Prochiral Sulfoxidation as a Probe for Flavin-Containing Monooxygenases

Asymmetric aryl alkyl sulfides (R-S-R′) are metabolized by flavin-containing monooxygenase (FMO) and cytochrome P450 enzymes to enantiomerically enriched sulfoxide products (R-SO-R′) that are readily analyzed with a host of commercially available chiral stationary phases. Prochiral sulfoxidation of probe compounds based on
p
-tolyl methyl sulfide is a particularly useful method for discriminating among FMO1, FMO3, and FMO5, because the stereochemistry of the resulting products is isoform dependent, but apparently species independent. If studies are performed with crude tissue microsomal preparations, the cytochrome P450 component must be quenched to unmask catalysis specifically by the FMO component of the tissue. This chapter details experimental protocols for stereochemical analysis of sulfoxides generated from methyl, ethyl,
n
-propyl, and
n
-butyl
p
-tolyl sulfide by purified FMO isoforms and tissue microsomal preparations.