To a stirred solution of (2S,4S)-2-amino-N-{4-[(4-amino-benzenesulfonyl)-isobutyl-amino]-5-hydroxy-pentyl}-3-naphthalen-1-yl-propionamide (0.09 g, 0.17 mmol, product of example 8) in K2CO3 1M (3 mL) and THF (1 mL) was added carbonic acid 2,5-dioxo-pyrrolidin-1-yl ester 2,2,2-trifluoroethyl ester (0.05 g, 0.20 mmol), prepared from 2,2,2-trifluoroethanol, N,N′-disuccinimidyl carbonate and triethylamine in tetrahydrofuran. The mixture was stirred to room temperature for 24 h. Ethyl acetate was added and the organic layer was washed with water, then dried with MgSO4 and concentrated. The residue was purified by flash chromatography eluting with a mixture of hexane/EtOAc. The yield obtained was 10%.
