Hydrochloric Acid → Pregabalin

Participants

Reaction Conditions

Reaction Steps

A reactor vessel (60 L) was charged with (S)-4-isobutyl-2-oxo-pyrrolidine-3-carboxylic acid (Formula 10), HCl (36-38%, 30 L), and water (29 L). HOAc (1 L) was added to the solution and the resulting slurry was heated for 36-38 h at 80° C. and for an additional 6 h at 110° C. The extent of reaction was monitored by HPLC(C18 column, 4.6 mm×150 mm, detection at 200 nm). Water and excess HCl were evaporated to afford an oil, which was washed with MTBE (2×15 L). Water was added to the oil and the mixture was stirred until the solution cleared. The pH of the solution was adjusted to 5.2-5.5 using KOH (about 6 kg), which resulted in the precipitation of pregabalin. The mixture was heated to 80° C. and subsequently cooled to 4° C. After 10 h, crystalline pregabalin was filtered and washed with IPA (12 L). The filtrate was concentrated under vacuum to afford a residual oil. Water (7.5 L) and EtOH (5.0 L) were added to the residual oil and the resulting mixture was heated to 80° C. and then cooled to 4° C. After 10 h, a second crop of pregabalin crystals were filtered and washed with IPA (1 L). The combined pregabalin crystals were dried in a vacuum oven at 45° C. for 24 h. MS m/z [M+H]+160.1340. 1H NMR (300 MHz, D2O): δ 2.97 (dd, J=5.4, 12.9 Hz, 1H), 2.89 (dd, J=6.6, 12.9 Hz, 1H), 2.05-2.34 (m, 2H), 1.50-1.70 (sept, J=6.9 Hz, 1H), 1.17 (t, J=7.0 Hz, 2H), 0.85 (dd, J=2.2, 6.6 Hz, 6H). 13C NMR (75 ppm, D2O) δ 181.54, 44.32, 41.28, 32.20, 24.94, 22.55, 22.09. Yield 80-85%; ee>99.5%.

Provenance & Evidence