Figure legends

Figure 1. General scheme for the imine reductase-catalyzed reduction of 2-methyl-1-pyrroline (2-MP) to (S )‑2‑methylpyrrolidine ((S )-2-MPN) and the developed downstream-processing with ion exchange resins including its subsequent desorption and release into ether to yield the pure product.
Figure 2. A) Conversion versus initial substrate concentration to determine the maximal substrate loading for the IRED-catalyzed synthesis. B) Time course of the imine reductase-catalyzed reaction using a substrate concentration of 150 mmol·L‑1. All experiments were carried out with 100 mg·mL-1 whole cell catalyst, sodium phosphate buffer (NaPi) pH 7.5 and 500 mmol·L-1 of d‑glucose in 500 µL-scale experiments at 30 °C. The dashed lines are a guide to the eye.
Figure 3. Adsorption after 30 min (A) and 24 h (B) of the imine-substrate 2-MP (grey) and of the amine-product (S )-2-MPN (black) onto seven different commercially available cation- and anion-exchange resins at 30 °C and 180 rpm from a test solution containing 100 mmol·L-1 either of the substrate and product together with 500 mmol·L-1 d-glucose in a NaPi buffer solution at pH 7.5.
Figure 4. A) Protonated form (brown) and non-protonated form (blue) of the imine substrate species and B) protonated form (red) and non-protonated form (grey) of the total amine product species with respect to the pH. Diagrams and pK s values calculated with “chemicalize” (www.chemicalize.com).
Figure 5. General presentation of styrene (blue)/divinylbenzene (red)-based cation exchange resin structure with sulfonic acid functional groups.
Figure 6. Tracking of the preparative-scale reaction from the reaction start (t  = 0 h) to the end (t  = 24 h). Retention times were verified by commercially available authentic reference substances (see SI for further information). Retention times: internal standard: 6.8 min, substrate 2-MP: 9.2 – 9.4 min, product (S )-2-MPN: 7.7 – 7.8 min.
Figure 1: