A solution of t-butyl 9-amino-6,10-dioxo-1,2,3,4,7,8,9,10-octahydro-6H-pyridazino[1,2-a][1,2]diazepine-1-carboxylate (GB 2,128,984; 831 mg, 2.79 mmol) and diisopropylethylamine (1.22 ml, 6.99 mmol, 2.5 equiv) in CH2Cl2 (10 ml) under dry nitrogen was treated with methanesulphonyl chloride (237 μl, 3.07 mmol 1.1 equiv). The mixture was stirred for 1 h, diluted with EtOAc (75 ml) and washed with saturated NaHCO3 (50 ml) and saturated aqueous sodium chloride (30 ml), dried (MgSO4) and concentrated. Flash chromatography (10-35% EtOAc in CH2Cl2) afforded (211b) (806 mg, 77%) as a colourless solid: mp 68-70° C.; [α]D23 -109 (c 1.09, CH2Cl2); IR (KBr) 3270, 2980, 2939, 1735, 1677, 1458, 1447, 1418, 1396, 1370, 1328, 1272, 1252, 1232, 1222, 1156, 1131, 991; 1H NMR (CDCl3) δ 6.15 (1H, d), 5.31 (1H, m), 4.65-4.11 (2H, m), 3.47 (1H, m) 2.99 (3H, s), 2.89 (1H, m), 2.72-2.51 (2H, m), 2.34 (1H, m), 2.26 (1H, m), 2.05-1.62 (4H, m), 1.47 (9H, s); Anal. Calcd for C15H23N3O6S: C, 47.97; H, 6.71; N, 11.19; S, 8.54. Found: C, 48.28; H, 6.68; N, 10.86; S, 8.28. MS (+FAB) 376 (M+ +1, 66%), 320 (100).
