Monoterpene alcohols

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). 

Evidence for de novo synthesis of pheromone components was obtained by showing that labeled acetate and mevalonate were incorporated into ipsdienol by male Ips pini [103,104]. Similarly, labeled acetate and other labeled intermediates were shown to be incorporated into frontalin in a number of Dendroctonus species [105]. Possible precursors to frontalin include 6-methyl-6-hep-ten-2-one, which was incorporated into frontalin by D. ruffipennis [106]. The precursor 6-methyl-6-hepten-2-one also was shown to be converted to bre-vicomin in the bark beetle, Dendroctonus ponderosae [107]. In addition, the expression patterns of HMG-CoA reductase and HMG-CoA synthase are tightly correlated with frontalin production in Dendroctonus jeffreyi [108, 109]. A geranyl diphosphate synthase cDNA from I. pini was also isolated, functionally expressed, and modeled [110]. These data indicate that the de novo isoprenoid biosynthetic pathway is present in bark beetles. A variety of other monoterpene alcohols such as myrcenol, pityol, and sulcitol are probably synthesized through similar pathways [111]... 

Naturally occurring monoterpene alcohols were heated in water without prior deriva-tization with typical biological water-solubilizing groups such as phosphates or glyco-sidic units. Biomimetic reactions that normally would be acid-catalyzed, proceeded on the underivatized compounds in the absence of added acidulant. Cooling of the mixtures rendered the products insoluble, readily isolable and the aqueous phase did not require neutralization before workup. 

Licht HJ, Coscia CJ. Cytochrome P-450LM2 mediated hydroxylation of monoterpene alcohols. Biochemistry 1978 17(26) 5638-5646. 

Many oxygenated monoterpenes (alcohols, carbonyl compounds, esters) serve as fragrances. Here inexpensive natural starting compounds are a-pinene (4), /1-pinene (5) and limonene (6), with production volumes of about 18000, 12 000, and 30000 t a-1, respectively. 

In order to obtain lactones from natural alkenols, we investigated the cyclocarbonylation of monoterpenic alcohols. The catalytic precursor is [PdCl2L2] in the presence of a slight excess of tin chloride and phosphine ligands. Dihydromyrcenol, a representative acyclic terpene containing a termi-... 

While earlier it was generally thought that the acyclic monoterpene alcohols 242-245 are derived from the host tree s oleoresin component, myreene [453], more recent results clearly show that at least in some species they are produced denovo [454-456]. 

Figure 11.2 Oxidation of the monoterpene alcohol geraniol to geranial by CPO in the presence of hydrogen peroxide and absence of halide ions.

Bezzubov and M. A. Bokuchava. Beta-D glucosides of monoterpene alcohols in tea shoots. Soobshch Akad Nauk Gruz SSR 1988 131(2) 397-400. CS124... 

Although cyclic terpene alcohols occur widely in nature, few have the physiological properties that make them important fragrance or flavor materials. Exceptions are a-terpineol and (—)-menthol, the latter because of its cooling/refreshing effect. Of the bicyclic monoterpene alcohols, bomeol deserves mention. 

Other important members of this class include oxygenated derivatives such as a-terpineol 32, menthol 33, isopulegol 34 and ds-hexahydrocuminyl alcohol 35, also classified as monoterpene alcohols. 

Experiments were also carried out at 80 and lOO C. According to our observations at these high temperatures, solid- phase chemical transformations may take place between certain flavor constituents and cyclodextrin hydroxyls/monoterpene alcohols and phenolic compounds appear as a result of a solid-phase transacetylation of terpeneaoetates and phenyl-acetates with the simultaneous formation of cyclodextrin-acetates/. Long term heat treatments of cyclpdextrin-flavor complexes should not be run above 6o°C in order to avoid such phenomena. 

In the eighties, the bioconversion of monoterpene alcohols by fungi had not been studied intensively [32]. However, a strain of Aspergillus niger was isolated from garden soil, able to transform geraniol, citronellol and linalool to their respective 8-hydroxy derivatives. This reaction was called fu-hydroxylation [39,40]. 

As mentioned before, a Pseudomonas incognita was isolated by enrichment technique on the monoterpene alcohol linalool that was also able to grow on geraniol, nerol and limonene [36]. The metabolism of limonene by this bacterium was also investigated [37]. After fermentation the medium yielded as main product a crystallic acid, perillic acid, together with unmetabolised limonene, and some oxygenated compounds dihydrocarvone, carvone, carveol, p-menth-8-en-1 -ol-2-one, p-menth-8-ene-1,2-diol or p-menth-1 -ene-6,9-diol (structure not fully elucidated) and finally / -isopropenyl pimelic acid. 

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