Terpenoids sesquiterpene

Pollen allelopathy is phenomenon when pollen chemicals (e.g., phenols, terpenoids, sesquiterpene lactones, etc.) inhibit sexual reproduction in heterospecific individuals due to influencing of fertilization (Murphy 1992). The phenomenon includes excretion of signaling compounds from the donor cell (pollens, pistil stigma), recognition of a specific signal, transmission of information (pollen), and the development of a characteristic response in the acceptor cell. The possible mechanism of the effect was described in Roshchina (2001). 

There are various chemical components present in plant-origin antimicrobials including, saponin and flavonoids, thiosulflnates and glucosinulates. EOs may contain different components including terpenoids, sesquiterpenes and possibly diter-penes with different groups of aliphatic hydrocarbons, acids, alcohols, aldehydes, acyclic esters or lactones. 

Pseudopterogorgia rigida Terpenoid (sesquiterpenes) Crude extract, curcuquinone, curcuhydroquinone m Deterred the fish Thalassoma bifasciatum [55]... 

Terpenes (and terpenoids) are further classified according to the number of 5-carbon units they contain. Thus, monoterpenes are 10-carbon substances biosynthesized from two isoprene units, sesquiterpenes are 15-carbon molecules from three isoprene units, diterpenes are 20-carbon substances from four isoprene units, and so on. Monoterpenes and sesquiterpenes are found primarily in plants, but the higher terpenoids occur in both plants and animals, and many have important biological roles. The triterpenoid lanosterol, for example, is the precursor from which all steroid hormones are made. 

From a chemical point of view, vegetable resins are a complex mixture of mono-, sesqui-, di- and triterpenes, which have, respectively, 10, 15, 20 and 30 carbon atoms per molecule. The mono- and sesquiterpenes are both present in most resins. The di- and triterpenes are rarely found together in the same resin, which means that terpenic resins can be divided into two main classes. Table 1.5 lists the botanical origin and the kind of terpenoid compounds of some natural resins. 

Experiment 2. Effects of terpenoid allelochemicals on pollen germination The effects of the terpenoids found in many allelopathically active plants are dependent on the concentration of the active matter (Fig. 4). Linalool, cymol, citral, gaillardine and austricine excreted by many flowers, stimulated the pollen germination upto 10 7-1()" M concentrations and depress in higher ones. Rodriguez et.al (1976) described the biological effects of some sesquiterpene lactones, which are allelochemicals. 

Other phenolic compounds of commercial importance include the terpenoids, including mono, di, tri, and sesquiterpenes. While most of these are used as essential oils, fragrances, and flavors in various products, they are toxins in certain species. For example the sesquiterpene lactones of the Centaurea species cause an irreversible Parkinson s-like condition in horses called nigro-pallidal encephalomalacia. This is a lethal condition and the prognosis for recovery is grave in most cases, affected horses should be euthanized before reaching the terminal stages. 

FIGURE 11.5 Terpenoids, (a) The basic five-carbon units isopentane and isoprene. (b) The monoterpenes borneol and a-pinene. (c) A monoterpene lactone, nepetalactone. (d) A sesquiterpene, germacrone. (e) A triterpene, papyriferic acid, from paper birch. 

Mabry, T. J. and Gill, J. E. (1979). Sesquiterpene lactones and other terpenoids. In Herbivores Their Interaction with Secondary Plant Metabolites, ed. G. A. Rosenthal and D. H. Janzen, pp. 501-537. New York Academic Press. 

A terpenoid, (—j-fl-caryophyllene, was identified as a gender specific sesquiterpene produced by the female multicolored Asian lady beetle, Har-monia axyridis Pallas (Coleoptera Coccinellidae). ... 

Among the acyclic terpene aldehydes, citral and citronellal hold key positions as fragrance and flavor chemicals, as well as starting materials for the synthesis of other terpenoids. Hydroxydihydrocitronellal is one of the most important fragrance materials. Derivatives of these aldehydes, particularly the lower acetals, are also used as fragrance materials. Acyclic sesquiterpene aldehydes are not very important as such, but they contribute to the characteristic fragrance and aroma of essential oils, for example, in the case of a- and /3-sinensal in sweet orange oil. 

