title: A biocatalytic route towards rose oxide using chloroperoxidase.
abstract: The chiral monoterpene alcohol citronellol was converted to the corresponding bromohydrin by the haem-thiolate enzyme chloroperoxidase (CPO) from Caldariomyces fumago in the presence of hydrogen peroxide and bromide ions. A conversion rate of 51% could be achieved under adapted reaction conditions, which easily yield product in the gramme per litre range while only needing catalytic amounts of enzyme. The bromohydroxylation was shown to be highly regioselective yielding 6-bromo-3,7-dimethyloctane-1,7-diol as the sole product. Product identity was confirmed by GC-MS, (1)H- and (13)C-NMR spectroscopy and the synthesis of reference compounds. However, the reaction was shown to be non-stereospecific because enantiopure (R)- and (S)-citronellol, respectively, gave 1:1-diasteromeric mixtures of the corresponding bromohydrins. A racemic mixture of (R/S)-citronellol was bromohydroxylated without any detectable enantiodiscrimination. The total lack of stereospecificity and enantiodiscrimination points to a reaction mechanism where the oxidised bromide intermediate is not a ligand to the Fe(III)-haem at the distal site but is released from the enzyme active site. The final bromide transfer occurs probably outside the active site via a diffusible oxidised bromide species and the demonstrated regioselectivity is purely chemically controlled. The generated bromohydrins can be straightforward converted via two reactions steps into rose oxide which is a highly valuable flavour and fragrance substance.
authors.affiliation: Institut Technologies du Vivant, Haute Ecole Spécialisée de Suisse occidentale, Route du Rawyl 47, CH-1950 Sion, Switzerland.
authors.forename: Umberto
authors.initials: U
authors.lastname: Piantini
authors.affiliation: DECHEMA e.V, Karl-Winnacker-Institut, Biochemical Engineering, Theodor-Heuss-Allee 25, D-60486 Frankfurt, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Schrader
authors.affiliation: Fachgebiet Lebensmittelchemie, Institut für Ernährungs- und Lebensmittelwissenschaften, Rheinische Friedrich-Wilhelms-Universität Bonn, Endenicher Allee 11-13, D-53115 Bonn, Germany.
authors.forename: Andrzej
authors.initials: A
authors.lastname: Wawrzun
authors.affiliation: Fachgebiet Lebensmittelchemie, Institut für Ernährungs- und Lebensmittelwissenschaften, Rheinische Friedrich-Wilhelms-Universität Bonn, Endenicher Allee 11-13, D-53115 Bonn, Germany. Electronic address: matthias.wuest@uni-bonn.de.
authors.forename: Matthias
authors.initials: M
authors.lastname: Wüst
keywords: Bioconversion; Enzymatic halogenation; Halohydrin; Haloperoxidase; Monoterpene