Step C. (R)-2-(4-chloro-N-(2-fluoro-4-(N'-hydroxyformamidinyl)benzyl)-benzenesulfonylamino)-5,5,5-trifluoropentanamide (246 g) was added to the reactor, followed by the addition of dry acetonitrile (509 mL), triethyl orthoformate (120 mL) and trifluoroacetic acid (7 mL). The reaction mixture was heated to 40-50 °C and the progress of the reaction was monitored by HPLC until the relative area percentage (AP) of the starting material was below 0.15. Upon completion of the reaction, a one-time addition of methanol (1.48 L) followed by water (1.034 L) was added to maintain the reaction system temperature at 45-50 °C. The reaction mixture was then cooled to 15-20 °C and the solid was collected by filtration. The filter cake was washed with a solvent mixture of acetonitrile:methanol:water (2:6:5, v/v/v) and dried under vacuum at 50-60 °C to afford (2R)-2-[N-[(4-chlorophenyl)sulfonyl]-N-[2-fluoro-4-(1 ,2,4-oxadiazol-3-yl)benzyl]amino]-5,5,5-trifluoropentanamide as a white solid (228 g, 90% yield) .
1H NMR (CDCl3, 300MHz) δ: 1.40-1.58 (m, 1H), 1.75-1.90 (m, 1H), 1.92-2.07 (m, 1H), 2.10-2.26 (m, 1H), 4.37 (dd, J = 8.67, 6.22Hz, 1H), 4.48 (d, J = 15.64Hz, 1H ), 4.64 (d, J = 15.82 Hz, 1H), 5.54 (s, 1H), 6.33 (s, 1H), 7.44-7.54 (m, 2H), 7.62 (t, J = 7.72 Hz, 1H), 7.68-7.76 (m, 3H), 7.85 (dd, J = 7.91, 1.51 Hz, 1H), 8.76 (s, 1H). 1H).
13C NMR (DMSO-d6, 75MHz) δ: 170.34, 167.75, 165.80, 159.64 (d, J = 244.5Hz, 1C), 138.19, 137.64, 131.25 (d, J = 3.75Hz, 1C), 129.31, 129.23, 129.05 (d, J = 14.25 Hz, 1C), 126.74 (q, J = 274.5 Hz, 1C), 126.91, 126.80, 123.12 (d, J = 3.75 Hz, 1C), 113.7 (d, J = 24.0 Hz, 1C), 57.92, 41.38 (d, J = 4.5 Hz, 1C), 30.04 (d, J = 30.0Hz, 1C), 22.90.
19F NMR (CDCl3, 282MHz) δ: -116.3, -66.5.
IR (KBr): 3454, 334, 3286, 2952, 1705, 1432, 1325, 1260, 1167, 1084, 828 cm-1.
Elemental analysis: Calculated values C20H17ClF4N4O4S: C, 46.11; H, 3.29; N, 10.71; S, 6.15; F, 14.58; Cl, 6.80. Measured values: C, 46.06; H, 3.24; N, 10.71; S, 6.25; F, 14.60; Cl, 6.88.