A solution of (1R,3S,4S)-3-amino-4-hydroxy-cyclopentanecarboxylic acid methyl ester hydrochloride (160 mg) in THF (5 ml) was treated under an argon atmosphere with N-ethyldiisopropylamine (0.56 ml), 5-chloro-2-thiophenecarboxylic acid (160 mg) and BOP (434 mg). The mixture soon turned to a clear light yellow solution and was then stirred for 18 h. The reaction mixture was concentrated. The crude product was purified by chromatography (silica gel; gradient: cyclohexane→cyclohexane/EtOAc 3:7) to give (1R,3S,4S)-3-[(5-chloro-thiophene-2-carbonyl)-amino]-4-hydroxy-cyclopentane-carboxylic acid methyl ester as colorless gum. MS: 304.0 ([M+H]+).
