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The pyrroline (4.68 g, 19.5 mM) was added to a mixture of 1M NaOH (80 ml) and ethanol (80 ml) and the solution stirred at 50° for 4 hrs. The solution was then cooled, sodium borohydride (1.0 g) added, and stirred at 25° for a further 10 hours. The solution was then carefully acidified with dilute HCl to pH 4, concentrated and applied to a column of Dowex 50WX8 resin (H+ form, 100 ml) Elution with aqueous ammonia (2 M) yielded a solution which on evaporation gave trans-3-ethyl-dl-proline (2.1 g) m.p. 208≈-209°; RF 3B 0.43. Analysis on a Jeol 6AH amino acid analyser (50 cm column, sodium citrate buffer 0.2 N, pH 3.25 temperature 57°) showed a single peak (elution time 117 mins).

1. temperatureThe solution was then cooled
2. stirringstirred at 25° for a further 10 hours
3. concentrationconcentrated
4. washapplied to a column of Dowex 50WX8 resin (H+ form, 100 ml) Elution with aqueous ammonia (2 M)
5. customyielded a solution which
6. customon evaporation