Bicyclic monoterpene ketones

The metabolism of 7-endo-fenchol to ci-fenchone in fennel has been studied in quite some detail by Croteau and co-workers (Croteau and Felton, 1980). Croteau et al. (1980a) later reported a soluble enzyme preparation from the leaves of fennel which catalysed the cation-dependent cyclization of both geranyl pyrophosphate and neryl pyrophosphate to the bicyclic rearranged monoterpene 1-enc/o-fenchol. Croteau et al. (1980b) found that (+)-(lS)-fenchone, an irregular bicyclic monoterpene ketone thought to be derived... 

Camphor a bicyclic monoterpene ketone found widely in plants. Both optical isomers occur naturally (-t)-C. (Japan C), m.p. 180°C, b.p. 204°C, [a] -h43.8° (c = 7.5 in abs. ethanol), and (-)-C. (Matricaria C), m.p. 178.6°C, b.p. 204°C, [o]g -44.2° (ethanol). C. is obtained commercially from camphor trees (Cin-namomum camphora) native to coastal areas of East Asia. Partial synthesis from pinene is also commercially important, the product being a racemic mixture... 

Bicozamycin benzoate, registered for use in aquaculture in Japan, 3 221t Bicyclic cryptands, 14 161 Bicyclic ketones, trans-fused, 13 655 Bicyclic monoterpenes, aroma chemicals,... 

The ketone fenchone and the alcohols a-fenchol (endo) and /8-fenchol (exo) constitute the fenchane family of bicyclic monoterpenes. Fenchanes are of rather limited distribution in the plant kingdom, and interest in this group of compounds stems primarily from the fact that their carbon skeleton appears to be derived by rearrangement of a pinane-type intermediate (Fig. 5). (-l-)-Fenchone is one of the m or terpenoids of the volatile oil of fennel (Foeniculum vulgare), and soluble enzyme preparations from fennel leaves convert GPP and NPP to fenchol in the presence of Mn and, in the pres-... 

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... 

The most abundant and widely used monoterpenes, pinenes and their analogues, are often upgraded to more sophisticated structures with a Robinson annelation as the key step. However, as a result of unusual stereochemical constrains imposed by the bicyclic ring, only certain conformational isomers of the pinane skeleton undergo the annelation. Whereas the diketone (41) derived from n. v-inethylnopinone cyclized satisfactorily to the tricyclic ketone under Robinson conditions (Scheme 5.18), the epimeric diketone would not.64... 

The problems associated with lability of double bonds during the mass spectro-metric examination of monoterpenes have been discussed. The mass spectra of ketones are not as easy to interpret as those of thioketones, the latter having a higher proportion of heteroatom-containing fragments. They are readily available by reaction of the ketones either with phosphorus pentasulphide, or with hydrogen sulphide and dry hydrogen chloride, and are recommended for the study of bicyclic ketones in the norbomane series. ... 

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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