Monocyclic monoterpene ketone

Figure 3.9 Ketones. /-Carvone (C10H140), a monocyclic monoterpene ketone. Courtesy Spiring Enterprises Ltd.

Monocyclic monoterpene ketone monooxygenase Rhodococcus erythropolis DCL 14 1 single polypeptide NADPH 60 FAD 9.0 [51]... 

The two ethyl-homologous carbonyl compounds (286) and (289) have so far only been found in tea oil (49J). The possibility that 5-ethyl-6-methylheptan-2-one (286) originates from the metabolism of a monocyclic monoterpene cannot be excluded (49J), although this ketone seems more likely to be formed by oxidative biodegradation of the sitosterol side chain. Thus, for instance, all the aroma compounds (282) to (291) listed here except (286) and (289) were detected in tobacco oil (777, J42, 306, 463, 590). 

Monoterpenic ketones are frequently very important aromatic substances of many food raw materials, spices and medicinal herbs. Monocyclic ketone (-F)-carvone (8-50) is a key component of caraway and diU oils, where it is accompanied by (-F)-( )-dihydrocarvone, that is (lS,4S)-dihydrocarvone (8-50) that also possesses caraway odour. (-)-Carvone (8-50) is a typical component of spearmint essential oil, where it is accompanied by (-)-( )-dihydrocarvone, (lE,4E)-dihydrocarvone, which has the same odour (see Table 8.32). Isomeric ( )-menthone (8-50) and its precursor (-F)-pulegone (8-50) occur in the essential oils of the European pennyroyal Menthaptdegium, Lamiaceae), a traditional culinary herb and folk remedy, and other Mentha species (such as M. longifolia), as well as in marjoram essential oil. In the essential oil of mint, (-)-menthone is accompanied by (-F)-isomenthone (8-50) and other terpenoids. 

The gaschromatographical analysis of the volatile compounds in comparison with the volatile pattern synthesized by whole daffodil flowers (Fig. 1) revealed that the compounds formed in vitro were monoterpene hydrocarbons plus linalool, mainproducts being myrcene (36.4 o), ocimene (18 o) and linalool (22 9 o). Moreover the bicyclic a-pinene (2.8 0 and the monocyclic limonene (l o) were formed. The low portion in cyclic monoterpenes is in good agreement with the natural pattern. Monoterpene ketones as well as sesquiterpenes which both occur in the natural pattern, were not obtained in chromoplast stroma incubations. On the other hand, linalool was not present in the in vivo pattern. 

The monoterpenes are subdivided into three groups acyclic, monocyclic and bicyclic (there is only one tricyclic terpene tricyclene). Each group contains hydrocarbon terpenes, terpene alcohols, terpene aldehydes, ketones, oxides etc... 

Monoterpenes (Cio) are the simplest members of the terpene series. They result from the condensation of two isoprene units and may be acyclic, monocyclic, bicyclic or tricyclic. The monoterpenes can have another functional moiety like alcohol (geraniol, linalool, menthol, bomeol), aldehyde (geranial, cihonellal), ketone (menthone, carvone, thujone), ester (bomyl acetate, linalyl acetate), ether (1,8-cineol) and phenol (thymol, carvacol). In the case of optically active molecules, the proportions of the enantiomers vary largely from one species to another. 

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