A solution of Intermediate 4 (45 mg, 0.14 mmol), and diisopropylethylamine (36 mg, 0.28 mmol) in dry dichloromethane (3 ml) was cooled to 0° C. using an ice/methanol bath. Ethyl isocyanate (10 mg, 0.14 mmol) was added with stirring under argon and the whole mixture stirred at room temperature for 1 h. The reaction mixture was partitioned between dichloromethane (5 ml) and 1N hydrochloric acid (5 ml). The organic layer was removed and reduced to minimum volume under reduced pressure. The crude mixture was purified by flash column chromatography eluting from 0-50% ethyl acetate in 40-60° C. petroleum ether to give the title compound as a colourless oil (13 mg, 24%); mass spectrum (ES): Found 400 (ES−), C21H27N3O3S requires 401; 1H-NMR (400 MHz, CDCl3) δ 1.16 (3H, m), 1.38 (6H, m), 2.93 (2H, m), 3.19 (1H, m), 3.32 (4H, m), 4.32 (1H, m), 4.44 (1H, m), 4.82 (1H, m), 6.48 (1H, s), 7.23 (3H, m), 7.36 (3H, m), 7.54 (1H, m).
