Monoterpenes activity

Terpenes, specifically monoterpenes, are naturally occurring monomers that are usually obtained as by-products of the paper and citms industries. Monoterpenes that are typically employed in hydrocarbon resins are shown in Figure 2. Optically active tf-limonene is obtained from various natural oils, particularly citms oils (81). a and P-pinenes are obtained from sulfate turpentine produced in the kraft (sulfate) pulping process. Southeastern U.S. sulfate turpentine contains approximately 60—70 wt % a-pinene and 20—25 wt % P-pinene (see Terpenoids). Dipentene, which is a complex mixture of if,/-Hmonene, a- and P-pheUandrene, a- and y-terpinene, and terpinolene, is also obtained from the processing of sulfate Hquor (82). 

In plant plastids, GGPP is formed from products of glycolysis and is eight enzymatic steps away from central glucose metabolism. The MEP pathway (reviewed in recent literature - ) operates in plastids in plants and is a preferred source (non-mevalonate) of phosphate-activated prenyl units (IPPs) for plastid iso-prenoid accumulation, such as the phytol tail of chlorophyll, the backbones of carotenoids, and the cores of monoterpenes such as menthol, hnalool, and iridoids, diterpenes such as taxadiene, and the side chains of bioactive prenylated terpenophe-nolics such as humulone, lupulone, and xanthohumol. The mevalonic pathway to IPP that operates in the cytoplasm is the source of the carbon chains in isoprenes such as the polyisoprene, rubber, and the sesquiterpenes such as caryophyllene. 

The activity of the FePeCli6-S/tert-butyl hydroperoxide (TBHP) catalytic system was studied under mild reaction conditions for the synthesis of three a,p-unsaturated ketones 2-cyclohexen-l-one, carvone and veibenone by allylic oxidation of cyclohexene, hmonene, and a-pinene, respectively. Substrate conversions were higher than 80% and ketone yields decreased in the following order cyclohexen-1-one (47%), verbenone (22%), and carvone (12%). The large amount of oxidized sites of monoterpenes, especially limonene, may be the reason for the lower ketone yield obtained with this substrate. Additional tests snggested that molecular oxygen can act as co-oxidant and alcohol oxidation is an intermediate step in ketone formation. 

Allylation of acyloyl-imidazoles and pyrazoles61 with allyl halide mediated by indium in aqueous media provides a facile regioselective synthesis of P, y-unsaturated ketones (Scheme 11.1), which has been applied to the synthesis of the monoterpene artemesia ketone. The same product can be obtained by indium-mediated allylation of acyl cyanide (Eq. 11.35).62 Samarium, gallium, and bismuth can be used as a mediator for the allylation of nitrones and hydrazones to give homoallylic hydroxylamine and hydrazides in aqueous media in the presence of Bu4NBr (Scheme 11.2).63 The reaction with gallium and bismuth can be increased dramatically under microwave activation. 

Treatment of the optically active gem-borazirconocene alkanes with deuterium oxide followed by alkaline oxidation affords the corresponding optically active 1-deuterio primary alcohols. The enantiomeric excess of the resulting primary alcohols represents the diaster-eoselectivity of the asymmetric hydrozirconation (Scheme 7.13). Based on the cost and availability of optically active ligands, three types were explored monoterpenes, 1,2-diols, and 1,2-amino alcohols. Hydrozirconation of optically pure 1-alkenyl boranes 39 provided optically active 1,1-bimetallics 40. 

A descriptor for an enzyme active site that permits binding of a family of related compounds (e.g., mimics of the reaction intermediate) that can be derived from the initial binding and conformational changes in the substrate. This concept arose from the observation that a number of monoterpene cyclases were incapable of discriminating between enantiomers of the reaction intermediate, even though the enzyme catalyzes the synthesis of an enantiomerically pure product from an achiral substrate. An example is trichodiene synthase which catalyzes the cyclization of farnesyl diphosphate to trichodiene. 

Several lines of evidence support the conclusion that allelopathic inhibition of germination and plant growth typically occurs from the joint action of several allelochemicals. Additive or synergistic effects have been shown in bioassays with combinations of monoterpenes, organic acids, and several classes of phenolic compounds. These experiments demonstrate that a specific compound may be present below its threshold for inhibition and still be active in allelopathic interference by its effect in concert with other allelochemicals. 

In the cyclopentanoid monoterpene family, compounds containing an iridoid-structure exhibit various bioactivities in Nature. For example, dehydroiridodiol, isolated from dry leaves of the cat-attracting plant Actinidia polygama Miq., is known to be an attractant for the male adults of the Chrysopidae and shows activity in amounts as small as lO"" pg [35]. Dehydroiridodial, a more oxidized product, was isolated as a pungent principle of Actinidia polygama Miq. and was characterized by T. Sakan et al. in 1978 [36]. 

An entirely different, in fact opposite, effect on insect reproduction by terpenes occurs with the desert locust. In this case the monoterpenes a-pinene, -pinene, llmonene, and euge-nol evaporating from desert shrubs about to bloom, precipitates synchronised sexual maturation and mating activity in the locusts (14). The spruce budworm is also stimulated to increased fertility levels by host tree monoterpenes (R.G. Cates, personal communication). It is possible that even opposite effects on reproduction in insects could occur depending on the specialisation of the insect species to its environment, the diversity of the biological activities of the compounds, and the high level of complexity of the reproductive processes. 

For Instance, many terpene derivatives mimic insect hormone actioa Juvabione (15) is the classical example of a juvenile hormone (JH) mimic that prevents egg maturation in Pyrrhocoris bugs. Aromatic terpene ethers (16), methylene dloxyphenyl terpene ethers (17), and other farnesyl derivatives also have JH activity and the latter ones (18) also cause sterility in Pyrrhocoris. For the most part JH active terpenes are among the sesquiterpenes but several monoterpenes also have insect sterilizing effects (19. 20). The acyclic monoterpene cltral reduces the fertility of rats by causing follicular degeneration (21). 

The cases where terpene metabolism has been studied In Insects are very few Indeed. Certain Ips and Dendroctonus bark beetles convert monoterpenes such as a-plnene, 6-plnene and myr-cene to oxidation products, some of which have pheromonal activities ( 5, 3A, 35). A Dendroc tonus bark beetle s cytochrome... 

Some volatile iridoid monoterpenes with biological activity are also found in essential oils and in insect pheromonal and defensive substances. Eisner ( ) found that 17 species of insects were repelled by the iridoid monoterpene nepetalactone. Lacewings (Chrysopa septempunctata) are attracted by the leaves and fruits of Actinidia polyqama (Actinidiaceae) which contain a series of volatile iridoid monoterpenes (67). 

Several non-volatile iridoid monoterpenes occur as glycosides and have been observed to have biological activity. For example, xylomolin, from the unripe fruits of Xylocarpus moluccensis Roem. (Meliaceae) has antifeedant activity against Spodoptera exempta an African armyworm at 100 ppm ( ) and crotepoxide from Croton macrostachys (Euphorbiaceae) possesses antifeedant activity against Spodoptera exempta (85). 

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