Enantiomeric monoterpene

Cyclases responsible for the formation of (+)-a-pinene and (+)-llmonene, monoterpenes which inhibit fungal growth and repel bark beetles, have been studied in herbaceous species. Two distinct types of enzymes synthesize antipodal monoterpene hydrocarbons. The differential expression of the cyclases responsible for co-productlon of enantiomeric monoterpenes may determine the highly selective resistance response conifers exhibit toward bark beetles and their fungal symbionts. 

Yassaa, N. Williams, J. Analysis of enantiomeric and non-enantiomeric monoterpenes in plant emissions using portable dynamic air sampling/solid-phase microextraction (PDAS-SPME) and chiral gas chroma-tography/mass spectrometry. Atm. Environ. 2005, 39, 4875 884. 

Mondello et al. (2, 20-23) have used a multidimensional gas chromatographic system based on the use of mechanical valves which were stable at high temperatures developed in their laboratory for the determination of the enantiomeric distribution of monoterpene hydrocarbons (/3-pinene, sabinene and limonene) and monoterpene alcohols (linalol, terpinen-4-ol and a-terpineol) of citrus oils (lemon, mandarin, lime and bergamot). Linalyl acetate was also studied in bergamot oil. The system consisted of two Shimadzu Model 17 gas chromatographs, a six-port two-position valve and a hot transfer line. The system made it possible to carry out fully... 

Figure 10.3 Gas cliromatograms of a cold-pressed lemon oil obtained (a) with an SE-52 column in the stand-by position and (b) with the same column showing the five heart-cuts (c) shows the GC-GC chiral chromatogram of the ti ansfeired components. The asterisks in (b) indicate electric spikes coming from the valve switcliing. The conditions were as follows SE-52 pre-column, 30 m, 0.32 mm i.d., 0.40 - 0.45 p.m film tliickness cairier gas He, 90 KPa (stand-by position) and 170 KPa (cut position) oven temperature, 45 °C (6 min)-240 °C at 2 °C/min diethyl-tert-butyl-/3-cyclodextrin column, 25 m X 0.25 mm i.d., 0.25 p.m film thickness cairier gas He, 110 KPa (stand-by position) and 5 KPa (cut position) oven temperature, 45 °C (6 min), rising to 90 °C (10 min) at 2 °C/min, and then to 230 °C at 2 °C/min. Reprinted from Journal of High Resolution Chromatography, 22, L. Mondello et al, Multidimensional capillary GC-GC for the analysis of real complex samples. Part IV. Enantiomeric distribution of monoterpene hydrocarbons and monoterpene alcohols of lemon oils , pp. 350-356, 1999, with permission from Wiley-VCH.

Mondello et al. (54) have developed some applications of on-line HPLC-HRGC and HPLC-HRGC/MS in the analysis of citrus essential oils. In particular, they used LC-GC to determine the enantiomeric ratios of monoterpene alcohols in lemon, mandarin, bitter orange and sweet orange oils. LC-GC/MS was used to study the composition of the most common citrus peel, citrus leaf (petitgrain) and flower (neroli) oils. The oils were separated into two fractions, i.e. mono- and sesquiterpene... 

L. Mondello, M. Catalfamo, R Dugo and G. Dugo, Multidimensional capillary GC-GC for the analysis of real complex samples. Part II. Enantiomeric distr ibution of monoter-pene hydrocarbons and monoterpene alcohols of cold-pressed and distilled lime oils , 7. Microcolumn Sep. 10 203-212 (1998). 

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. 

None of the monoterpene pheromones of bark beetles is represented by a specific compound per se however, species specificity of the signal is accomplished by qualitatively and quantitatively fine-tuned mixtures including enantiomeric proportions. 

ENANTIOMERIC DISTRIBUTION OF ODOROUS OXYGENATED MONOTERPENES IN AROMATIC PLANTS... 

Enantiomeric Distribution of Odorous Oxygenated Monoterpenes in Aromatic Plants... 

CHIRAL- GC DETERMINATION OF ENANTIOMERIC COMPOSITION OF OXYGENATED MONOTERPENES... 

Ravid U, Enantiomeric distribution of oxygenated monoterpenes in some Mentha essential oils, Perfum Flavor 23(4) 25-30, 1998. 

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. 

Metabolic transformations are characterized by high speed and yield, as well as high regio-, diastereo-and enantio-specificity. Errors in the stereochemistry of the molecules that serve to construct the genetic material are smaller than for the planetary motions. With secondary metabolites, however, enantiomerically inq)ure con unds are also encoimtered, typkally with monoterpenes and alkaloids from terrestrial plants even ant dal pathways in the same organism have been found, albeit as rare events (Guella 1998). 

Other cyclic A-acylurethanes derived from enantiomerically pure monoterpenes are useful in diastereoselective enolate alkylations95-97. Thus, enolates from the tricyclic A-acyloxazolidi-nones 20 and 21 give alkylation products with benzyl or allyl bromide with high diastereoselec-tivities 2095 [yield 60 and 80%, respectively d.r. >99 1 (2 S)] and 2196 [only with benzyl bromide yield 74% d.r. >91 9 (2 / )]. The camphor-derived A-acyloxazinone 22 shows excellent diastereoselectivity [R = Bn alkylating agent CH3I yield 81 % d.r. 99.7 0.3 (2 / )]97. 

Limonene is a monoterpene that occurs in citrus fruits. Two enantiomers of limonene produce two distinct flavours (—)-limonene is responsible for the flavour of lemons and (+)-limonene for orange. Similarly, one enantiomeric form of carvone is the cause of caraway flavour, while the other enantiomer has the essence of spearmint. 

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