7.5 g of BOP are added to a mixture of 4.06 g of 2-(tert-butoxycarbonylamino)-3-(4-cyanophenyl)propionic acid and 1.15 ml of pyrrolidine in 20 ml of DMF, and the mixture is stirred for 2 hours at RT, while keeping the pH at 7 by adding N-ethylmorpholine. The reaction mixture is concentrated under vacuum and the residue is chromatographed on silica gel, eluting with a chloroform/MeOH mixture (95/5; v/v). The product obtained is taken up in 20 ml of TFA in 20 ml of DCM, and the reaction mixture is stirred for 30 minutes at RT and concentrated under vacuum. The residue is taken up in ether and the precipitate formed is filtered off by suction. 3.95 g of the expected product are obtained after drying.
