808 mg (4 mmol) of 1-(4-fluorophenyl)-2,5-dimethyl-pyrrole-3-carboxylic acid (Enamine, Kiev, Ukraine) was dissolved in 100 ml methylene chloride and 30 ml dimethyl sulfoxide, and added with stirring to 4 g of PS-carbodiimide (Biotage, Charlotte, N.C., USA), substituted at 1.33 mmol/g, wetted with 40 ml methylene chloride. 892 mg (4 mmol) of 4-(aminomethyl)benzamidine hydrochloride (Astatech, Bristol, Pa., USA), and 540 mg of HOBt were dissolved in 50 ml dimethyl sulfoxide, added to the stirred mixture, followed by 1.4 ml of diisopropylethylamine (Sigma-Aldrich). The mixture was stirred for seven days at room temperature, followed by filtration to remove the consumed resin. 50 ml of water was added to 150 ml of the filtrate, stirred vigorously for 10 minutes, then allowed to settle for 20 minutes to separate aqueous phase from the methylene chloride. The aqueous phase was carefully removed, neutralized by adding Tris base to 20 mM final concentration, then applied to a 20 ml bed volume CM-Sepharose (Sigma-Aldrich) cation-exchange column equilibriated with 20 mM Tris-HCl, pH 8. The column was washed with 40 ml of methanol and then eluted with 40 ml of 5% formic acid in methanol. The target compound was recovered as a yellowish oily solid following removal of the solvent by evaporation. The mass of the compound was verified by LC-MS/MS.
