Chemo-biocatalytic one-pot two-step conversion of cyclic amine to lactam using whole cell monoamine oxidase

BACKGROUND: Most biocatalysts currently involved in one-pot chemoenzymatic cascades are pure enzymes, while whole cells and crude enzyme extracts remain unexplored. This work aims to develop a chemo-biocatalytic one-pot two-step system involving whole cell monoamine oxidase (MAO, EC 1.4.3.4) coupled with a Cu-based oxidative system (CuI/H₂O₂) for the transformation of 1,2,3,4-tetrahydroisoquinoline (THIQ) to 3,4-dihydroisoquinolin-1(2H)-one (DHIO). RESULTS: MAO-N variants D9 and D11 were tested as whole cell and crude lysate biocatalysts for biological oxidation. Whole Escherichia coli OverExpress C43(DE3) cells expressing MAO-N D9 showed the best performance (V_max = 36.58 mmol L⁻¹ h⁻¹, K_M = 8.124 mmol L⁻¹, maximum specific productivity 89.3 μmol min⁻¹ g^{− 1} _DCW) and were employed in combination with CuI/H₂O₂ in a sequential one-pot two-step process. The biotransformation was scaled-up to the initial volume of 25 mL and after triple THIQ feeding, 48.2 mmol L⁻¹ of the intermediate 3,4-dihydroisoquinoline (DHIQ) was obtained with a yield of 71.3%. Afterwards, chemical catalysts (1 mol% CuI and 10 eq. H₂O₂) were added to the biologically produced DHIQ, which was transformed to ∼30 mmol L⁻¹ DHIO at 69.4% overall yield. CONCLUSION: As MAO-N variants have wide substrate specificity, this work broadens the portfolio of one-pot chemoenzymatic processes employing whole cell biocatalysts, representing an alternative to using pure enzymes.