Limonene biological activities

The stmctural complexity and biological activity of the cyathane family of diterpenes has stimulated considerable interest from synthetic chemists, as reflected in the number and diversity of approaches reported thus far [42]. Our own strategy for cyathane synthesis is based on a rhodium-catalyzed [5+2] cycloaddition. The precursor for this reaction was fashioned ultimately from commercially available and inexpensive (S)-(-)-limonene. Treatment of the ketone 139 with 5 mol% [RhCl(CO)2]2 in 1,2-dichloro-ethane gave cycloadduct 140 (Scheme 13.14) in 90% yield and in analytically pure form after simple filtration through a plug of neutral alumina [43]. 

Besides the synthesis of racemic dehydroiridodiol [37], some ex-chiral-pool syntheses using (S)-limonene have been described [38]. Dehydroiridodial was synthesized in the same manner [39]. Since the increasing number of cyclopentanoid natural products and their interesting biological activity has stimulated considerable interest in the synthesis of such compounds, we have used our methodology to provide a new asymmetric synthesis of dehydroiridodial, dehydroiridodiol, as well as analogues [40]. 

It was also reported that there were slight differences in the activity of enantiomers. (R)-(-i-)-Limonene and (iI)-(-t)-carvone were more biologically active than their isomers (S)-(-)-limonene and (S)-(-)-carvone [115],... 

The existence of chirality in nature is of particular importance in numerous recognition processes, often illustrated by examples detectable by non-spectroscopic methods such as the different orange and lemon odors of R-(+)- and S-(-)-limonene, respectively (Fig. 3) [8]. As such, chiral discrimination is also of considerable consequence in the medical sciences, as often one enantiomer is pharmaceutically active whereas the other may show adverse side effects. A historic example is the anti-emetic activity of one of the enantiomers of thalidomide, while the other can cause fetal damage [9,10]. These considerations highlight the importance of chiral discrimination in the production of biologically active materials, whereas on the other hand, the design of routes to asymmetric synthesis presents an active challenge to synthetic chemists worldwide. 

Citrus fruits provide a diverse range of flavonoids [35] naringenin, a flavonone, has been shown to posses cholesterol-lowering and anticancer properties [36]. The naringin content of lime juice has been estimated to be -100 pg/g [37], and the lime is also a source of limonene, a biologically active terpene (see above). Other bioactive substances in lime (Table 4) include coumarins that possess anticoagulatory and anti-inflammatory properties. 

Biological oxygen uptake of the isolates grown on (+)-limonene with potential intermediates of limonene degradation (activities in nmol 02-min -[mg protein] )... 

The EO of Elionurus elegans Kunth. (African pasture grass, Poaceae) was investigated for its biological activities. GC/MS analyses showed that the oil contains a-bisabolol (1.6% in the roots and 1.2% in the aerial parts). None of the other compounds exhibited in individual test systems antioxidative activities with the exception of limonene and, which were available only in low amounts. The antioxidant activity of the EO was tested with the chemiluminescence method using a luminometer, where the chemilnminescence intensity of the reaction mixture containing the EO or a standard (a-tocopherol), AAPH, and luminol was measured. The IC50 value for the EO obtained from the aerial parts amonnted to 30% and the 50% inhibition rate of the roots EO to 46%. 

Monoterpenes sesquiterpenes (-i-)-limonene p-caryophyllene a-humulene myrcene (—)-menthol nerolidol farnesol linalool bisabolol carvacrol thymol perillyl alcohol 1,8-cineol thujone camphor citral pulegone biological activity... 

Cold-pressed essential oils from the peel are some of the most important by-products recovered during the processing of Citrus fruits. The presence of limonene in the aqueous discharges, with its antimicrobial activity [1], decreases the effectiveness of the waste treatment system and increases the time necessary for the biological breakdown of the organic matter produced in the peel oil recovery system [2,3]. Additional recovery of essential oils from waste water would increase industry s returns and reduce the pollution problems associated with the disposal of waste water [4,5]. Several methods for reducing the levels of residual essential oils in the aqueous effluent have been developed over the years [6-11]. 

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