6-Methyl-2-(methylsulfonyl)-1,3-benzoxazole → methyl (1R,2R)-2-({3'-fluoro-4'-[(6-methyl-1,3-benzoxazol-2-yl)amino]-1,1'-biphenyl-4-yl}carbonyl)-cyclopentanecarboxylate

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To a solution of methyl (1R,2R)-2-[(4′-amino-3′-fluoro-1,1′-biphenyl-4-yl)carbonyl]-cyclopentanecarboxylate (800 mg, 2.34 mmol, 78% ee) in dichloroethane (15 mL), 6-methyl-2-(methylsulfonyl)-1,3-benzoxazole (891 mg, 4.22 mmol) was added, and the mixture was heated at 85° C. overnight. The solvent was removed by rotary evaporation, and the residue was purified by using a Biotage QuadUV flash chromatography system (eluant: 80:20 hexane/EtOAc) to give methyl (1R,2R)-2-({3′-fluoro-4′-[(6-methyl-1,3-benzoxazol-2-yl)amino]-1,1′-biphenyl-4-yl}carbonyl)-cyclopentanecarboxylate (472 mg). This ester intermediate was redissolved in 1:1 dioxane/THF 20 mL), a solution of 1 N aqueous NaOH (7.02 mL, 7.02 mol) was added, and the mixture was heated at 50° C. overnight. The solvent was removed by rotary evaporation, and water (20 mL) and EtOAc (40 mL) were added to the residue. The aqueous layer was separated, acidified to pH 5 by the addition of 1 N aqueous HCl, and then extracted with EtOAc (2×60 mL). The combined organic phases were washed with saturated NaCl and dried (Na2SO4). The solvent was removed by rotary evaporation and the residue was redissolved in DMF (10 mL) and methanol (20 mL). The crude product was purified by preparative reverse-phase HPLC (water/acetonitrile gradient, containing 0.1% TFA) to afford (1R,2R)-2-({3′-fluoro-4′-[(6-methyl-1,3-benzoxazol-2-yl)amino]-1,1′-biphenyl-4-yl}carbonyl)cyclopentanecarboxylic acid as an off-white solid (161 mg, 15% yield, 80% ee). 1H NMR (300 MHz, DMSO-d6) δ 8.40 (m, 1 H), 8.00–7.60 (m, 6 H), 7.30 (d, 2 H), 7.00 (d, 2 H), 4.05 (m, 1 H), 3.20 (m, 1 H), 2.40 (s, 3 H), 2.20 (m, 1 H), 1.95 (m, 1 H), 1.80–1.60 (m, 4 H); LC-MS ret. time 3.57 min, m/z 459.3 (MH+).

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