To a solution of 1.50 g 4-{(S)-4-tert-butoxycarbonyl-2-[(5-hydroxy-1-phenyl-1H-pyrazole-3-carbonyl)-amino]-butyryl}-piperazine-1-carboxylic acid ethyl ester in 12 ml DMF were added 670 μl ethyl 2-bromopropionate and 3.2 g cesium carbonate. After stirring at RT for 24 h the solution was diluted with ethyl acetate and extracted with aqueous LiCl (4% w/w). The crude product obtained after evaporation of the solvent was dissolved in THF and treated with 1 N NaOH. When conversion was complete (4 h) Amberlite IR-120® was added, the suspension filtrated and the filtrate evaporated to give the crude product (1.56 g)
