Valencene biotransformations

Scheme 23.12 Biotransformation of (+)-valencene to (+)-nootkatone via a-nootkatol and/or fi-nootkatol...

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. 

Valencene, another olefinic sesquiterpene, has been studied in the same context using microorganisms isolated from soil1 741. It was observed that these biotransformations led in reasonable yields to a mixture of three main metabolites, including an epoxide and nootkatone, an interesting flavoring compound. 

Biotransformation of Valencene (1) by Aspergillus niger and Aspergillus wentii.910... 

In the time course of the biotransformation of 1 by C. pyrenoidosa, the yield of nootkatone (2) and nootkatol (4) without 2a-hydroxy valencene (3) increased with the decrease in that of 1, and sub sequently, the yield of 2 increased with decrease in that of 3. In the metabolic pathway of valencene... 

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. 

FIGURE 20.9 Possible pathway of biotransformation of valencene (1) by cytochrome P 450. 

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. 

Furusawa, M, T. Hashimoto, Y. Noma, andY. Asakawa, 2005a. Biotransformation of Citrus aromatics nootka-tone and valencene by microorganisms. 53 1423-1429. 

Hashimoto, T., Y. Noma, C. Murakami, N, Nishimatsu, M. Tanaka, and Y. Asakawa, 2001b, Biotransformation of valencene and aristolene. Proceedings of 45th TEAC, pp. 345 347. 

FIGURE 15.7 Biotransformation of valencene (1) and nootkatone (2) by Aspergillus wentii, Epicoccum purpurascens, and Chaetomium globosum. 

Although Mucor species could give nootkatone (21) from valencene (1), this fungus biotransformed the same substrate (25) to the same alcohol (30, 13.2%) obtained from the same starting compound (25) in Aspergillus sojae, a new epoxide (34, 5.1%) and a diol (35,9.9%). 

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