Activities of monoterpenes

In the pertinent literature there are only very few articles concerning the biological activities of monoterpene enantiomers. All the available results can be divided into several groups ... 

Many monoterpenes are used as a medicinal means in cases of antifungal and antibacterial infections. The expected pharmacological activity of monoterpenes depends on their structure (optical activity) and on the organisms which they affect. Our investigations concern the differences in bioactivities between the enantiomers of two monoterpenes a- pinene and limonene [78, 79]. 

Those results indicate that plant drugs containing optically active compounds should be standardised. There is also a necessity to perform investigations into the biological activity of monoterpens enantiomers. 

It is possible to distinguish the following activities of monoterpens in connection with insects ... 

The penetration-enhancing activities of monoterpenes, sesquiterpenes, and diter-penes were evaluated. Terpenes with relatively high lipophilic index exhibited absorption-promoting effects however, extremely high Upophilicity led to lower enhancing activities (Takayama et al., 1991). It was suggested that the difference in percutaneous absorption enhancing efficiency of terpenes arose from the difference in their thermodynamic activities in the vehicle (Obata et al., 1993). 

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. 

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. 

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. 

Rovirosa J, Sanchez I, Palacios Y, Darias J, San-Martin A (1990) Antimicrobial Activity of a New Monoterpene from Plocamium cartilagineum from Antarctic Peninsula. Bol Soc Chil Quint 35 131... 

Argandona V, Del Pozo T, San-Martin A, Rovirosa J (2000) Insecticidal Activity of Plocamium cartilagineum Monoterpenes. Bol Soc Chil Quim 45 371... 

Monoterpenes Some antioxidant properties aid in activity of Basil, citrus fruits, broccoli, orange and... 

As Barr et al. (2003) pointed out, the importance of such emissions is determined mainly by their impact on the three processes taking place in the atmosphere. The first consists in that such NMHCs as isoprene form in the course of carboxylization in plants and contribute much thereby to the formation of biospheric carbon cycle. The second process is connected with NMHCs exhibiting high chemical activity with respect to such main oxidants as hydroxyl radicals (OH), ozone (03), and nitrate radicals (N03). Reactions with the participation of such components result in the formation of radicals of alkylperoxides (R02), which favor efficient transformation of nitrogen monoxide (NO) into nitrogen dioxide (N02), which favors an increase of ozone concentration in the ABL. Finally, NMHC oxidation leads to the formation of such carbonyl compounds as formaldehyde (HCHO), which stimulates the processes of 03 formation. Finally, the oxidation of monoterpenes and sesquiterpenes results in the intensive formation of fine carbon aerosol with a particle diameter of <0.4 pm... 

Rovirosa, J., Sanchez, I., Palacios, Y., Darias, J., and San-Martin, A., Antimicrobial activity of a new monoterpene from Plocamium cartilagineum from Antarctic peninsula, Bol. Soc. Chil. Quim., 35, 131, 1990. 

---