A solution of sodium methylate (12 mmol) in methanol (10 ml) was added to a solution of hydroxylamine hydrochloride (0.56 g, 8 mmol) in methanol (16 ml). The mixture was stirred for 10 min, and NaCl was filtered off 6-(Pyridine-3-sulfonylamino)hexanoic acid methyl ester (93c) (0.58 g, 2 mmol) was added to the filtrate and the mixture was left to stand overnight at ambient temperature. The precipitate was filtered off, dissolved in water (20 ml) and oxalic acid (0.36 g, 4 mmol) was added to the solution. Water was removed under reduced pressure and the product was crystallised from methanol. The title compound (0.33 g, 44%) was obtained as white solid. M.p. 132-134° C. 1H NMR δH. (90 MHz, DMSO-d6) δ: 0.78-1.49 (6H, m, CH2), 1.83 (2H, t, J=6.5 Hz, CH2); 2.76 (2H, t, J=6.5 Hz, CH2N); 7.54 (1H, dd, J=5.0 Hz, J=8.2 Hz, C5HN); 8.12 (1H, dt, J=2.0 Hz, J=8.2 Hz, C5HN); 8.61 (1H, dd, J=2.0 Hz, J=5.0 Hz, C5HN); 8.81 (1H, d, J=2.0 Hz, C5HN). HPLC analysis on Symmetry C18 column: impurities <1% (column size 3.9×150 mm; mobile phase acetonitrile—0.1M phosphate buffer (pH 2.5), 5: 95; detector UV 254 nm; sample concentration 1.0 mg/ml). Anal. Calcd for C11H17N3O4S*(COCH)2: C 41.38, H 5.07, N 11.13. Found: C 41.53, H 5.10, N 19.83.
