A Chemoenzymatic Route to Chiral Intermediates Used in the Multikilogram Synthesis of a Gamma Secretase Inhibitor

A chemoenzymatic route for the production of an intermediate to a gamma secretase inhibitor is described. The route is robust and was run at multikilogram scale. The process employs both a transaminase catalyzed reductive amination of a substituted tetralone and an alcohol dehydrogenase catalyzed reduction of an α-ketoester to generate the two chiral centers in the molecule, with nearly perfect stereoselectivity. The process also features simple isolation schemes, including a direct drop isolation of the aminotetralin phosphate salt.