Triethylamine → 4-{2-[(Morpholine-4-carbonyl)-amino]-3-phenylmethanesulfonyl-propionylamino}-3-oxo-azepane-1-carboxylic acid benzyl ester

3-Hydroxy-4-{2-[(morpholine-4-carbonyl)-amino]-3-phenylmethanesulfonyl-propionylamino}-azepane-1-carboxylic acid benzyl ester (100 mg, 0.167 mmol) was dissolved in DMSO (5 mL). Triethylamine (0.3 mL) and then SO3 pyridine complex (150 mg) were added and the mixture was stirred at ambient temperature for 3 hours. After dilution with ethyl acetate (100 mL), the solution was washed with water (50 mL) and brine, dried with MgSO4 and evaporated under vacuum. The residue was purified by flash chromatography on silica gel (Eluent: 5% methanol in ethyl acetate) to yield 4-{2-[(morpholine-4-carbonyl)-amino]-3-phenylmethanesulfonyl-propionylamino}-3-oxo-azepane-1-carboxylic acid benzyl ester (75 mg); 1H NMR: (DMSO) 8.23–8.08 (m, 1H), 7.40–7.29 (m, 10H), 7.06–6.98 (m, 1H), 5.20–5.09 (m, 2H), 4.79–4.65 (m, 1), 4.52–4.31 (m, 3H), 4.02–3.80 (m, 2H), 3.62–3.23 (m, 11H), 3.00–2.78 (m, 1H), 1.88–1.55 (m, 4H); MS: (M+H)+ 601.