Scheme 34. Cyclic deracemization of rac-1-phenyl-1,2,3,4-tetrahydroisoquinoline through enantioselective oxidation by a variant of monoamine oxidase from Aspergillus niger (MAO-N) and nonselective reduction with ammonia–borane complex. The (S)-amine was then employed to access solifenacin in two steps.²⁹⁵.