Metabolic reactions, essential oils

Sclareol, a natural product first isolated from the essential oil of Salvia sclarea L. (Labiatae) in 1931, is used for diverse applications in the perfumery and flavoring industries and in folk medicine. This diterpene has been described recently to be hydroxylated by three strains, i.e. Cunninghamella sp., Septomyxa affinis 66 and Mucor plumbeus 67, 68, leading essentially to hydroxylation reactions on the A ring of this compound (Fig. 16.1-12). Some of these metabolites could be used for further synthesis of some biologically active targets or as mammalian metabolism models. 

However, the distribution of the individual compounds is restricted. This was first pointed out by Sachs (1882) and Pfeffer (1897), who demonstrated the lack of phylogenetic continuity of secondary substances such as oxalate, resins, and essential oils in the plant kingdom. Usually the more chemical reactions necessary for the synthesis of a given secondary product, the more restricted is its distribution. The alkaloid, nicotine, which is formed by a relatively simple biosynthetic pathway (D 16.2) occurs in many different plant species, whereas the much more complicated alkaloid brucine (D 21.3), is synthesized by only one genus of the Loganiaceae. In other words, the probabiUty that a given metabolic pathway... 

Camphor, a bicyclic monoterpene, is extracted from the woods of Cinnamomum camphora, a tree located in Southeast Asia and North America. Furthermore, it is also one of the major constituents of the essential oil of common sage (Salvia officinalis). Solid camphor forms white, fatty crystals with intensive camphoraceous odor and is used commercially as a moth repellent and preservative in pharmaceuticals and cosmetics (Wichtel, 2002). In dogs, rabbits, and rats, camphor is extensively metabolized whereas the major hydroxylation products of d- and L-camphor were 5-endo-md 5-ex -hydroxycamphor. A small amount was also identified as 3-e do-hydroxycamphor (Figure 8.2). Both 3- and 5-bornane groups can be further reduced to 2,5-bornanedione. Minor biotransformation steps also involve the reduction of camphor to borneol and isoborneol. Interestingly, all hydroxy-lated camphor metabolites are further conjugated in a Phase II reaction with glucuronic acid... 

A significant example of hydroxylation reactions of cyclic terpenic compounds is illustrated by the microbial metabolism of sclareol. Sclareol 14, a labdane diterpene, can be easily isolated from the essential oil of Salvia sclarea L. (Labiatae) (clary sage oil) or... 

---