Enzyme-Mediated Two-Step Regio- and Stereoselective Synthesis of Potential Rapid-Acting Antidepressant (2S,6S)‑Hydroxynorketamine

Recently, the anesthetic (S)-ketamine has been approved as a rapid-acting and long-lasting antidepressant. Its metabolite, (2S,6S)-hydroxynorketamine, has been found to have a similar antidepressant effect but with less undesirable side effects, which make this compound an interesting target for synthesis. Using the first-sphere mutagenesis of the cytochrome P450 154E1 from Thermobifida fusca YX, we constructed a triple mutant that enables the effective production of (2S,6S)-hydroxynorketamine from (S)-ketamine. This engineered P450 monooxygenase catalyzes the consecutive oxidative N-demethylation and highly regio- and stereoselective C6-hydroxylation reactions leading directly to the desired product with 85% product selectivity. The integration of this selective monooxygenase into an Escherichia coli whole-cell biocatalyst allowed the production of (2S,6S)-hydroxynorketamine at a semipreparative scale. The metabolite was purified and its structure was confirmed by NMR spectroscopy.