To a stirred solution of the aldehyde (5-8, 2.01 g, 5.15 mmol, 1 equiv) and N-(2-hydroxyacetyl)piperazine (2.97 g, 20.60 mmol, 4 equiv) in dichloroethane (400 mL) was added at ambient temperature acetic acid (1.2 mL). The reaction mixture was treated with sodium triacetoxyborohydride and stirred for 3 h. The reaction stopped at 76% of conversion and treated with MgSO4 and additional 1 g of the hydride. After further stirring for 1 h the reaction was complete. The reaction mixture was partitioned between ethyl acetate and saturated aqueous NaHCO3. The organic layer was once again washed with saturated aqueous NaHCO3, and then with brine, separated, dried with (Na2SO4) and concentrated in vacuo. The crude solid was dissolved in N,N-dimethylformamide and treated with the activated carbon. The filtrate solution (celite) was concentrated to syrup which was quickly triturated with methanol (100 mL). The resulting solid was collected by filtration, redissolved in N,N-dimethylformamide, concentrated to syrup, triturated with methanol (100 mL), collected by filtration and vacuum-dried to give 5-[4-(2-hydroxy-ethanoyl)-piperazin-1-ylmethyl]-2-(2-oxo-1,2-dihydro-quinolin-3-yl)-indole-1-carboxylic acid tert-butyl ester (5-9, 1.51 g, 57%) as a white powder; 1H NMR (500 MHz, DMSO-d6) δ 12.24 (br s, 1H), 8.21 (d, 1H, J=8.7 Hz), 7.91 (s, 1H), 7.61 (d, 1H, J=6.9 Hz), 7.52 (s, 1H), 7.49 (m, 1H), 7.36 (d, 1H, J=8.1 Hz), 7.33 (dd, 1H, J=8.4, 1.5 Hz), 7.24 (m, 1H), 6.67 (s, 1H), 4.15 (s, 2H), 3.69 (m, 2H), 3.65 (s, 2H), 3.28 (m, 2H), 2.49 (m, 4H), 1.40 (s, 9H).
