Autoxidation versus biotransformation of alpha-pinene to flavors with Pleurotus sapidus: regioselective hydroperoxidation of alpha-pinene and stereoselective dehydrogenation of verbenol.
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.
Krings
Ulrich
U
Zentrum Angewandte Chemie der Leibniz Universitat Hannover, Institut fur Lebensmittelchemie, Callinstrasse 5, D-30167 Hannover, Germany. krings@lci.uni-hannover.de
Lehnert
Nicole
N
Fraatz
Marco A
MA
Hardebusch
Björn
B
Zorn
Holger
H
Berger
Ralf G
RG
D000081008:Bicyclic Monoterpenes; D001711:Biotransformation; D005421:Flavoring Agents / Q000737:chemistry / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism; D039821:Monoterpenes / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism; D020076:Pleurotus / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism*; D013237:Stereoisomerism
D000081008:Bicyclic Monoterpenes; D005421:Flavoring Agents; D005656:Fungal Proteins; D039821:Monoterpenes; D010088:Oxidoreductases; C009951:verbenol; C005451:alpha-pinene