To a stirred solution of biphenyl-2-ylcarbamic acid 1-(2-{[3-(4-formyl-phenylcarbamoyl)propyl]methylcarbamoyl}ethyl)piperidin-4-yl ester (91 mg, 0.16 mmol) in DCM (2 mL) was added 5-[(R)-2-amino-1-(tert-butyldimethylsilanyloxy)ethyl]-8-hydroxy-1H-quinolin-2-one acetic acid salt (101 mg, 0.256 mmol) (see, e.g., U.S. Patent Publication No. 2006/0035931 A1, published Feb. 16, 2006) followed by MeOH (1 mL). The resulting yellow solution was stirred at room temperature for 10 min and then sodium triacetoxyborohydride (89 mg, 0.40 mmol) was added and this mixture was stirred overnight. LC-MS (Method 2-90) showed product was present (Rt 3.25 min; m/z 889.8 [M+H]+). Water and DCM were added and the layers were separated. The organic layer was washed with water (2×) and brine, dried over sodium sulfate, filtered and concentrated under reduced pressure to give the title compound, which was used without further purification.
