DL-leucine → 2-(1,3-Dioxo-1,3-dihydro-2H-isoindol-2-yl)-4-methylpentanoic acid

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Reaction Steps

To a stirred solution of d,l-leucine (3.31 g, 25.0 mmol) and sodium carbonate (2.78 g, 26.25 mmol) in 50 mL of water is added N-carboethoxyphthalimide (5.65 g, 25.0 mmol). After 1 hour at room temperature, the reaction slurry is filtered, the filtrate stirred, and the pH adjusted to 1-2 with 4N hydrochloric acid. The mixture is stirred overnight, the resulting slurry is filtered, and the solid washed with water and dried in vacuo (60° C., <1 mm) to afford 5.32 g (81%) of the 2-phthalimido-4-methylpentanoic acid as a white powder: mp 134°-137° C.; 1H NMR (dmso-d6, 250 M Hz) δ 12.50 (br s, 1H), 8.00-7.80 (m, 4H), 4.79 (dd, 1H, J=4.3), 2.28-2.10 (m, 1H), 1.94-1.77 (m, 1H), 1.51-1.34 (m, 1H), 0.89 (d, 3H, J=4.4), 0.86 (d, 3H, J=4.5); 13C NMR (dmso-d6) δ 170.8, 167.4, 134.8, 131.1, 123.3, 50.2, 36.7, 24.6, 23.0, 20.8. Anal. Calculated for C14H15NO4. Theoretical: C, 64.36; H, 5.74; N, 5.36. Found: C, 64.18; H, 5.73; N, 5.98.

Provenance & Evidence