The crude (1S,2R)-2-{(4-fluoro-benzyl)-[2-(7-methanesulfonylamino-1,1-dioxo-1,4-dihydro-1λ6-benzo[1,2,4]thiadiazin-3-yl)-acetyl]-amino}-cyclohexanecarboxylic acid methyl ester (4.97 mmol) was dissolved in ethanol (50 mL) at 25° C. and a 21% w/w solution of sodium ethoxide in ethanol (2.86 mL) was added. The reaction mixture was heated to 60° C. for 8 h, then was cooled to 25° C. and partitioned between 1.0 M aqueous hydrochloric acid solution (150 mL) and ethyl acetate (2×150 mL). The combined organic layers were dried over sodium sulfate, decanted, and were concentrated in vacuo. The residue was purified by flash column chromatography (Teledyne Isco RediSep Flash Column 150 g; 0-6% methanol in dichloromethane) to afford the desired product, (4aS,8aR)-N-{3-[1-(4-fluoro-benzyl)-4-hydroxy-2-oxo-1,2,4a,5,6,7,8,8a-octahydro-quinolin-3-yl]-1,1-dioxo-1,4-dihydro-1λ6-benzo[1,2,4]thiadiazin-7-yl}-methanesulfonamide (0.96 g, 1.75 mmol, 40% over 4 steps), as a pale yellow foam. 1H NMR (400 MHz, DMSO-d6) δ: 1.10-1.26 (3H, m), 1.36-1.48 (3H, m), 1.61-1.64 (1H, m), 1.77-1.80 (1H, m), 2.27-2.31 (1H, m), 3.06 (3H, s), 3.59 (1H, bs), 4.32 (1H, bs), 4.45 (1H, s), 4.99 (1H, d, J=15.3 Hz), 7.07-7.11 (1H, m), 7.12-7.17 (2H, m), 7.29-7.33 (1H, m), 7.39-7.42 (1H, m), 7.51 (1H, dd, J1=2.3 Hz, J2=8.5 Hz), 7.57 (1H, s), 7.58-7.59 (1H, m), 10.17 (1H, s), 13.80 (1H, s). LC-MS (ESI) calcd for C24H25FN4O6S2 548.12, found 549.4 [M+H+]. >99.5% e.e. as determined by chiral HPLC analysis: column: Chiralpak AS-RH 4.6×250 mm ID 5 um, solvent: acetonitrile+0.05% trifluoroacetic acid (mobile phase B); water+0.05% trifluoroacetic acid (mobile phase A), gradient: 50% to 90% mobile phase B over 15 min.
