Efficient Biochemical Cascade for Accessing Green Leaf Alcohols

The biotechnological production of six-carbon membered green leaf aldehydes and alcohols appreciated for their fruity, green-grassy odors in fragrances and flavors exploits the 13-lipoxygenase pathway found in higher plants. Homogenized seeds, fruits, or wild-type microorganisms have traditionally served as catalysts used in a one-pot reaction. However, many of these catalysts can be advantageously replaced by enzymes produced in engineered microorganisms for improved process performance. Substituting guava fruits by an engineered 13-hydroperoxide lyase produced in E. coli was recently shown to provide increased efficiency for cleaving fatty acid 13-hydroperoxides into green leaf aldehydes. Replacing baker's yeast by a cosubstrate-dependent recombinant ketoreductase was found to offer superior productivity and chemo-selectivity in the reduction of hexenals to the corresponding alcohols. Finally, combining both cellular catalysts at reasonable loading in a simple one-pot cascade reaction offered the green leaf alcohol (Z)-3-hexenol at high isomeric purity (>99%) and high titers (8 g L-1) in spite of challenging, nonphysiological but otherwise benign reaction conditions.