The oils have a high terpene hydrocarbon content (>90%, mainly (+)-limonene), but their content of oxygen-containing compounds differs and affects their quality. Important for aroma are aldehydes, mainly decanal and citral, and aliphatic and terpenoid esters. The sesquiterpene aldehydes a-sinensal [17909-77-2] and/3-sinensal [6066-88-8], which contribute particularly to the special sweet orange aroma, also occur in other citrus oils, although in lower concentration [369-370a, 370d, 394,421, 430-438]. 

Terpenoids are a diverse group of conqiounds showing a wide spectrum of biological activities. Among the most biologically active terpenoids are the sesquiterpene lactones. Their biological activity has been reviewed (56, 57, 58). 

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. 

Essential oils may comprise volatile compounds of terpenoid or non-terpe-noid origin. All of them are hydrocarbons and their oxygenated derivatives. Some may also contain nitrogen or sulphur derivatives. They may exist in the form of alcohols, acids, esters, epoxides, aldehydes, ketones, amines, sulphides, etc. Monoterpenes, sesquiterpenes and even diterpenes constitute the composition of many essential oils. In addition, phenylpropanoids, fatty acids and their esters, or their decomposition products are also encountered as volatiles [1-16, 21-33, 36-38]. 

Sesquiterpenes are formed by the addition of one more isoprene units to a monoterpene molecule, and thus have the molecular formula C15H24 (see also Fig. 4.2). There are linear, branched or cyclic sesquiterpenes. Sesquiterpenes are unsaturated compounds. Cyclic sesquiterpenes may be monocyclic, bicyclic or tricyclic. They are the most diverse group among the volatile terpenoids [2, 3, 7-11, 13,14, 16, 20-24, 37-39, 49]. The DNP treats sesquiterpenoids in 147 different structural types [37]. Various types of sesquiterpenes (69-109) can also be seen in Structure 4.16. 

The root of carrot Daucus carota) is eaten raw or cooked. The characteristic aroma and flavour of carrots are mainly due to volatile compounds, although non-volatile polyacetylenes and isocoumarins contribute significantly to the bitterness of carrots [1,2]. More than 90 volatile compounds have been identified from carrots (Table 7.9) [207-215]. The carrot volatiles consist mainly of terpenoids in terms of numbers and amounts and include monoterpenes, sesquiterpenes and irregular terpenes. Monoterpenes and sesquiterpenes account... 

One year later, Schalk [89] described a process for cloning sesquiterpene synthases from patchouli plants Pogostemon cablin) and the enzyme-catalysed terpenoid production. Various sesquiterpenes can be obtained by this method, for instance patchoulol and other germacrene-type sesquiterpenes. 

Terpenoids are synthesised by the condensation of a series of isoprene (2-meth-ylbuta-1,3-diene) units, followed by enzymatic cyclisation by a terpene cyclase, and subsequent modification such as hydroxylation, and are grouped on the basis of their carbon chain length. Monoterpenes and sesquiterpenes consisting of ten and 15 carbon atoms, respectively, are ranked among the most important aroma compounds. Despite their diversity, all terpenoids are synthesised... 

Much attention has been paid to the last step of the formation of monoter-penes and sesquiterpenes, which is catalysed by terpenoid synthases. Over 30 complementary DNAs (cDNAs) encoding plant terpenoid synthases involved in the primary and secondary metabolism have been cloned, characterised, and the proteins heterologously expressed [6]. However, because geranyl diphosphate and farnesyl diphosphate are not readily available substrates, their biotransformation by terpenoid synthases is not economically viable. As a result, considerable effort has been put into engineering the total plant terpenoid biosynthetic pathway in recombinant microorganisms. 

Sesquiterpenes, 15-carbon-containing terpenoids, are composed of three isoprene units, and found abundantly in plants, e.g. artemisinin from... 

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