Nootkatone production from valencene

Recently, an industrial process development for nootkatone production from valencene by microbial transformation (bacteria, fungi) was mentioned [199, 200]. Although no details were given, the author claimed the development of an in situ product-removal technique by which an extremely selective recovery of nootkatone from the reaction mixture and the excess precursor during the proceeding production was achieved and which was said to be essential for an economically viable bioprocess. 

Highly Ef cient Production of Nootkatone (2) from Valencene (1).908... 

Although Mucor species produced a large amount of nootkatone (2) from valencene (1), however, only poor yield of similar products as those from valencene (1) was seen in the biotransformation of tricyclic substrate (36). Possible biogenetic pathway of (+) 1(10)-aristolene (36) is shown in Figure 20.20. 

Franssen et al. [24] pointed out an alternative method of production of nootkatone from valencene catalysed by (-i-)-germacrene A hydroxylase, an enzyme of the cytochrome P450 monooxygenase type that was isolated from chicory roots. In general, this enzyme appeared to accept a broad range of sesquiterpenes and hydroxylates exclusively at the side-chain s isopropenyl group. Valencene is an exception it was not hydroxylated at the side chain, but -nootkatol was formed in the first step (Scheme 22.5) it is not yet clear if the second step is enzyme-catalysed. 

Scheme 22.5 Production of nootkatone from valencene catalysed by (+)-germacrene A hydroxylase [81]...

For the synthesis of flavour-active compounds numerous methodologies have been developed [17], In many cases natural products served as starting materials such as eugenol from clove oil for the synthesis of vanillin. In case of complex stereochemistry natural materials are still welcome for the synthesis of valuable flavour compounds such as nootkatone, which is obtained by oxidation from valencene. 

Furusawa, M., T, Hashimoto, Y. Noma, and Y. Asakawa 2005b. Highly ef cient production of nootkatone, the grapefruit aroma from valencene, by biotransformation. 53 1513-1514. 

Fumsawa M, Hashimoto T, Noma Y, Asakawa Y. Highly efficient production of nootkatone, the grapefruit aroma, from valencene hy hiotransformation. Chem. Pharm. Bull 2005 53 1513-1514. 

The same rational P450cam mutants which have already been described for limonene and pinene oxyfunctionalisations were also successfully applied to valencene. In whole-cell biotransformations -nootkatol and nootkatone formed as main products with up to 25% overall yield, corresponding to activities of up to 9.9 nmol (nmol P450) min [201]. Higher activities (up to 43 min ) but lower selectivities than those with P450cam were obtained with mutants derived from Bacillus megaterium P450 BM3. 

Two bacterial strains, one from soil and the other from infected local beer, which utilised calarene as the sole source of carbon and energy have been isolated by enrichment culture techniques [149]. Both these bacteria were adapted to grow on valencene as the sole carbon source. Fermentations of valencene (5) by these bacteria of the genus Enterobacter in a mineral salts medium yielded several neutral metabolic products dihydro alpha-agarofuran (200) (7.5%), nootkatone (6) (12%), another ketone (201) (18%) and a-cyperone (202) (8%), Fig. (40). 

The expensive grapefruit aromatic nootkatone (2) used by cosmetic and ber manufacturers was obtained in high yield by biotransformation of (+)-valencene (1), which can be cheaply obtained from Valencia orange, by Chlorella species, fungi such as Mucor species, B. dothidea, and B. theobromae. This is a very inexpensive and clean oxidation reaction, which does not use any heavy metals, and thus, this method is expected to nd applications in the industrial production of nootkatone. 

The extraction of natural nootkatone from citrus oil and peel is too expensive, because the process is characterized by low yields and high biomass production, and it suffers from annual harvest fluctuations. The chemical oxidation of the sesquiterpene valencene extracted from orange peels often results in off-notes, and it has the disadvantage of employing heavy-metal salts as strong oxidants thus the final product cannot be labeled as natural. Therefore, biotechnological routes have been extensively studied in the last decade to find an economical and sustainable synthetic procedure to natural nootkatone. Most of them make use... 

Microbial cell factories [194] have recently been developed for the production of terpenoids such as sclareol [195], and, as was shown in the previous section, valencene and nootkatone. The genes responsible for the biosynthesis of the desired compound, such as prenyltransferases, terpene synthases, and additional transformation enzymes, are selected from a natural source and transferred into a host, usually S. cerevisiae or . coli, suitably engineered to overproduce IPP and DMAPP. High productivity values for a commercially exploitable production are achieved by further metabolic and bioprocess engineering improvements of the microbial system. 

---