To a solution of acetoxyacetic acid (0.13 g, 1.10 mmol) in 5 ml dimethylformamide were added 1,1′-carbonyl-diimidazole (0.18 g, 1.10 mmol). The mixture was stirred at room temperature for 10 minutes, heated to 40° C. for a few minutes and cooled to room temperature. 4-{[(4-Chloro-benzenesulfonyl)-(2-oxo-azepan-3-yl)-amino]-methyl}-N-hydroxy-benzamidine (0.45 g, 1.00 mmol) was added and the mixture was stirred at 100° C. for 5 hours and then poured into water. Filtration and chromatography on silicagel with ethylacetate/heptane (3/1) yielded 0.15 g (29%) acetic acid 3-(4-{[(4-chloro-benzenesulfonyl)-(2-oxo-azepan-3-yl)-amino]-methyl}-phenyl)-[1,2,4]oxadiazol-5-ylmethyl ester as white solid, MS: m/e (%)=533.0 (MH+, 100).
