Terpenoids microbial hydroxylation

Over the past 20 years, research has uncovered many microbial transformations of the terpenoids. Terpenes are important constituents of flavors and fragrances, and can be the center of a wide variety of microbial hydroxylations, oxidations, reductions, degradation and rearrangement reactions. See Ciegler(58),... 

R Azerad, Regio- and stereoselective microbial hydroxylation of terpenoid compounds, in Stereoselective Biocatalysis, R N Patel (ed), 2000, Marcel Dekker New York. p. 152-180. 

The hydroxylation of nonactivated centers in hydrocarbons is one of the most useful biotransformations [1040,1074—1079] due to the fact that this process has only very few counterparts in traditional organic synthesis [1080-1082]. In general, the relative reactivity of carbon atoms in bio-hydroxylation reactions declines in the order of secondary > tertiary > primary [1083], which is in contrast to radical reactions (tertiary > secondary > primary) [1084]. There are two main groups of hydrocarbon molecules, which have been thoroughly investigated with respect to microbial hydroxylation, i.e., steroids and terpenoids. Both have in common, that they possess a large main framework, which impedes the metabolic degradation of their hydroxylated products. 

Regio- and Stereoselective Microbial Hydroxylation of Terpenoid Compounds... 

There have been a number of previous reviews on microbial oxidations of teipenes. Monoter-penes are often degraded progressively after an initial hydroxylation step, but di-, tri- and sesqui-tetpenes can be converted more selectively, to accumulate useful quantities of hydroxyla products. Less systematic work on the microbial oxidation of terpenoids has l n carried out than in the case of steroids, and therefore prediction of the regio- and stereo-chemistry is scarcely possible. 

Acyclic triteipenes can be considoed as aliphatic hydrocarbons and are a-hydroxylated by a number of microorganisms. The microbial oxidation of a variety of acyclic terpenoid hydrocarbons has been investigated by Nakajima, and although terminal alcohols can be obtained, for example pristanol (39) from pristane (38 equation 11), further oxidation can also occur. 

The biotransformation of spirostructural terpenoids was not carried out. cnt-la-Hydroxy P-chamigrene (367) was inoculated in the same manner as described earlier to give three new metabolites (368-370), of which 370 was the major product (46.2% in isolated yield). The hydroxylation of vinyl methyl group has been known to be very common in the case of microbial and mammalian biotransformation (Furusawa et al., 2005a, 2006) (Figure 20.105). 

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