A mixture of N-methyl N-methoxy isoquinoline-1-carboxamide (0.75 g, 3.47 mmol) in dry toluene (25 ml) is cooled to −37° C. and a solution of diisobutylaluminumhydride (DIBAL-H) in toluene (1M, 3.8 ml) is added. The reaction temperature is slowly increased to −4° C. over 4 h and a 20% aqueous solution of tartaric acid (10 ml) is added. The mixture is stirred for 10 min at ambient temperature, saturated aqueous sodium bicarbonate is added and the mixture extracted with dichloromethane. The combined organic layers are dried over sodium sulfate, filtered, and concentrated. The crude product and 4-(isobutylamino)-piperidine-1-carboxylic acid tert-butyl ester (0.89 g, 3.47 mmol), acetic acid (0.2 ml), and 1,2-dichloroethane (15 ml) are mixed and sodium triacetoxyborohydride (1.03 g, 4.86 mmol) is added. The reaction is stirred at ambient temperature over night. Aqueous sodium hydroxide (2M) is added and the mixture is extracted with diethyl ether. The combined organic layers are dried over sodium sulfate, filtered, and concentrated. The crude product is purified by column chromatography [silica, acetone/hexane (15:85)], followed by [silica, ethyl acetate/hexane (5:95), followed by ethyl acetate/hexane (1:3)] to give 0.23 g of 4-{(isobutyl)-[(isoquinolin-1-yl)-methyl]amino}-piperidine-1-carboxylic acid tert-butyl ester: mass spectrum (ion spray): m/z=398.1 (M+1). 1H NMR (CDCl3): δ=8.60 (1H, d), 8.39 (1H, d), 7.79 (1H, d), 7.65 (1H, dd), 7.53-7.56 (2H, m), 4.10-4.30 (4H, m), 2.50-2.70 (3H, m), 2.25-2.35 (2H, m), 2.80-2.85 (2H, m), 1.45-1.60 (3H, m), 1.46 (9H, s), 0.68 (6H, d).
