) reported that the leaves of S. leucophylla contained several volatile terpenes, and growth inhibition was attributed to camphor and cineole. 

A considerable number of mycotoxins that show high toxicity to vertebrates and/ or invertebrates are produced by organisms associated with crop plants (Flannigan 1991). There are many known cases of human poisoning caused by such compounds. There are three broad categories of mycotoxins represented here, based on the structures of the intermediates from which these secondary metabolites are derived. They are (1) compounds derived from polyketides, (2) terpenes derived from mevalonic acid, and (3) cyclic peptides and derivatives thereof. 

Reduction of carbonyl groups Terpene and aromatic aldehydes (lOOppm) were reduced by microalgae. In a series of chlorinated benzaldehyde, m - or p-chlorobenzaldehyde reacted faster than the o-derivative. Due to toxicity, the substrate concentrations are difficult to increase. Asymmetric reductions of ketones by microalgae were reported. Thus, aliphatic " and aromatic " ketones were reduced. 

The great diversity of terpenes helps to cormteract tolerance by herbivores. In all, terpenes are not very toxic to vertebrates. Many mammals ingest a significant amount of terpenoids with their diet. Monoterpenes from pine oil added to the diet reduces food intake in red deer, Cervuselaphus, calves (Elliot and Loudon, 1987). The brush-tailed possmn, Trichosurus vulpecula, detoxifies (-l-)-a-pinene to alcohol and carboxylic acid derivatives. 

In all three studies, but particularly In the 2 dealing with resistance-susceptibility characteristics of foliage quality, specifically the higher quantities of terpenes were correlated with reduced budworm success. At any particular site all of the trees sampled contained the same basic complement of terpenes, albeit, some were present In low quantities. The effect, which we assume Is one of toxicity, of the terpenes In reducing budworm success, then, was due to an Increase In their quantitative amounts. In other words, the terpenes were acting In a quantitative or dosage dependent fashion. 

The complex Interactions of terpenes with insect growth and reproduction and with the Insects ability to metabolise potentially toxic, lipophilic foreign compounds will be discussed briefly in the following. 

Mammalian PLANT RESISTANCE TO INSECTS Table I acute toxicities of plant terpenes ... 

The biological activity and toxicity of terpenoids to herbivores has been discussed (56,84) and representatives of each major type of terpene are known to be active. Well known examples are sesquiterpene lactones, pyrethrins, and several classes of diter-penes and triterpenes. 

Rabdosia lasiocarpus (Flayata) Mao Guo Yan Ming Cao (whole plant) Terpenes, oridonin, rubescensins, 5-fluoro uracil.50 This herb is toxic. For carcinomas of esophagus and stomach, antiarthritic, antidotal, febrifuge. 

Besides thymol, other terpenes have been tested for their toxicity against Varroa jacobsoni. Imdorf et al. determined in vitro the effective miticidal air concentrations, but with minimal effects on the bees as follows 5-15 pg/litre air for thymol, 50-150 pg/litre for camphor and 20-60 pg/litre for menthol 1,8-cineole was too toxic for honey bees [86], Another interesting paper considered the efficacy of different isomers of menthol on Acarapis woodi [87]. The natural crystals obtained from the plant, synthetic crystals and the L-form gave more than 96% mite mortality, while the D-form crystals only a 37% mortality. 

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