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Exploiting Enzymatic Carbonyl Reduction in Organic Synthesis and Characterization of Human Serine Racemase
An alcohol dehydrogenase from Clostridium acetobutylicum (CaADH) recently reported by our lab and deployed in the stereoselective reduction of β-ketoesters to medicinally relevant chiral synthons, has now been applied to the reduction of α,α- difluoro-β-ketophosphonates bearing γ,δ-unsaturation. To our knowledge, these represent the first examples of a dehydrogenase-based entry into valuable enantioenriched α,α-difluorinated phosphonate building blocks. Importantly, the resulting phosphonatebearing, allylic alcohols are found to undergo an exceptionally facile (half time ~3 min @ rt) thiono-Claisen rearrangement (RR) with high conservation of enantiomeric excess when derivatized with the appropriate thiono-ester functionality. This hybrid bio/chemocatalytic approach serves as an entry into an advanced building block for a new family of potential zinc-aminopeptidase A inhibitors. There is currently great interest in human serine racemase (hSR), the vitamin B6- dependent enzyme responsible for D-serine production and only human racemase yet identified. D-serine is an important neurotransmitter that co-activates the NMDA receptor at the glycine site. Potential correlation of D-serine levels with disease states such as Alzheimer’s (elevated), brain damage pursuant to stroke (elevated) and schizophrenia (reduced) further raises interest in hSR. Here, we demonstrate the use of a new construct that serves as an excellent platform for site-directed mutagenesis studies. Namely, site directed mutagenesis has allowed us the ability to modulate the activity and substrate preference of hSR. Along with computational modeling, these studies serve to advance our mechanistic understanding of this underexplored enzyme.
Applegate, Gregory A, "Exploiting Enzymatic Carbonyl Reduction in Organic Synthesis and Characterization of Human Serine Racemase" (2016). ETD collection for University of Nebraska-Lincoln. AAI10247739.