A dioxygenase of Pleurotus sapidus transforms (+)-valencene regio-specifically to (+)-nootkatone via a stereo-specific allylic hydroperoxidation.
A selective and highly efficient allylic oxidation of the sesquiterpene (+)-valencene to the grapefruit flavour compound (+)-nootkatone was achieved with lyophilisate of the edible mushroom Pleurotus sapidus. The catalytic reaction sequence was elucidated through the identification of intermediate, (+)-valencene derived hydroperoxides. A specific staining of hydroperoxides allowed the semi-preparative isolation of two secondary (+)-valencene hydroperoxides, 6(R)-Isopropenyl-4(R),4a(S)-dimethyl-2,3,4,4a,5,6,7,8-octahydro-naphthalen-4(S)-yl-hydroperoxide and 6(R)-Isopropenyl-4(R),4a(S)-dimethyl-2,3,4,4a,5,6,7,8-octahydro-naphthalen-2(R)-yl-hydroperoxide. Chemical reduction of the biotransformation products yielded a tertiary alcohol identified as 2(R)-Isopropenyl-8(R),8a(S)-dimethyl-1,3,4,7,8,8a-hexahydro-2H-naphthalen-4a(R)-ol. This suggested a lipoxygenase-type oxidation of (+)-valencene via secondary and tertiary hydroperoxides and confirmed homology data of the key enzyme obtained previously from amino acid sequencing.
Krügener
Sven
S
Zentrum für Angewandte Chemie der Leibniz Universität Hannover, Institut für Lebensmittelchemie, Wunstorfer Str. 14, D-30453 Hannover, Germany.
Krings
Ulrich
U
Zorn
Holger
H
Berger
Ralf G
RG
D001711:Biotransformation; D002845:Chromatography / Q000379:methods; D049308:Dioxygenases / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D020076:Pleurotus / Q000201:enzymology*; D012717:Sesquiterpenes / Q000378:metabolism*; D013056:Spectrophotometry, Ultraviolet; D013237:Stereoisomerism
D012717:Sesquiterpenes; C506706:valencene; D006861:Hydrogen Peroxide; D049308:Dioxygenases