Reaction Steps
To a solution of the crude (1S,2R,3S,4R)-3-{(4-fluorobenzyl)-[2-(7-methanesulfonylamino-1,1-dioxo-1,4-dihydro-1λ6-benzo[1,2,4]thiadiazin-3-yl)-acetyl]-amino}-bicyclo[2.2.1]heptane-2-carboxylic acid ethyl ester in absolute ethanol (3 mL) was added a 21 wt. % solution of sodium ethoxide in ethanol (0.51 mL, 1.37 mmol). After stirring at 60° C. for 2 h, the mixture was diluted with ethyl acetate and acidified with 1.0M aqueous hydrochloric acid solution to pH 1. The organic layer was separated and the aqueous layer was extracted with ethyl acetate (2×20 mL). The combined organic layer was dried over magnesium sulfate, filtered, and concentrated in vacuo. The crude mixture was purified by flash column chromatography (Teledyne Isco RediSep column; 0 to 100% ethyl acetate in hexanes) to afford the desired product, N-{3-[(1R,2S,7R,8S)-3-(4-fluoro-benzyl)-6-hydroxy-4-oxo-3-aza-tricyclo[6.2.1.02,7]undec-5-en-5-yl]-1,1-dioxo-1,4-dihydro-1λ6-benzo[1,2,4]thiadiazin-7-yl}-methanesulfonamide (131.5 mg, 0.235 mmol, 68% over two steps), as an off-white solid. 1H NMR (400 MHz, CD3OD) δ 1.28 (2H, d, J=11.0 Hz), 1.47 (1H, t, J=10.8 Hz), 1.57-1.74 (3H, m), 2.56 (1H, d, J=3.2 Hz), 2.75 (1H, d, J=2.3 Hz), 2.96 (1H, d, J=9.2 Hz), 3.02 (3H, s), 3.58 (1H, d, J=9.2 Hz), 4.42 (1H, d, J=15.5 Hz), 5.03 (1H, d, J=15.7 Hz), 7.04 (2H, t, J=8.5 Hz), 7.31 (2H, dd, J1=7.9 Hz, J2=5.5 Hz), 7.37 (1H, d, J=8.8 Hz), 7.54 (1H, dd, J1=8.3 Hz, J2=2.3 Hz), 7.69 (1H, d, J=2.3 Hz). LC-MS (ESI) calcd for C25H25FN4O6S2 560.12, found 561.4 [M+H+]. ee=98.5% [HPLC-analysis: Chiralpak AS-RH 2.1×150 mm, 5 micron at r.t., Solvent A-Solvent B (see table for gradient), 0.3 mL/min, 312 nm, t1=7.58 min (major), t2=8.95 min].
