Stereoselective oxidation of R-(+)-limonene by chloroperoxidase from Caldariomyces fumago

The oxidation of R-(+)-limonene by chloroperoxidase (CPO) from Caldariomyces fumago is reported. The reaction was performed in 60 mM phosphate buffer at pH 3.0 and 6.0, and in the absence and in the presence of chloride ions. In the absence of chloride ions, at both pH values, the reaction was regio and stereoselective with a diasteromeric excess (de) > 99% of (1S,2S)-4R-limonene-1,2-diol. On the other hand, when the reaction was carried out in the presence of chloride ions an enhancement in the reaction rate was observed, maintaining the regioselectivity, but not the stereoselectivity (de < 5.4). The reaction products under these conditions were identified as ( 1S, 2S)-4R-limonene-1,2-diol and (1R,2R)-4R-limonene-1,2-diol. It seems that in the absence of chloride ions the stereoselectivity is determined by stereospecific interaction of limonene with CPO active site, as supported by docking analysis, while in the presence of potassium chloride the limonene oxidation also occurs by the produced hypochlorite without stereoselectivity.