DIPEA (0.033 mL, 0.19 mmol) was added to a cold (0° C.) mixture of (4S,7S,10aS)-4-(tert-butoxycarbonylamino)-5-oxooctahydro-2H-pyrido[2,1-b][1,3]thiazepine-7-carboxylic acid (50 mg, 0.15 mmol), propan-1-amine (10.3 mg, 0.174 mmol) and 1-hydroxy-7-azabenzotriazole (23.7 mg, 0.174 mmol) in DMF (0.3 mL). Then, EDC (33.4 mg, 0.174 mmol) was added. The reaction was stirred at rt for 8 hr. The crude mixture was purified by RP prep-HPLC (Method B) to give tert-butyl (4S,7S,10aS)-5-oxo-7-(propylcarbamoyl)octahydro-2H-pyrido[2,1-b][1,3]thiazepin-4-ylcarbamate (56 mg, 0.15 mmol, 100% yield) as a white solid. Anal. Calcd. for C18H31N3O4S m/z 385.5. found: 386.2 (M+H)+. 1H NMR (400 MHz, CDCl3) δ ppm 6.02 (br s, 1H), 5.27 (br s, 1H), 5.02 (br s, 1H), 4.77 (m, 1H), 3.23 (m, 2H), 2.89 (m, 1H), 2.36 (m, 1H), 2.41 (m, 2H), 2.05 (m, 2H), 1.53-1.50 (m, 6H), 1.50 (s, 9H), 0.90 (t, J=7.5 Hz, 3H).
