0.064 mmol of benzimidazolecarboxylic acid 4l was dissolved in DMF together with 0.064 mmol of the amine 5c, a solution of TBTU (0.096 mmol) in DMF, HOBT (0.026 mmol) in DMF and 0.32 mmol of DIPEA were added successively, and the mixture was stirred at room temperature. After 2.5 hours, 0.25 eq. of acid was added, and the mixture was stirred overnight. After further addition of 0.5 eq. of acid, the reaction mixture was diluted with water after 16 hours and extracted a number of times with ethyl acetate. The combined organic phases were washed 2× with water, dried, filtered and evaporated. The residue was digested with ethyl acetate/methanol (a little).
