of cases. Sulfides are always oxidized to sulfoxides. (8) An important limitation of the reaction is that only a single enantiomer of product is available when the wild type enzyme is used. Enzymes that generate "unnatural" enantiomers must be engineered via site-directed mutagenesis or other biochemical techniques. The development of organisms and enzymes that exhibit "unnatural" stereoselectivity is an ongoing research activity. Applications in organic synthesis Because of concerns about the efficiency and selectivity of oxidation of more complex substrates, MAO is usually carried out early in synthetic sequences. However, simple dihydrodiols may be manipulated to give complex products through a variety of methods. In addition, the microbial oxidation process is compatible with a number of functional groups. For instance, thioether-containing dihydrodiols may be accessed by the oxidation of iodobenzene followed by cross-coupling in the presence of tin sulfides. (9) Dihydrodiols have been elaborated to a variety of alkaloid natural products. Two examples are shown below. (10) (11) Conditions of MAO reactions require handling microbes in an aseptic environment. Often, specialized bacterial strains are needed to effect particular transformations. Dihydrodiols themselves must be stored under basic conditions (pH > 9) to prevent acid-catalyzed dehydration. References Organic oxidation reactions