Meso-diols, stereoselective oxidation

The authors then used a modification of their Lipase-AK route to produce the natural enantiomer, as described in detail in the chapter by Kenji Mori in this volume. Instead of using the enzyme to execute a stereoselective monohydrolysis of meso diacetate 140, the enzyme was used to esterify selectively one of the hydroxy groups of meso diol 128, resulting in the antipodal hydroxyester. After oxidation of the free hydroxyl to the acid, and recrystallization of its salt with (JR)-l-naphthylethylamine, the purified acid was then carried through the remaining steps to furnish the chiral pheromone compound (see the chapter by Kenji Mori in this volume). 

Horse liver alcohol dehydrogenase (HLADH) catalyzes the oxidoreduction of a variety of compounds [61,62]. It has been demonstrated that HLADH catalyzes the stereospecific oxidation of only one of the enantiopic hydroxyl groups of acyclic and monocyclic me o-diols [63,64]. The oxidation of meso-exo- and enfto-7-oxabicyclo[2.2.1]heptane dimethanol to the corresponding enantiomerically pure y-lactones by HLADH has been demonstrated. Nicotinamide adenine dinucleotide (NAD" ) and flavin adenine dinucleotide (FAD) were required for the stereoselective oxidation of substrate. Due to the high cost of enzyme and required cofactors, this process for preparing chiral lactones was econom-... 

For the enantioselective preparations of chiral synthons, the most interesting oxidations are the hydroxylations of unactivated saturated carbons or carbon-carbon double bonds in alkene and arene systems, together with the oxidative transformations of various chemical functions. Of special interest is the enzymatic generation of enantiopure epoxides. This can be achieved by epoxidation of double bonds with cytochrome P450 mono-oxygenases, w-hydroxylases, or biotransformation with whole micro-organisms. Alternative approaches include the microbial reduction of a-haloketones, or the use of haloperoxi-dases and halohydrine epoxidases [128]. The enantioselective hydrolysis of several types of epoxides can be achieved with epoxide hydrolases (a relatively new class of enzymes). These enzymes give access to enantiopure epoxides and chiral diols by enantioselective hydrolysis of racemic epoxides or by stereoselective hydrolysis of meso-epoxides [128,129]. 

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