To a solution of 55 mg of 1-(1-Ethyl-propyl)-2-(tetrahydro-furan-2-ylmethyl)-1H-benzoimidazole-5-carboxylic acid in 1 ml of dry DMF 26 mg of HOBT, 37 mg of EDC and 0.05 ml of DIPEA were added at 0° C. After 15 min 100 mg of L-leucine tert-butyl ester-hydrochloride and 0.05 ml of DIPEA were added and the reaction was stirred at rt for 16 h. The reaction was then poured into water and the pH was adjusted to 3 by the addition of 2 M aqueous hydrochloric acid. The reaction was extracted with ethyl acetate three times. The combined organic phases were washed with saturated aqueous sodium bicarbonate solution and brine, dried over magnesium sulphate and concentrated. 75 mg (88%) of (S)-2-{[1-(1-Ethyl-propyl)-2-(tetrahydro-furan-2-ylmethyl)-1H-benzoimidazole-5-carbonyl]-amino}-4-methyl-pentanoic acid tert-butyl ester were obtained.
