Nootkatone biotransformation

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. 

Asakawa, Y., T. Ishida, M. Toyota, and T. Takemoto, 1986. Terpenoid biotransformation in mammals. IV. Biotransformation of (+)-longifolene, (-)-caryophyllene, (-)-caryophyllene oxide, (-)-cyclocolorenone, (+)-nootkatone, (-) -elemol, (-)-abietic acid and (+)-dehydroabietic acid in rabbits. Xenobiotica, 16 753-767. 

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 biotransformation from 1 to 2 was also examined using the plant pathogenic fungi B. dothidea and B. theobromae (a total of 31 strains) separated from fungi infecting various types of fruit, and so on. B. dothidea and B. theobromae were both inoculated and cultivated while stationary in Czapek-peptone medium (pH 7.0) at 30°C for 7 days. The same size of the substrate 1 was added to each medium and incubated for a further 7 days to obtain nootkatone (42%-84%) (Furusawa et al., 2005a). 

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. 

Epoxide (14) obtained by epoxidation of nootkatone (2) with meta-chloroperbenzoic acid (mCPBA) was biotransformed by A. niger for 1 day to afford 6 and 7 (11/ 115 = 1 1) in good... 

Biotransformation of Nootkatone (2) by Fusarium culmorum AND Botryosphaeria dothidea... 

The biotransformation of nootkatone (2) was examined by the plant pathogenic fungus B. dothidea separated from the fungus that infected the peach. (+)-Nootkatone (2) was cultivated with B. dothidea (Peach PP8402) for 14 days to afford nootkatone diols (6 and 7) (54.2%) and 7a-hydroxynootkatone (16) (20.9%). Ratio of compounds 6 and 7 was determined as 3 2 by HPLC analysis of the thiocarbonates (12,13) (Noma et al., 2001b). Nootkatone (2) was administered into rabbits to give the same diols (6,7) (Asakawa et al., 1986 Ishida, 2005). 

The biotransformation of 2 by A. niger and B. dothidea resembled to that of the oral administration to rabbit since the ratio of the major metabolites 115- (6) and ll/ -nootkatone 11,12 diol (y) was similar. It is noteworthy that the biotransformation of 2 by F. culmorum affords stereospeci cally nootkatone-ll/f,12-diol (7) (Noma et al 2001b) (Figure 20.10). 

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

Takahashi, T. and M. Miyazawa, 2005. Biotransformation of (+)-nootkatone hy Aspergillus wentii, as biocatalyst. Proceedings of 49th TEAC, pp. 393-394. 

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

Epicoccum purpurascens also biotransformed nootkatone (2) to 5-7,14, and 15a (Takahashi and Miyazawa, 2006). 

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%). 

The grapefruit aroma, (-H)-nootkatone (2) was administered into rabbits to give 11,12-diol (6,7). The same metabolism has been found in that of biotransformation of nootkatone by miCTOorganisms as mentioned in the previous paragraph. Compounds (6, 7) were isolated from the urine of hypertensive subjects and named urodiolenone. The endogenous production of 6, 7 seem to occur inter-dentally from the administrative manner of nootkatone or grapefruit. Synthetic racemic nootkatone epoxide (14) was incubated with rabbit-liver microsomes to give 11,12-diol (6, 7) (Ishida, 2005). Thus, the role of the epoxide was clearly confirmed as an intermediate of nootkatone (2). 

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