Autoxidation versus Biotransformation of α-Pinene to Flavors with Pleurotus sapidus: Regioselective Hydroperoxidation of α-Pinene and Stereoselective Dehydrogenation of Verbenol

Abstract

The enzymatic conversion of alpha-pinene to verbenols, verbenone, and minor volatile flavors was studied using submerged cultured cells, lyophilisate, and microsomal fractions of the edible basidiomycete Pleurotus sapidus . The similarity of the product range obtained by the bioconversions with the range of products found after autoxidation of alpha-pinene at 100 degrees C suggested similar initial pinene radicals. Extracts of the bioconversions were analyzed using thin layer chromatography with hydroperoxide staining and cool on-column capillary gas chromatography-mass spectrometry. Two isomer alpha-pinene hydroperoxides were identified as the key intermediates and their structures confirmed by comparison with synthesized reference samples and by microchemical reduction to (Z)- and (E)-verbenol. When the biocatalysts were supplemented with one of the verbenols, only the (Z)-isomer was oxidized, indicating the activity of a highly stereospecific monoterpenol dehydrogenase. The structural comparison of subunits shows that fungal oxifunctionalization reactions of some common terpene substrates, such as (+)-limonene or (+)-valencene, might likewise be catalyzed by dioxygenases rather than by CYP450 enzymes, as previously assumed.

Significant Alteration of Gene Expression in Wood Decay Fungi Postia placenta and Phanerochaete chrysosporium by Plant Species

“…Little is known regarding the metabolism of softwood extractives, but consistent with the observed transcript profiles (Fig. 2), cytochrome P450s and dioxygenases have been proposed to be involved (35). In addition to extractives, hardwood and softwood species differ substantially in anatomical features and in lignin composition (1, 7), a factor long ago suggested as important in white rot decay (24).…”

LOXPsa1, the first recombinant lipoxygenase from a basidiomycete fungus

“…(+)-Valencene, a sesquiterpene from orange oil, was converted to (+)-nootkatone and nootkatols [26]. Lyophilisates of P. sapidus catalyzed the oxyfunctionalization of R-(+)-limonene to carvone [40], of˛-pinene to verbenone/ol [41] and of (+)-car-3-en to car-3-ones/ols [42] as well as the transformation of various cycloalkenes to the corresponding enones [43]. This promiscuity calls for a biotechnological application to produce other bioactive or fragrant terpenoids.…”

Bioprocess Engineering for Microbial Synthesis and Conversion of Isoprenoids

“…In contrast, biotechnological strategies take advantage of the pronounced regio-and stereo selectivities of enzymatic reactions (usually by use of microbial cells) and the possibility of overproducing isoprenoids in tailored bioprocesses. One strategy is whole-cell biocatalysis, which is usually favored if structurally closely related precursor molecules are abundantly available, for example, the monoterpenes limonene or pinene for carvone or verbenone production, respectively [44,46], and therefore represent cheap starting materials. The target products are often obtained by selective oxyfunctionalization reactions catalyzed by only one or a few enzymes, such as P450 monooxygenases and alcohol dehydrogenases.…”