To a solution of 1-(4-nitro-benzyl)-5-(2-oxo-propyl)-1H-indole-2-carboxylic acid benzyl ester (540 mg, 1.22 mmol) and 1-amino-3-phenoxypropan-2(S)-ol (245 mg, 1.46 mmol) in dichloroethane (20 ml) was added powdered sodium sulfate (1.73 g, 12.2 mmol), and the mixture was stirred for about one hour at room temperature under nitrogen. Acetic acid (87.9 mg, 0.084 ml, 1.46 mmol) and sodium triacetoxyborohydride (388 mg, 1.83 mmol) were added. After about 6 hours, additional sodium triacetoxyborohydride (194 mg, 0.915 mmol), acetic acid (0.2 ml, 3.5 mmol) and 1-amino-3-phenoxypropan-2(S)-ol (122 mg, 0.73 mmol) were added, and the mixture was stirred for about two days at room temperature under nitrogen. The reaction was then diluted with methylene chloride, washed with dilute sodium bicarbonate and brine, dried over sodium sulfate, filtered, and the solvent was removed in vacuo. The residue was flash chromatographed on silica (55 g), eluting with 5% methanol/methylene chloride, to give the title compound (500 mg) as a mixture of diastereomers.
