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: